1250519/SBSSTC,FZR

INTRODUCTION TO PLC

Programmable logic controllers (PLCs) are members of the computer family capable of storing instructions to control functions such as sequencing, timing, and counting, which control a machine or a process. The PLC is composed of two basic sections, the Central Processing Unit (CPU) and the Input/output (I/O) interface system. The PLC measures input signals coming from a machine and through the internal program provides output or control back to the machine.

Ladder logic is the programming language used to represent electrical sequences of operation. In hardwired circuits the electrical wiring is connected from one device to another according to logic of operation. In a PLC the devices are connected to the input interface, the outputs are connected to the output interface and the actual wiring of the components is done electronically inside the PLC using ladder logic. This is known as soft wired.

PLC is a device that is capable of being programmed to perform a controlling function. Before the advent of PLC, the problem of industrial control was usually solved by relays or hardwired solid-state logic blocks. These are very flexible in design and easy for maintenance personal to understand. However, they involved a vast amount of interconnection. For the wiring cost to be minimized, relays and logic blocks had to be kept together. This led to development of control panel concept for larger and more complex logic control system.

The PLC was first conceived by group of engineers from hydromantic division of GM in 1968.This was designed to provide flexibility in control based on programming and executing logic instruction. Adopting the ladder diagram programming language, simplifying maintenance and reducing the cost of spare parts inventories realized major advantages.

History of PLCs

The first Programmable Logic Controllers were designed and developed by Modicon as a relay replacer for GM and Landis.

The primary reason for designing such a device was eliminating the large cost involved in replacing the complicated relay based machine control systems for major U.S. car manufacturers.

These controllers eliminated the need of rewiring and adding additional hardware for every new configuration of logic.

The first PLC, model 084, was invented by Dick Morley in 1969.

The first commercial successful PLC, the 184, was introduced in 1973 and was designed by Michel Greenberg.

Communications abilities began to appear in approximately 1973. The first such system was Modicon's Modbus. The PLC could now talk to other PLCs and they could be far away from the actual machine they were controlling. PLC Basic Block Diagram

A Programmable Controller is aspecialized computer.Since it is a computer, it has all the basic component parts that any other computer has; a Central Processing Unit, Memory, Input Interfacing and Output Interfacing. A typical programmable controller block diagram is shown below,

Figure 1. PLC Basic Block Diagram The Central Processing Unit (CPU) is the control portion of the PLC.

1. It interprets the program commands retrieved from memory and acts on those commands.

2. In present day PLC's this unit is a microprocessor based system.

3. The CPU is housed in the processor module of modularized systems. Memory in the system is generally of two types; ROM and RAM.

1. The ROM memory contains the program information that allows the CPU to interpret and act on the Ladder Logic program stored in the RAM memory.

2. RAM memory is generally kept alive with an on-board battery so that ladder programming is not lost when the system power is removed.

3. This battery can be a standard dry cell or rechargeable nickel-cadmium type.

4. Newer PLC units are now available with Electrically Erasable Programmable ReadOnly Memory (EEPROM) which does not require a battery.

5. Memory is also housed in the processor module in modular systems. Input units can be any of several different types depending on input signals expected as described above.

1. The input section can accept discrete or analog signals of various voltage and current levels.

2. Present day controllers offer discrete signal inputs of both AC and DC voltages from TTL to 250 VDC and from 5 to 250 VAC.

3. Analog input units can accept input levels such as 10 VDC, 5 VDC and 4-20 ma. current loop values.

4. Discrete input units present each input to the CPU as a single 1 or 0 while analog input units contain analog to digital conversion circuitry and present the input voltage to the CPU as binary number normalized to the maximum count available from the unit.

5. The number of bits representing the input voltage or current depends upon the resolution of the unit.

6. This number generally contains a defined number of magnitude bits and a sign bit.

7. Register input units present the word input to the CPU as it is received (Binary or BCD).

Output units operate much the same as the input units with the exception that the unit is either sinking (supplying a ground) or sourcing (providing a voltage) discrete voltages or sourcing analog voltage or current.

1. These output signals are presented as directed by the CPU. The output circuit of discrete units can be transistors for TTL and higher DC voltage or Triacs for AC voltage outputs.

