Instrumentation & control

Control န႔ပကသက၇ငသပကယၿပန႔လြနးေပမ႔ သေဘၤါေပၚအလပလပဖ႔ေလါကဘေလ႔လါၿကည႔၇ငေတါ႔သပမဆးလပါဘး။

Basic Control Concepts

basic process control systems ( process ဆတါ ကယထနးေကာငးၿခငတ႔ အ၇ာတခပါ။ (ဥပမါ - ဘြ ငလါ၇႔ေ၇ level)

Measurement - Process ၇႔ လက၇အေၿခအေန။၇ေနတ႔ အပခန။ဖအါး စသၿဖင႔ ကတငးတယ။

Controller ၇႔ comparator ထမာ - တငးလ႔၇တ႔ measured value က လခငတ႔ တနဖး(set point) န႔ယဥတယ။

၇လါတ႔ကြါၿခားမတနဖးက မတညၿပး control action လပတ႔ component က actuator နားလညတ႔ Output signal တခကတြကထတေပးမယ။

အဒ signal က actuator ကပ႔ေပးမယ။ ဒေတါ႔ actuator စအလပလပမယ။

ဒလနညးန႔ process ကလသလ ထနးေကာငးေနတယ။

အဒထမာ signal 2 ခအဓကပါပါတယ။

• Process Variable or PV

သက process ၇႔အေၿခအေနက တငးလ႔ ၇လါတ႔ ေၿပာငးလေနတ႔ signal ၿဖစပါတယ။အဒါက controller ထ က comparator ထက ထည႔ေပးပါတယ။ဘြ ငလါတလး၇႔ ေ၇ level ကတငးလ၇တတနဖးေပါ႔ ။

• Manipulated Variable or MV

သကေတါ controller ကထတေပးတ႔ signal ပါ။(အမားအါးၿဖင႔ mA သ႔မဟတ mV ၿဖစတတပါတယ။) boiler တလး ကေ၇တငတ႔ အနအမားကထနးတ႔ valve ၇႔ pneumatic actuator က ေပးတ႔ mA signal ေပါ႔။ တခါတေလP/I convertor ဆတ႔ mA to pneumatic signal pump လညလက၇ပလကလပေပးတ႔ signal ဆလ၇ပါတယ။ဘြ ငလါ ပ၇က၇ာခနတါဆ damping valve က control လပတ႔ signal ပါ။

ေအါကကပက PR 4116 Universal transmitter က၀ငတ႔ signal ေတြၿဖစပါတယ။အဒ Input signal ေတြၿဖစတ႔Current, voltage, RTD, TC, potentiometer output ေတြ အသးမားတ႔ process ေတြ၇ sensor ေတြက လါတ႔ signal ေတြ။ တနညးအါးၿဖင႔ဆ၇င PV ေတြၿဖစပါတယ။ အဒ PR 4116 က အဒ PV ေတြက controller အတြကကကညတ႔signal အၿဖစၿပနေၿပာငးေပးတါၿဖစပါတယ။

အဒ PV န႔ MV ကပၿပး ၿမငနငဖ႔ သေဘါၤေပၚလကေတြ႔သးေနက အ၇ာေတြန႔ စဥးစါးၿကည႔မယဆ၇င

The LT3-S thermistor relay provides complementary protection by direct measurement of the temperature of motors equipped with PTC thermistor probes, for operation: in hard ambient conditions: high temperature, dust, humidity with severe duty: fast operating cycles, use of DC injection braking.

အေပၚပမာ TELEMECANIQUE ၇႔ MOTOR ကါကြယေ၇းစနစ ကၿပထါးပါတယ။ ပမနအါးၿဖင႔ ေတြ႔၇တ႔ Overload relay က contactor ေအါကမာကပတပထါးတါေတြ႔၇ပါမယ။

Thermal overload relay တလးဟါ အေပၚက သေဘါတ၇ားကယထါးပါတယ။ အဗါလပ ၿဖစလါတ႔ overload current ဟါ အဒ overload relay ထ၇တ႔ heating element ကအပေပးပါတယ။ အဒထြကလါတ႔အပက overload relay

ထပါတ႔ bi-metal strip ကအပေပးလ႔ အဒ bi metal strip ေကြးလါတ႔အခါ normally close contact က trip လပလ႔ေမၚတါ က ပါ၀ါေကြးတ႔ contactor ၇႔ holding coil A1 A2 ကပါ၀ါ မေ၇ာကေတါ႔ပါဘး။ အဒေတါ႔ ေမၚတါကေပးတ႔ပါ၀ါကၿဖတေတါကၿပးၿဖစလ႔ ေမၚတါ၇ပသြါးကါ ေမၚတါေလါငမ႔ေဘးက ကငးေ၀းသြါးပါတယ။

အဒါေၿကာင႔ အဒ အဗါလပကြနထ၇း၇႔ PV က အဒ အဗါလပ HEATING COIL ကၿဖတတ႔ CURRENT ၿဖစပါတယ။သ႔၇႔MV ကေတါ႔ BI METAL STRIP ၇ယ။ သန႔တြထါးတ႔ TRIP ၇ယၿဖစပါတယ။ ဒါေၿကာင႔ တကယလ႔ BI METAL STRIP က အၿကးေ၇ြးၿပ၊းေမၚတါအေသးမာသးခ႔၇င ေမၚတါေလါငဘ႔မားပါတယ။ဘါလ႔လဆေတါ႔ MV ဟါေမၚတါေလါငတါကကါကြယနငတ႔ SET POINT အတြကကကညတ႔ တနဖးမဟတေတါ႔လ႔ပါဘ၊

ဒါေၿကာင႔ CONTROLLER ACTION မနဖ႔အေ၇းၿကးပါတယ။ ေနာကတခါထပစဥးစါးစ၇ာက CURRENT တနဖးတခမာ ၇MOTOR WINDING TEMPERATURE က အဗါလပထက HEATING COIL န႔ကယစါးၿပ အလပလပတ႔အတြကေမၚတါက အပခနၿမင႔တ႔ေန၇ာမာထါး။ OVERLOAD RELAY က အပခနနမ႔တ႔ေန၇ာမာထါး၇ငလေမၚတါေလါငနငပါတယ။ဘါလ႔လဆေတါ႔အဒ CURRENT ဟါ ေမၚတါမာတကယၿဖစေပၚေစတ႔အပခနကကယစါးမၿပလ႔ၿဖစပါတယ။ အဒါေၿကာင႔ TELEMECANIC က LT3 THERMISTOR RELAY ကထပတပထါးတါၿဖစပါတယ။အဒမာ ေမၚတါအပခနက MOTOR ထၿမပထါးတ PTC Thermistor probe ကေနယတ႔အတြကတကယ႔ေမၚတါအပခနက ကယစါးၿပတ႔ PV က၇ပါတယ။

PV & MV န႔ပတသကလ႔ေနာကတခကၿကည႔၇င

IP CONVERTOR

ဒါက CONTROLLER ကထတေပးတ႔ mA က သန႔အခးက ေလ pressure signal ေၿပာငးေပးတါၿဖစပါတယ။အခ႔ကလmA or V ၂ မးလးသးလ႔၇ပါတယ။ SIGNAL အ၀င ၿကး ေၿပာငးတပ၇ပါဘ၊

The electropneumatic converter consists of an I/P module which operates according to the principle of force equilibrium and a downstream volume booster. When operated, the supplied direct current (4) flows through the plunger coil (2) located in the field of a permanent magnet (3). At the balance beam (1), the force of the plunger coil, which is proportional to the current, is balanced against the force of the dynamic back-pressure. The back-pressure is produced on the flapper plate (6) by the air jet leaving the nozzle (7). The air supply (8) flows into the lower chamber of the volume booster. A certain amount of air determined by the position of the diaphragm reaches the sleeve (9) and flows to the output (36). When the input current increases and, as a result, the force of the plunger coil increases as well, the flapper moves closer to the nozzle. This causes the dynamic back-pressure and the cascade pressure pK forming upstream of the restrictor (8.2) to increase. The cascade pressure increases until it corresponds to the input current and pushes both the diaphragm (10) and the sleeve (9) downwards, causing the output pressure pA to increase until a new state of equilibrium is reached in the diaphragm chambers. When the cascade pressure decreases, the diaphragm is pressed upwards and it releases the sleeve. The output pressure pA escapes through the sleeve to the vent (EXHAUST) until the forces on the diaphragm are balanced again.

ပမာၿပထါးသလ milliamp က plunger coil (2) ေပၚသကေ၇ာကတ႔အခါ nozzle & flapper (6&7) ၿကားအကြါအေ၀းက ေၿပာငးေစလ႔ PK PRESSURE ကေၿပာငးေစပါတယ။အဒ PK ဟါ Diaphragm 10 ကအခးကလပ၇ားေစလ႔ milliamp န႔အခးက PA ကထတေပးပါတယ။

Pneumatic to pneumatic positioner

Controller ၇႔ အထြက MV ဟါ ၄-၂၀ mA အတြငးၿဖစပါတယ။ ဥပမါ - ၁၂ mA ဆပါေတါ႔။ အဒ ၆ mA က I/P Convertor ထေၿပာငးယတ႔အခါ ၂၀-၁၀၀ KPa ၿကားတခခတနဖးအၿဖစ၇လါပါတယ။ ၆၀ KPa ဆပါေတါ႔။ အဒ ၃၀ KPa ၇ SIGNAL PRESSURE ၿဖစတ႔ ေလSignal က positioner ကေ၇ာကလါၿပး input chamber ထက၀ငၿပး flapper ကေ၇ြ႔လားေစပါတယ။ အလေ၇ြ႔လားလ႔ nozzle န႔ flapper ၿကားအကြါအေ၀းလ တးလါပါတယ။ ဒါေၿကာင႔ nozzle back pressure လကဆငးလါပါတယ။ဒါေၿကာင႔ pilot stem 9 က ညာဖကကေ၇ြ႔လါပါတယ။ဒါေၿကာင႔ Output 1 ကဖြင႔လကလ႔ diaphragm actuator ကေလေပးပါတယ။ တကယလ႔ diaphragm က ေအါကကေန ေလေကြး၇ငဗါးပြင႔ပါမယ။ diaphragm အေပၚကေန ေလေကြး၇င ဗါးပတပါမယ။ တကယလ႔ MV ဟါ ၄ mA ၿဖစခ႔၇င flapper ကnozzle နားကပလါလ႔ nozzle feed back pressure တကၿပး pilot stem 9 က ဘယဖကကေ၇ြ႔လ႔ diaphragm actuator ကေလေပးတါ၇ပပါမယ။

CONTROL SYSTEM

Feedback loop = signal path from the output back to the input to correct for any variation between the output level from the set level. In other words, the output of a process is being continually monitored, the error between the set point and the output parameter is determined, and a correction signal is then sent back to one of the process inputs to correct for changes in the measured output parameter. Controlled or measured variable = the monitored output variable from a process. The value of the monitored output parameter is normally held within tight given limits.

Manipulated variable = the input variable or parameter to a process that is varied by a control signal from the processor to an actuator. By changing the input variable the value of the measured variable can be controlled.

Set point = the desired value of the output parameter or variable being monitored by a sensor. Any deviation from this value will generate an error signal.

Instrument = the name of any of the various device types for indicating or measuring physical quantities or conditions, performance, position, direction, and the like.

Sensors are devices that can detect physical variables, such as temperature, light intensity, or motion, and have the ability to give a measurable output that varies in relation to the amplitude of the physical

variable. The human body has sensors in the fingers that can detect surface roughness, temperature, and force. A thermometer is a good example of a line-of-sight sensor, in that it will give an accurate visual indication of temperature. In other sensors such as a diaphragm pressure sensor, a strain transducer may be required to convert the deformation of the diaphragm into an electrical or pneumatic signal before it can be measured. Transducers are devices that can change one form of energy to another, e.g., a resistance thermometer converts temperature into electrical resistance, or a thermocouple converts temperature into voltage. Both of these devices give an output that is proportional to the temperature. Many transducers are grouped under the heading of sensors. Converters are devices that are used to change the format of a signal without changing the energy form, i.e., a change from a voltage to a current signal. ( Transducer ဆတါ signal တခ၇႔ energy က မေၿပာငးေစဘ format ( သ႔မဟတ unit - ဥပမါ mA ကေန ဗ႔ ကေၿပာငးတါ) ကေၿပာငးေပးတ႔ က၇ယါၿဖစပါတယ။)

Actuators = devices that are used to control an input variable in response to a signal from a controller. Atypical actuator will be a flow-control valve that can control the rate of flow of a fluid in proportion to the amplitude of an electrical signal from the controller. Other types of actuators are magnetic relays that turn electrical power on and off. Examples are actuators that control power to the fans and compressor in an air-conditioning system in response to signals from the room temperature sensors.

Controllers = devices that monitor signals from transducers and take the necessary action to keep the process within specified limits according to a predefined program by activating and controlling the necessary actuators.

Programmable logic controllers (PLC) are used in process-control applications, and are microprocessor-based systems. Small systems have the ability to monitor several variables and control several actuators, with the capability of being expanded to monitor 60 or 70 variables and control a corresponding number of actuators, as may be required in a petrochemical refinery. PLCs, which have the ability to use analog or digital input information and output analog or digital control signals, can communicate globally with other controllers, are easily programmed on line or off line, and supply an unprecedented amount of data and information to the operator. Ladder networks are normally used to program the controllers.

An error signal = the difference between the set point and the amplitude of the measured variable. A correction signal is the signal used to control power to the actuator to set the level of the input variable. Transmitters = devices used to amplify and format signals so that they are suitable for transmission over long distances with zero or minimal loss of information. The transmitted signal can be in one of the several formats, i.e., pneumatic, digital, analog voltage, analog current, or as a radio frequency (RF) modulated signal. Digital transmission is preferred in newer systems because the controller is a digital system, and as analog signals can be accurately digitized, digital signals can be transmitted without loss

of information. The controller compares the amplitude of the signal from the sensor to a predetermined set point.

Control system အေၿကာငးေလ႔လါမ႔သဟါ လပစစန႔ပကသကလ႔ ေအါက က ဟါေတြအၿကမးဖငးေလါကေတါ႔သထါး၇ပါတယ။

၁- Basic passive components (resistors, capacitors, and inductors) used in electrical circuits ၂-Applications of Ohm’s law and Kirchoff’s laws ၃- Use of resistors as voltage dividers ၄- Effective equivalent circuits for basic devices connected in series and parallel ၅- The Wheatstone bridge ၆-Loading of instruments on sensing circuits ၇-Impedances of capacitors and inductors

အလကထ၇ြနးနစန႔ပကသက၇ငေတါ႔

၁- The terms active and passive as applied to electronic components ၂- Signal amplification, gain adjustment, and feedback in amplifiers ၃- Operation of amplifiers ၄- Different types of amplifiers ၅-The difference between digital and analog circuits ၆- The instrument amplifier ၇-Conversion of analog signals to digital signals

ဘါလ႔လ ဆေတါ႔ amplifier ဟါ instrumentation ေန၇ာအေတၚမားမားမာသးေနလ႔ၿဖစပါတယ။

၁-Capacitance multiplier Gyrator Sine wave oscillators ၂- Power supply regulators ၃-Level detection ၄-Voltage-to-frequency converters ၅-Voltage-to-digital converters ၆-Pulse amplitude modulation

PV & MV ေတြၿပး၇ငေလ႔လါ၇မာက CONTROLLER ေတြပါဘ။( SENSOR ေတြကလေလ႔လါဖ႔မေမ႔ပါန႔)

သေဘါၤေပၚအတြကေလါကက အေသးစတ အတြကအခကေတြန႔ ဒဇငးဆနဆနေလ႔လါစ၇ာမလေတါ႔တးမေခါကမေလါကဘေလလါၿဖစပါတယ။

PRESSURE REGULATOR( REDUCING VALVE ဘေပါ႔)

ပကအတငး SPRING က ADJUST လပၿပး DIAPHRAGM ေပၚလအပတ႔ ဖအါး၇ေအါငလပပါတယ။ REGULATED PRESSURE က DIAPHRAGM PRESSURE ထကမား၇င ဗါးပတပါတယ။ မဟတ၇င ဗါးပြင႔ပါတယ။ဒနညးန႔ လအပတ႔PRESSURE က ထနးပါတယ။

တကယ႔လ႔ FEED BACK သးတ PILOT OPERATED PRESSURE REGULATOR ဆ၇င ေအါကက လၿဖစပါမယ။

LEVEL က တငးမယ။ထနးမယဆ၇င ေအါကကလအသးမားပါတယ။ တငးတ႔ INSTRUMENTေတြကေတါ႔အမးမးကြၿကတါပေပါ႔။

အေပၚကတြၿပး FLOW CONTROL လပမယဆ၇င

GLOBE VALVE ကသးခ႔၇င ေအါကက အခကက ဂ၇စက၇ပါမယ။

The globe type valve can be designed for quick opening, linear, or equal percentage operation. In equal percentage operation the flow is proportional to the percentage the valve is open, or there is a log relationship between the flow and valve travel. The shape of the plug determines the flow characteristics of the actuator and is normally described in terms of percentage of flow versus percentage of lift or travel.

အဒေတါ႔ ကယသးတ႔ PROCESS န႔ VALVE PLUG DESIGN ကကဖ႔လပါတယ။

POWER CONTROL

ေနာကပငးမာ ELECTRONIC CONTROL ေတြကပအသးမားလါတါေတြ႔၇ပါတယ။ ဘါလ႔လဆေတါ႔

In electronic devices the problem of electrical isolation between drive circuits and output power circuits can easily be overcome with the use of opto-isolators. Electronic power devices have excellent longevity and are very advantageous due to their switching speeds in variable power control circuits.

