Survey of PLC Development on Embedded Platform · AC500-eCo PLC: AC500-eCo PLC is supplied by ABB....

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Technovision-2014: 1st International Conference at SITS, Narhe, Pune on April 5-6, 2014

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International Journal of Electronics Communication and Computer EngineeringVolume 5, Issue (4) July, Technovision-2014, ISSN 2249–071X

Survey of PLC Development on Embedded PlatformMs. Sneha Goyanka

Department of Electronics and Telecommunication,Smt. Kashibai Navale College of Engineering, Pune, India

Email: [email protected]

Prof. Mrs. Rohita PatilDepartment of Electronics and Telecommunication

Smt. Kashibai Navale College of Engineering, Pune, IndiaEmail: [email protected]

Abstract – Technological advances in recent years haveresulted in the development of the programmable logiccontroller and a consequential revolution of controlengineering. This paper is introduction to programmablelogic controllers. A programmable logic controller (PLC) orprogrammable controller is a digital computer used forautomation of electromechanical processes, such as control ofmachinery on factory assembly lines, amusement rides, orlight fixtures. PLCs are used in many industries andmachines. Unlike general-purpose computers, the PLC isdesigned for multiple inputs and output arrangements,extended temperature ranges, immunity to electrical noise,and resistance to vibration and impact. Programs to controlmachine operation are typically stored in battery-backed-upor nonvolatile memory. A PLC is an example of a hard realtime system since output results must be produced inresponse to input conditions within a limited time, otherwiseunintended operation will result.

After investigating the conception and features of PLCfrom different vendors and embedded system, thedevelopment of the embedded PLC is proposed here with theseamless combination of the LabVIEW software and theARM Microcontroller with the LabVIEW embedded module.The flexibility of the proposed PLC makes it relatively easyand less costly. The ARM microcontroller is selected todevelop embedded PLC because it is widely used acrossmany embedded designs due to its low price, low powerconsumption, and wide variety of peripherals for many of themajor silicon vendors. In addition, the LabVIEW EmbeddedModule for graphical programming to ARM microcontrollercan be used.

Keywords – Programmable Logic Controller (PLC), LabVIEW, LabVIEW Embedded Module for ARMMicrocontroller, ARM Microcontroller.

I. INTRODUCTION

Embedded Systems are hardware and softwarecomponents working together to perform a specificapplication. They exist in abundance in our modernsociety and play a vital role in our everyday lives [1].They can be found in places such as our automobiles, inthe medical field, in industrial control systems, and inentertainment electronics to name just a few. Thehardware platform of the embedded system often consistsof a microprocessor, on-board memory, an output display,an input device for a user to enter data and applicationsoftware. Moreover embedded systems are easy to use,low power consuming, less costly for wide variety ofapplications.

Programmable logic controllers (PLCs) are a specializedtype of embedded systems used to control machines andprocesses [4]. They have been introduced in the early1970s to replace the existing relay control logic thatbecame obsolete and expensive for implementing systemsat that time. On the other hand, PLCs have offeredflexibility, higher reliability, better communicationpossibilities, faster response time, and easiertroubleshooting.

II. LITERATURE REVIEW

A. Programmable Logic Controller (PLC)A programmable logic controller(PLC) is a special form

of microprocessor-based controller that uses aprogrammable memory to store instructions and toimplement functions such as logic, sequencing, timing,counting and arithmetic in order to control machines andprocesses and are designed to be operated by engineerswith perhaps a limited knowledge of computers andcomputing languages.

The basic structure of a programmable logic controllerhas four main functional blocks as shown in Fig. 1.1. Processor2. Input Module3. Output Module4. Programming Software1. Processor: The processor is a computer that executes aprogram to perform the operations specified in a ladderdiagram or a set of Boolean equation [5]. The processorperforms arithmetic and logic operations on input variabledata and determines the proper state of the outputvariables.

Fig. 1 Basic Structure of Programmable Logic Controller(PLC)

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The processor functions under a permanent supervisoryoperating system that directs the overall operations fromdata input and output to execution of user programs.