2. For higher current applications and situations where a physical contact closure is required, mechanical relay contacts are available.

3. These higher currents, however, are generally limited to about 2-3 amperes.

4. The analog output units have internal circuitry which performs the digital to analog conversion and generates the variable voltage or current output.

Extending PLC:

1. Every PLC controller has a limited number of input/output lines.

2. If needed this number can be increased through certain additional modules by system extension through extension lines.

3. Each module can contain extension both of input and output lines.

4. Also, extension modules can have inputs and outputs of a different nature from those on the PLC controller (ex. in case relay outputs are on a controller, transistor outputs can be on an extension module).

PLC ARCHITECTURE

Figure 2. PLC Architeture Input pins :- It gets signal from real world input devices (switch or sensors) and provides the signal to the controller.

Output Pins :- It gets signal from controller and provide it to real world output devices ( motor , lamp, valve ).

Communication Port :- It acts as data source.

Communication Cable :- It acts as medium.

Indicator or Monitor :- With the help of these monitor or indicator we come to know about the status of input and output and also the different modes of PLC. Controller :- It is a combination of processor and memory.

Processor :- Which let a programme run.

Memory :- Data storage is known as memory .Pin Diagram of PLC

Figure 3. Pin Diagram Of PLCWORKING OF PLC

Bringing input signal status to the internal memory of CPU

The field signals are connected to the I/P module. At the output of I/P module the field status converted into the voltage level required by the CPU is always available.

At the beginning of each cycle the CPU brings in all the field I/P signals from I/P module & stores into its internal memory called as PII, meaning process image input.

The programmable controller operates cyclically meaning when complete program has been scanned; it starts again at the beginning of the program.

I/O BUSA PLC works by continually scanning a program. We can think of this scan cycle as consisting of 3 important steps. There are typically more than 3 but we can focus on the important parts and not worry about the others. Typically the others are checking the system and updating the current internal counter and timer values.

Figure 4. Working Of Block Diagram Of PLCStep 1-Check Input Status-First the PLC takes a look at each input to determine if it is on or off. In other words, is the sensor connected to the first input on? How about the second input? How about the third... It records this data into its memory to be used during the next step.

Step 2-Execute Program-Next the PLC executes your program one instruction at a time. Maybe your program said that if the first input was on then it should turn on the first output. Since it already knows which inputs are on/off from the previous step it will be able to decide whether the first output should be turned on based on the state of the first input. It will store the execution results for use later during the next step.

Step 3-Update Output Status-Finally the PLC updates the status of the outputs. It updates the outputs based on which inputs were on during the first step and the results of executing your program during the second step. Based on the example in step 2 it would now turn on the first output because the first input was on and your program said to turn on the first output when this condition is true.

Figure 5. Wiring Diagram Of PLCBasics About Conventional Ladder And PLC Ladder Logic Electrical sequence of operation in hardwired relay circuits can be represented by electrical ladder diagram. Ladder diagram shows the interconnection of field devices. In the ladder diagram, each rung shows how a field device is turned on and also shows how it interacts with next field devices.

The difference between a PLC ladder program and relay ladder rungs is the continuity. In an electrical rung diagram, there is an electrical continuity only when the current flows from left power rail to right power rail.

Fig (a), shows electrical continuity when SW1 is closed, as the current flows from L-1 to L-2 energizing the load.

Even though PLC ladder logic was modelled after the conventional relay ladder, there is no electrical continuity in PLC ladder logic. PLC ladder rungs should have logical continuity in order for the output to energize. PLC ladder program uses familiar terms like "rungs" and "normally open" and "normally closed" contacts, but the relay ladder logic has no electrical continuity between an input and the controlled output.

Note: - There is no physical conductor that carries the input signal through to the output.

Each rung in a ladder diagram is a program statement. This program statement consists of a condition or sometimes conditions, along with some type of action. Inputs are the conditions, and the action, or output, is the result of the conditions.

As in case of physical wiring hardware devices connected in series or parallel, PLC also combines ladder program instructions in series or parallel. However, rather than working in series or parallel, the PLC combines instructions logically using logic operators. Logical operations performed by PLC are nothing but fundamental logic operation, using fundamental logic operators like: AND, OR, and NOT. These operators are used to combine the instructions on a PLC rung so as to make the outcome of each rung either true or false.