တကယလ႔ scr သးခ႔၇င

ပမာၿကည႔၇င ေအါကၿခမးမပါတါေတြ႔၇ပါမယ။

ဒါေၿကာင႔ ေအါကၿခမးပါၿခင၇င - တနညးအါးၿဖင႔ - AC လခင၇ငTRIAC ကသး၇ပါမယ။

ACTUATOR ေတြ ေမၚတါေတြအလပလပဖ႔ CONTROL POWER ေပးနညးမားထက အခ႔

ေအါကက11,15 a မာ Transister သးၿပး CONTROL POWER ေပးပ။ b က MOS သးၿပး RELAY က OPERATE လပပ။

Figure 11.15c မာ opto-coupler ကသးထါးလ႔ ေမၚတါ ပတလမးန႔ electrically isolated လပထါးတါေတြ႔၇ပါမယ။

ဒါက DC MOTOR အတြကၿပထါးေပးမ႔ ေအစေမၚတါေတြမာလ OPTO- COUPLER သး CONROLLER ေတြ၇ပါတယ။

Servo motors = Servo motors can rotate to a given position, be stopped, and reversed. In the case of a servo motor the angular position and speed can be precisely controlled by a servo loop, which uses feedback from the output to the input. The position of the output shaft is monitored by a potentiometer which provides an analog feedback voltage to the control electronics (an encoding disc would be used in

Boiler FD Fan damper ကအပတအဖြင႔လပတ႔ အထနးေလ(control air )က လသေလါကလြတေပးတ႔ servo valve

( 4-20 mA န႔ အနအမားထနးပါတယ။)

a digital system), so that the control electronics can use this information to power the output motor and stop it in any desired position or reverse the motor to stop at any desired position.

ဆါဗေမၚတါဆတါက သ၇႔ လညပတနနးန႔ DIRECTION က လအပသလထနးနငတ႔ေမၚတါကေၿပာတါပါ။ေမၚတါ၇ပေပၚမာ POT METER တပၿပး FEED BACKက၇ယပါတယ။ DIGITAL မာဆ ENCODING DISC န႔ယပါတယ။

STEPPER MOTOR

Stepper motors rotate at a fixed angle with each input pulse. The rotor is normally a fixed magnet with several poles and a stator with several windings. Stepper motors are available in many different designs with a wide selection of the number of poles and drive requirements, all of which define the stepper motor characteristics and rotation angle for each input phase. Stepper motors can be reversed by changing the sequence of the driving phases. Stepper motors are available with stepping angles of 0.9, 1.8, 3.6, 7.5, 15, and 18 degrees. Since the motor steps a known angle with each input pulse, feedback is not required. However, as only the relative position is known, loss of power will cause loss of position information, so that in a system using stepper motors a position reference is usually required.

အခ ႔ CPP SYSTEM ေတြမာ PITCH CONTROL အတြက STEPPER MOTOR ကသးတတပါတယ။

Position feedback

Valve position feedback In Fig. 11.18a a globe valve operated by an electric motor is shown. The screw driven by the motor can move the plug in the valve up or down. A potentiometer wiper is attached to the valve stem and gives a resistance directly proportional to the amount the valve is open. This resistance value can be fed back to the controlling electronics, so that the position of the valve can be monitored. The system could also be digital, in which case, a digital encoding technique would be used for feedback.

အေတၚမားမား POSITION FEEDBACK ေတြဟါ potentiometer ကသးၿကပါတယ။ steering gear rudder angle feed back ေတြမာေတြ႔၇ပါတယ။

Pneumatic feedback In Fig. 11.18b pneumatic control is used in a local closed loop system for maintaining water at a set temperature. Cold water and steam are mixed in a heat exchanger; the temperature of the exiting hot water is monitored by a pressure– spring thermometer. The pressure from the thermometer is used to operate and control a linear globe valve in the incoming steam pipe. If the temperature of the hot water increases above a set temperature, the pressure from the thermometer increases and starts to close the valve in the steam line, keeping the hot water at the set temperature. If the flow of hot water increases, the temperature of the water will start to lower and this will reduce the pressure from the thermometer to the valve increasing the steam flow, bringing the temperature back to its set point.

အေတၚမား မား tanker pump room ထက control system feed back ေတြဟါ pneumatic feedback ၿဖစတတပါတယ။

Directional Control ValvesDirectional control valves have been commonly referred to as switching valves because they simply direct or “switch” fluid passing through the valve from the source of flow to one of a selection of available cylinder ports. The flow control variety of valve generally selects an orifice which only allows a specified volume of flow to pass. The specified volume controls the speed of a cylinder or hydraulic motor. Likewise, the pressure control type is used to select a particular pressure setting.

Changing direction, flow or pressure during machine operation with these valves would require a separate individual valve for each direction, flow or pressure desired. The hydraulic circuit would become quite complex very quickly!

Proportional ValvesThe technological solution to these more complex circuits has been the development of proportional valves. These revolutionary valves allow infinite positioning of spools, thus providing infinitely adjustable flow volumes. Either stroke-controlled or force-controlled solenoids are used to achieve the infinite positioning of spools.

This variable positioning allows spools to be designed with metering notches to provide flow/speed control as well as directional control functions all in one valve, instead of requiring separate valves for direction and speed. The other major benefit is when the circuit requires more than one speed. The various speeds are achieved by changing the electrical signal level to deliver the flow/speed required. No additional hydraulic components are required! These proportional directional valves are controlled by DC power.

The proportional controls, used with their associated electronic controls, also add the desirable features of acceleration and deceleration. This offers a variety of machine cycles, safely operated at greater speeds, yet with controlled start and stop characteristics. Regulated acceleration and deceleration result in improved machine overall cycle times and production rates. Servo ValvesThe third type of hydraulic directional control technology is the servo valve. Servo valves are not a new technology as servo valves were first used in the 1940s. Servo valves operate with very high accuracy, very high repeatability, very low hysteresis, and very high frequency response. Servo valves are used in conjunction with more sophisticated electronics and closed loop systems. As a result, servo valves are always much more expensive. A proportional control valve system can be used to improve control of most machines without the high price tag of servo control systems.

Principles of Control Systems

အဒေတါ႔ control system တခကစ မကငခင ေသခာသေအါငၿကည႔၇မာက

MV ကတငေပးလက၇င PV ကသြါးလါး။(Damping valve ဆ၇င ေကြးတ႔ mili amp ကတငေပး၇င valve ပပတတါမးလပထါးတတတယ။ဒါဆsteam pressure တကမာေပါ႔။

ဒေတါ႔ • Will the output rise or fall? ဆ၇င rise လ႔ေၿပာ၇မာေပါ႔။)

ဘါးဘယေလါကႏနး န႔ၿမနၿမနပတလ၊

အဒလပတလက၇င ပ၇က၇ာတကတါ ဘယေလါကၿကာလ၊

အဒါေတြထည႔စဥးစါးၿပး controller maker ေပးထါးတ႔ setting ေတြကခန၇မာပါ။

Control Modes

Process Control မာ ထနးပထနးနညး - ၅ ခ၇ပါတယ။

• On-Off

• Modulating

• Open Loop

• Feed Forward

• Closed loop

On-Off control:

two-position control.လ႔လေခၚပါတယ။ perfect on-off controller တခဟါ SET POINT (SP) ေအါကမာ ON ၿပး MV က အမားဆး၇၇ပါမယ။ SP အေပၚေ၇ာကတါန႔ OFF ၿဖစၿပး MV ကအနဆးၿဖစ၇မယ။

ေ၇ၿပည႔ခါနး ပန႔၇ပ။ ေ၇ LEVEL က၇ငၿပနေမါငး လပတါမး။ သက OPEN LOOP OR CLOSE LOOP အတြကသးနငပါတယ။

Modulating control:

အေပၚက လ CONTROLLER OUTPUT က ON/OF ပစ မဟတဘ ေတါကေလာက အနညး န႔ အမားတြငး ညကညကေညာေညာ

ေၿပာငးလထနးေနတါၿဖစပါတယ။ ဥပမါ - ပန႔ ေတါကေလာကလညေနၿပး BY PASS VALVE ကကစါးေပးၿပး ေ၇အနညးအမားကထနးတါမး ။ သကလညး OPEN OR CLOSE LOOP အတြကသးနငပါတယ။

Open loop control:

PV ဆတ႔ Process ၿကးေလါေလါဆယၿဖစေနတတနဖး က ထည႔မတြကဘ MV ဆတ႔ Controller ကထနးတ႔signalထတေပးတ႔ ထနးေကာငးမ ( ေ၇ၿပည႔ၿပးလကေနလ ေ၇ထည႔တ႔ valve ကဖြင႔ေပးေနမာၿဖစပါတယ။)

Feed forward control:

ဒ control စနစကလ PV တခတညး ကထည႔မတြကပါဘး။ တခါတေလ feed back signal ကမသးပါဘး။ဒါေပမ႔ဒစနစမာ လခငတ႔ PV အတြက မနကနတ႔ MV က တတကက တြကခကထည႔ေပးေနတါၿဖစလ႔ OPEN LOOP ထကအဆင႔အတနးၿမင႔ပါတယ။ PROCESS ၇႔သေဘါသဘါ၀ကအေသအခာသၿပး ထနးေကာငးေနတ႔ CONTROL တခၿဖစပါတယ။

Closed loop or feedback control:

ဒ CONTROL စနစက PV အေပၚမာမတညၿပး MV ကေၿပာငးေပးတ႔ စနစၿဖစပါတယ။

FEED BACK CONTROL LOOP

Close loop control မာ - PV(process variable) က SP (Set point)န႔ ယဥၿကည႔ပါတယ။ ၿပးေတါ႔လအပတ႔ control action ကတြကထတပါတယ။ MV ဆတ႔ Contoller output (ပမာေတါ႔ output = OP လ႔ၿပထါးပါတယ။) က Process ကထနးေကာငပါတယ။

ဒေတါ႔ကါ OP ဆတါ၇ဘ႔ ERROR(ERR) လပါတယ။

ERR = PV – SP ၿဖစပါတယ။( ERR = SP – PV)ဆ၇င REVERSE CONTROL ACTION ၿဖစပါမယ။

Control modes in closed loop control

Closed loop Controllers မာ control modes - ၃ ခပါပါတယ။အဒ ၃ ခကတြသးသး ။ ခြသးသး၇ပါတယ။

အဒါေတြက( ဒါက 3 terms of control လ႔ေၿပာပါတယ။ 3 elements of control မဟတပါ)

• Proportional Control (P)

• Integral, or Reset Control (I)

• Derivative, or Rate Control (D)

တ႔ၿဖစပါတယ။

၇း၇းေလးစဥးစါးၿကည႔၇ငေတါ႔

လ ၂ ေယါက A န႔ B ၇ငေဘါငတနး၇ပေနတယ။ A ကေ၇႔ဘကကေၿခတလမးတးတယ။ A ကေစါင႔ၿကည႔ေနတ႔ B က ခဏေနေတါ႔ေနာကကေန A တးသေလါက႔ႏနးန႔ ေၿခလမးလကတးမယ။ A စေ၇ြ႔ၿပးမ B လကေ၇ြ႔လ႔ေၿခတလမးၿခငးတေပမ႔ ၇ငေဘါငတနးၿပနၿဖစဘ႔ မၿဖစနငေတါ႔ပါဘး။ နနေလးၿကာမ ေနာကကလက၇တ႔ အတြကနနေတါ႔ကြါေနမာဘ။ အဒလ A တလမးတးတငး B က A လမးနနးအတငးေနာကကလကၿပး တလမးလကတးတါက PROPORTIONAL။

ၿပန-၇ငေဘါငးတနးေ၇ာကဘ႔ဆ ေ၇ြ႔တါေနာကကတ႔ အခနေလါကအတြကေၿခလမးပလမးေပး၇မာ။ အဒလပလမးတ႔ေၿခလမးက INTEGRAL

အဒမာ A က တလမးစလမးတါမဟတဘ ေႏးလကၿမနလကေၿပးေနတယဆ၇င B ကလသေႏး၇ငေႏးသလၿမန၇ငၿမနသလ လကေၿပး၇ေတါ႔မယ။အဒလတြကခကၿပးေၿပး၇င DERIVATIVE ၿဖစပါတယ။

Proportional control(P)

automatic controller တခဟါ ERR ေပၚမတညၿပး Controller output ( OP လ႔ဘေခၚေခၚ MV လ႔ဘေခၚေခၚ) ကထတေပးတါၿဖစပါတယ။

Proportional error and manual value: ERR မ၇ဘ ဒ CLOSE LOOP ကအလပမလပပါဘး။သေဘါက Proportional control က အၿမ error တခခနထါးပါတယ။ အဒ error က manual ဒါမမဟတ integral န႔ လပေပးမေပာကပါမယ။

Proportional band: Controllers Proportional Band ဆတါ

Percentage change in measure value ( PV ) န႔၁၀၀% MV အေၿပာငး တ႔၇႔ အခး (မား၇ငၿငမၿပးေႏး)

Proportional band န ၇င - PV နနေလါကေၿပာငးတါန႔ အမားၿကးတန႔ၿပနAction ယၿပး ၿမနၿမန set point ကၿပနေ၇ာကေအါငလပေဆါငတယ။ဒါေၿကာင႔GAIN ကၿမင႔၇င Proportional band နညး သါြးပါမယ။

Integral control(I)

Proportional န႔ ကနတ႔ error က လး၀ေဖာကဖ႔ သးတ႔ control က integral control (I)လ႔ေခၚပါတယ။

Intergral control က proportional control န႔တြသးတတၿပး PI Controller လ႔ေခၚပါတယ။

Derivative control (D)

Derivative က close loop control system ရ႔ stability အတြကသါထည႔ထါးေပးတါၿဖစပါတယ။derivative control ၇႔ပမါဏက PV ၇႔ ေၿပာငးလမႏနးန႔တက၇ကအခးကပါတယ။အထးသၿဖင႔ အခကၿပSignal ေတြက amplify လပတါက ထြကလါတ႔ noise ေတြက ေလာ႔ခဖ႔အသးၿပတတပါတယ။ဒါေၿကာင႔ အမားအါးၿဖင႔ PID

အေနန႔တြသးပါတယ။သခညးသးခပါတယ။derivative action ဟါ၃ ခါဘၿဖစတယ။

PID controller တလးခနနညး

UG governor စါအပကေၿပာတါက oscillation cycle က 1 sec ထကန၇င proportional gain ကေလာ႔ပါ။1sec ထကမား၇င proportional ကတငၿပး integral ကေလာ႔ပါ။

1- I & D value က minimum ထါးပါ

2- Oscillation ၿဖစတ႔အထ gain ကၿမင႔ပါ။

3- အဒ gain တနဖးတ၀ကေလါက ထၿပနေလာ႔ပါ။

4- I က ခနငက Oscillation time ၇႔ ၂ ဆ ထါးပါ။

5- D က I တနဖး၇႔ 1/8 ထါးပါ။

မတသါးစ၇ာက I : D = 4:1 ဆ၇င Oscillation ၿဖစတတတယ။

1-process start to change

2-when rate of change takes place in the process

3-when the process stops changing

Amount of integral is function of four thing (1-the magnitude of the deviaton,2-the duration of the deviation, 3-the proportional gain setting, 4-the integral setting)

အခ ႔က integral gain က in unit of repeats per second ( reset rate) န႔ၿပတယ။

Measurement

1. Cooling water / L.O temperature automatic control ေတြ2. ဘြ ငလါ pressure ေပၚမတညၿပး nozzle တလးထးမလါး။၂ လးထးမလါး။ load control လ႔ေခၚတါေပါ႔။low fire

/high fire ထနးေကာငးတ႔စနစ3. Boiler water level automatic control 4. Boiler steam pressure မား၇င dump steam condenser ဖကက by pass လပၿပး boiler steam pressure

ကခနတယ။ 5. F.O viscosity controller 6. Engine speed automatic control ( Governor ) 7. IGG System ေတြမာ combustion chamber pressure က ခနတယ။( ဒ pressure မမန၇င oxygen မမနတတ။

soot ထြကတတပါတယ။)။ fuel and oxygen အခးကခနပါတယ။ ဘါကဘ control လပလပ sensing device က အေ၇းၿကး ပါတယ။ သ sense လပတါမမနဘန႔ control မနေအါငမလပနငပါဘး။ sensor မာ transmitter ပါ၇င ပမနအါးၿဖင႔ တငးလ႔ ၇တ႔ analog န႔ အခးက DC Signal တခက လြတထတေပးပါတယ။

SENSING DEVICES ေတြက physical properties ေတြၿဖစတ႔ temperature, pressure, flow, viscosity, level, position စတါေတြက detect လပပါတယ။

Temperature instruments.

