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INTRODUCTION LABVIEW is a program development application, much like C or FORTRAN.LABVIEW is however, different from those applications in one important respect. Other programming systems use text based languages to create lines of code, while LABVIEW uses a graphical programming language, to create programs in block diagram and its controlling and indicating unit as front panel. LABVIEW, like C or FORTRAN, is a general- purpose programming system with extensive libraries of functions for many programming tasks. LABVIEW includes libraries for data acquisition, data analysis, data presentation and data storage. A LABVIEW program is called a virtual instrument (VI) because its appearance and operation can imitate an actual instrument.

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INTRODUCTIONLABVIEW is a program development application, much like C or FORTRAN.LABVIEW is however, different from those applications in one important respect. Other programming systems use text based languages to create lines of code, while LABVIEW uses a graphical programming language, to create programs in block diagram and its controlling and indicating unit as front panel. LABVIEW, like C or FORTRAN, is a general-purpose programming system with extensive libraries of functions for many programming tasks. LABVIEW includes libraries for data acquisition, data analysis, data presentation and data storage. A LABVIEW program is called a virtual instrument (VI) because its appearance and operation can imitate an actual instrument.

VIRTUAL INSTRUMENTSVirtual instrument (VI) is a program in graphical programming language. It models the appearance and function of a physical instrument. The distinction between traditional and virtual instrument is illustrated in fig.1.

Fig. 2 shows two LabVIEW windows: front panel (containing controls and indicators) and block diagram (containing terminals, connections and graphical code). The front panel is the user interface of the virtual instrument. It consists of controls and indicators, which are the iterative input and output terminals of the VI, respectively.

ControlsControls are knobs, push buttons, dial, and output input devices. Indicators are graphs, LEDs, and other displays.

FIGURE: FRONT PANNEL

FIGURE: BLOCK DIAGRAM.

Controls simulate instrument input devices and supply data to the block diagram of the VI. Indicators simulate instrument output devices and display data the block diagram acquires or generates. The code is built using graphical representations of functions to control the front panel objects. The block diagram contains this graphical source code. Front panel objects appear as terminals on the block diagram. Additionally, the block diagram contains functions and structures from built-in LabVIEW VI libraries. Wires connect each of the nodes on the block diagram, including control and indicator terminals, functions, and structures. From the aspect of distance learning, the most important issue of virtual instruments is the fact that they can be used to simulate physical phenomena to generate signal that appears as it would appear if it had been acquired by real transducers. The same software is being used for real and virtual phenomena. That way virtual instrument becomes the part of virtual laboratory.

FIGURE 3:Virtual instrument

Transducer

Signal conditioning

data acquisition

VirtualPhysical LaboratoryPhenomenon Control

Data Analysis Measurement Results

Fig: Virtual Laboratory

Some Palettes Used In LABVIEW:

Some features of LabVIEW: Graphical programming Data-flow-controlled execution, as compared to sequential execution of text-line based languages. Real time visual debugging features Built in drivers and function libraries for the serial, parallel and network computer ports. Simple file input-output operations.

Plug-and-play interface devices for most types of external equipment.

Direct program portability (binary files) between different platforms: PCs, Macintosh, Sun, HP-UX and operating systems. A wealth of visual debugging tools. Add-on software packages for specific extension of the program features, for instance image processing. Built-in interactive graphic control and display Database (SQL) interfacing, libraries for industrial PLCs Ready to use analysis functions including: Signal generation (sine wave, triangular wave, square wave, saw tooth, uniform, Gaussian white and periodic white noise etc.)

Digital signal processing (FFT, power spectrum, Hilbert transform, convolution, derivative, integral etc.)

Measurement (power spectrum, time domain windowing, transfer function, harmonic analyzer, pulse parameters, peak detection etc.) Filtering (Butterworth, IIR, Chebyshev, Bessel filter, median filter etc.) Windows (Hanning, hamming, triangle, flat top, force window, exponential window etc.)

Curve fitting (Linear, exp., poly. nonlinear Lev-Mar. fit, interpolation etc.) Probability and statistics functions (mean, standard deviation, RMS, histogram, distributions(chi square,F,t, inverse distributions, erfc(x), erf(x), contingency table etc), ANOVA(1D,2D,3D) etc)

Array operations (numerical methods, root, etc.) Code interface function to use DLLs written any other language. This feature gives the opportunity to use the codes written in conventional languages (C/C++, Visual Basic, etc.) to be used in a LabVIEW program. Add-on software packages for specific extension of the program features, for instance image processing.