Of course, the processor, being a computer, can onlyperform one operation at a time. That is, like mostcomputers, it is a serial machine [5]. Thus, it mustsequentially sample each of the inputs, evaluate the ladderdiagram program, provide ach output, and then repeat thewhole process. The speed of the processor is important.The heart of a PLC is a microprocessor, much like the oneused in the modern personal computers. Because much ofthe data in PLC is processed bit by bit, specialmicroprocessors optimized for such operation, such as theADM 2901 and 2903, are often employed. With the greatincreases in the processor speed, it is now possible toemploy a desktop personal computer with data I/O boardsrunning PLC software to emulate PLC operation.2. Input Module: The input module examines the state ofphysical switches and other input devices and put theirstate into a form suitable for processor. The PLC is able toaccommodate a number of inputs, called channels [5].

Fig.2. Typical wiring to PLC input module

In keeping with the industrial settings of most PLCapplications and the history of relay control, the input statesystems are often designed to provide 0 or 110V ac to theinput module. This type of connections assumes thatswitches, for example, are wired to the PLC as shown infigure 2. If the switch is closed, the input will be 110V ac,and if open, the input will be 0 V ac. The input moduleconverts this into the 1 or 0 state needed by the processor.In many cases, PLCs are now being designed to operatefrom dc voltages for which the switch is connected to theinput with a dc supply. The input module have a certainnumber of channels per module. Each channel is oftenequipped with an indicator light to show if the particularinput is ON or OFF. Fig 2 shows a input module.3. Output Module: The output module supply ac powerto external devices such as motors, lights, solenoids, andso on, just as required in the ladder diagram. The outputmodule can supply a certain maximum power. If therequired power is greater, an external relay may be used,as shown in Fig 3.

Internally, the output module accepts a 1 or 0input fromthe processor and uses this to turn ON or OFF an ACpower-control device such as a TRIAC. In this sense, theoutput module is a solid-state relay [5]. ProgrammableControllers also are designed with output modules toprovide other outputs, such as dc voltages or variableratepulse outputs (such as would be required by a steppingmotor).

An output module can have one or several channels perunit. Each channel is usually provided with an indicatorlight to show whether that particular channel is beingdriven ON or OFF.4. Programming Software: The logic in which theprocessor has to process the input and produce the desiredoutput is loaded into the processor by programmingthrough the programming software. All the PLC vendorshave their own programming softwares for their PLC’s.these softwares are vendor and processor specific. Somesoftwares support one languge and some support all thelanguages.

Fig.3. Typical wiring to PLC output module

B. PLC market surveySome of the different PLC available in market are as

follows1. Micrologix 1000: Micrologix 1000 control system is the

one of the PLC from Micro & Nano systems from

Fig.4. (a) Micro Logix 1000 Fig.4. (b) SIMATIC S7-200

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Rockwell Automation. It is the most compact of themicrologix family. This controller fits a wide variety ofapplications upto 32 I/O points, while using a fraction ofthe space of a full-size controller. It contains embeddedanalog I/O, providing compact and cost-effective analogperformance [7].2. SIMATIC S7-200: SIMATIC S7-200 is a micro PLCfor basic automation from SIEMENS. This PLC is fast,communication capable and highly productive in real-timemode, the consistently modular design facilitates thecreation of tailor-made, expandable solutions in the low-end performance range. The S7-200 Micro PLC fromSiemens can be used as either a stand-alone Micro PLCsolution or in conjunction with other controllers [8].3. AC500-eCo PLC: AC500-eCo PLC is supplied byABB. ABB is the supplier of choice for small equipmentcontrol applications to complex systems like web pressesand distributed systems. ABB's PLCs are some of thefastest and most reliable available. AC500-eCo PLC is theeconomical PLC for smaller systems and equipmentcontrol.

Fig.5. (a) AC500-eCo Fig.5. (b) Modicon M340

4. Modicon M340: Modicon M340 is a mid range PLC forindustrial process and infrastructure from SchneiderElectric. Modicon Programmable Automation Controllers(PACs) are built to suit the needs of the process industryand a wide range of demanding automation applicatios.Modicon M340 can be used individually but is also theperfect companion of Modicon Premium and ModiconQuantum, increasing the performance, the quality and theprofitability of industrial process, facilities or of machines.Compact shaped Modicon M340 offers in small boxflexibility and integrated functions, in the heart of process,it provides Plug & Work solutions with both SchneiderElectric and third party devices. The large capacity ofUnity Pro is So Collaborative software, ease and shortenthe programming and commissioning time.