PT 100 OHM \ C°°C 0 1 2 3 4 5 6 7 8 9 10 °C-200 18,49 -200-190 22,80 22,37 21,94 21,51 21,08 20,65 20,22 19,79 19,36 18,93 18,49 -190-180 27,08 26,65 26,23 25,80 25,37 24,94 24,52 24,09 23,66 23,23 22,80 -180-170 31,32 30,90 30,47 30,05 29,63 29,20 28,78 28,35 27,93 27,50 27,08 -170-160 35,53 35,11 34,69 34,27 33,85 33,43 33,01 32,59 32,16 31,74 31,32 -160-150 39,71 39,33 38,88 38,46 38,04 37,63 37,21 36,79 36,37 35,95 35,53 -150-140 43,87 43,45 43,04 42,63 42,21 41,79 41,35 40,96 40,55 40,13 39,71 -140-130 48,00 47,59 47,18 46,76 46,35 45,94 45,52 45,11 44,70 44,28 43,87 -130-120 52,11 51,70 51,29 50,88 50,47 50,06 49,64 49,23 48,82 48,41 48,00 -120-110 56,19 55,78 55,38 54,97 54,56 54,15 53,74 53,33 52,92 52,49 52,11 -110-100 60,25 59,85 59,44 59,04 58,61 58,22 57,82 57,41 57,00 56,60 56,19 -100-90 64,30 63,90 63,49 63,09 62,68 62,28 61,87 61,47 61,06 60,66 60,25 -90-80 68,33 67,92 67,52 67,12 66,72 66,31 65,91 65,51 65,11 64,70 64,30 -80-70 72,33 71,93 71,53 71,13 70,73 70,33 69,93 69,53 69,11 68,73 68,33 -70-60 76,33 75,93 75,53 75,13 74,73 74,33 73,93 73,53 73,13 72,73 72,33 -60-50 80,31 79,91 79,51 79,11 78,72 78,32 77,92 77,52 77,13 76,73 76,33 -50-40 84,27 83,88 83,48 83,08 82,69 82,29 81,39 81,50 81,10 80,70 80,31 -40-30 88,22 87,83 87,43 87,04 86,64 86,25 85,35 85,46 85,06 84,67 84,27 -30-20 92,16 91,77 91,37 90,59 90,59 90,19 89,80 89,40 89,01 88,62 88,22 -20

-10 96,09 95,69 95,30 94,91 94,52 94,12 93,73 93,34 92,95 92,55 92,16 -100 100,00 99,61 99,99 98,83 98,44 98,04 97,65 97,26 96,87 96,48 96,09 0° 0 1 2 3 4 5 6 7 8 9 10 °C0 100,00 100,39 100,78 101,17 101,56 101,90 102,34 102,73 103,12 103,51 103,90 010 103,90 104,29 104,68 105,07 105,46 105,85 106,24 106,63 107,02 107,40 107,79 1020 107,79 108,18 108,57 108,96 109,35 109,73 110,12 110,51 110,90 111,28 111,67 2030 111,67 112,06 112,45 112,83 113,21 113,61 113,99 114,38 114,77 115,15 115,54 3040 115,54 115,93 116,31 1 i 6,70 117,08 117,47 117,85 118,24 118,02 119,01 119,40 4050 119,40 119,78 120,16 120,55 120,93 121,31 121,70 122,09 122,47 122,86 123,24 5060 123,24 123,62 124,01 124,39 124,77 125,16 125,54 125,91 126,31 126,69 127,07 6070 127,07 127,45 127,84 128,21 128,60 128,98 129,37 129,75 130,13 130,51 130,89 7080 130,89 131,17 131,66 132,04 137,41 132,80 133,18 133,56 133,94 134,32 134,70 8090 134,70 135,08 135,46 135,84 136,22 136,60 136,98 137,36 137,74 138,12 138,50 90100 138,50 138,88 139,26 139,64 140,02 140,39 140,77 141,15 141,53 141,91 142,29 100110 142,29 142,66 143,04 143,41 143,80 144,17 144,55 144,91 145,31 145,68 146,06 110120 146,06 146,44 146,81 147,19 147,57 147,94 148,31 148,70 149,07 149,45 149,81 120130 149,82 150,20 150,57 150,95 151,33 151,70 151,08 152,45 152,83 153,20 153;58 130140 153,58 153,95 154,32 154,70 155,07 155,45 155,81 156,19 156,57 156,94 157,31 140150 157,31 157,69 158,06 158,43 158,81 159,18 159,55 159,93 160,30 160,67 161,04 150160 161,04 161,42 161,79 162,16 162,53 162,90 163,27 163,65 164,01 164,39 164,76 160170 164,76 165,13 165,50 165,87 166,24 166,61 166,98 167,35 167,72 168,09 168,46 170180 168,46 168,83 169,20 169,57 169,94 170,31 170,68 171,05 171,41 171,79 172,16 180190 172,16 172,53 172,90 173,26 173,63 174,00 174,37 174,74 175,10 175,47 175,84 190200 175,84 176,21 176,57 176,94 177,31 177,68 178,04 178,41 178,78 179,14 179,51 200210 179,51 179,88 180,24 180,61 180,97 181,34 181,71 182,07 182,44 182,80 183,17 210220 183,17 183,53 183,90 184,26 184,63 184,99 185,36 185,72 186,09 186,45 186,82 220230 186,81 187,18 187,54 187,91 188,27 188,63 189,00 189,36 189,71 190,09 190,45 230240 190,45 190,81 191,18 191,54 191,90 192,26 192,63 192,99 193,35 193,71 194,07 240250 194,07 194,44 194,80 195,16 195,51 195,88 196,24 196,60 196,96 197,33 197,69 250260 197,69 198,05 198,41 198,77 199,13 199,49 199,85 200,21 200,57 200,93 201,19 260270 201,29 201,65 202,01 202,36 202,71 203,08 203,44 203,80 204,16 204,51 204,88 270280 204,88 205,23 205,59 205,95 206,31 206,67 207,01 207,38 207,74 208,10 208,45 280290 208,45 208,81 209,17 209,51 209,88 210,24 210,59 210,95 211,31 211,66 212,02 290300 212,02 212,37 212,73 213,09 213,44 213,80 214,15 214,51 214,86 215,22 215,57 300310 215,57 215,93 216,28 216,64 216,99 217,35 217,70 218,05 218,41 218,76 219,12 310320 219,12 219,47 219,82 220,18 220,53 220,88 221,24 221,59 221,94 222,29 222,65 320

330 222,65 223,00 223,65 223,70 224,06 224,41 224,76 225,11 225,46 225,81 226,17 330340 226,17 226,52 226,87 227,22 227,57 227,92 228,27 228,62 228,97 229,32 229,67 340350 229,67 230,02 230,37 230,72 231,07 231,42 231,77 232,12 232,47 232,82 233,17 350360 233,17 233,52 233,87 234,22 234,56 234,91 235,26 235,61 235,96 236,31 236,65 360370 236,65 237,00 237,35 237,70 238,04 238,39 238,74 239,09 239,43 239,78 240,13 370380 240,13 240,47 240,82 241,17 241,51 241,86 242,20 242,55 242,90 243,24 243,49 380390 243,59 243,93 244,28 244,62 244,97 245,31 245,66 246,00 246,35 246,69 247,04 390° 0 1 2 3 4 5 6 7 8 9 10 °c400 247,04 247,38 247,73 248,07 248,41 248,76 249,10 249,45 249,79 250,13 250,48 400410 250,48 250,82 251,16 251,50 251,85 252,19 252,53 252,88 253,22 253,56 253,90 410420 253,90 254,24 254,64 254,93 255,27 255,61 255,95 256,29 256,64 256,98 257,32 420430 257,32 257,66 258,00 258,34 258,68 259,02 259,36 259,70 260,04 260,38 260,72 430440 260,72 261,06 261,40 261,74 262,08 262,42 262,76 263,10 263,43 263,77 264,49 440450 264,11 264,45 264,79 265,13 265,47 265,80 266,14 266,48 266,82 267,15 267,49 450

2 PT 100 & K-TERMOCOUPLE TABL 04.06.2005 Yermoshkin O

460 267,49 267,83 268,17 268,50 268,84 269,18 269,51 269,85 270,19 270,52 270,86 460470 270,86 271,20 271,53 271,87 272,20 272,54 272,38 273,21 273,55 273,88 274,22 470480 274,22 274,55 274,89 275,22 275,56 275,89 276,23 276,56 276,89 277,23 277,56 480490 277,56 277,90 278,22 278,56 278,90 279,23 279,56 279,90 280,23 280,56 280,90 490500 280,90 281,23 281,56 281,89 282,23 282,56 282,39 283,22 283,55 283,89 284,22 500510 284,22 284,55 284,88 285,21 285,54 285,87 286,21 286,54 286,87 287,20 287,53 510520 287,53 287,86 288,19 288,52 288,85 289,18 289,51 289,84 290,17 290,50 290,83 520530 290,83 291,16 291,49 291,81 292,14 292,47 292,80 293,13 293,46 293,79 294,11 530540 294,11 294,44 294,77 295,10 295,43 295,75 296,08 296,42 296,74 297,06 297,39 540550 297,39 297,72 298,04 298,37 298,70 299,02 299,35 299,68 300,00 300,33 300,65 550560 200,65 300,98 301,31 301,63 301,96 302,28 302,61 302,93 303,26 303,58 303,91 560570 303,91 304,23 304,56 304,88 305,20 305,53 305,85 306,18 306,50 306,82 307,15 570580 307,15 307,47 307,79 308,12 308,44 308,76 309,09 309,41 309,73 310,05 310,38 580590 310,38 310,70 311,02 311,34 311,67 311,99 312,31 312,63 312,95 313,27 313,49 590600 313,59 313,92 314,24 314,56 314,88 315,20 315,51 315,84 316,16 316,48 316,80 600610 316,80 317,12 317,44 317,76 318,08 318,40 318,72 319,04 319,36 319,68 319,99 610620 319,99 320,31 320,63 320,95 321,27 321,59 321,91 322,22 322,44 322,86 323,18 620630 323,18 323,49 323,81 324,13 324,45 324,76 325,08 325,40 325,72 326,03 326,35 630640 326,35 326,66 326,98 327,30 327,61 327,93 328,25 328,56 328,88 329,19 329,51 640650 329,51 329,81 330,14 330,45 330,77 331,08 331,40 331,71 332,03 332,34 332,66 650660 332,66 332,97 333,28 333,60 333,91 334,23 334,54 334,85 335,17 335,48 335,79 660670 335,79 336,11 336,41 336,73 337,04 337,36 337,67 337,98 338,29 338,61 338,92 670680 338,91 339,23 339,54 339,85 340,16 340,48 340,79 341,10 341,41 341,72 342,03 680690 342,03 342,34 342,65 341,96 343,27 343,58 343,89 344,20 344,51 344,82 345,13 690700 345,13 345,44 345,75 346,06 346,37 346,68 346,99 347,30 347,60 347,91 348,22 700710 348,21 348,53 348,84 349,15 349,45 349,76 350,07 350,38 350,69 350,99 351,30 710720 351,30 351,61 351,91 352,22 352,53 352,83 353,14 353,45 353,75 354,06 354,37 720730 354,37 354,67 354,98 355,28 355,59 355,90 356,20 356,51 356,81 357,12 357,42 730740 357,41 357,73 358,03 358,34 358,64 358,95 359,25 359,55 359,86 360,16 360,47 740750 360,47 360,77 361,07 361,38 361,68 361,98 362,29 362,49 362,89 363,19 363,50 750760 363,50 363,80 364,10 364,40 364,71 365,01 365,31 365,61 365,91 366,22 366,51 760770 366,51 366,81 367,11 367,42 367,71 368,01 368,31 368,63 368,93 369,23 369,53 770780 369,53 369,83 370,13 370,43 370,73 371,03 371,33 371,63 371,93 372,22 372,51 780790 372,41 372,81 373,12 373,42 373,71 374,02 374,32 374,61 374,91 375,21 375,41 790800 375,51 375,81 376,10 376,40 376,70 377,00 377,29 377,59 377,89 378,19 378,48 800810 378,48 378,78 379,08 379,37 379,67 379,97 380,26 380,56 380,85 381,15 381,45 810820 381,45 381,74 382,04 382,33 382,63 382,91 383,21 383,41 383,81 384,10 384,40 820830 384,40 384,69 384,98 385,28 385,57 385,87 386,16 386,45 386,75 387,04 387,34 830840 387,34 387,63 387,92 388,21 388,51 388,80 389,09 389,39 389,68 389,97 390,26 840850 390,26 850° 0 1 2 3 4 5 6 7 8 9 10 °c

TABLE Pt 100 ohm x 0°C

Temperature is a reference to the 'hotness or coldness' of a body With SI units, the Kelvin scale is used where the unit of temperature is the kelvin (K), Two fixed points are assigned in this scale. Absolute zero, or 0 K, is the theoretical minimum temperature possible for any substance.

X0C = ( X + 273.1 ) K An approximation to 273 is made in most temperature conversion. A unit value, or the actual graduations on a scale, would be the same for each scale.

The second law of thermodynamics states that heat must flow front a hot body to a cold body. To measure temperature, therefore an equilibrium must be set up between the sensor and the body. တငးမ႔ အ၇ာန႔ SENSOR equilibrium ၿဖစဖ႔လပါတယ။ the transmission and indicating elements of the measuring system may be subject to temperature changes and some form of compensation will therefore be necessary.

Temperature measurement does not take place directly; some effect brought about by temperature changes is used. There are three broad classifications for the methods used: expansion, electrical and radiation.

Pyrometers.( 0 K အထကမာ၇ အ၇ာတငး Electromagnetic radiation လြင႔ထတၿကတယ။)All bodies above 0 K, i.e. absolute zero, will emit electromagnetic radiation. The intensity of the radiation is a measure of the temperature of the body. The intensity ranges from the invisible infra-red rays to the visible light range and is measured using a radiation pyrometer. The temperature measuring range for radiation pyrometers is about 700 to 2000°C. A pyrometer is generally understand to be a high temperature measuring thermometer. The radiation emitted from the hot body is measured or detected in some way and the instrument is calibrated for black body conditions. Black body conditions are considered ideal for radiation measurement. The black body is a thermodynamic concept of a body, which need not be black, which absorbs all energy incident upon it and also is a good emitter of radiation. The emitted radiation should result only from the temperature of the body itself and not from any other reflected radiation. The nearest practical example is a furnace which is observed through a very small aperture and hence any radiation detected will be only from the furnace. Two main types of radiation pyrometer – 1) the infra-red pyrometer, 2) the optical pyrometer. The infra-red pyrometer can theoretically measure temperatures from about 0 K up to 3300 K but would normally be used only for high temperature measurements, i.e. greater than 750 K The optical pyrometer by measuring visible radiation is only able to measure temperatures greater than about 900 K. REMARK - instruments the sensing device does not come into physical contact with the hot body. The disappearing filament type of optical pyrometer is most common. A heated filament lamp is positioned in the path of incoming light from the hot body. The current Flowing through the filament is varied until the filament 'disappears'. The current through the lamp is thus a measure of the temperature of the hot body The absorption screen is used to absorb some of the radiant energy from the source and thus extend the measuring range of the instrument. The monochromatic filter produces single colour, usually red, light to simplify filament mating.

The infra-red pyrometer uses a thermopile at the focus of the light rays instead of a filament lamp. There is no requirement for either screen or filter and the unit will produce a continuous reading of temperature

Pyroelectric detector – pyroelectric film ေတြဟါ dielectric material ၿဖစၿပး သရ႔ မကႏာၿပငက infrared (IR) ၇႔RADIATED ကလကခ၇၇င charge ၿဖစပါတယ။plastic film ကသးလ၇ေပမ႔ PIR ဆတ႔ modern passive infrared detection system က lithium tantalate ကသးပါတယ။သ႔က metal ၿပားတခန႔ကပၿပး လပသတခလလပထါးပါတယ။ infrared effect ေၿကာင႔ pyroelectric material မာ လပစစစၿပး voltage တခၿဖစလါပါတယ။သက high impendence ၿဖစလ႔ MOSFET န႔တြသးတတပါတယ။ သကလပ၇ားတ႔ အငဖါ၇ကထတအ၇ာေတြကေထါကလမးနငလ႔သခးဖမးစကေတြမာသးတတပါတယ။

RADIANT HEAT ENERGY SENSING အလငး။အပ။ေ၇ဒယလငး။Ionizing radiation စတါေတြကတငးဖ႔ bolometer ကသးပါတယ။ သမာပါတ႔ blackened material က radiation ကစတယၿပး သ႔အပခနတကလါပါတယ။အဒတကတ႔အပကတငးၿခငးၿဖင႔ radiation လြတတ႔ဟါ၇႔အပကbridge circuit န႔တငးယတါပါ။ေခတေပၚ က၇ယါေတြက semiconductor ေတြကသးလါပါတယ။

A thermometer (Liquid -in-glass thermometer)Various liquids are used in this type of instrument depending on the temperature range required, e.g. mercury —35 to +500*C, alcohol -80 to +70’C. A bulb containing the liquid is used to sense the temperature change. An increase in temperature causes the expanding liquid to rise up a capillary tube in the narrow glass stem. The temperature reading is taken from a scale marked on the glass stem. High temperature measuring mercury liquid thermometers will have the space above the mercury filled with nitrogen under pressure. Most marine-use thermometers of this type will be enclosed within a metal guard with the bulb surrounded by a metal sheath.

Liquid-in-metal thermometer

A more robust instrument which can be read remotely has a metal bulb to contain the liquid, A flexible metal capillary tube joins the bulb to a Bourdon-tube gauge to provide a reading of temperature. The complete unit is filled with the liquid under pressure and expansion causes a movement which is indicated on the Bourdon gauge. The use of mercury provides a range from —39 to +650°C and alcohol from -46 to + 150*C. The Bourdon tube may be spiral or helical and with increasing temperature will tend to straighten. The free end movement is transmitted through linkages to a pointer moving over a scale.