ADVANTAGES OF VIRTUAL INSTRUMENTS FlexibilityExcept for the specialized components and circuitry found in traditional instruments, the general architecture of stand-alone instruments is very similar to the PC-based virtual instrument. Both require one or more microprocessors, communication ports (for example, serial and GPIB), and display capabilities, as well as data acquisition modules. What makes one different from other are their flexibility and the fact that you can modify and adapt the instrument to your particular needs. A traditional instrument might contain an integrated circuit to perform a particular set of data processing functions; in a virtual instrument, these functions would be performed by software running on the PC processor.

Lower CostBy employing virtual instrumentation solutions, you can lower capital costs, system development costs, and system maintenance costs, while improving time to market and the quality of your own products.

Plug-In and Networked HardwareThere is a wide variety of an available hardware that you can either plug into the computer o access through a network. These devices offer a wide range of data acquisition capabilities at a significantly lower cost than that of dedicated devices. As integrated circuit technology advances, and off-the self components become cheaper and more powerful, so do the boards that use them. With these advances in technology comes an increase in data acquisition rates, measurement accuracy, precision and better signal isolation. Depending on the particular application, the hardware you choose might include analog input or output, digital input or output counters, timers, filters, simultaneous sampling, and waveform generation capabilities. The wide gamut of boards and hardware could include any one of thee features or a combination of them.

Distributed ApplicationsA virtual instrument is not limited or confined to a stand-alone PC. In fact, with recent developments in networking technologies and the internet, it is more common for instruments to use the power of connectivity for the purpose of task sharing. Typical examples include supercomputers, distributed monitoring and control devices, as well as data or result visualization from multiple locations.

Reduces Cost and Preserves InvestmentsBecause you can use a single computer equipped wit LabVIEW for countless application and purpose, it is a versatile product. It is not only versatile but also extremely cost-effective. Virtual instrumentation with LabVIEW proves to be economical, not only in the reduced development costs but also in its preservation of capital investment over along the period of time. As your needs change, you can modify systems easily without the need to buy new equipment. You can create complete instrumentation libraries for less than the cost of a single traditional, commercial instrument.

Flexibility and ScalabilityEngineers and scientists have needs and requirements that can change rapidly. They also need to have maintainable, extensible solutions that can used for a long time. By creating virtual instruments based on powerful development software such as LabVIEW, you inherently design an open framework that seamlessly integrates software and hardware. This ensures that your applications not only work well today but that you can easily integrate new technologies in the future as they become available, or extend your solutions beyond the original scope, as new requirements that require a broad range of solutions.

Other Advantages: The users are able to define instruments inside the software. Lower costs of instrumentation Portability between various computer platforms

Easy-to-use graphical user interface. Graphical representation of program structures Code can be compiled to standalone.EXE or .DLL file. TCP/IP connectivity (Web server integrated into virtual instrument) Virtual instruments are easily adaptable to changing demands. The user interface can be adapted to the needs of different users.

COMPONENTS IN A VIA VI consists of two panels: one is the front panel, and other is the block diagram. These are defined below: The interactive user interface of a VI is called the front panel, because it simulates the panel of a physical instrument. The front panel can contain knobs, push buttons, graphs, and other controls and indicators. You enter data using a mouse and keyboard, and then view the results on the computer screen. The VI receives instructions from a block diagram, which you construct in G. the block diagram a pictorial solution to a programming problem. The block diagram is also the source code for the VI.

Indicators:Indicators are used to output numeric (integer or floating point), character, and Boolean data in LabVIEW. On the block diagram, indicators are represented with a thin border.

Controls:Controls are used to input numeric (integer or floating point), character, and Boolean data in LabVIEW. On the block diagram, controls are represented with a thick border.

For Loop Structure:A For Loop executes its sub-diagram N times, where the count equals the value contained in the terminal.

You set the count explicitly by writing a value from outside the loop to the left of the count terminal. The iteration terminal, I, contains the current number of completed iterations; 0 during the first iteration, 1 during the second, and so on up to N-1. If you write 0 to the count terminal, the loop does not execute.

While Loop Structure:A While Loop executes its sub- diagram until a Boolean value you write to the conditional, terminal is FALSE. LABVIEW checks the conditional terminal value at the end of each iteration, and if the value is TRUE, iteration occurs, so the loop always executes at least once. The default value of conditional terminal is FALSE, so if it s unwired, the loop iterates only once.