The AND-logic function The series circuit of 2 switches can be looked as an AND logic function. In fig (b) and fig (c), both switch1 and switch2, must be closed to have electrical continuity. When there is electrical continuity, output (light1) will energize. Hence the keyword here is AND.

The circuit in fig (b) is represented as a schematic diagram ladder rung in fig (c).When the switch1 and switch2 is closed, electrical continuity is established to L-2. This is shown in fig (d).

The various possible switch combinations are shown in the truth table below.

Table 1: Truth table for AND logic Fig (d) can be written in PLC ladder format as shown in the figure below

Here is the program listing for a typical PLC, if you are entering the program with a handheld programmer.

LOAD I1 AND I2

OUT O5

The above instruction tell the processor to load input 1 (I1) into memory,

AND it with input 2 (I2) and then output the result to output 5 (O5). The resulting output will be based on the truth table fig (e). The OR-logic function

In an OR - LOGIC function, the output is true if any input is true. The OR logic also states that if all inputs are true, the output will be true.

In the above figure, if switch1 OR switch2 is energized then light1 will energize. Also, if both SW1 and SW2 are true, the output will also be true. Fig (g) is converted to PLC ladder rung and it looks like fig (h)

A PLC rung of logic will have normally open or normally closed contacts instead of normally open or normally closed switch symbols. Addresses and instructions are included. Here, in additions to each contact and its address, text information such as SW1, SW2 and L-1 is used and they are referred to as instruction comments. These instruction comments can be added from programming software.

The NOT-logic functionA normally closed relay contact passes power any time when the relay coil is not energized. In the same manner, the normally closed PLC ladder logic instruction will pass power any time when the input status file bit associated is not a 1. In this condition, the physical hardware input is not sending an input signal into the PLC's input module. The opposite of normally open PLC instruction or contact is the NOT logic. NOT logic can be used in conjunction with AND or OR logic, when a logical 0 in the status file is expected to activate some output device. In other words, NOT logic is used when an input is not energized i.e., 0 in the associated status bit, the output should be energized. Also, when the input is energized i.e., 1 in the associated status bit, the output should not be energized.

Truth table for NOT function

Analysis of rung 1

When I1 is true i.e. the input status file bit regarding I1 is true (1), the instruction I1 will energize the output. The instruction I1 is considered true when it passes logical continuity. If there is no valid input signal from the field input devices attached to I1's screw terminal on the input module, a logical 0 will be placed in the associated input status file bit. A logical 0 in the input status file will make the normally open input instruction to become false .When normally open instruction is false, it will not pass logical continuity.

Analysis of rung 2

The normally closed instruction works much like normally closed contacts on a hardware relay. In the fig (k), when the normally closed instruction I2 is true, i.e. the associated status file bit has a valid zero (0), logical continuity is established to energize the output. When the associated status file bit has valid 1, the NC instruction goes false and there is no logical continuity and the output is not energized.

The EXCLUSIVE OR-logic function

Truth Table for Input and output relation of an exclusive OR function.

Ladder rung of EXOR GATE would look like this

Case 1 When I1 = 0 and I2 = 0:

Let us analyse main rung. When I1 = 0, the normally open instruction is false and, normally closed instruction is true, but since normally open instruction is false, there is no logical continuity and output cannot be energized. Similar analysis can be done in parallel rung, normally closed instruction will be true and normally open instruction will be false and output is not energized. Case 2 When I1= 0 and I2 = 1:

In main rung, normally open instruction will be false and, normally closed instruction will be true, but since there is no logical continuity this rung logic cannot energize the output. But, in parallel rung, normally closed instruction will be true, as well as normally open instruction will also be true, hence there is logical continuity, and output is energized.

Case 3When I1 = 1 and I2 = 0:

This case is similar to case 2, only the role of inputs are interchanged i.e. here main rung is true and energizes the output and parallel rung is false .

Case 4

When both inputs are true, the main ladder rung as well as the parallel ladder rung goes false. In main rung, normally open instruction is true but normally closed instruction is false. Hence, there is no logical continuity. In parallel ladder rung, normally closed instruction is false and normally open instruction is true, and here also there is no logical continuity. Hence, the output is not energized.