Gas expansion and vapor pressure thermometers

Gas expansion thermometers and vapor pressure thermometers are identical in construction to liquid-in-metal thermometers, using a Bourdon tube to provide indication.Gas expansion thermometers use an inert gas such as nitrogen or neon as the sensing and operating medium. A rise in temperature will cause expansion of the gas and an increase in pressure? in the Bourdon tube. A short response time is obtained with a gas expansion thermometer, and the indicating scale is linear. The measuring range is from -130 to +540°C. The vapor pressure thermometer has a bulb which is partially filled with a volatile liquid such as methyl chloride or diethyl ether. The remainder of the bulb, the capillary and the Bourdon tube are filled with the liquid vapor. A rise in temperature will cause some liquid to evaporate and an increase in pressure will occur in the Bourdon tube. A short response time is obtained with a vapor pressure thermometer, although the indicating scale is non-linear. The measuring range varies according to the liquid used, The Lower temperature measurement used with methyl chloride 0 to 50°C, diethyl ether 60 to 160°C.

Bimetallic strip thermometers

A bimetallic strip is made up of two different metals which are firmly bonded together. Typical metals used would be Invar (an iron-nickel alloy), which has a low coefficient of expansion, and either brass or nickel, which have high coefficients of expansion. When a temperature change occurs different amounts of expansion occur in the two metals causing a bending or twisting of the strip. A helical coil of bimetallic material with one end fixed is used in one form of thermometer.

temperature change will cause movement of a pointer fitted to the free end of the bimetallic strip. The choice of metals for the strip will decide the range, which can be from -30 to +550 degree C.

THERMOCOUPLE RTD

Thermocouple

PT 100

အပခနတငးမယဆ၇င platinumresistance temperature detector(RTD)ကအသးမားပါတယ။သက အပခနအနအမားေပၚမတညၿပး ခခမေၿပာငးတါကသးထါးပါတယ။အပခနမား၇င ခခမတကလါပါတယ. PT 100 Ωဆတါ RTD ပါဘ။ပလကတနမက 0’C မာ ၁၀၀Ω ၇လ႔ PT 100 လ႔ေခၚပါတယ။

ေဘးပက က၇းယါးထတ MPT 100 ဆတ႔ RTD တခပၿဖစပါတယ။ Resistance element,inner wires, protection tube,terminal box စတါေတြပါပါတယ။ပမနအါးၿဖင႔ အပခနအၿမင႔တငးတါန႔အနမ႔တငးတါ ဆၿပးထတၿကပါတယ။ဘါဘၿဖစၿဖစ သ၇႔ element က oxidized alumina က platinum wire န႔ပတထါးၿ႔ပး terminal board ဆကဆြထတထါးပါတယ။insulation tube & terminal board က high quality ceramic insulation material န႔လပထါးပါတယ။

High temp အတြငဆ၇ငေတါ႔ super ceramic sleeve type insulation tube ထမာ element ကထည႔ထါးပါတယ။ဒါေၿကာင႔ vibration&shock ကခနငပါတယ။ inner wire က nickel ၿဖစၿပး resistor element မာ weld လပထါးပါတယ။

ေအါကမာ သ၇႔ အပခနန႔လကၿပး Resistance ေၿပာငးတ႔chart ကၿပထါးပါတယ။

Temp switch with capillary tub

Thermistor က temperature signal transmit လပဖ႔မသးတတပါဘး။ safety cutout ေတြအတြက overheat temp က sense လပဖ႔ေလါကဘသးၿကပါတယ။ဥပမါ။ ေမၚတါ winding temp high ၿဖစ၇င၇ပဖ႔။သ႔က PTC Thermistor , NTC Thermistor ဆၿပး ၂ မးခြထါးပါတယ။ thermocouple temp sensor ေတြက platinum RTD ေတြ အတြက recommend မလပတ႔အပခန ( ၉၈၀ဒဂ၇ စငတ၈၇တ အထက)အတြကသးၿကပါတယ။ ဘါလ႔လဆေတါ႔ thermocouple ေတြက millivolt ထတေပးလ႔ သအတြက condition circuit ေတြလတတလ႔ပါ။thermocouple ေတြက သးတ႔ Temp & volt range ေပၚမတညၿပးအမးမးခြထါးပါတယ။ main engine exh gas temp, boiler combustion application အတြက K Type (၁၈-၁၃၀၀’C ) ကအသးမားပါတယ။အဒ ေ၇ြးခယသး၇င transmitter or condition circuit မာအမးအစါးေ၇ြးေပး၇တတပါတယ။

အမးအစါးမတတ႔ conductor ၂ ခက အစြနး ၂ ဖကမာ ခေဆၚၿပး အဒ ၂ ဖကက မတတ႔ အပခနမာထါးခ႔၇င thermoelectromotive force ၿဖစေပၚလါၿပး အဒ close circuit ထမာ thermocurrent စးပါတယ။အဒေတါ႔

အဒအစြနး၂ဖက၇႔ အပခနကါြၿခားခကက အဒမာၿဖစေပၚတ႔ thermoelectromotive force ကေနတြကယနငပါတယ။

Compensating Cable To enable the cold junction to be transferred from the end of the thermocouple to the measuring instrument which is usually remote from the former, compensating cable is used which has the same thermo-electric properties as the thermocouple wire but over a lower temperature range, i.e. 0 to 100°C For base metal thermocouples stranded wire of the same material but lower quality is used and for rare metal thermocouples, copper-nickel alloy. တကယလ႔ A point ကအပခနကB ကေနတငး၇င point B temp + thermoelectromotive force ၿဖစပါတယ။ဒလဘ႔ temp variation နတ႔ point C ဖကမာ တငး၇င C ေန၇ာအတြက compensating circuit ထည႔ေပး၇မာၿဖစပါတယ.တညေဆါကပက inner part of thermocouple မာ element wire ပါၿပး protection tube ထထည႔ထါးပါတယ။အဒကထြကတ႔ mV terminal က converter ဆပ႔ေပး၇ပါတယ။ အဒ converter မာ ambient temp compensating probe တပဖ႔ ပါပါတယ။

Thermocouple ေတြက စပတ႔ metal ေတြေပၚမတညၿပး S/R/J/K/T/E ဆၿပး အမးခြထါးပါတယ။

Temp switch ေတြက bi metallic (သ႔) အပခနေၿပာငး၇င လကေၿပာငးတ႔ element ေၿကာင႔ ခနထါးတ႔ အပခနတခမာ contact ေတြ အပတအဖြင႔ ၿဖစတါကအသးခထါးပါတယ။

Pressure instruments.

Pressure transducer ေတြဟါ အမားအါးၿဖင႔ pressure ေၿကာင႔ elastic membrane ပပကတါက အသးခထါးတတပါတယ။ pressure transducer အမ းမးေတြကေတါ႔ bellow,diaphragm,bourdon tube, strain gauge စတါေတြသးထါးတတပါတယ။ တငးတါကလ gauge pressure, absolute pressure, differential pressure စတါေတြက တငးတတပါတယ။pressure switch ေတြကေတါ႔ သကေပးသြငးတ႔ pressure ေၿကာင႔ contact ေတြ ပတ။ဖြင႔ ၿဖစတါကအသးခထါးပါတယ။ manual or automatic reset အမးအစါးေတြ၇ပါတယ။

m.e h.t in/out temp က sense လပ။ feed back controller ၂ခပါ cascade method န႔ထနးပါတယ။

Bourdon tube

Strain gauge

အေပၚက differential pressure cell ေတြက pressure တငးတါမာ။ flow တငးတါေ၇ာ။ level တငးတါေ၇ာ သးၿကပါတယ။

IGG Plant combustion chamber pressure control valve 6001 was control by pressure transmitter PT 6006 ( PLC 8005 ကသးၿပး)

Vortex shedder flow meter မာ bar တတေခာငးပါၿပး သ႔က စးေၿကာငးမာထါး၇ပါတယ။ စးေၿကာငးတခမာ vortex (whirlpool) ေ၇၀ ေတြၿဖစလါၿပး အဒဘါးတက ၇ကလ႔ ဘါးတတနခါလါပါတယ။ အဒ flow န႔ အခးကတ႔ တနခါမ ၿကမနနးကေန တြကယပါတယ။Orifice flow meter - Orifice တခက စးေၿကာငးမာထါးၿပး အဒ orifice ကအၿဖတ pressure drop ကတငးယပါတယ။ အဒ pressure drop ပမါဏေပၚမတညၿပး flow ကတြကယပါတယ။သက liquid, steam, gas အါးလးအတြကအသးမားၿပး တကမနကနပါတယ။

Vortex Shedder Flow Orifice flow meter

Turbine flow meter

Flow instruments.

Flow ကတက၇ကတငးတါ။သြယ၀ကၿပးတငးတါ ဆၿပး ၂ မး၇ပါတယ။တက၇ကတငး၇င သတမတခနအေတါအတြငး volume or weight ကတငးယပါတယ။( သေဘါၤေပၚသးတ႔ အေတၚမားမား flow meter ေတြကဒါမးပါဘ) သြယ၀ကတငး၇င constricted flow area ( orifice ) တခက ၿဖတတ႔အခန pressure drop ကတငးပါတယ။ Reynolds number of 2000 န႔ အထက steady flow ၇ liquids, vapor,gas ဆ၇င Concentric orifice plates ကသးတယ။ reynolds number 5000 န႔ အထကဆ flow nozzle ဒါမမဟတ venture tube သးတယ။ ၿဖတ တပ အ၇ငသးခင၇င annular pilot tube (or) turbine flow meter ကသးတတတယ။ Flow switch ေတြကေတါ႔ flow စးလါ၇င contact အပတအဖြင႔ လပတါက သးထါးပါတယ။

Capacitive liquid level sensor, steam flow meter ေတြသးၿပး sense လပကါfeed water control valve ကထနးပ

သတမတခန

တြငVolume measure

Reynold no 100 to 2300

2300 to 100000

Turbulent မားေလ reynold မားေလ

Level instruments.

Pressure transducer က tank bottom tap မာတပၿပး level ကတငးတတပါတယ။ density တနဖးသ၇ငတြကထတနငပါတယ။ density က အပခနေပၚမတညေၿပာငးလ႔ အပခနလ ထည႔တြက၇မယ။ တကယလ႔ အဒ tank က pressurized လပထါး၇င differential pressure transducer ကသး၇ပါမယ။

ဘြငလါ အခ႔က capacitive liquid level sensor ကသးထါးပါတယ။ bubbler type liquid level sensor က fuel tank / ballast tank/ corrosive liquid ေတြ၇တ႔ tank ေတြအတြကသးတတပါတယ။ အခ ႔ tanker ေတြက float ေတြသးၿပး အခ ႔ က radar system ကသးတတပါတယ။ Liquid level switches ေတြဟါအမားအါးၿဖင႔ displacer float က switch housing မာ တပထါးၿပး contact ေတြက level အနအမားေပၚလကၿပး contact ေတြကအပတအဖြင႔ၿဖစေစပါတယ။

Float အမးမး

Bubbler level

Conductivity probe

in a closed top tank

ဒအမးအစါးသး၇ငတနဖးေတါကေလာကတငးနငပါတယးဒါေၿကာင႔ modulate a control valve ကထနးနငပါတယ။ low level /high level stop အတြကလသးနငပါတယ။(Cb

ကေ၇အနမ႔အၿမင႔ေပၚမတညေၿပာငးလ႔ (Ca-Cb )လေၿပာငး

Bubbler level measurement တခ အေၿကာငး manual

Tank ထ၇အ၇ည၇႔အေလးခနေၿကာင႔ ၿဖစေပၚလါတ႔ hydrostatic pressure ကတငးၿပး level ကတြကယတ႔စနစၿဖစပါတယ။

Liquid hydrostatic pressure န႔ တေအါင ေလ ေကြးပါတယ။tank ထက အ၇ညမကနာၿပငၿမင႔လါလ႔ counter pressure တကလါမယ။အဒကေကာဖ႔ constant speed controller က ေကြးတ႔ flow ကေပးထါးတ႔ဂ၇ပအတငးတကလါ၇င ေကြးတ႔ေလ၇႔ pressure က hydrostatic pressure န႔တလါပါမယ။ အဒေလဖအါးေလးကelectrical pressure sensor န႔တငးၿပး အခးက electrical signal ကေၿပာငးေပးပါတယ။အဒတငးလ႔၇တ႔ ဖအါးကေအါကက ပေသနညးထထည႔တြကလက၇င အထ၇ အ၇ည၇႔ အၿမင႔က၇ပါမယ။

ေပးတ႔ေလက ၅-၈ ဘါး ဆေတါ႔ pressure reducing valve န႔ေလာ႔ယပါတယ။ၿပးေတါ႔ constant flow speed controller ဆပ႔ပါတယ။flow adjustment screw က 0.5l/min ေလါကမာၿငမေနေအါငခနထါးပါတယ။ေသခာၿကည႔၇ငဒ control က orifice ခၿပးတညေဆါကထါးတ႔ windlass hydraulic system ၇႔ load control piston ၇႔ function န႔အတတပါဘ၊

အဒ flow က rotameter က ေဘါေလးက ၿပပါတယ။အဒေလစးေၿကာငးက measuring line အတငးသြါးပါတယ။ tank level height က အဒေလဖလးေပၚ counter pressure ၿပနေပးပါတယ။အဒါဆေလပေကြးမယ။ဒါဆပကလငးထ၇ေလဖအါးတကမယအဒေလဖအါးကတငး၇ငအၿမင႔တြကလ႔၇ၿပၿဖစပါတယ။

ဒါေၿကာင႔ ဒconstant flow speed controller က စနစ၇႔ အသကပါဘ။ သက counter pressure ဘယေလါက၇၇ ပမန0.5 l/min flow ၇ေအါငထနးေပးပါတယ။ အခ ႔ အငဂင lever တေအါကမာ ၇တ႔ pneumatic speed control valve ပစမး တညေဆါကထါးပါတယ။ ၿပးေတါ႔ hydraulic system load controller လတညေဆါကထါးတယ။ ခခမတး၇ငေလပေကြးမယ။ေလာ႔သြါး၇င ေလေကြးတါၿပနေလာ႔မယ။ဒါမးတညေဆါကထါးပါတယ။

အေပၚပမာၿကည႔လက၇င tank level ၿမင႔လ႔ counter pressure ၿမင႔လါ၇င ေလကပဖြင႔ေပးမယ။ ဒါေၿကာင႔ပမန ၀.၅l/min rotameter မာၿပဘ႔ေကြးတ႔ေလက ၁.၂ ဘါး counter pressure အတြက ၀.၉ l/min တကယေကြး၇လမ႔မယ။အလ ခနထါးတ႔ 5l//min က၇ေအါငသဟါသ ေကြးတ႔ေလကတငေပးတါကေန ၿဖစလါတ႔pressure အေၿပာငးအလကpressure sensor န႔ယၿပး အၿမင႔ကတြကထတယပါတယ။

ဆ အမားၿကး၇၇႔န႔ flow meter ကမၿပ၇င air flow to tank line ပတသြါးတါၿဖစနငတယ။ purge line ကေန purge hose ကေလန႔ မတထတပါ။

Position sensors - အေ၇ြ႔ကတငးတါၿဖစပါတယ။ ဗါးတလးဘယေလါကဖြင႔။ပတဆတါ Control ပငးမာအေ၇းပါပါတယ။ ဒါက position sensor န႔တငးပါတယ။ အသးမားတါက limit switch &

potentiometer တ႔ၿဖစပါတယ။

Limit switch က သ၇႔ arm က လပ၇ားေနတ႔အ၇ာက လါထ၇င contact အပတအဖြင႔လပပါတယ။ Potentiometer ဆတါ resistor တခၿဖစၿပး သမာ wiper ဆတ႔ sliding contact ပါပါတယ။ အဒ wiper ေ၇ာကတ႔ေန၇ာေပၚမတညၿပး ခခမေၿပာငးၿပးၿပပါတယ။

Governor ဆ၇င အင၇င rpm က fly weight (သ႔) rpm pick up န႔ sense လပၿပး load အေၿပာငးအလၿဖစ၇ငေတါငသတမတ rpm အတြငးၿငမေအါငထနးမယ။

Limit switch &,proximity sensor Valve open/close control by

positioner

Inductive proximity sensor.