III. PROGRAMMING LANGUAGES

IEC 61131-3 currently defines five programminglanguages for programmable control systems:1. LD (Ladder diagram)2. FBD (Function block diagram)3. ST (Structured text, similar to the Pascal programminglanguage)

4. IL (Instruction list, similar to assembly language)5. SFC (Sequential function chart)

1. Ladder Diagram (LD) programming is commonlyused in the industry and even in the academics. It is asymbolic and schematic way of representing both thesystem hardware and the process controller. It is called aladder diagram because the various circuit devicesconnected in parallel across the ac line from somethingthat looks like a ladder, with each parallel connection a”rung” on the ladder [5].

Fig.6. Ex-OR gate representation in a ladder diagram

In the construction of a ladder diagram, it is understoodthat each rung of the ladder is composed of a number ofconditions or input states and a single command output.The nature of the input states determines whether theoutput is to be energized or not energized.

Special symbols are used to represent the various circuitelements in a ladder diagram. Fig.6 shows a ladderdiagram representation of the Ex-OR gate. The output “O”will be energized only if either of the input A or B will be1 and other will be 0.

2. Function block diagram (FBD) is used for PLCprograms described in terms of graphical blocks. It isdescribed as being a graphical language for depictingsignal and data flows through blocks, these being reusablesoftware elements. A function block is a programinstruction unit which, when executed, yields one or moreoutput values. Thus a block is represented in the mannershown in Fig.7 (a) with the function name written in thebox [4].

Fig.7. (a) Function Block Fig.7 (b) Ex-OR gate shown inFBD

A function block is depicted as a rectangular block withinputs entering from the left and outputs emerging fromthe right. The function block type name is shown in theblock, e.g. Ex-OR as shown in fig.7 (b). Names offunction block inputs are shown within the block at theappropriate input and output points. Cross diagramconnectors are used to indicate where graphical lineswould be difficult to draw without cluttering up orcomplicating a diagram and show where an output at onepoint is used as an input at another.

3. Structured Text (ST) is a programming language thatstrongly resembles the programming language PASCAL.

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Programs are written as a series of statements separated bysemicolons [4]. The statements use predefined statementsand subroutines to change variables, these being definedvalues, internally stored values or inputs and outputs.Assignment statements are used to indicate how the valueof a variable it to be changed, e.g. Light := Switch A; isused to indicate that a light is to have its ‘value’ changed,i.e. switched on or off, when switch A changes its ‘value’,i.e. is on or off. The general format of an assignmentstatement is: X := Y; where Y represents an expressionwhich produces a new value for the variable X.

4. Instruction List (IL) is a programming method, whichcan be considered to be the entering of a ladder programusing text. Instruction list gives programs which consist ofa series of instructions, each instruction being on a newline. An instruction consists of an operator followed byone of more operands, i.e. the subjects of the operator [4].In terms of ladder diagrams an operator may be regardedas a ladder element. Each instruction may either use orchange the value stored in a memory register.

For this, mnemonic codes are used, each codecorresponding to an operator/ladder element. The codesused differ to some extent from manufacturer tomanufacturer, though a standard IEC 1131- 3 has beenproposed and is being widely adopted.

5. Sequential Function Chart (SFC) is used for apictorial representation of a system’s operation to showthe sequence of the events involved in its operation [4].The operation is described by a number of separatesequentially connected states or steps which arerepresented by rectangular boxes, each representing aparticular state of the system being controlled. Eachconnecting line between states has a horizontal barrepresenting the transition condition that has to be realizedbefore the system can move from one state to the next.Two steps can never be directly connected; they mustalways be separated by a transition. Two transitions cannever directly follow from one to another; they mustalways be separated by a step. When the transferconditions to the next state are realized then the next stateor step in the program occurs. The process thus continuesfrom one state to the next until the complete machinecycle is completed. Outputs/actions at any state arerepresented by horizontally linked boxes and occur whenthat state has been realized.

6. Comparison of different PLC: Each of the PLCvendors has their own programming software for theirPLC. The programming languages these software supportdepend on the processor used and the applications. Someprogramming software support additional tools likeSCADA, Offline simulation of program etc. A table of theprogramming software, language supported by them forthe above discussed PLC is as follows.