Generally Used Instructions & symbol For PLC Programming

Input Instruction

--[ ]-- This Instruction is Called IXC or Examine If Closed.

ie; If a NO switch is actuated then only this instruction will be true. If a NC switch is actuated then this instruction will not be true and hence output will not be generated.

--[\]-- This Instruction is Called IXO or Examine If Open. ie; If a NC switch is actuated then only this instruction will be true. If a NC switch is actuated then this instruction will not be true and hence output will not be generated.

Output Instruction--( )-- This Instruction Shows the States of Output.

ie; If any instruction either XIO or XIC is true then output will be high. Due to high output a 24 volt signal is generated from PLC processor.

Rung

Rung is a simple line on which instruction are placed and logics are created

E.g.; ---------------------------------------------

Here is an example of what one rung in a ladder logic program might look like. In real life, there may be hundreds or thousands of rungs.

Practical ExamplesExample-1------[ ]--------------[ ]----------------O---

Key Switch 1 Key Switch 2 Door Motor

This circuit shows two key switches that security guards might use to activate an electric motor on a bank vault door. When the normally open contacts of both switches close, electricity is able to flow to the motor which opens the door. This is a logical AND.

Example-2Switching on/off the Lamp whether they are at the bottom or the top of the staircase

Figure 6. Example Switching on/off the Lamp

Topics Covered in this example isusingContacts in parallel.

Number of PLC Inputs Required

X0 Switch at the bottom of Staircase i.e. X0 turns ON when the bottom switch is turned to the right.X1 Switch at the top of Staircase i.e. X1 turns ON when the top switch is turned to the right.

Number of PLC Outputs RequiredY0 LampPLC Ladder Programming:

PLC Ladder Program Description: If the states of the bottom switch and the top switch are the same, both ON or OFF, the light will be ON. If different, one is ON and the other is OFF, the light will be OFF

When the light is OFF, users can turn on the light by changing the state of either top switch at the bottom switch of the stairs. Likewise, when the light is ON, users can turn off the light by changing the state of one of the two switches.Example-3 .Programming For Start/Stop of Motor by PLCOften we have a little green "start" button to turn on a motor, and we want to turn it off with a big red "Stop" button --+----[ ]--+----[\]----( )---

| start | stop run

| |

+----[ ]--+

run

Figure 7. Pin Diagram For Start/Stop of Motor by PLCThe pushbutton switch connected to input X1 serves as the "Start" switch, while the switch connected to input X2 serves as the "Stop." Another contact in the program, named Y1, uses the output coil status as a seal-in contact, directly, so that the motor contactor will continue to be energized after the "Start" pushbutton switch is released. You can see the normally-closed contact X2 appear in a colored block, showing that it is in a closed ("electrically conducting") state.

Starting of MotorIf we were to press the "Start" button, input X1 would energize, thus "closing" the X1 contact in the program, sending "power" to the Y1 "coil," energizing the Y1 output and applying 120 volt AC power to the real motor contactor coil. The parallel Y1 contact will also "close," thus latching the "circuit" in an energized state:

Figure 8. Starting Condition of Motor. Logic for Continous Running of motor When Start Button is Released Now, if we release the "Start" pushbutton, the normally-open X1 "contact" will return to its "open" state, but the motor will continue to run because the Y1 seal-in "contact" continues to provide "continuity" to "power" coil Y1, thus keeping the Y1 output energized:

Figure 9. Condition Of Continuous Run of Motor To Stop the MotorTo stop the motor, we must momentarily press the "Stop" pushbutton, which will energize the X2 input and "open" the normally-closed "contact," breaking continuity to the Y1 "coil:" Figure 10. Condition Of Stop MotoWhen the "Stop" pushbutton is released, input X2 will de-energize, returning "contact" X2 to its normal, "closed" state. The motor, however, will not start again until the "Start" pushbutton is actuated, because the "seal-in" of Y1 has been lost.Counters

Counters count rung transitions. The CTU runs the accumulated value of the counter up

on the false to true rung transition, and the CTD instruction runs the accumulated value

down. The CTU and CTD can be used in conjunction with each other.