Viscosthem ဆ၇င fuel ၇႔ viscosity က sense လပၿပး fuel injection အတြကလတ႔ Injection viscosity ၇ေအါင temp က အတးအေလာ႔လပၿပးထနးမယ။

B14- back flush autom filter, B16- viscometer , D01/D02-supply pump ,Q01-Flow meter,D03/D04-ME FO circulating pump, B10/B11-heater , B05-mixing column ,B15-by pass filter

B14

B16

From MEheater

D01

Q01 D03

B05

Viscosense viscometer - Sensor housing က ductile iron န႔လပထါးၿပၤး fuel line မာတပနငပါတယ။ sensor ကstainless steel န႔လပထါးပါတယ။ sensor ၇႔ အဓကအစတအပငး ၂ ခၿဖစတ႔ pendulum န႔ flowtube က special Teflon coating လပထါးပါတယ။interface box န႔ဆကဘ႔ 5 meter signal cable ပါပါတယ။viscosense interface box က wall mount electronic unit ၿဖစၿပး sensor ကလါတ႔ signal က process လပပါတယ။အဒ interface box က4-20 mA signal က controller ဆပ႔ေပးၿပး viscosity & temp ကထနးဘ႔လပေပးပါတယ။

သ၇႔ အလပလပပက Liquid ထမာ pendulum ၇႔ rotational vibration ေပၚတ႔ၿပနမက အေၿခခထါးပါတယ။ sensor မာ pendulum ပါပါတယ။ အဒ pendulum(1) က base plate (2) မာ torsion tube (3) န႔ လါတြထါးပါတယ။ piezo-electric element ၂ set က pendulum အထမာထည႔ထါးပါတယ။ 1 set က pendulum ကလပ၇ားေစဘ႔။ေနာကတခက pendulum ၇႔ rotational movement က feed back circuit ကေန control လပဘ႔ၿဖစပါတယ။ဒါေၿကာင႔ pendulum က resonance frequency န႔ vibration ၿဖစေနပါတယ။

အဒ vibration က damping ၿဖစေစတ႔ ပမါဏ က စးဆငးတ႔ ဆ၇႔ square root of the dynamic viscosity န႔တက၇ကအခးကပါတယ။အဒ damping ၿဖစတ႔အခါထြကလါတ႔ resulting frequency က phase difference 2 ခ န႔တငးယပါတယ။mechanical damage ကကါကြယဖ႔ pendulum က flow tube (5) န႔ ငထါးပါတယ။အဒ flow tube inlet က တငးတါဖ႔ လေလါကတ႔ ဆ ပမါဏက ၀ငေ၇ာကေစပါတယ။

အခ ႔ control ေတြက simple feed back က မသးဘ feed forward ေတြ။ cascade ေတြ။ ratio ေတြ။ slave follow master & lead lag ေတြကသးၿကပါတယ။

Cascade control ဆတါက feed back control loop ၂ ခပါၿပး primary loop ( outer loop) ၇႔ output က secondary loop (inner loop) အတြက set point အၿဖစေပးထါးတါမးၿဖစပါတယ။ အဒ loop ၂ ခ interaction ေၿကာင႔ control instability မၿဖစေအါင respond time ေတြခြါထါး၇ပါမယ။ ပမနအါးၿဖင႔ primary loop က တန႔ၿပနမပေနးၿပး သ၇႔႔response time က ၅ ဆ ကေန ၁၀ ဆထ secondary loop ထကပမားတတပါတယ။

သ႔က turn လပ၇င - outer loop ( primary) က manual ထါးၿပး inner loop ( secondary ) က turn လပပါ။ ၿပး၇ငprimary က turn လပပါ။ ( inside out လ႔ေၿပာၿကပါတယ ) integral windup ဆတ႔ အထနးလြနမက ကါကြယဖ႔လအပ၇င outer loop output က limit လပပါ။

ဒါေပမ႔ cascade control တခက disturbance တခ၀ငလါ၇င ထနးနငစြမး၇ညကဆငး ပကစးတတပါတယ။(a)ကအတငး

တကယလ႔ အဒ disturbance က တငးတါတြကခကနငခ႔၇င အဒအတြက correcting signal က outer controller output signal ထထးထည႔ၿပး compensate လပဖ႔သးနငပါတယ။အဒလ inner controller မတငခင correcting signal က feed back မပါဘ သးတါက feed forward control လ႔ေခၚပါတယ။

ၿပးေတါ႔ တငးတ႔ အမ းအစါးေပၚမတညၿပး single element, two element, three element control ဆၿပး ကြပါေသးတယ။

ဥပမါ - ဘြငလါေ၇ level က ထနးတ႔ control မာ ေ၇ level တခထ တငးၿပးထနးတါဆ single element control ၿဖစပါတယ။ steam flow, feed water flow , level ၃ ခတငးၿပးထနးတါဆ 3 element control ၿဖစပါတယ

2 element with feed forward -ေနာကပငးၿပမ႔ စနစလ feed water flow က feed back မယဘ drum level controller( အဒမာေတါ႔ feed back ပါပါတယ)အထြကန႔ steam flow signal ၂ ခက summer လပလ႔ ၇တ႔ output န႔တက၇ကfeed water control valve က control လပလ႔ feed forward ၿဖစပါတယ။ သမာ မေကါငးတါက feed water flow မမနခ႔၇င drum pressure အေၿပာငးအလ ၿဖစမာမ႔ level ကလ လကကစါးမာၿဖစပါတယ။

3 elements, feed forward, cascade loop control

Steam demand ၇တတ၇က တက၇င ဘြငလါpressure လက။အလကလ႔ မးပထးလ႔ steam generation ပမားတါ၇ယေၿကာင႔ boiler water level မာ၇တ႔ steam bubble ေတြပၿကးလါပါတယ။ဒါေၿကာင႔ boiler water level က တကယ၇တါထက ပမားေနသလ လါၿပေနပါတယ။အဒါက swell effect လ႔ေခၚပါတယ။ Shink က အဒါ၇႔ေၿပာငးၿပနပါ။

အဒ effect ေတြေၿကာင႔ control ကထခကမမ၇ေအါင steam flow, water flow & water level ဆတ႔ 3 element ကတငးယၿပး control လပပါတယ။ ေအၚကပက drum level ( element) အၿပင steam flow &water flow စတ႔အၿခား element 2 ခကပါအသးခထါးတါၿဖစပါတယ။သ႔မာ ၿကည႔လက၇င feed back loop, feed forward loop, cascade loop ေတြပါတါေတြ႔၇ပါတယ။ feed water flow controller က inner controller ( secondary controller) ၿဖစၿပး level controller က Outer controller( primary controller) ၿဖစပါတယ။ primary controller မာ set point က A ၿဖစပါတယ။ feed back က LT ကလါတ႔ Level signal ၿဖစပါတယ။swell effect ေၿကာင႔ ေ၇ level တကေပမ႔ steam flow က summer ထထည႔ထါးလ႔ စါးသြါးတ႔ steam ေပၚတညၿပး ေ၇ပၿဖည႔ပါမယ။primary controller output ၇ယ။

steam flow အေၿပာငးအလ၇ယကoutput of summer(∑)ကေၿပာငးေပးပါတယ။အဒ summer က feed controller အတြက set point အၿဖစပ႔ေပးပါတယ။ inner controller အတြက - feed water flow က feed back အၿဖစေပးပါတယ။ ဒါေၿကာင႔ feed flow အ၇မးမားလ႔ drum pressure အေၿပာငးအလၿဖစတါကကါကြယပါတယ။

Ratio control –boiler burner ေတြမာ ဆန႔ ေလ ratio မနဘ႔သးတတပါတယ။ အဒလ ratio လပတ႔အခါ flow တခကmaster အၿဖစသတမတပါတယ။အဒ master flow က plant အတြကလအပတ႔ ထြကနနး throughput က၀ငဖ႔ set လပပါတယ။ ကန တ႔ slave flow က လအပတ႔ ratio ၇ေအါငလကလပေပးတ႔ flow အၿဖစ သတမတပါတယ။

level

ဒစနစက feed forward, controller 2 ခ cascade, ၃element ၿဖစပါတယ။

Controller 2 လးသး၇င

Master flow က require ratio set လပတ႔ ratio block ( multiplier) ထ ၿဖတၿပး သ႔အထြကက slave controller ၇႔set point အၿဖစေပးထါးပါတယ။ ဒါေၿကာင႔ slave flow က master flow ေနာကက လကပါတယ။ master loop က ဘါးေတြကပသြါး၇င Slave controller က correct ratio ကထနးထါးပါမယ။Slave flow က master flow ေနာကကလက၇လ႔ ( lag ၿဖစလ႔) gas/air burner ေတြမာ air flow က master , gas loop က slave ထါးပါတယ။ဒါက air master gas slave ( gas follow air ) လ႔ေၿပာပါတယ။ ၿဖစနင၇င slowest loop က master, fastest loop ကslave ထါးသငပါတယ။( lag ကေကာဖ႔)။အဒမာ ratio block က multiplier ၇း၇းၿဖစၿပး ကယလခငတ႔ ratio က၇ကထည႔လက၇ပါဘ။ဒါေပမ႔ တခ ၇တါက slave သါပကသြါး၇င ratio ေတြကေမါကကမ ၿဖစနငပါတယ။ဒါကကါကြယဖ႔ lead/lag ကသးၿကပါတယ။

Controller တလးထသး၇င

FUEL FOLLOW AIR With 2 feed back controller

Boiler combustion system with lead lag control for ( air and fuel)

LEAD LAG CONTROL

အဒမာေတါ႔ cross linking & selector ကသးၿပး air set point က highest set point အၿဖစသတမတၿပး fuel set point ႕က lowest set point အၿဖစသတမတပါတယ။တကယလ႔ fuel valve jamၿဖစ၇ငေတါင air က ratio အတငးသြါးးေနလ႔ explosive atmosphere ကေန ကါကြယပါတယ။

The types of enclosures are standardized by the National Electrical Manufacturers Association (NEMA). NEMA enclosure types are selected according to the environment in which the equipment is installed.

(အေပၚမာ NEMA enclosure type ေတြက အဆင႔သတမတထါးတါပါ)

The Occupational Safety and Health Administration (OSHA) regulations require that once the emergency stop switch has activated, the control process cannot be started again until the actuating stop switch has been reset to the on position.

OSHA ကသတမတထါးတါက Emergency stop ႏပၿပး၇င reset မလပမခငးေမါငး၇မ၇ေအါငစမထါး၇ပါမယ။ေအါကကလေပါ႔

Pilot lights provide visual indication of the status for many motor-controlled processes permitting personnel at remote locations to observe the current state of the operation.

Selector switch - The difference between a push button and selector switch is the operator mechanism. A selector switch operator is rotated (instead of pushed) to open and close contacts of the attached contact block. Switch positions are established by turning the operator knob right or left. These switches may have two or more selector positions, with either maintained contact position or spring return to give momentary contact operation.

Selector switch က အေတၚမားမား circuit ေတြမာ၇ပါတယ။ လည႔ၿပး ေ၇ြး၇တါမး။ ဥပမါ - auto / manual ေၿပာငးတါမး

drum switch consists of a set of moving contacts and a set of stationary contacts that open and close as the shaft is rotated. Reversing drum switches are designed to start and reverse motors by connecting them directly across the line.

Limit switches are designed to operate only when a predetermined limit is reached, and they are usually Contacts may consist of the normally open, normally closed, momentary (spring-returned), or maintained-contact types. The terms normally open and normally closed refer to the state of the contacts when the switch is in its normally deactivated state. actuated by contact with an object such as a cam.

Normally open / normally close ဆတါ အလပမလပေသးတ႔အခန ( deactivated state)မာ၇တ႔ contact အေၿခအေနကေၿပာတါပါ။

MSB က phase

voltage တငးတ႔

switch

micro limit switch is a snap action switch housed in a small enclosure. Snap action switches are mechanical switches that produce a very rapid transfer of contacts from one position to another. They are useful in situations that require a fast opening or closing of a circuit. In a snap-action switch, the actual switching of the circuit takes place at a fixed speed no matter how quickly or slowly the activating mechanism moves. One difference between traditional limit switches and micro limit switches is the electrical configuration of the switch contacts. Micro switches use a single-pole, double-throw, contact arrangement that has one terminal connected as a common between the normally open and normally closed contacts instead of two electrically isolated contacts. The micro switch body is normally constructed of molded plastic, which offers a limited amount of electrical isolation and physical protection for contacts.

Micro switch မာ၇ NC န႔ NO contact ၂ ခဟါ ဘအမတ၇တ႔ single pole , double throw အမးအစါးၿဖစပါတယ။

Temperature switch

Temperature switches open or close when a designated temperature is reached. Temperature control devices are used in heating or cooling applications where temperature must be maintained within preset limits.

သတမတအပခနေ၇ာက၇င capillary tube & bulb ထက temperature-sensitive liquid ၇႔ ၿပန႔ကါး က႔၀ငတ႔ effect န႔ switch က အလပလပတါပါ။ cold room ( meat room စတ႔) အခနးေတြ၇႔ solenoid ကactivate လပတ႔ switch မးပါ.

Pressure switches are used to monitor and control the pressure of liquids and gases. They are commonly used to monitor a system and, in the event that pressure reaches a dangerous level, open relief valves or shut the system down. The three categories of pressure switches used to activate electrical contacts are positive pressure, vacuum (negative pressure), and differential pressure.

ပ၇က၇ာဆြစေတြမာ vacuum / positive/ differential pressure – switch ဆၿပး၇ၿကပါတယ။

air condition compressor အတြက oil pressure switch ( differential pressure switch)

Air condition compressor အတြကdifferential pressure switch

Sewage plant အတြက vacuum pressure switch

Sensor

Proximity sensor and symbols

Proximity sensors detect the presence of an object (usually called the target) without physical contact. Detection of the presence of solids such as metal, glass, and plastics, as well as most liquids, is achieved by means of a sensing magnetic or electrostatic field. These electronic sensors are completely encapsulated to protect against excessive vibration, liquids, chemicals, and corrosive agents found in the industrial environment. Proximity sensors are available in various sizes and configurations to meet different application requirements. One of the most common configurations is the barrel type, which houses the sensor in a metal or polymer barrel with threads on the outside of the housing.

Proximity sensor ေတြက 3 မးခြထါးပါတယ။ inductive proximity sensor ။ capacitive proximity sensor , magnetic proximity sensor ဆၿပး၇ပါတယ။ inductive proximity sensor က ferrous metal and non ferrous metal ေတြက detect လပဖ႔သးနငပါတယ။

INDUCTIVE PROXIMITY SENSORS Proximity sensors operate on different principles, depending on the type of matter being detected. When an application calls for noncontact metallic target sensing, an inductive-type proximity sensor is used. Inductive proximity sensors are used to detect both ferrous metals (containing iron) and nonferrous metals (such as copper, aluminum, and brass). Inductive proximity sensors operate under the electrical principle of inductance, where a fluctuating current induces an electromotive force (emf) in a target object.

သ႔၇႔အလပလပပက sensor က ထတလြတေနတ႔ high frequency electromagnetic field ထ တငးမ႔ အ၇ာ ၀ငလါ၇ငEDDY CURRENT ေၿကာင႔ OSCILLATOR STRENGTH အေၿပာငးအလကမတညၿပး တြကယတါၿဖစပါတယ။ FERROUS METAL ဆ၇င 2 INCHES အကါြကတငးနငၿပး NON FERROUS ဆ၇ငအဒအကါြအေ၀းထကန႔မတငးနငပါတယ။

Set Distance The distance from the reference surface that allows stable use, including the effects of temperature and voltage, to the (standard) sensing object transit position. This is approximately 70% to 80% of the normal (rated) sensing distance.

Sensing Distance The distance from the reference position (reference surface) to the measured operation (reset) when the standard sensing object is moved by the specified method.

Hysteresis (Differential Travel) With respect to the distance between the standard sensing object and the Sensor, the difference between the distance at which the Sensor operates and the distance at which the Sensor resets.

Leakage current ဆတါ - In the off state, enough current must flow through the circuit to keep the sensor active. This off state current is called leakage current

The oscillator circuit generates a high-frequency electromagnetic field that radiates from the end of the sensor.

When a metal object enters the field, eddy currents are induced in the surface of the object. • The eddy currents on the object absorb some of radiated energy from the sensor, resulting in a loss of energy and change of strength of the oscillator. • The sensor’s detection circuit monitors the oscillator’s strength and triggers a solid-state output at a specific level. • Once the metal object leaves the sensing area, the oscillator returns to its initial value.

Capacitive proximity sensors are similar to inductive proximity sensors. The main differences between the two types are that capacitive proximity sensors produce an electrostatic field instead of an electromagnetic field and are actuated by both conductive and nonconductive materials. Capacitive sensors contain a high-frequency oscillator along with a sensing surface formed by two metal electrodes .When the target nears the sensing surface, it enters the electrostatic field of the electrodes and changes the capacitance of the oscillator. As a result, the oscillator circuit begins oscillating and changes the output state of the sensor when it reaches certain amplitude. As the target moves away from the sensor, the oscillator’s amplitude decreases, switching the sensor back to its original state. Capacitive proximity sensors will sense metal objects as well as nonmetallic materials such as paper, glass, liquids, and cloth. They typically have a short sensing range of about 1 inch, regardless of the type of material being sensed. The larger the dielectric constant of a target, the easier it is for the capacitive sensor to detect. This makes possible the detection of materials inside nonmetallic containers.

An ordinary Capacitive Proximity Sensor is similar to a capacitor with two parallel plates, where the capacity of the two plates is detected. One of the plates is the object being measured (with an imaginary ground), and the other is the Sensor's sensing surface.

Detection Principle of Magnetic Proximity Sensors

The reed end of the switch is operated by a magnet. When the reed switch is turned ON, the Sensor is turned ON. Magnetic proximity switches detect magnetic fields at greater distances of up to 60 mm, even through non-ferromagnetic materials like stainless steel. Depending on the permanent magnets used, different sensing distances can be implemented. The permanent magnet can be installed independent of polarity and with large tolerances, which allows many different installation options, even in cramped spaces. Precise switching is thus guaranteed even when used in dirty or damp environments. This means that applications in cranes or heavy vehicles are also easy to implement.

A photoelectric sensor is an optical control device that operates by detecting a visible or invisible beam of light, and responding to a change in the received light intensity. Photoelectric sensors are composed of two basic components: a transmitter (light source) and a receiver (sensor). These two components may or may not be housed in separate units. The basic operation of a photoelectric sensor can be summarized as follows:

• The transmitter contains a light source, usually an LED along with an oscillator.

. The oscillator modulates or turns the LED on and off at a high rate of speed.

• The transmitter sends this modulated light beam to the receiver.

• The receiver decodes the light beam and switches the output device, which interfaces with the load.