The iteration terminal behaves exactly as it does in the For Loop. In the LABVIEW, there is also a stop termination for the while loop; i.e., the loop will continue to execute until the stop condition is TRUE.

Shift Register:Both loop structures can have terminals called shift registers that you use for passing data from the current iteration to the next iteration.

Shift Registers are local variables that feed forward or transfer values from the completion of one iteration to the beginning of the next. A shift Register has a pair of terminals directly opposite each other on the vertical sides of the loop border. The right terminal, the rectangle with the up arrow, stores the data at the completion of the iteration. LABVIEW shifts that data at the end of the iteration, and it appears in the left terminal, the rectangle with the down arrow, in time for the next iteration. You can use shift registers for any type of data, but the data you write to each register terminals must be of the same type.

Case Structure:

The Case Structure has two or more sub-diagrams, or cases, of which only one will execute when the structure executes. This depends in the value of the Boolean or numeric scalar you wire to the external side of the selection terminal. If a Boolean is wired to the selector, the case structure must have two cases, FALSE and TRUE. If a numeric is wired to the selector, the structure can have from 0 to N cases.

Arrays And Graphs in LABVIEW: Initialize Array:

Returns an N-dimensional array in which every element is initialized to the specified value. This function is resizable, so we typically define an array of one element. The element cannot be an array.

Build Array:

Concatenate inputs in a top to bottom order. Pop-up on an input node and select change to Array to change it in to an array input. For an Ndimensional array, element inputs must have N-1 dimension and array inputs must have N dimensions.

Index Array:

Returns an element of the array at the index input. If the array is multi-dimensional you must add additional index by resizing or popping up and adding terminals. You can also slice out sub- arrays (e.g. rows or coloums) by disabling the index terminals from the popup.

XY GRAPHA graph indicator is a two dimensional display of one or more plots. The graph receives and plots data as a block. The XY graph is a general-purpose, Cartesian graphing object that you can use to plot multi-valued functions.

Use this arrangement to bundle two 1D arrays into a cluster, to be plotted. The input into an XY graph indicator for a single plot is a cluster a X array and a Y array. You can also display multiple plots on a XY graph.

Sample Simulation Of Few Programs Using LABVIEW. 1: Square Wave Generation:

Figure: Block Diagram Of Square Wave Generation.

Output Waveforms Obtained After Simulation.

2: Amplitude Modulation:

Figure: Block Diagram Of Amplitude Modulation.

Output Waveform After Simulation

INTRODUCTION TO PROJECT

HARDWARE REQUIREMNTThe following hardware is required to implement PC Based Automatic Car Parking System: Personal Computer with Pentium Processor PCI CB68LP DAQ Card & I/O Connector Proximity Sensors & Signal Conditioners Wooden Base DC Stepper Motor

AUTOMATIC CAR PARKING SYSTEM

The diagram shows the layout of a simple car park. It has an entry barrier and an exit barrier. The car park itself has six spaces and series of displays to indicate whether it is full, has spaces or is empty, with a numerical indicator to determine the exact amount. Designing need to be done that will allow cars into the parking zone when it is empty or has spaces and to exit the car park through the correct barrier. Designing must also do to control the display boxes in the center of the screen.

1 System Planning:The system planning begins with the understanding of what to do and what we are going to develop is feasible or not from the users perspective. Here we mainly thinks about to provide the user better facilities then the earlier one so that his efficiency and performance is improved. So first of all we perform the feasibility study to understand the projects feasibility under mainy areas then we think about the main characteristics that are must for the projecty. All the description is as below.

Feasibility Study: a) Technical Feasibility There is work going on electrical components with the help of assembly language. The proposed equipment has the technical capability to make a decision required to use the system. This system will be upgraded later. Using this technology there are technical guarantees of accuracy, reliability ease of access and security.

b) Economical Feasibility: This system that can be developed technically and that will be used must still be profitable for the users. Its financial benefits must exceed then costs when we investigate the full system.

c) Operational Feasibility: This system is beneficial because that will meet the operating requirements of the organization if it is developed and installed.

There is sufficient for the project from the user. The people are involved and give suggestion time to time when the project is planned and developed. This proposed system has no harm. It increase the performance of the user.