Table I. Comparision of Programming Software fordifferent PLC

IV. APPLICATION OF PLC

A Programmable Logic Controller, PLC is a digitalcomputer used for automation of electromechanicalprocesses, such as control of machinery on factoryassembly lines, amusement rides, or light fixtures. PLCsare used in many industries and machines. Unlike general-purpose computers, the PLC is designed for multipleinputs and output arrangements, extended temperatureranges, immunity to electrical noise, and resistance tovibration and impact. PLC has a wide range of applicationin all the industries. Some of the industries where PLC isused are listed below.i. Material Handlingii. Packaging Applicationsiii. General Industrial Machineryiv. Printingv. Food and Beveragevi. Pharmaceuticalvii. Water Wastewater / SCADAviii. Clutch/Brake controlix. Position Control - Pick-and-place / ConveyorCase Study: Continuous Bottle Filling System In foodand beverage industry a very common application iscontinuous bottle filling system. It is most importantapplication in whole plant, where bottles are moving on aconveyor belt, to be automatically detected and filled byany liquid. This example is considered and explained here.Objective: Empty bottles are moving on a conveyor belt.The position of the bottle is detected via a limit switch.The quantity of the liquid is controlled by a photo detectorwhich checks if the bottle is full or empty. Once the bottleis filled a buzzer sounds. The filled bottle is then movedfurther and the next empty bottle is moved forward forfilling. A diagram of this example is as shown in figure 8.

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Fig.8. Automatic Bottle Filling System

The ladder diagram for execution of the bottle fillingsystem is as shown in figure 9

Fig.9. Ladder Diagram for Automatic Bottle FillingSystem

Execution of Ladder: When the START switch ispressed a light ON glows till STOP is pressed. TheSTART switch also activated out feed motor M2. The feedmotor M1 is activated moves till limit switch detects abottle and gets activated. Then the SOLENOID valve ofthe liquid tank activates to fill the bottle. The level ofliquid in bottle is continuously checked by a photodetector PD which activates after the liquid in bottle isfilled to its mark. This turns off the SOLENOID valve andturns on M1 and the bottle moves further to next conveyor.The positions of limit switch and photo detector controlM1 and SOLENOID.

V. SYSTEM DESIGN

PLC based on ARM 7 processor is designed. Thesystem has all the basic features of a PLC with 8 digitalinput, 8 digital output, 4 analog input and 1 analog output.ARM 7 will act as the processor for processing theinstructions. Input and output module will be designed tosupport analog and digital I/O. LavView embeddedmodule will serve as the programming software for thePLC. Fig 10 shows the block diagram for embedded PLC.It consists of the following blocks:

1. ARM processor2. Input Module3. Output Module4. LabVIEW s/w for Programming

Except the fourth block which is the software part restall are the hardware parts of the PLC.A. Hardware Design1. ARM Processor: The ARM microcontroller isselected to develop embedded PLC because it is widelyused across many embedded designs due to its low price,low power consumption, and wide variety of peripheralsfor many of the major silicon vendors. In addition, theLabVIEW Embedded Module for graphical programmingto ARM microcontroller can be used. Block diagram ofthe embedded PLC is shown in fig 10. Besides theLabVIEW Embedded Module for ARM Microcontrollerincludes support for the RealViewμVision ARMsimulator, which provides cycle accurate timing and logicsimulation. With this capability, a large portion of theapplication could be developed and tested before thehardware design is complete.

Fig.10. Block Diagram of an Embedded PLC

This is the main reason that ARM is most suitable fordeveloping the embedded PLC. Moreover largefunctionality can be implemented using the ARMprocessor which makes the use of this PLC possible inwide range of applications [1]. The ARM processor willdo the processing on the input signals and depending uponthe program will produce the output.2. Input Module: The input to the processor will be fromthe input module. The input signals can be analog ordigital depending upon the input device connected to theinput module. The ARM processor works on 3.3V but theanalog input devices work in the range of 0-10V so avoltage divider circuit has to be added between the inputmodule and ARM processor and for digital input thevoltage is generally use 24V so there is a need to add anisolator circuit to reduce the signal to 3.3V.3. Output Module: The ARM processor gives theprocessed output to the output module which in turnconnects to the output devices such as relays, bulbs,motors etc. These devices may be analog or digitaldevices. As the output of the ARM processor is 3.3V thereis need of an isolator circuit to isolate and amplify theoutput voltage to 24V for digital devices and a voltageamplifier to amplify the voltage for the analog devices to0-10 V.