• The receiver is tuned to its emitter’s modulation frequency, and will only amplify the light signal that pulses at the specific frequency.

• Most sensors allow adjustment of how much light will cause the output of the sensor to change state. • Response time is related to the frequency of the light pulses. Response times may become important when an application calls for the detection of very small objects, objects moving at a high rate of speed,

or both. T he scan technique refers to the method used by photoelectric sensors to detect an object. Common scan techniques include through-beam, retro reflective, and diffuse scan. Understanding the differences among the available photoelectric sensing techniques is important in determining which sensor will work best in a specific application.

photoelectric sensor

The through-beam scan technique (also called direct scan) places the transmitter and receiver in direct line with each other. The operation of the system can be summarized as follows:

• The receiver is aligned with the transmitter beam to capture the maximum amount of light emitted from the transmitter.

• The object to be detected placed in the path of the light beam blocks the light to the receiver and causes the receiver’s output to change state.

• Because the light beam travels in only one direction, through-beam scanning provides long-range sensing. The maximum sensing range is about 300 feet.

• This scan technique is a more reliable method in areas of heavy dust, mist, and other types of airborne contaminants that may disperse the beam and for monitoring large areas.

• Quite often, a garage door opener has a through beam photoelectric sensor mounted near the floor, across the width of the door. For this application the sensor senses that nothing is in the path of the door when it is closing.

RETROREFLECTIVE SCANNING In a retro reflective scan , the transmitter and receiver are housed in the same enclosure. This arrangement requires the use of a separate reflector or reflective tape mounted across from the sensor to return light back to the receiver. This sensor is designed to respond to objects that interrupt the beam normally maintained between the transmitter and receiver. In contrast to a through-beam application, retroreflective sensors are used for medium-range applications.

Retroreflective scan sensors may not be able to detect shiny targets because they tend to reflect light back to the sensor. In this case the sensor is unable to differentiate between light reflected from the target and that from the reflector. A variation of retroreflective scan, the polarized retrorefl ective scan sensor is designed to overcome this problem. Polarizing filters are placed in front of the emitter and receiver lenses. The polarizing filter projects the emitter’s beam in one plane only. As a result, this light is considered to be polarized. A corner-cube reflector must be used to rotate the light reflected back to the receiver. The polarizing filter on the receiver allows rotated light to pass through to the receiver.

DIFFUSE SCANNING In a diffuse scan sensor (also called proximity scan), the transmitter and receiver are housed in the same enclosure, but unlike similar retroreflective devices, they do not rely on any type

of reflector to return the light signal to the receiver. Instead, light from the transmitter strikes the target and the receiver picks up some of the diffused (scattered) light.

When the receiver receives enough reflected light the output will switch states. Because only a small amount of light will reach the receiver, its operating range is limited to a maximum of about 40 inches. The sensitivity of the sensor may be set to simply detect an object or to detect a certain point on an object that may be more reflective. Often this is accomplished using various colors with different reflective properties.

FIBER OPTICS Fiber optics is not a scan technique, but another method for transmitting light. Fiber optic sensors use a flexible cable containing tiny fibers that channel light from emitter to receiver. Fiber optics can be used with throughbeam, retroreflective scan, or diffuse scan sensors. In through-beam scan, light is emitted and received with individual cables. In retroreflective and diffuse scan, light is emitted and received with the same cable. Fiber optic sensors systems are completely immune to all forms of electrical interference. The fact that an optical fiber does not contain any moving parts and carries only light means that there is no possibility of a spark. This means that it can be safely used even in the most hazardous sensing environments such as a refinery for producing gases, grain bins, mining, pharmaceutical manufacturing, and chemical processing. Another advantage of using optical fibers is the luxury it affords users to route them through extremely tight areas to the sensing location. Certain fiber optics materials, particularly the glass fibers, have very high operating temperatures (450°F and higher).

fi

Hall effect sensors are used to detect the proximity and strength of a magnetic field. When a current-carrying conductor is placed into a magnetic field, a voltage will be generated perpendicular to both the current and the field. This principle is known as the Hall effect. A Hall effect sensor switch is constructed from a small integrated circuit (IC) chip . A permanent magnet or electromagnet is used to trigger the sensor on and off. The sensor is off with no magnetic field and triggered on in the presence of a magnetic field. Hall effect sensors are designed in a variety of body styles. Selection of a sensor based on body style will vary by application. Analog -type Hall effect sensors put out a continuous signal proportional to the sensed magnetic field. An analog linear Hall effect sensor may be used in conjunction with a split ferrite core for current measurement. The magnetic field across the gap in the ferrite core is proportional to the current through the wire, and therefore the voltage reported by the Hall effect sensor will be proportional to the current. Clamp on ammeters that can measure both AC and DC current use a Hall effect sensor to detect the DC magnetic field induced into the clamp. The signal from the Hall effect device is then amplified and displayed. Digital- type Hall effect devices are used in magnetically operated proximity sensors. In industrial applications they may serve to determine shaft or gear speed or direction by detecting fluctuations in the magnetic field.

One such application, which involves the monitoring of speed of a motor. The operation of the device can be summarized as follows:

• When the sensor is aligned with the rotating ferrous gear tooth, the magnetic field will be at its maximum strength.

• When the sensor is aligned with the gap between the teeth, the strength of the magnetic field is weakened.

• Each time the tooth of the target passes the sensor, the digital Hall switch activates, and a digital pulse is generated.

• By measuring the frequency of the pulses, the shaft speed can be determined.

• The Hall effect sensor is sensitive to the magnitude of flux, not its rate of change, and as a result the digital output pulse produced is of constant amplitude regardless of speed variations.

• This feature of Hall effect technology allows you to make speed sensors that can detect targets moving at arbitrarily slow speeds, or even the presence or absence of nonmoving targets.

An ultrasonic sensor operates by sending high-frequency sound waves toward the target and measuring the time it takes for the pulses to bounce back. The time taken for this echo to return to the sensor is directly proportional to the distance or height of the object because sound has a constant velocity. The 4-20 mA represents the sensor’s measurement span. The 4-mA set point is typically placed near the bottom of the empty tank, or the greatest

ultra sonic sensor

Fixed-Speed Alternators with Variable-Speed Synchronous Motors

Static frequency converters are used in a number of ship’s installations as the controlling intermediary between fixed-speed alternators and variable-speed synchronous propulsion motors

The output from the alternators is delivered at constant voltage mid frequency. For manoeuvring or slow speeds, the output is passed on to propulsion motors at a lower frequency and with its voltage adjusted. The speed of a synchronous motor is governed by the frequency of the current supplied. Many synchronous drives are based on conversion of the output (from fixed-speed alternators), first to direct current and then back to a.c, at a lower frequency (the opposite of the converter scheme for variable-speed shaft generators).

Synchronous motor အေၿကာငးနန ဖတၿကည႔ပါ။

လပစစ ေမၚတါန႔ ပနကါလည႔တ႔ လပစစ သေဘါၤေတြမာ သးၿကတါက 3 phase synchronous motor ပါဘ။ ေနာက ၿပး 4 stroke engine သး cpp propulsion မာ redundancy propulsion အေနန႔ shaft generator က ေမၚတါေၿပာငးၿပးပနကါကၿပနလည႔၇ငလ ဒလ ေမၚတါမးပါဘ။(PTO & PTH လ႔ေၿပာၿကပါတယ။ PTO ဆတါ POWER TAKE OUT – Engine ကေန shaft generator ကေမါငးတါ။ PTH – power take home – shaft generator က ေမၚတါေၿပာငး-မးစကပါ၀ါန႔ ပနကါလည႔ၿပး အမၿပနတါ) သက no load to full load တငတ႔ အတြငး constant speed န႔ တကနငလ႔လၿဖစပါတယ။သလညနနးက ေတါ႔ ပါတ႔ pole အေ၇အတြကန႔ ေက ြးတ႔လပစး၇႔ ၿကမနနးေပၚတညပါတယ။မးစကတလးက နဂကတက rotary diode န႔၇တါက D.C ေပးထါးလ႔ Synchronous motor ေၿပာငးလ႔၇ပါတယ။

The three-phase synchronous motor is a unique and specialized motor. As the name suggests, this motor runs at a constant speed from no load to full load in synchronism with line frequency. As in squirrel-cage induction motors, the speed of a synchronous motor is determined by the number of pairs of poles and the line frequency.

၇တါလညနနး န႔ စေတတါ ၇႔ လညေနတ႔ သလကစကကြငးၿကားနငး၇ rpm သညၿဖစတ႔အခါ ၇တါ သလက၀င၇းစြနး န႔ စေတတါသလက ၀င၇းစြနးတ႔ကပသါြးပါတယ။

The operation of the motor can be summarized as follows.

• Three-phase AC voltage is applied to the stator windings and a rotating magnetic field is produced.

• DC voltage is applied to the rotor winding and a second magnetic field is produced.

• The rotor then acts like a magnet and is attracted by the rotating stator field.

• This attraction exerts a torque on the rotor and causes it to rotate at the synchronous speed of the rotating stator field.

• The rotor does not require the magnetic induction from the stator field for its excitation. As a result, the motor has zero slip compared to the induction motor, which requires slip in order to produce torque.

ေၿပာတ႔သေဘါက ၇တါက စေတတါ၇႔လညေနတ႔ သလကစကကြငးမာ သလကေကၚန႔ကပသလကပေနတယ။ ၿပးေတါ႔ စေတတါသလကစကကြငးလညသလ ၇တါကလကလညေနတယ။ဒါေၿကာင႔ zero slip ၿဖစေနတယ။

ဒါေပမ႔တခလတါက အဒ လညေနတ႔ စေတတါသလကစကကြငးက၇တါကလကမေတါ႔မ ၇တါက ဒစေပးၿပး သလကေကၚန႔ကပလ႔၇မာ။ ဒေတါ႔ ပထမ အမလကလညဘ႔ squirrel case rotor coil လကြငတခၿမပပတထါးတတတယ။ amortisseur windings လ႔ေခၚၿကတယ။

Synchronous motors are not self-starting and therefore require a method of bringing the rotor up to near synchronous speed before the rotor DC power is applied. Synchronous motors typically start as a normal squirrel cage induction motor through use of special rotor amortisseur windings. Also, there are two basic methods of providing excitation current to the rotor. One method is to use an external DC source with current supplied to the windings through slip rings. The other method is to have the exciter mounted on the common shaft of the motor. This arrangement does not require the use of slip rings and brushes.

အဒေတါ႔အခပေၿပာ၇၇င induction motor ( squirrel cage or wound motor ) က ထ၇နစေဖၚမါ primary(စေတတါ) & secondary winding(၇တါ) သေဘါသးထါးၿပးလညေနတ႔စေတတါသလကစကကြငးကတြနးဆြၿပး ၇တါလကလညတါၿဖစၿပး

Synchronous motor ကေတါ႔ ၇တါက သလကေကၚန႔ လညေနတ႔ စေတတါသလကစကကြငး မာ လါ လမးကပၿပးလညတါပါ

The vessel, when operating at full speed, will receive power at normal frequency and voltage straight from the switchboard.

Cycloconverter Method of Speed Control

The cycloconverter method of controlling speed relies on the ability of the converter to accept current from the switchboard at constant frequency and voltage. The controller also passes this current to the a.c. motor at a reduced frequency, with its voltage adjusted. The cycloconverter is different; it operates without an intermediate d.c. stage in the conversion.

The fixed-frequency supply from the a.c. generators simultaneously goes to the three pairs of thyristor bridges of the cycloconverter. The upper and lower bridges of each pair are arranged to operate alternately so that a number of triggering pulses develop in the top set of thyristors - followed by an equal number from the bottom set, to deliver an output with a lower frequency.

'The two bridges for each phase are required to supply both the positive and negative half-cycles.

Adjustable speed motoR

motor control –

1- adjustable speed drives

2- programmable logic controllers.

The use of adjustable-speed drives in pump and fan systems can greatly increase their efficiency. Outdated technology most often used throttles or dampers to interrupt the flow as a means to control it.

The North American designation for load conductors is T1, T2, and T3; the European designation for load conductors is U, V, and W.

Squirrel-cage induction motors are the most common three-phase motors used in commercial and industrial applications. The preferred method of speed control for squirrel-cage induction motors is to alter the frequency of the supply voltage. Since the basis of the drive’s operation is to vary the frequency to the motor in order to vary the speed, the best-suited name for the system is the variable frequency drive (VFD). However, other names used to reference this type of drive include adjustable-speed drive (ASD), adjustable-frequency drive (AFD), variable-speed drive (VSD), and frequency converter (FC). A VFD controls the speed, torque, and direction of an AC induction motor. It takes fixed voltage and frequency AC input and converts it to a variable voltage and frequency AC output.

Converter: A full-wave rectifier that converts the applied AC to DC.

• DC bus: Also referred to as a DC link, connects the rectifier output to the input of the inverter. The DC bus functions as a filter to smooth the uneven, rippled output to ensure that the rectified output resembles as closely as possible pure DC.

• Inverter: The inverter takes the filtered DC from the DC bus and converts it into a pulsating DC waveform. By controlling the output of the inverter, the pulsating DC waveform can simulate an AC waveform at different frequencies.

• Control logic: The control logic system generates the necessary pulses used to control the firing of the power semiconductor devices such as SCRs and transistors. Fairly involved control circuitry coordinates the switching of power devices, typically through a control board that dictates the firing of power components in the proper sequence. An embedded microprocessor is used for all internal logic and decision requirements.

Sometimes called the front end of the VFD, the converter is commonly a three-phase, full-wave bridge rectifier. However, one of the advantages of variable-frequency drives is being able to operate a three-phase AC motor from a single-phase AC supply. The key to this is process is the rectification of the AC input to a DC output. At this rectification point, the DC voltage has no phase characteristics; the VFD is simply producing a filtered pulsating DC waveform. The drive inverts the DC waveform into three different pulse-width modulated waveform signatures that duplicate an AC three-phase waveform. AC input voltage levels that are different from that required to operate the motor require the converter section to raise or lower the voltage to the proper operating level of the motor. As an example, an electric motor drive supplied with 115 V AC that must deliver 230 V AC to the motor requires a transformer capable of stepping up the input voltage.

Variable frequency drive

Block diagram of a typical three-phase variable-frequency drive

The frequency pattern is shown very simply to illustrate the principle. There is greater variation in reality, because the triggering of the thyristors is continually changed relative to the three-phase supply so that the output can be customised to provide the exact frequency and amplitude of the voltage required. Frequency is variable from 0 to 60 Hz.

The windings of the propulsion motor shown in the sketch are separate from each other in order to maintain electrical isolation between phases. If they are to be connected as a common winding, transformers are required at the input from the switchboard to each pair of bridges.

The VFD offers an alternative to other forms of power conversion in areas where three-phase power is unavailable. Since it converts incoming AC power to DC, the VFD really doesn’t care if its source is single or three phase. Regardless of the input power, its output will always be three phase. Drive sizing, however, is a factor since it must be capable of rectifying the higher-current, single-phase source. As a rule of thumb, most manufacturers recommend doubling the normal three-phase capacity of a drive that will be operating on a single-phase input.

Input source က single phase or 3 phase ေပးလ႔၇ပါတယ။ d.c ၿပနေၿပာငးမာမ႔ ၿဖစပါတယ။

After full-wave rectification of an AC supply into a VFD, the DC output passes through a DC bus.

The inductor ( L ) and capacitor ( C ) connections within the DC bus that were shown at above diagram, work together to filter out any AC component of the DC waveform. The principal energy storage element is the bus capacitors. Any ripple that is not smoothed out will show up as distortion in the motor output waveform. Most VFD manufacturers provide a special terminal block for DC bus voltage measurement. With a 460-V AC input you should read an average DC bus voltage of about 650 to 680 V DC. The DC value is calculated by taking the root mean square (RMS) value of the line voltage and multiplying it by 1.414. AC voltage readings of more than 4 V AC on the bus may indicate a possible capacitor filtering problem or a problem with the diode bridge converter section.

The inverter is the final output section of a VFD. This is the point where the DC bus voltage is switched on and off at specific intervals. In doing so, the DC energy is changed into three channels of AC energy that an AC motor uses to operate. Today’s inverters use insulated-gate bipolar transistors (IGBTs) to switch the DC bus on and off.

ၿကားၿဖတၿပး IGBT အေၿကာငး ဖတၿကည႔ပါ။

The insulated-gate bipolar transistor (IGBT) is a cross between a bipolar transistor and MOSFET in that it combines the positive attributes of both. BJTs have lower on resistance, but have longer switching times, especially at turn-off. MOSFETs can be turned on and off much faster, but their on-state resistance is higher. IGBTs have lower on-state power loss in addition to faster switching speeds, allowing the electronic motor drive to operate at much higher switching frequencies and control more power. T he two different schematic symbols used to represent an N-type IGBT and its equivalent circuit are shown at Fig

.

Notice that the IGBT has a gate like a MOSFET yet it has an emitter and a collector like a BJT. The equivalent circuit is depicted by a PNP transistor, where the base current is controlled by a MOS

BJT

MOSFET

IGBT

transistor. In essence, the IGFET controls the base current of a BJT, which handles the main load current between collector and emitter. This way, there is extremely high current gain (since the insulated gate of the IGFET draws practically no current from the control circuitry), but the collector-to emitter voltage drop during full conduction is as low as that of an ordinary BJT.

As applications for IGBT components have continued to expand rapidly, semiconductor manufacturers have responded by providing IGBTs in both discrete (individual) and modular packages

The control logic and inverter section control the output voltage and frequency to the motor. Six switching transistors are used in the inverter section. The control logic uses a microcontroller to switch the transistors on and off at the proper time. The main objective of the VFD is to vary the speed of the motor while providing the closest approximation to a sine wave for current.