Counters consist of the following components:

ACC Accumulated Value

PRE Preset Value

CD Count Down Bit

CU Count Up bit

OV Overflow Bit

UN Underflow bit

By default, data file C5 stores counters, however, other counter files can be added as well.

Below is how the C5 Data file would appear:

Figure 11. Counter Input In Plc

For the CTU instruction: The CU bit is high when the CTU instruction is true. The

ACC value increments by the value of 1 each time the CU bit goes high. When the ACC reaches the PRE, the DN bit will be set. The CTU will continue to increment the

accumulated value until it reaches the maximum possible value for a 16 bit signed integer(32767). If the CU bit goes high one more time, the OV bit will be set, and the ACC value will go to -32768. Each time the CU bit goes high, the ACC value will still

continue to increment (become less negative).

For the CTD instruction: The CD bit is high when the CTD instruction is true. The ACC value decrements by the value of 1 each time the CD bit goes high. Any time the

ACC is above or equal to the PRE, the DN bit will remain set. The DN bit is reset if the

ACC falls below the PRE at any time. The CTD will continue to decrement the accumulated value until it reaches the minimum possible value for a 16 bit signed integer (-32768). If the CD bit goes high one more time, the UN bit will be set, and the ACC value will go to 32767. Each time the CD bit goes high, the ACC value will still continueto decrement (become less positive)

Example for counter in plc programmingThe production line may be powered off accidentally or turned off for noon break. The program is to control the counter to retain the counted number and resume counting after the power is turned ON again. When the daily production reaches 500, the target completed indicator will be ON to remind the operator for keeping a record. Press the Clear button to clear the history records. The counter will start counting from 0 again.

Figure 12. Counting Process

Topics Covered in this example isLatched 16 bit UP counter.

Number of PLC Inputs RequiredX0 Product Detecting Sensor. X1 Production Counter RESET/Clear

Number of PLC Outputs RequiredY0 Production Counter Target Completed.

Number of PLC Counter RequiredC120 16 Bit Latched Counter. (Max Count =32,768)

PLC Ladder Programming:

PLC Ladder Programming Practice Problem 5

PLC Ladder Programming Description:The latching counter is demanded for the situation of retaining data when power-off.When a product is completed, C120 will count for one time. When the number reaches 500,target completed indicator Y0 will be ON.For different series of PLC, the setup range of 16-bit latching counter is different. Timers

Timers are generally used for delaying an event from taking place, or to delay a device

from shutting off either on an on transition or an off transition. There are three types of

timers: The Timer ON delay (TON), Timer Off delay (TOF), and the Retentative Timer

On delay (RTO).

By default, timers are stored in the T4 Data file, however other time files can be created..

A timer consists of the following components: Preset word (PRE), Accumulate word

(ACC), Done bit (DN), Timer Timing bit (TT), and Enable bit (EN). For Timers, the

Enable bit follows the rung condition.

Figure 13.Input for TimerThe entire timer is addressed by it's element (example: T4:0) Pieces of the timer can be

used in logic however such as the DN bit on an XIC (T4:0/DN), or the Accumulated

value in a MOV statement (T4:0.ACC)Timer On Delay (TON)

The Timer On delay delays an event from taking place. Once the timer becomes true, the enable bit becomes true instantly. The timer will also start timing instantly, so the TT bit becomes high. Since the timer is timing, the accumulated value will increment. Once the Accumulated value reaches the preset, the done bit (DN) will go high, and the timer will stop timing. The accumulated value remains at (or near) the preset until the rung goes false again. Here is what a typical timer might look like in logic:

Figure 14. TON DelayWhen the switch is energized, the timer will begin timing. When the ACC value reaches

the PRE value, the DN bit goes high, and the main motor will start. Since the Time Base

is .01, therefore 500 (preset) times .01 (timebase) = 5 second delay.

Timer Off Delay (TOF)

The Off Delay Timer is generally used to delay an event from shutting off. Image a lube system on a large motor. As long as the main motor is turning, the lube pump should be running. When the main motor shuts off, you wouldn't want to shut off the lube pump immediately because the main motor needs time to coast down to zero RPM's. The Main motor could run off the EN bit, and the Lube motor could run off the DN bit.