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B. Software DesignLabVIEW s/w for Programming: The PLC needs

software to provide a platform for the user to program theprocessor so as to produce the desired process for the inputand output devices. To program the ARM processor theLabVIEW Embedded Module and the PLC programminglanguage FBD is used. The LabVIEW Embedded Modulefor ARM Microcontrollers is a comprehensive graphicaldevelopment environment for embedded design. Thismodule seamlessly integrates the LabVIEW graphicaldevelopment environment and ARM microcontroller. Thismodule builds on LabVIEW Embedded technology, whichfacilitates dataflow graphical programming for embeddedsystems and includes hundreds of analysis and signalprocessing functions, integrated I/O, and an interactivedebugging interface. With the Embedded Module forARM Microcontrollers, optimize linking and viewing livefront panel updates using JTAG, serial, or TCP/IP can bedone [2]. The Embedded Module for ARMMicrocontrollers includes the LabVIEW C CodeGenerator, which generates C code from the LabVIEWblock diagram. For the creation of FBD language blocks,the available tools in LabVIEW can be used and a basicfunction of FBD language according to IEC 61131-3standards required for PLC can be created.

The decision to use the FBD language for programmingthe PLC because LabVIEW is a graphical developmentenvironment and it is easy to program using functionblocks for any desired function of the PLC.

First step in software design is to design the standardfunction blocks of FBD language in number of sub VI andintegrate them into a pallet so that they can be used forPLC application.

VI. RESULT

Various function blocks such as AND, OR, INV, ADD,SUB, CTU, TON etc are designed using LabVIEW andthese block are called for creating a simulation of aautomatic bottle filling plant disscussed in section IV.These blocks are designed as per the function blockdiagram programming language of PLC.

Fig.11. Front Panel View of Automatic Bottle FillingSystem

The input to the system is given through switches andoutput is displayed using LED. Fig. 11 shows the frontpanel view of the automatic bottle filling system inLabVIEW. The block diagram view of the same system isas shown in Fig. 12 with reference to Fig. 9.

Fig.12. Block Diagram View of Automatic Bottle FillingSystem

The system consists of four inputs and four outputswhich are controlled using function blocks designed in theLabVIEW. Table II gives the description of input andoutput of the system.

Table II: Comparison of Programming Software fordifferent PLC

Different states of the system are depicted using theprobe watch window of LabVIEW. STATE 1 is when thesystem is turned on i.e. start switch is moved to ONposition. In this state the ON (probe no. 3), M1 (probe no.8) and M2 (probe no. 3) LED glows as can be seen fromfigure 13 as True. In STAGE 2 as shown in figure 13 thelimit switch (probe no. 4) is activated and this has stopped

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M1 (probe no. 8) and turned the solenoid valve on (probeno. 9). In STAGE 3 as shown in figure 15 when the photodetector (probe no. 6) is turned on the solenoid valve(probe no. 9) turns off and M1 (probe no. 8) turns on sothat bottle can move to next conveyor.

Fig.13. STAGE 1

Fig.13. STAGE 2

Fig.13. STAGE 3

IV. CONCLUSION

In this paper the market survey of Programmable LogicController is disscussed with the ARM controller platformwith full software support of Labview. In addidtion to thisthe PLC from different vendors and supportingprogramming languages of PLC were discussed. Differentindustries where PLC are used were also listed and

automatic bottle filling system application which is animportant application of food and beverage industry isdesigned in LabView to implement on hardware platformARM controller to test real time application.

REFERENCES

[1] Pornjit Pratumsuwan and Watcharin Pongaen, “An EmbeddedPLC Development for Teaching in Mechatronics Education”, 6thIEEE Conference on Industrial Electronics and Applications2011 pp.1477- 1481

[2] “Getting Started with the LabVIEW Embedded Module forARM Microcontrollers 1.1,” National Instruments Corporation,2008.

[3] J. Staunstrup and W. Wolf, ” Data books of ARM7/ARM9”,Kluwer Academic Publishers, 1997.

[4] W. Bolton,“Programmable Logic Controllers”,Fourth Edition,Elsevier Newnes publications..

[5] Curtis D. Johnson ,“Process Control InstrumentationTechnology”, Seventh Edition , Prentice-Hall, Inc.

[6] “Introducing PS501 Control Builder Plus Common engineeringtool for PLC, drives, HMI, field bus, network, web services”,ABB corporation.

[7] “Allen-Bradely MicroLogix_ 1000 Programmable Controllers(Bulletin 1761 Controllers)” Rockwell Automation.

[8] “SIEMENS SIMATIC S7-200 Programmable Controller SystemManual” SIEMENS, Edition 08/2008.
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Survey of PLC Development on Embedded Platform · AC500-eCo PLC: AC500-eCo PLC is supplied by ABB....

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