In the simplest circuit implementation, two IGBTs are placed in series across the DC supply and are switched on and off to generate one phase of the three phases for the motor. Two other identical circuits generate the other two phases.

Above Fig is a simplified circuit of a pulse width modulation (PWM) inverter. Switches are used to illustrate the way that the transistors are switched to produce one phase (A to B) of the three-phase output. The output voltage is switched from positive to negative by opening and closing the switches in a specific sequence of steps. The operation can be summarized as follows:

• During steps 1 and 2, transistor switches Q1 and Q4 are closed.

• The voltage from phase A to B is positive.

• During step 3, transistor switches Q1 and Q3 are closed.

• The difference in voltage between phase A and phase B is zero, resulting in zero output voltage.

• During steps 4 and 5, transistor switches Q2 and Q3 are closed.

• This results in a negative voltage between phases A and B.

• The other steps continue in a similar manner.

• Output voltage is dependent on the state of the switches (open or closed), and the frequency is dependent on the speed of switching.

Above Fig shows the sine-wave (AC) line voltage, superimposed on the pulsed inverter output, or simulated AC. Notice that the pulses are the same height for each pulse. This is because the DC bus voltage the drive uses to create these pulses is constant. Output voltage is varied by changing the width and polarity of the switched pulses. Output frequency is adjusted by changing the switching cycle time. The resulting current in an inductive motor simulates a sine wave of the desired output frequency. Most true RMS-measuring multimeters are fast enough to measure the RMS value of the PWM voltage and current. There are two frequencies associated with a PWM variable-frequency drive: the fundamental frequency and the carrier frequency.

The fundamental frequency is the variable frequency a motor uses to vary speed. In a typical VFD, the fundamental frequency will vary from a few hertz up to a few hundred hertz. The inductive reactance of an AC magnetic circuit is directly proportional to the frequency ( XL = 2 f L) . Therefore, when the

frequency applied to an induction motor is reduced, the applied voltage must also be reduced to limit the current drawn by the motor at reduced frequencies.

The microprocessor control adjusts the output voltage waveform to simultaneously change the voltage and frequency to maintain the constant volts/hertz ratio.

The carrier frequency (also known as the switch frequency) is the frequency at which the pulses in pulse-width modulation switch at. The carrier frequency is a fixed frequency substantially higher than the fundamental frequency. This high switching speed produces the classic whine associated with variable-frequency drives. Higher carrier frequency allows a better approximation to the sinusoidal form of the output current. However, higher switch frequencies decrease the efficiency of the drive because of increased heat in the power transistors. The carrier frequency for VFDs is in the 2- to 16-kHz range. Adjusting the carrier frequency automatically in accordance with the changing load and temperature will result in quieter operation.

The inverter-duty motor shown at above is designed for optimized performance to operate in conjunction with a variable-frequency drive. An inverter duty motor can withstand the higher voltage spikes produced by all VFDs and can run at very slow speeds without overheating. SCR drives are most commonly used to control DC motors, but the system is also used in some older AC inverter drives. Earlier types of VFDs used silicon controlled rectifiers (SCRs) to do the switching. As they have become available in higher voltage and current ratings, faster-switching transistors became the preferred switching components for use in inverter circuits. Speed control can be open loop , where no feedback of actual motor speed is used, or closed loop, where feedback is used for more accurate speed regulation. How a motor reacts is very dependent on the load conditions. An open loop VFD knows nothing about load conditions; it only tells the motor what to do. If for example it provides 43 Hz to the motor, and the motor spins at a speed equivalent to 40 Hz, the open loop doesn’t know. With closed-loop control the controller tells the motor what to do, then checks to see if it did it, then changes its command

to correct for any error. Often a tachometer is used to provide the necessary feedback in a closed-loop system.

The tachometer is coupled to the motor, as above Fig , and produces a speed feedback signal that is used by the controller. With closed-loop control, a change in load demand is compensated by a change in the power supplied to the motor, which acts to maintain a constant speed. I n general, AC drives control motor speed by varying the frequency of the current supplying the motor. Although frequency can be varied in different ways, the two most common speed control methods in use today are volts per hertz (V/Hz) and flux vector.

CONTACTOR AND MOTOR STARTER

National Electrical Manufacturers Association (NEMA) အဆအ၇ - magnetic contactor ဆတါ magnetically actuated device for repeatedly establishing or interrupting an electric power circuit လ႔ေၿပာပါတယ။

The magnetic contactor န႔ electromechanical relay ကါြၿခားခကက megnetic contactors ဟါ electric power circuit loads in excess of 15 A က အပကအစးမ၇ဘ break လပနငဖ႔တညေဆါကထါးပါတယ။.

A typical NEMA magnetic contactor used for switching AC motor loads for which overload protection is not required or provided separately. In addition to the three power contacts, one normally open auxiliary hold-in contact is provided to accommodate three-wire pushbutton control.

two circuits were included in a magnetic contactor 1)_the control circuit and the power circuit. The control circuit is connected to the coil, 2)-the power circuit is connected to the main power contacts. The operating principle of a three-pole magnetic contactor in above diagram.

When voltage is applied to the terminals of the coil ( control circuit at above Fig), the current flows through the coil, creating a magnetic field. The coil, in turn, magnetizes the stationary iron frame, turning it into an electromagnet. The electromagnet draws the armature toward it, pulling the movable and stationary contacts together. Power then flows through the contactor from the line side to the load side. Generally a contactor is available in two-, three-, or four-pole contact configurations.

Switching load

Contactors are used in conjunction with pilot devices to automatically control high-current loads. The pilot device, with limited current handling capacity, is used to control current to the contactor coil, the contacts of which are used to switch heavier load currents.

Above Fig illustrates a contactor used with pilot devices to control the pressure of a tank. In this application the contactor coil connects with the pressure switch of air bottle to automatically open and close the power contacts to run the air compressor motor. Contactors may be used for switching motor loads when separate overload protection is provided. The most common use for a contactor is in conjunction with an overload relay assembly in an AC motor starter.

Below Fig show IEC contactor used in combination with an overload relay plus The LT3-S thermistor relay

Heater control circuit ဆ၇ငေတါ႔ overload relay မပါပါဘး။

The auxiliary contacts of a contactor have a much lower current rating than the main contacts and are used in control circuits for interlocking, holding, and status indication. Above Fig shows the schematic circuit for a three-phase heater circuit controlled by a three-pole magnetic contactor and operated by a three-wire control circuit. The operation of the circuit can be summarized as follows: • A control transformer is used to lower the 480-V line voltage to 120 V for control purposes. • The three-wire control circuit is used to switch power to the heating elements. • With the on/off switch closed, the heat on push button is depressed to energize coil CR of the contactor. • Main power contacts CR-1, CR-2, and CR-3 close, energizing the heating elements at line voltage. • Auxiliary contact CR-4 closes to hold in the contactor coil by completing a circuit around the heat on push button. • At the same time, auxiliary contact CR-5 opens to switch off the green (off) pilot light and contact CR-6 closes to switch on the red (on) pilot light. • Depressing the heat off push button or opening the on/off switch will deenergize the coil, returning the circuit to its off state.

Definite-purpose contactors are specifically designed for applications such as air conditioning, refrigeration, resistive heating, data processing, and lighting. Lighting contactors provide effective control

in applications such as office buildings, industrial plants, hospitals, stadiums, and airports. They can be used to handle the switching of tungsten (incandescent filament) or ballast (fluorescent and mercury arc) lamp loads, as well as other general non-motor loads. Contactors may be electrically held or mechanically held. With an electrically held contactor the coil needs to be energized continuously all the time the main contacts are closed. Mechanically held contactors require only a pulse of coil current to change state. Once changed, a mechanical latch holds the main contacts in place so the control power can be removed, resulting in the contactor operation that is quieter, cooler, and more efficient.

Below Fig shows examples of mechanically and electrically held lighting contactors mounted in enclosures.( အခ႔ lighting system ေတြမာ သးပါတယ။ contactor coil က ပါ၀ါ ေတါကေလာကေပးစ၇ာမလဘmech or electrical latch လပထါးတ႔ contactor မ းၿဖစပါတယ.။)

The operation of the circuit can be summarized as follows: • When the on button is momentarily depressed, the latch coil is energized through the N.C. clearing contact. • As a result, the contactor closes and latches mechanically to close the main contacts (M), lighting the bank of lamps, provided that the circuit breaker is closed. • The coil clearing contacts change state (N.C. to N.O. and vice versa) alternately with a change in contactor latching position. • To unlatch the contactor, thereby turning the lamps off, the off button is momentarily depressed, unlatching the contactor to open contacts M. • Since the latch and unlatch coils are not designed for continuous duty, they are automatically disconnected by the coil clearing contacts to prevent accidental coil burnout should the push button remain closed.

Contactor assembly contained three typical operating mechanisms for magnetic contactors: bell-crank, horizontal-action, and clapper. Contactor operating mechanisms should be inspected periodically for proper functioning and freedom from sticking or binding. The magnetic circuit of the operating mechanism consists of soft steel with high permeability and low residual magnetism. The magnetic pull

Mechanically held contactor

developed by the coil must be sufficient to close the armature against the forces of gravity and the contact spring. The contactor coil is molded into an epoxy resin to increase moisture resistance and coil life. Its shape varies as a function of the type of contactor.

A permanent air gap between the magnetic circuit in the closed state prevents the armature from being held in by residual magnetism.

I f a coil exhibits evidence of overheating (cracked, melted, or burned insulation), it must be replaced. To measure the coil resistance, disconnect one of the coil leads and measure the resistance by setting the ohmmeter to its lowest resistance scale. A defective coil will read zero or infinity, indicating a short or opened coil, respectively. Contactor coils have a number of insulated turns of wire designed to give the necessary ampere-turns to operate on small currents. As contactors are used to control different line voltages, the voltage used to control the coil may vary. Therefore, when selecting coils you must choose one that matches the available control voltage.

Control voltage range ကဂ၇စက၇မ႔အေၿကာငး -The operational limit of the contactor is between 85 and 110 percent of the rated coil voltage. A coil voltage variation of ±5 percent will minimize the contact wear. The reason for this is that higher voltages will increase the speed of the electromagnet at closing. Lower voltages will decrease the speed at closing. Both these factors can lead to a higher level of contact bounce at closing, which can be a major cause of wear and erosion. Magnetic coil voltage specifications include rated voltage, pickup voltage, hold-in voltage, and dropout voltage.

Rated voltage - the coil supply voltage and must match that of the control circuit power source.

Pickup voltage - the amount of voltage required to overcome the mechanical forces, like gravity and spring tension, trying to keep the contacts from closing.

Hold-in voltage - the amount of voltage needed to maintain the contacts in their closed position after pickup voltage is reached (hold-in voltage is normally less than pickup voltage). All contactors that are electrically held in are sensitive to voltage dips occurring in the electrical supply.

The dropout voltage - the amount of voltage below which the magnetic field becomes too weak to maintain the contacts in their closed position.

A C and DC contactor coils with the same voltage ratings are not normally interchangeable, the reason being that with a DC coil only the wire ohmic resistance limits the current flow, whereas with AC coilsboth resistance and reactance (impedance) limit the current flow.

Direct current contactor coils have a large number of turns and a high ohmic resistance compared to their AC counterparts. For a DC-operated coil, since current is limited by resistance only, the current flow through the coil upon closing is the same as the normal energized current flow. However, this is not the case when the coil is AC operated. With a de-energized AC coil, part of the magnetic path has an air gap because the armature is not pulled in.

When the contactor closes, the armature closes the magnetic path, causing the inductive reactance of the coil to increase and the current to decrease. This results in a high current to close the contactor and low current to hold it. The inrush current for an AC coil may range from 5 to 20 times that of the sealed current.

When current in an inductive load, such as a contactor coil, is turned off, a very high voltage spike is generated. If not suppressed, these voltage spikes can reach several thousand volts and produce surges of damaging currents. This is especially true for applications requiring interface with solid-state components such as PLC modules.

ဒစ ကြင န႔ ေအစကြ င မတတ႔အေၿကာငး

- လသးလ႔မ၇တ႔အေၿကာငး

Above Fig shows an RC suppression module wired in parallel (directly across) a contactor coil. The resistor and capacitor connected in series slows the rate of rise of the transient voltage.

Contactor coils operated from an AC power source experience changes in the magnetic field surrounding them. The attraction of an electromagnet operating on alternating current is pulsating and equals zero twice during each cycle. As the current goes through zero, the magnetic force decreases and tends to drop the armature out. When magnetism and force build up again, the armature is pulled back in. This motion of the armature, in and out, makes the contactor buzz or chatter, creating a humming noise and wear on the contactor’s moving parts. The noise and wear of AC contactor assemblies can be prevented by the use of shading coils or rings , as shown in below Fig. Unlike the contactor coil, shading coils are not electrically connected to the power source, but mounted to inductively couple with the contactor coil. The shading coil consists of a single turn of conducting material (generally copper or aluminum) mounted on the face of the magnetic assembly. It sets up an auxiliary magnetic attraction that is out of phase with the main field and of sufficient strength to hold the armature tight to the core even though the main magnetic field has reached zero on the sine wave. With well-designed shading coils, AC contactors can be made to operate very quietly.

A broken or open shading coil will make its presence known; the contactor will immediately become extremely noisy. The core and armature of an AC contactor assembly are made of laminated steel, whereas DC assemblies are solid. This is due to the fact that there are no eddy currents generated with continuous direct current applied. Eddy currents are small amounts of current flow induced in the core and armature material by the varying magnetic field produced by AC current flow through the contactor coil. Using a solid iron core would result in greater circulating currents and for this reason the core of AC coils is made up of a stack of thin insulated laminations.

Misalignment or obstruction of the armature’s ability to properly seat when energized causes increased current flow in an AC coil. This could occur as a result of pivot wear or binding, corrosion, or dirt buildup, or pole face damage from impact over a long period of time. Depending on the amount of increased current, the coil may merely run hot, or it may burn out if the current increase is large enough and remains for a sufficient length of time. Improper alignment will create a slight hum coming from the contactor in the closed position. A louder hum will occur if the shading coil is broken because the electromagnet will cause the contactor to chatter. Today, most contactor contacts are made of a low resistance silver alloy.

Silver contacts are used because they ensure a lower contact resistance than other less expensive materials. Depending on the size of the contactor, the main power contacts can be rated to control several hundred amperes. Most often silver inserts are brazed or welded on copper contacts (on the heel), so silver carries the current and copper carries the arc on interruption. Most manufacturers recommend that silver contacts never be filed. Silver contacts need not be cleaned because the black discoloration that appears is silver oxide, which is a relatively good conductor of electricity.

( အမေ၇ာငေပၚေန၇င ဒအတငးထါး) Contacts are subject to both electrical and mechanical wear as they establish and interrupt electric currents. In most cases mechanical wear is minimal compared to electrical wear. Arcing when the contacts are establishing and interrupting currents causes electrical wear or erosion. Also, contacts will overheat if they transmit too much current, if they do not close quickly and firmly, or if they open too frequently. Any of these situations will cause significant deterioration of the contact surface and erratic operation of the contactor.

Arc suppression - One of the main reasons contacts wear is the electric arc that occurs when contacts are opened under load. As the contacts open there will still be current flow between the contact surfaces if the voltage across the two points is high enough).

The path for this continued flow is through the ionized air that creates the arc. As the distance between contacts increases, the resistance of the arc increases, the current decreases, and the voltage necessary to sustain the arc across the contacts increases.

Finally, a distance is reached at which full line voltage across the contacts is insufficient to maintain the arc. Arc current can create a substantial temperature rise on the surface of the contacts. This temperature rise may be high enough to cause the contact surfaces to become molten and emit vaporized metal into the gap between the contacts. Therefore, the sooner the arc is extinguished, the better; if allowed to continue, the hot arc will melt the contact surface. Most contactors contain some type of arc chamber to help extinguish the arc.

Factors that contribute significantly to contact arcing include:

• The level of voltage and current being switched. As circuit voltage and current increase, the gap between the opening contacts ionizes more rapidly into a conductive path.

• Whether the voltage being switched is AC or DC. Direct current arcs are considerably more difficult to extinguish than AC arcs. An AC arc is self-extinguishing; the arc will normally extinguish as the AC cycle passes through zero. In the case of a DC supply there is no current zero, as the current is always in one direction, so no natural arc extinction properties exist.

• The type of load (resistive versus inductive). With resistive loads the duration of the arc is primarily determined by the speed at which the contacts separate. With inductive loads the release of stored energy built up in the magnetic field serves to maintain the current and cause voltage spikes. Inductive loads in AC circuits are less of a problem than in DC circuits.

• How quickly the contactor operates. The faster the speed of contact separation, the quicker the arc will be extinguished. Arcing may also occur on contactors when they are closing, for example, if the contacts come close enough together that a voltage breakdown occurs and the arc is able to bridge the open space between the contacts. Another way this can occur is if a rough edge of one contact touches the other first and melts, causing an ionized path that allows current to flow. In either case, the arc lasts until the contact surfaces are fully closed. One major difference between AC and DC contactors is the electrical and mechanical requirements necessary for suppressing the arcs created in opening and closing contacts under load. To combat prolonged arcing in DC circuits, the contactor switching mechanism is constructed so that the contacts will separate rapidly and with enough air gap to extinguish the arc as soon as possible on opening. DC contactors are larger than equivalently rated AC types to allow for the additional air gap .