2 FUNCTIONAL REQUIREMENTS OF THE SYSTEMThe performance requirements of the system mainly encompass processing and response time requirements. The system developed must follow certain performance criteria namely.

a)FunctionalThe system should satisfy stated needs. It should be suitable, accurate, interoperable, compliant and secure.b)Reliable

The system should be mature, fault tolerant and recoverable.c)Usable

The system should be easy to use i.e. it should be understandable, learnable and operable.d)Efficient

The system should make optimal use of system resources.f)Maintainable

Repairing of the system should be easy, it should be analyzable, changeable, stable and testable.g)Portable

The system should be easy to transpose from one environment to other. It should be adaptable, installable and replaceable.

3.Cost Benefit Analysis Cost incurred:1.Personnel CostThese include staff salaries and benefits as well as pay for those who are involved in developing the system. These cost are one time costs and are labeled as developmental costs. In time was consumed. Hence, it can be said that a there was a little personnel cost involved.

2.Supply CostsThese costs are variable and basically include cost of components used ( resisters, capacitors, transistors, transformer, relays etc.), cost of tools which are used ( electric iron, punching device, programmer, screw drivers etc.) and thee like. These costs are high and generally dominate other cost.

3.Operational and Maintenance Cost:These costs are associated with the running cost of the project. These include replacement of component as the component become faulty, cost of personnel involved in running the project or the other cost that are necessary for the maintenance of the maintenance of the project. Generally these costs are very low and are variable. These are not the regular periodic cost but occur very occasionally.

Benefits Achieved 1.Cost-Savings BenefitsThis system leads to reduction in administrative and required than earlier method. Also now the same work requires less time. So this project reduces the running cost by a large factor, this is a beneficial one.

2. Improved- Service-Level BenefitsThis system improves the performance of handling the power supply and also controlling the generator functioning. It reduces time gap between different stages of work, earlier the user go to the generator and manually start or stop the generator. This communication took time. With earlier systems the user faces the difficulty when one of the phases is gone then only one phase output is provided but by this we get the two phase output at the time. This is a major enhancement in the performance of the system. So by using this new system there are some more development cost then earlier one but the running cost and the maintenance cost are reduces by this. So by this project there are always an overall benefit achieved.

SENSORS:A sensor is a type of transducer. Direct-indicating sensors, for example, a mercury thermometer, are human-readable. Other sensors must be paired with an indicator or display, for instance a thermocouple. Most sensors are electrical or electronic, although other types exist. Sensors are used in everyday life. Applications include automobiles, machines, aerospace, medicine, industry and robotics. Technological progress allows more and more sensors to be manufactured on the microscopic scale as microsensors using MEMS technology. In most cases a microsensor reaches a significantly higher speed and sensitivity compared with macroscopic approachesTypes Since a significant change involves an exchange of energy, sensors can be classified according to the type of energy transfer that they detect.

Thermal:

temperature sensors: thermometers, thermocouples, temperature sensitive resistors (thermistors and resistance temperature detectors), bi-metal thermometers and thermostats heat sensors: bolometer, calorimeter

Electromagnetic:

electrical resistance sensors: ohmmeter, multimeter electrical current sensors: galvanometer, ammeter electrical voltage sensors: leaf electroscope, voltmeter electrical power sensors: watt-hour meters magnetism sensors: magnetic compass, fluxgate compass, magnetometer, Hall effect device metal detectors RADAR

Mechanical:

pressure sensors: altimeter, barometer, barograph, pressure gauge, air speed indicator, rate of climb indicator, variometer gas and liquid flow sensors: flow sensor, anemometer, flow meter, gas meter, water meter, mass flow sensor mechanical sensors: acceleration sensor, position sensor, selsyn, switch, strain gauge

Chemical:Chemical sensors detect the presence of specific chemicals or classes of chemicals. Examples include oxygen sensors, also known as lambda sensors, ion-selective electrodes, pH glass electrodes, and redox electrodes. A carbon monoxide detector is a chemical sensor often used in the home. These detectors continually sample air and will sound an alarm if the amount of invisible, odorless, and potentially deadly carbon monoxide levels in our home and/or workplace rises above 400 PPM. In manufacturing, chemical sensors are used to manage process controls, quality assurance, and safety. The engine management systems of automobiles take information from sensors and adjust engine parameters to achieve the best mix of fuel economy, performance and emissions. Oxygen sensors have been used in automobiles since the late 70s. Many areas require automobiles to pass an emissions test annually. The test equipment also uses chemical sensors to check the exhaust emissions. Chemical sensors have been developed to detect threats from explosives and biological weapons. Monitoring for these threats includes border crossings, major transportation systems, and large public spaces.[1] For example, airport security utilizes chemical sensors used to sniff out explosives and even drugs. Chemical sensors are also being developed to sniff out illnesses in people.