On the Off delay timer, as soon as the rung goes true, The EN bit goes true as it does for all timers. Since the Off delay timer does not delay the DN bit from shutting off, the DN bit goes high immediately. Remember, the TOF instruction delays the DN bit from shutting off, not turning on. (Plus if we are delaying the DN bit from shutting off, it needs to be high to begin with). While the rung is true, the timer is not timing, and the ACC value is at zero. When the rung is shut off, the EN bit shuts off immediately. The ACC value will start timing until it reaches PRE then the DN bit will shut off.

Here is what the TOF instruction might look like in logic:

Figure 15. TOFF DelayWhen the motor switch is energized, both the main motor and the lube motor will energize immediately. When the main motor switch is shut off, the main motor shuts off immediately, but since the TOF delays the DN bit from shutting off, the Lube motor will shut off 30 seconds later. Warning: Using the RES instruction on a TOF instruction could cause unpredictable operation.

Retentative On Delay Timer (RTO)

The RTO instruction works a lot like the TON instruction with one main exception: When the rung goes false on the RTO instruction, it will retain the ACC value. When the rung becomes true again, the ACC value will pick up from where it left off. One good application for the RTO would be an hour meter to indicate total runtime for machinery. Since the RTO does not reset itself when the rung goes false, the RES instruction must be used to reset a timer. Here is a practical application:

Figure 16. RTO DelayIn this example, once the machine accumulates 1 hour of run time, a light might come on indicating that a lubrication needs to be engaged. Once the operator lubricates the machine, he can reset the hour meter.

Example for Timer in PLC

Enabling the indicator to be ON immediately when switch pressed and OFF after a 5 sec delay by the switch.

Topics Covered in this example isPLC Timer (OFF Delay).Number of PLC Inputs RequiredX1 Start Switch.

Number of PLC Outputs RequiredY1 Output Indicator

Number of PLC Timer RequiredT0 5 second Timer, 100 ms Time Base. (See K50 Preset Value for Timer)

PLC Ladder Programming:

Figure 17. Program for timerPLC Ladder Program Description:When X1 = ON, TMR instruction will be executed. Timer T1 will be ON and start counting for 3 sec. When T1 reaches its set value, the NO (Normally Open) contact T1 will be activated and indicator YI will be ON.

When X1 = OFF, TMR instruction will not be executed. Timer T1 will be OFF and so will NO contact T1. Therefore, the indicator Y1 will be OFF.PLC Program For Filling Of Bottle In Industries

Figure 18. Program for bottle fillingADVANTAGES OF PLC

1. Reduced space.

2. Energy saving.3. Ease of maintenance.

4. Economical.

5. Greater life and reliability.

6. Tremendous flexibility.

7. Shorter project time.

8. Easier storage, archiving and documentation.9. PLCs are armored for severe conditions (such as dust, moisture, heat, cold) and have the facility for extensive input/output (I/O) arrangements.

10. PLCs read limit switches, analog process variables (such as temperature and pressure), and the positions of complex positioning systems.

11. PLCs are used in many "real world" applications. If there is industry present, chances are good that there is a plc present. If you are involved in machining, packaging, material handling, automated assembly or countless other industries you are probably already using them. If you are not, you are wasting money and time. Almost any application that needs some type of electrical control has a need for a plc.PLC DISADVANTAGES

1. There's too much work required in connecting wires.2. There's difficulty with changes or replacements.3. It's always difficult to find errors; and require skillful work force.4. When a problem occurs, hold-up time is indefinite, usually long.5. In contrast to microcontroller systems that have what is called an open architecture, most PLCs manufacturers offer only closed architectures for their products.

6. PLC devices are proprietary, which means that parts and software from One manufacturer cant easily be used in combination with parts of another manufacturer, which limits the design and cost options.

APPLICATIONS OF PLC SYSTEM

In industry, there are many production tasks, which are of highly repetitive nature. Although repetitive & monotonous, each stage needs careful attention of operator to ensure good quality of final product.

Many times, a close supervision of the processes cause high fatigue on operator resulting in loss of track of process control.