Blowout coil for DC contactor

It is also necessary in closing DC contacts to move the contacts together as quickly as possible to avoid some of the same problems encountered in opening them. For this reason, the operating speeds of DC contactors are designed to be faster than those of AC contactors.

An arc chute or shield is a device designed to help confine, divide, and cool an arc, so that the arc is less likely to sustain itself. There is one arc chute for each set of contacts that is fitted above the moving and fixed contact as above Fig. Arc chutes split the arc established at contactor tips while breaking the current to quench the arc. In addition, they also provide barriers between line voltages. The arc chutes used in AC contactors are similar in construction to those used in DC contactors. However, in addition to arc chutes, most DC contactors employ magnetic blowout coils to assist with arc suppression. Blowout coils consist of heavy copper coils mounted above the contacts and connected in series with them. Current flow through the blowout coil sets up a magnetic field between the breaking contacts that “blows” out the arc. When an arc is formed, the arc sets up a magnetic field around itself. The magnetic field of the arc and the blowout coil repel each other. The net result is an upward push that makes the arc become longer and longer until it breaks and is extinguished. Blowout coils seldom wear out or give trouble when operated within their voltage and current ratings. Arc chutes are constantly subjected to the intense heat of arcing and may eventually burn away, allowing the arc to short-circuit to the metal blowout pole pieces. Therefore, arc chutes should be inspected regularly and replaced before they burn through. A s part of a preventive maintenance program, large contactors should be checked periodically for contact wear, contact wipe, shunt terminal connections, free movement of the armature, blowout structure, blowout coil connections, coil structure, correct contact spring tension, and correct air gap. Normally the slight rubbing action and burning that occur during normal operation keep the contact surfaces clean for proper operation. Copper contacts, still used on some contactors, should be cleaned to reduce contact resistance. Worn contacts should always be replaced in pairs to ensure that complete and proper surface contact is maintained. High contact resistance produces overheating of contacts as well as a significant voltage drop across the contacts, resulting in less voltage being delivered to the load. A vacuum contactor switches power contacts inside a sealed vacuum bottle. The vacuum provides a better environment than free air for breaking the arc because without air to ionize, the arc extinguishes more quickly. Housed in vacuum bottles, the arc is isolated and the contacts are protected from dust and corrosion. Compared to conventional air contactors they offer a significantly higher electrical endurance and are the preferred switching devices in applications with a high switching frequency, for heavy-duty starting, and for line voltages above 600 V.

vacuum contactor

Contactor ေတြေလါငလ႔ တတ႔ brand အပမ၇ခ႔၇ငမာ ၇မာၿဖစပါတယ။

မာ၇ငပမနအါးၿဖင overload န႔ contactor ကတြမာမတပ၇တါအဆငပၿပးေၿပပါတယ။

ဒါက telemecanique contactor ေတြ၇႔ control coilေတြေပၚက စါလးေတြ အေၿကာငး

Thermal overload relay(LRD) –

up to 75KW / 400 V

LR 2k ဆ၇ငေတါ႔ ၀.၀၆KW TO 5.5 KW

contactor rating

The National Electric Manufacturers Association (NEMA) and the International Electrotechnical Commission (IEC) maintain guidelines for contactors.

Understand these differences between NEMA & IEC

A philosophy of the NEMA standards is

- to provide electrical interchangeability among manufacturers for a given NEMA size. Because the customer often orders a contactor by the current, motor horsepower, and voltage ratings, without including the application or duty cycle planned for the load, the NEMA contactor is designed by convention with sufficient reserve capacity to assure performance over a broad band of applications. ( contactor မာ၇င horse power & voltage rating ေပးတါန႔တငမလေလါကပါဘး။ duty cycle ပါ သမေကါငးပါတယ။)

ပထမဆး contactor က သးမ႔motor ပမန running ampere ထကပၿကးတါေ၇ြး။ ၿပးေတါ႔ အဒampere န႔တတ႔ overload ကေ၇ြးပါ။ overload အေၿကာငးအေသးစတကအ၇ငpost ေတြထ၇ာၿကည႔ပါ။

- The continuous current rating and horsepower at the rated voltages categorize NEMA size ratings. NEMA contactor size guides for AC and DC contactors are shown at below list.

-

- Because copper contacts are used on some contactors, the current rating for each size is an 8-hour open rating—the contactor must be operated at least once every 8 hours to prevent copper oxide from forming on the tips and causing excessive contact heating. For contactors with silver to silver-alloy contacts, the 8-hour rating is equivalent to a continuous rating. The NEMA current rating is for each main contact individually and not the contactor as a whole.

- Copper oxide ေတြၿဖစတါကကါကြယဖ႔ တေန႔ ၈ နာ၇ အၿမေမါငးေပး၇ပါမယ..silver alloy contact ဆ၇ငcontinuous rating ၿဖစပါတယ။

As an example, a Size 00 three-pole AC contactor rated at 9 A can be used for switching three separate 9-A loads simultaneously. Additional ratings for total horsepower are also listed. When selecting always ensure that the contactor ratings exceed the load to be controlled. NEMA contactor sizes are normally available in a variety of coil voltages. As the NEMA size number classification increases, so does the current capacity and physical size of the contactor. Larger contacts are needed to carry and break the higher currents, and heavier mechanisms are required to open and close the contacts.

ဥပမါ - ၄၈၀ ဗ႔ ၆၀ အမပယါ heater အတြက NEMA SIZE 3 က ေ၇ြးပါ။ ၉၀ အမပယါ ။ ၆၀၀ဗ႔ မ႔စတခ၇ပါတယ။

အ၇င ေ၇းခ႔သလ ၀နေတြက lighting load, heating element load, inductive load ( for example for motors), power factor corrective load( IGBT သး ေမၚတါေတြအတြက) စၿပး အမးမး၇ပါတယ။

Magnetic contactors are also rated for the type of load to be utilized or for actual applications. Load utilization categories include:

• Nonlinear loads such as tungsten lamps for lighting (large hot-to-cold resistance ratio, typically 10:1 or higher; current and voltage in phase). ဒါေၿကာင႔သမာ ေအါကကလ electrically held ပါပါတယ။

Tungsten lamp ေတြဟါ non linear load ၿဖစပါတယ။ စထြနးတ႔အခနေအးေနတ႔အခနန႔ ပလါတ႔အခန resistance 1 က 10:1 ေလါကၿဖစေနလ႔ပါ။

• Resistive loads such as heating elements for furnaces and ovens (constant resistance; current and voltage in phase).

• Inductive loads such as industrial motors and transformers (low initial resistance until the transformer becomes magnetized or the motor reaches full speed; current lags behind voltage).

• Capacitive loads such as industrial capacitors for power factor correction (low initial resistance as capacitor charges; current leads voltage).

IEC contactors

IEC contactors, compared to NEMA devices, generally are physically downsized to provide higher ratings in a smaller package. IEC devices are 30 to 70 percent smaller than their NEMA counterparts. IEC contactors are not defined by standard sizes, unlike NEMA contactors. Instead, the IEC rating indicates that a manufacturer or laboratory has evaluated the contactor to meet the requirements of a number of defined “applications.” With knowledge of the application you can choose the appropriate contactor by defining the correct utilization category. This makes it possible to reduce contactor size, and therefore cost. The IEC rating system is broken down into different “utilization categories” that define the value of the current that the contactor must make, maintain, and break. The following category definitions are the most commonly used for IEC contactors:

AC CATEGORIES

AC-1: This applies to all AC loads where the power factor is at least 0.95. These are primarily non-inductive or slightly inductive loads. ( HEATER ေတြမာတပတါမားပါတယ။)

AC-3: This category applies to squirrel-cage motors where the breaking of the power contacts would occur while the motor is running. On closing, the contactor experiences an inrush, which is 5 to 8 times the nominal motor current, and at this instant, the voltage at the terminals is approximately 20 percent of the line voltage. (ကြနေတၚတ႔ အမားဆးသေဘါၤေပၚသးတ႔အမးအစါး)

AC-4: This applies to the starting and breaking of a squirrel-cage motor during an inch or plug reverse. On energization, the contactor closes on an inrush current approximately 5 to 8 times the nominal current. On de-energization, the contactor breaks the same magnitude of nominal current at a voltage that can be equal to the supply voltage.

DC CATEGORIES

DC-1: This applies to all DC loads where the time constant ( L / R) is less than or equal to 1 millisecond. These are primarily noninductive or slightly inductive loads.

DC-2: This applies to the breaking of shunt motors while they are running. On closing, the contactor makes the inrush current around 2.5 times the nominal rated current.

IEC type contactor

DC-3: This applies to the starting and breaking of a shunt motor during inching or plugging. The time constant is less than or equal to 2 ms. On energization, the contactor sees current similar to that in category DC-2. On deenergization, the contactor will break around 2.5 times the starting current at a voltage that may be higher than the line voltage. This would occur when the speed of the motor is low because the back emf is low.

DC-5: This applies to the starting and breaking of a series motor during inching or plugging. The time constant is less than or equal to 7.5 ms. On energization, the contactor sees about 2.5 times the nominal full-load current. On deenergization, the contactor breaks the same amount of current at a voltage that can be equal to the line voltage.

IEC contactor က အ၇ြယအစါး န႔ အတနးခြတါမဟတဘ သးတ႔ utilization categories ေပၚမတညၿပး ခြလ႔ NEMA န႔စါ၇င အ၇ြယအစါးေသးပါတယ။

Enclosure - Enclosed magnetic contactors approved enclosure ထထည႔သြငးထါးၿပး သတ႔ operate လပတ႔ပတ၀နးကငေပၚမတညၿပး mechanical and electrical protection ေပးနငတ႔ အတနးအစါးခြထါးပါတယ။. Severe environmental factors ကထည႔တြကတ႔အခါ • Exposure to damaging fumes. • Operation in damp places. • Exposure to excessive dust. • Subject to vibration, shocks, and tilting. • Subject to high ambient air temperature စတါေတြထည႔စဥးစါး၇မာပါ။

Two general types of NEMA enclosures:

1- nonhazardous-location enclosures န႔ 2)- hazardous-location enclosures. ဆၿပး ၂ မးခြထါးပါတယ။

2- Nonhazardous-location enclosures က ေအါကကလ categories ခြထါးပါတယ။

• General-purpose (least costly)

• Watertight

• Oiltight

• Dust-tight

Hazardous-location enclosures ေစးပၿကးေပမ႔ safety အတြကမၿဖစမေနလအပပါတယ။ tankers pump room ေတြမာတပတ႔ explosion proof light ေတြလေပါ႔။ Hazardous location, explosion-proof enclosures ေတြကforged or cast material and special seals with precision-fit tolerances ေတြန႕လပထါးပါတယ။The explosion-proof enclosures are constructed so that an explosion inside will not escape the enclosure. သတ႔ အထမာ ေပါကကြမ ဟါ အၿပငက လြင႔ထြကမလါေအါင seal လပပါတယ။ တါဘခာဂာေတြ၇႔ anti burst arrange လေပါ႔။

Hazardouslocation enclosures ေတြက ၂ မးခြထါးပါတယ။

a)- Gaseous vapors (acetylene, hydrogen, gasoline, etc.).

b)- Combustible dusts (metal dust, coal dust, grain dust, etc.). All industrial electrical and electronic enclosures must conform to standards published by NEMA to meet the needs of location conditions.

Typical NEMA enclosure types ေတြက ေတါ႔ NEMA Type 1 —general-purpose type, which is the least costly, and used in a location where unusual service conditions do not exist. NEMA Type 4 and 4X— Watertight and dust-tight. NEMA Type 12 —Provides a degree of protection from noncorrosive dripping liquids, falling dirt, and dust. NEMA Type 7 and 9 —Designed for use in hazardous locations.

Solid state contactor - အေပၚကေၿပာတ႔ explosion proof enclosure ေတြဟါ ေပါကကြမအၿပငမထြကေအါင ကါကြယမ ၇တ႔ တညေဆါကမနလပထါးေပမ႔ internal wiring and physical construction of the device ကေတါ႔ ပမန ၇း၇း က၇ယါေတြန႔အတတပါဘ။ဥပမါ- explosion proof lamp ေတြ၇႔အထက ခပေတြ။မးေခာငးေတြ။ ကေတါ႔ ပမနအတငးပါဘ၊. Consult the National Electrical Code (NEC) and local codes to determine the proper selection of an enclosure for a particular application. The IEC provides a system for specifying the enclosures of electrical equipment on the basis of the degree of protection provided by the enclosure. Unlike NEMA, IEC does not specify degrees of protection for environmental conditions such as corrosion, rust, icing, oil, and coolants. For this reason, IEC enclosure classification designations cannot be exactly equated with NEMA.

Above table provides a guide for converting from NEMA enclosure type numbers to IEC enclosure classification designations. The NEMA types meet or exceed the test requirements for the associated IEC classifications; for this reason the table should not be used to convert from IEC classifications to NEMA types and the NEMA to IEC conversion should be verified by test.

Solid-State Contactor - Solid-state switching refers to interruption of power by nonmechanical electronic means.

Above Fig is single-pole AC solid-state contactor ေတြဟါ electronic switchingကသးလ႔ magnetic contactor ေတြ၇႔ “contacts” ေတြလ wear out မၿဖစပါဘး။ ဒါေၿကာင႕ Static contactors ေတြက high switching frequency, such as heating circuits, dryers, single- and three-pole motors, and other industrial applications ေတြမာသးၿကပါတယ။

အသးမားတ႔ high-power switching semiconductor ကေတါ႔ silicon controlled rectifier (SCR).ၿဖစပါတယ။ သ႔အေၿကာငးေဖၚၿပခကကေတါ႔ (An SCR is a three-terminal semiconductor device (anode, cathode, and gate) that acts like the power contact of a magnetic contactor. A gate

NEMA ကေန IEC ကေၿပာငးလ႔၇တယ

IEC ကေန NEMA ကၿပနေၿပာငးလ႔မ၇ပါ

NEMA ကပၿမင႔လ႔

signal, instead of an electromagnetic coil, is used to turn the device on, allowing current to pass from cathode to anode. ) လ႔ၿပထါးပါတယ။ ဆလခငတါက gate signal က SCR က Turn on လပပါတယ။

Above Fig shown three types of SCR construction styles designed for higher current applications: the disk (also known as puck type), stud mount, and module. Flexible-lead stud-mounted SCRs have a gate wire, a flexible cathode lead, and a smaller cathode lead that is used only for control purposes. The heat generated by the SCR must be dissipated; thus all contactors have some means to cool the SCR. Typically an aluminum heat sink, with fins to increase the surface area, is used to dissipate this energy to air.

The SCR မာ on state (closed contact) or the off state (open contact) ဆၿပး၇ပါတယ။SCRs ကTURN ON လပဖ႔ the gate electrode က small current pulse ေပး၇ပါတယ။ အလ turned on (or triggered) ၿဖစတ႔အခန gate signal ကမေပးလ ဆကၿပး turn on ေနမာပါ. anode-to-cathode current falls below a certain minimum or if the direction of the current is reversed ၿဖစမသါ turn off ၿဖစပါမယ။ ဒါက ၿကည႔ၿခငးၿဖင႔ SCR ဟါ latched contactor circuit န႔ သေဘါတ၇ားၿခငးတပါတယ။

once the SCR is triggered, it will stay on until its current decreases to zero.

The SCR testing circuit shown at above is practical both as a diagnostic tool for checking suspected SCRs and as an aid to understanding how they operate. The operation of the circuit can be summarized as follows: • A DC voltage source is used for powering the circuit, and two pushbutton switches are used to latch and unlatch the SCR, respectively. • Momentarily closing the on push button connects the gate to the anode, allowing current to flow from the negative terminal of the battery, through the cathode-gate junction, through the switch, through the bulb, and back to the battery. • This gate current should cause the SCR to latch on, allowing current to go directly from cathode to anode without further triggering through the gate. • Momentarily opening the normally closed off push button interrupts the current flow to the SCR and bulb. The light turns off and remains off until the SCR is triggered back into conduction. • If the bulb lights at all times, this is an indication that the SCR is shorted. • If the bulb fails to light when the SCR is triggered into operation, this is an indication that the SCR is faulted open.

Since an SCR passes current in one direction only, two SCRs are necessary to switch single-phase AC power. The two SCRs are connected inverse-parallel (back-to-back), as shown in above Fig one to pass current during the positive half-cycle and the other during the negative half-cycle. Half the current is carried by each SCR, and sinusoidal AC current flows through the resistive load R when gates G1 and G2 are fired at 0 degrees and 180 degrees of the input, respectively. Inductive loads and voltage transients are both seen as problem areas in solid-state AC contactor control because they could falsely trigger an SCR into conduction. For this reason, for driving an inductive load, a snubber circuit is used to improve the switching behavior of the SCR.

Above Fig shows an electronic contactor, with a simple RC snubber circuit used to control an inductive transformer load. The snubber circuit consists of a resistor and capacitor wired in series with each other and placed in parallel with the SCRs. This arrangement suppresses any rapid rise in voltage across the SCR to a value that will not trigger it. The abrupt switching of an SCR, particularly at higher current levels, can cause objectionable transients on the power line and create electromagnetic interference (EMI). By electrically switching an SCR on at the AC sine wave zero crossing point, it remains on through the half cycle of the sine wave and turns off at the next zero crossing. In this scheme, known as zero-fired control , the SCR is turned on at or nearly at the zero crossing point so that no current is being switched under load. The result is virtually no power line disturbances or EMI generation.