In supramolecular analytical chemistry novel molecular sensors are developed for a wide range of such applications.

Optical radiation:

light time-of-flight. Used in modern surveying equipment, a short pulse of light is emitted and returned by a retroreflector. The return time of the pulse is proportional to the distance and is related to atmospheric density in a predictable way. LIGHT SENSORS: OR (PHOTODETECTORS), including semiconductor devices such as photocells, photodiodes, phototransistors, CCDs, and Image sensors; vacuum tube devices like photo-electric tubes, photomultiplier tubes; and mechanical instruments such as the Nichols radiometer. INFRA-RED SENSOR: especially used as occupancy sensor for lighting and environmental controls.SCANNING LASER:- A narrow beam of laser light is scanned

over the scene by a mirror. A photocell sensor located at an offset responds when the beam is reflected from an object to the sensor, whence the distance is calculated by triangulation.

Ionizing Radiation:

radiation sensors: Geiger counter, dosimeter, Scintillation counter, Neutron detection subatomic particle sensors: Particle detector, scintillator, Wire chamber, cloud chamber, bubble chamber. See Category:Particle detectors

Acoustic:

Acoustic : uses ultrasound time-of-flight echo return. Used in mid 20th century polaroid cameras and applied also to robotics. Even older systems like Fathometers (and fish finders) and other 'Tactical Active' Sonar (Sound Navigation And Ranging) systems in naval applications which mostly use audible sound frequencies.

Sound sensors : microphones, hydrophones, seismometers.

Other Types:

MOTION SENSORS: radar gun, speedometer, tachometer,

odometer, occupancy sensor, turn coordinator. ORIENTATION SENSORS: gyroscope, artificial horizon, ring laser gyroscope DISTANCE SENSOR (NONCONTACTING): Several technologies can be applied to sense distance: magnetostriction

Non Initialized Systems:

Gray code strip or wheel- a number of photodetectors can sense a pattern, creating a binary number. The gray code is a mutated pattern that ensures that only one bit of information changes with each measured step, thus avoiding ambiguities.

Initialized Systems:These require starting from a known distance and accumulate incremental changes in measurements.

Quadrature Wheel- A disk-shaped optical mask is driven by a gear train. Two photocells detecting light passing through the mask can determine a partial revolution of the mask and the direction of that rotation. Whisker Sensor- A type of touch sensor and proximity sensor

Biological sensors:All living organisms contain biological sensors with functions similar to those of the mechanical devices described. Most of these are specialized cells that are sensitive to:

Light, motion, temperature, magnetic fields, gravity, humidity, vibration, pressure, electrical fields, sound, and other physical aspects of the external environment;

Physical aspects of the internal environment, such as stretch, motion of the organism, and position of appendages (proprioception); An enormous array of environmental molecules, including toxins, nutrients, and pheromones; Many aspects of the internal metabolic milieu, such as glucose level, oxygen level, or osmolality; An equally varied range of internal signal molecules, such as hormones, neurotransmitters, and cytokines; And even the differences between proteins of the organism itself and of the environment or alien creatures.

Artificial sensors that mimic biological sensors by using a biological sensitive component, are called biosensors. The human senses are examples of specialized neuronal sensors. See Sense.

INTRODUCTION TO PROXIMITY SENSORS

PROXIMITY SENSOR:The Inductive Proximity Sensor (IPS) is a solid state device that generates an output signal when metal objects are either inside or entering into its sensing area from any direction. No physical contact is required nor desired. IPS's work best with ferrous metals, however, they also work well with non-ferrous metals (aluminum, brass, copper etc.) at reduced sensing distances. First introduced in the mid 60's, Inductive Proximity Sensors were designed as an alternative to mechanical limit switches for many applications. Initially, IPS's were made with housing similar in size and dimension to the limit switch, but had short sensing distances. Following very good results with these new devices, market pressure led to the development of larger sensors with increased sensing distances. Inductive Proximity Sensors have no moving parts, operate very fast, are extremely reliable, require no maintenance, and operate under extreme environmental conditions. They typically interface with Programmable Logic Controllers (PLC), process and personal computers with appropriate hardware and software. They also can control relays, solenoids, valves, etc., up to their maximum output current.