Sometimes its hazardous also as in the case of potentially explosive chemical processes.

Under all such conditions we can use PLCs effectively in totally eliminating the possibilities of human error.

Some capabilities of PLCs are as follows:

Logic control

PID control

Coordination & automation

Operator control

Signaling and listing etc.

In short, wherever sequential logic control & automation is desired the PLCs are the best suited to meet the task. It includes simple interlocking functions to complicated analog signal processing to PID control action in closed loop control etc.

Few examples of industries where PLCs are used for control & automation purpose are listed below: -

1. Tyre industry.

2. Blender reclaimer.

3. Bulk material handling system at ports.

4. Ship unloader.

5. Wagon loaders.

6. Steel plants.

7. Blast furnace charging.

8. Brick-molding press in refectories.

9. Galvanizing plant.

10. Dairy automation.

11. Pulp factory.

12. Printing industry etc.

Today the PLCs are used for control and automation job in a single machine and it increases up to full automation of manufacturing or testing process in a factory.

In robotics:PLC is used for two tasks in robotics:

1) As the controller or un-programmable part of robot.

2) As an overall system controller.

In flexible manufacturing system:

The logical development from linking machines in this manner is to group programmable machines into flexible manufacturing cells, each capable of machining a variety of products under fully automatic control.In factory automation:

The plant produces multi style car body from individual body panels .The process consists of following activities:

Pass tagged bodies to a main jig for automatic alignment & framing.

Conduct material transfer in which sub-assemblies are selected, transported & distributed to workstation by conveyor system Maintain quality control by automatic monitoring & manual inspection of each process.

The PLC tracks each component as it moves through the production area, communicating this information to each appropriate robot as necessary. Data send between PLC & robot includes handshaking signals to indicate robot busy parked, action complete etc. Data in binary coded decimal form is used to send component information & weld sequences from the PLC to root, which must acknowledge receipt of the correct data before the PLC will allow it to commence operation.CONCLUSION

PLC is a device that is capable of being programmed to perform a controlling function. The PLC was designed to provide flexibility in control based programming and executing logic instruction. PLC allowed for shorter installation time and faster commissioning through programming rather than wiring.

The PLC have in recent years experienced an unprecedented growth as universal element in industrial automation .It can be effectively used in applications ranging from simple control like replacing a small number of relays to complex automation problems.

Today the PLCs are used for control & automation job in a single machine & it increases up to full automation of manufacturing / testing process in a factory.

INDEX

Contents.Page No.

Certificate...... i

Acknowledgement.... ii

Preface......iii

1Introduction To PLC

1History Of PLCs

2PLC Basic Block Diagram

4PLC Architecture

5Pin Diagram of PLC

6WORKING OF PLC

8Basics About Conventional Ladder And PLC Ladder Logic

9The AND-logic function

10The OR-logic function

11The NOT-logic function

14Generally Used Instructions & symbol For PLC Programming

14Practical Examples

19Counters

20Example for counter in plc programming

21Timers

22Timer On Delay (TON)

22Timer Off Delay (TOF)

23Retentative On Delay Timer (RTO)

24Example for Timer in PLC

25PLC Program For Filling Of Bottle In Industries

26Advantages Of PLC

26PLC Disadvantages

27Applications Of PLC System

29Conclusion

Table Of Figures

Figure Contents .Page No.

2Figure 1. PLC Basic Block Diagram

Figure 2. PLC Architeture4Figure 3. Pin Diagram Of PLC5Figure 4. Working Of Block Diagram Of PLC6Figure 5. Wiring Diagram Of PLC7Figure 6. Example Switching on/off the Lamp15Figure 7. Pin Diagram For Start/Stop of Motor by PLC16Figure 8. Starting Condition of Motor.17Figure 9. Condition Of Continuous Run of Motor18Figure 10. Condition Of Stop Moto18Figure 11. Counter Input In Plc19Figure 12. Counting Process20Figure 13.Input for Timer21Figure 14. TON Delay22Figure 15. TOFF Delay23Figure 16. RTO Delay23Figure 17. Program for timer24Figure 18. Program for bottle filling25

CPU

:

PII: PIQ

:

:

INPUT

MODULE

FIELD

SIGNALS

iv20