Wiring Diagram:

Connection:

Operation:An Inductive Proximity Sensor consists of an oscillator, a ferrite core with coil, a detector circuit, and output circuit, housing, and a cable or connector. The oscillator generates a sine wave of a fixed frequency. This signal is used to drive the coil. The coil in conjunction with ferrite core induces a electromagnetic field. When the field lines are interrupted by a metal object, the oscillator voltage from the coil. The reduction in the oscillator voltage is caused by eddy currents induced in the oscillator voltage is caused by eddy currents induced in the metal interrupting the field lines. This reduction in voltage of the oscillator is detected by the detecting circuit. In standard sensors, when the ouptput signal is generated. In an Analog Proximity Sensor, a pre-set level is not used. The Analog sensor circuitry utilizes the change of the oscillator output voltage to generate a DC output

voltage proportional to the distance the metal object is from the sensing head.

Sensor Configuration:

Operation configuration:Output may be Normally Open (NO) or Normally Closed (NC). Some models feature both a normally open (NO) and normally closed (NC) output which is called a complementary output. Fig: Electronic Output Circuits

DC Inductive Proximity Sensor may be 2-wire, or 4-wire, A3wire or 4-wire DC sensor can be an NPN or PNP output transistor. If the output load is connected to the negative power source than a sensor with a PNP output transistor is required. A PNP sensor is also known as a source sensor. If the output load is connected to the positive power source, then a sensor with an NPN output transistor is required. An NPN sensor is also known as a sink sensor. Flush Mount sensors are sometimes called Shielded or Embeddable. A metal band surrounds the sensing head which contains a coil wound around a ferrite core.

Fig. Sensor Electromagnetic Field

The resulting electromagnetic field is directed in front of the sensor face. Flush sensors have a narrow sensing field which may be desirable in certain applications. In a Non-Flush (Non-shielded or Non-embeddable) sensor, (Figure 4), there is no metal band and the resulting electromagnetic field lines larger sensing distance than Flush sensor. Sensing Distance: There are several sensing distance definitions used in industry. The nominal sensing distance (Sn), is the conventional quantity to designate the operational distance, it is specified in the ordering pages, and does not include variations in production tolerances, supply voltage tolerances, and ambient temperature tolerances. A standard target used to specify sensing distance is a square piece of mild steel having a thickness of 1mm (0.04 in.) The sides of the square are equal to the diameter of the circle inscribed on the sensor face or three times the rated operating distance Sn, whichever is greater. The assured operation distance (Sa) is the smallest useful sesing distance which guarantees operation under variations in temperature, voltage and manufacture. It is given as 81 % of Sn. See Figure % 0.81 Sn. The effective sensing distance (Sr), is measured at nominal supply voltage and nominal ambient temperature and takes into account manufacturing tolerances: 0.9 SnSu1.21 Sn

FIG. 5 SENSING DISTANCE DEFINITIONS Sr.-MNFG. TOLERANCES

Hysteresis:Hysteresis is the switch-on point when the object approaches the sensors active surface, and switch off point, when the object is moving away from the sensors active surface. Without sufficient Hysteresis, an Inductive Proximity Sensor would chatter (continuously switching on and off), so it is designed into the sensor circuitry. The differential travel (Hysteresis) is given as a percent of the expected rated operating distance sr. Fig 6: Hysteresis

Maximum switching frequency:The switching frequency indicates the maximum number of switching operations of a sensor per second. The value listed in the product specifications is achieved with the conditions shown in Figure7. the value is always dependent on target size, distance from sensing face and speed of target. Using a smaller target or space may result in a reduction of a specific sensor maximum switching frequency. Fig: Switching Frequency

LINEAR STEPPER MOTORS

Overview:The linear stepper motor has been made flat instead of round so its motion will be along a straight line instead of rotary. A picture of a linear motor and its amplifier is shown in Fig. 11-69, and the basic parts of the linear motor are shown in Fig. 11-70. In this diagram you can see the motor consists of a platen and aforcer. The platen is the fixed part of the motor and its length will determine the distance the motor will travel. It has a number of teeth that are like the rotor in a traditional stepper motor except it is passive and is not a permanent magnet. The forcer consists of four pole pieces that each have three teeth. The pitch of each tooth is staggered with respect to the teeth of the platen. It uses mechanical roller bearings or air bearings to ride above the platen on an air gap so that the two never physically come into contact with each other. The magnetic field in the forcer is changed by passing current through its coils. This action causes the next set of teeth to align with the teeth on the platen and causes the forcer to move from tooth to tooth over the platen in linear travel. When the current pattern is reversed, the forcer will reverse its direction of travel. A complete switching cycle consists of four full steps, which moves the forcer the distance of one tooth pitch over the platen. The typical resolution of a linear motor is 12,500 steps per inch, which provides a high degree of resolution. The typical load for a linear motor is low mass that requires high-speed movements.

Fig: A linear motor and its amplifier.(Courtesy of Parker Compumotor Division).

Fig: The forcer is shown on top of the platen of a linear motor. The electromagnets are identified on the forcer. (Courtesy of Parker Compumotor Division.)

Theory of Operation:

The forcer consists of two electromagnets that are identified in Fig. 11-70 as magnet A and magnet B and one permanent magnet. The permanent magnet is a strong rare-earth permanent magnet. The electromagnets are formed in the shape of teeth so that their magnetic flux can be concentrated. In the diagram you can see that the forcer has four sets of teeth and these teeth are spaced in quadrature so that only one set of teeth is aligned with the teeth on the platen at any time. When current is applied to the coil (field winding) of the electromagnets, their magnetic flux passes through the air gap between the forcer and the platen, causing a strong attraction between the two. The magnetic flux from the electromagnets also tends to reinforce the flux lines of one of the permanent magnets and cancels the flux lines of the other permanent magnet. The attraction of the forces at the time when peak current is flowing is up to ten times the holding force. When a pattern of energizing one coil and then another is established, the resulting magnetic field will pull the motor in one direction from one tooth to the next. When current flow to the coil is stopped, the forcer will align itself to the appropriate tooth set and create a holding force that tends to keep the forcer from moving left or right to another tooth. The linear stepper motor controller sets the pattern for energizing and de-energizing the field coils so that the motor moves smoothly in either direction. By reversing the pattern, the direction the motor travels is reversed.

Figure shows a block diagram of the linear stepper motor controller. From this diagram you can see that it has a microprocessor that interfaces with a digital-to-analog converter, a force angle modifier, and a power amplifier. It also has a power supply for the amplifiers and it may have an accelerometer amplifier as an option. The microprocessor has ROM and EPROM memory to store programs.

Fig: A block diagram of a linear motor controller. (Courtesy of Parker Compumotor Division.)

Applications:

The applications for a linear motor tend to be straight-line motion. These types of applications are slightly different from traditional stepper motor applications where the rotary motion is converted to linear motion with a ball and screw, rack and pinion, or other method. Figure 11-72 shows the linear motor used in a coil winding positioner application. The linear motor in this application is teamed with a servomotor that controls the speed of the coil winding mechanism. The linear motor determines the exact location of the next coil that is added to the spool. The speed of the linear motor can be increased or decreased when the machine is spooling larger-diameter or smaller-diameter wire. The ability of the linear motor to provide small incremental steps makes it a good match for this application. Figure 11-73 shows a second application where the linear motor is used to transport a semiconductor wafer through a precision laser inspection station. The linear motor provides excellent locating ability for this application. A Compumotor L-L20-P96 system acts as the traverse element to guide the wire, while a Z Series servo motor rotates the spindle. Both axes are coordinated by a Compumotor 4000 indexer preprogrammed to produce a number of different coil types. Precise position control and mechanical simplicity over a long length of travel are provided by the linear motor.

Fig: A linear stepper motor used in a coil winding application. The linear motor is used to control the position of the coil winder. (Courtesy of Parker Compumotor Division.)

In this application, the linear motor acts as a transport for semiconductor wafers. The L20 linear motor system offers increased throughput and gentle handling of the wafer.

Fig: A linear stepper motor used to transport a silicon

semiconductor wafer through a laser inspection station. (Courtesy of Parker Compumotor Division.)

Motor Fundamentals:Overview: Motors come in many different types, shapes, and sizes. Most of the motors used in motion control can be divided into two categories: stepper motors and servo motors. This document describes these two types of motors.

Table of Contents:1. Stepper Motors 2. Advantages of Stepper Motors 3. Disadvantages of Stepper Motors 4. Servo Motors 5. Advantages of Servo Motors 6. Disadvantages of Servo Motors

Stepper Motors:Stepper motors are less expensive and typically easier to use than a servo motor of a similar size. They are called stepper motors because they move in discrete steps. Controlling a stepper motor requires a stepper drive and a controller (For more information about stepper drives, see the related link, Stepper Motor Drives below). You control a stepper motor by providing the drive with a step and direction

signal. The drive then interprets these signals and drives the motor. Stepper motors can be run in an open loop configuration (no feedback) and are good for low-cost applications. In general, a stepper motor will have high torque at low speeds, but low torque at high speeds. Movement at low speeds is also choppy unless the drive has microstepping capability (for more information on microstepping see the microstep section of the Stepper Motor Switching Sequence link below). At higher speeds, the stepper motor is not as choppy, but it does not have as much torque. When idle, a stepper motor has a higher holding torque than a servo motor of similar size, since current is continuously flowing in the stepper motor windings. Advantages of Stepper Motors: Some of the advantages of stepper motors over servo motors are as follows:

Low cost Can work in an open loop (no feedback required) Excellent holding torque (eliminated brakes/clutches) Excellent torque at low speeds Low maintenance (brushless) Very rugged - any environment Excellent for precise positioning control No tuning required

Disadvantages of Stepper Motors:Some of the disadvantages of stepper motors in comparison with servo motors are as follows:

Rough performance at low speeds unless you use microstepping Consume current regardless of load. Limited sizes available . Noisy . Torque decreases with speed (you need an oversized motor for higher torque at higher speeds) . Stepper motors can stall or lose position running without a control loop .

COCLUSIONS:Development of PC based automated systems is very popular for its easy monitoring and controlling from remote place or near the plant itself. There are various ways to develop these automated systems. A PC based automatic car parking is a typical system based on the National Instruments DAQ product and Lab View Software. Using NI DAQ and Lab View, it is very easy to develop any automated system. It faced a problem in receiving to and sending signals fro DAQ Card when the system was in operation. This was because of loading effect on DAQ Card when all lines of DAQ Card are activated, which caused voltage drop. However, this problem overcomes by isolating all inputs and outputs by Optoisolator and also designing all external circuits to give low output impedance and high input impedance. This automatic car parking system may be further improved by introducing the latest image sensors for identifying the car and also payment of car parking charge.

FUTURE PROSPECT:The system can also be used to make car parking completely automatic. Pressure sensors have been installed at the entry and exit gate to sense the car waiting for entry or exit and give input signals to the computer to count the number of vehicles entering and leaving the park respectively. The number of cars available in the park will be the difference of the number of vehicles entering and the number of vehicles leaving. When a car approaches top entry gate, the computer will decide whether any space available or not. If no space is available, the computer will then send signal to entry gate to keep the gate closed and also to the monitor to display the message Car Park Full. If there is space in the park, the user will enter his car number in the keyboard located at entry gate and the entry gate will open to allow the care to enter the park. The computer will then store the number of the car and the time of entering in to the park in the data base. Similarly, at the time of exit, as soon as the car approaches the exit gate, the user has to enter his car number. The computer will then calculate the parking charge multiplying the rate fixed by the authority and the total period spent in the park and this amount will be displayed to draw attention opf the car owner to pay. As soon as the amount paid, the computer will send signal to the exit gate to open and allow the car to leave the park.

BLOCK DIAGRAM FOR AUTOMATIC CAR PARKING:

1 Personal Computer:The PC must be compatible with Pentium processor of minimum 800 MHz, speed and minimum 64 MB RAM and PCI slot.

2DAQ Card And Other Accessories:PCI card of the National Instruments Inc. has been used for data acquisition. PCI has 40 channels out of which 32 I/O (4 ports of 8 lines), 4 dedicated output and control & 4 dedicated input and status.

3Keypads With LCD Display:Standard alphanumeric keypad with LCD display have been used for keying in car number at the time of entry or exit.

4 Visual Display Unit(VDU):In order to display the status of the car park before entering in to car park, either CRT or LCD can be used.

5Cash Counter (Coin Separator) With Display:At the time of leaving the car park, the parking charge is required to display. A cash counter is required to place in the convenient place to pay the parking charge by the users. LCD with coin separator has been placed at the exit gate to count number of coins of different denominations.

6 Linear Stepper Motor:12V DC, 0.6 A motor with an arm mounted on the shaft of the motor has been chosen for closing and opening the gate.