Development of a Programmable Logic Controller Experiential
Contents
1. For Help press F1 2 0000 APP READ Z Measurenner IL NC L U Ill amp Automation Instrumen start 3230 RSLogix 500 Starter ERAS Y 328 2 34PM Figure 4 Screen Shot of RSLogix 500 PLC Program with PLC Lab Sim2 RSS File Open 3 Chck on the pull down menu Remote Run in the upper left corner of the screen and select the Download option This will download the currently opened program to the PLC With the ladder logic program PLC Lab Sim2 RSS downloaded to the PLC there are two options for running its ladder logic a The PLC can simply be powered on with 120 VAC and ladder logic operated using the PLC and associated hardware without the RSLogix 500 software running or b The PLC can be operated in conjunction with the RSLogix 500 software running interactively at the same time This is done by using the Remote Run pull down menu in the upper left corner of the RSLogix 500 software and selecting the Go Online option Running online with the ladder logic software open together with the PLC operating allows the user the additional option of modifying inputs to the ladder logic 1 e turning on switches etc through software input 4 To test the ladder logic features flip the toggle switch 0 of the 1796 SIM1500 Input Simulator to the up position Note that the fan turns on This occurs because output 5 O 0 5 of the PLC is activated from 0 OFF to 1 ON Referenc2. a A s 3 0 PLC Demonstration Procedure The ladder logic control program used to run this demonstration platform is given in Appendix A Note that the ladder logic diagram has ten basic control rungs O thru 9 Rung O is used to turn on an incandescent light or other 120 VAC load not shown in Figure 2 This is done either by turning on switch 2 of the 1796 SIM1500 Input Simulator or entering a value of 1 directly into the ladder logic program for location N9 6 Source A at Rung 0 Rung 1 is used to turn on the fan This is done either by turning on switch 0 of the 1796 SIM1500 Input Simulator or entering a value of 1 directly into the ladder logic program for location N9 4 Source A at Rung 1 Rung 2 is used to turn on a blinking red light This is done either by turning on switch 1 of the 1796 SIM1500 Input Simulator or entering a value of 1 directly into the ladder logic program for location N9 4 Source A at Rung 2 Note from Figure 2 that three gears are mounted side by side on the PLC demonstration unit And positioned on the outside diameter of each gear is a counter which is activated by the passing gear teeth as the gears are rotated In the ladder logic program Appendix A Rungs 3 and 4 are used to count the gear teeth of the largest gear which has 33 teeth per revolution Rungs 5 and 6 are used to count the gear teeth of the middle gear which has 24 teeth per revolution And Rungs 7 and 8 are used to count t
3. effectiveness of the learning experience provided by the platform These results are planned to be reported in a future paper XI Relay Start button O Valve x ss Timer 7 Float switch Timer 90 T 2 Tank Figure 5 Ladder Logic Diagram for Storage Tank Example 1 7 0 References 1 Groover M P Automation Production Systems and Computer Integrated Manufacturing Prentice Hall Upper Saddle River NJ 2nd ed 2001 p 268 2 Rockwell Software RSLogix 500 Getting Results Guide Rockwell Automation 2002 3 Allen Bradley Micrologix 1500 Programmable Controllers Bulletin 1764 User Manual Rockwell Automation March 2002 Appendix A PLC Demonstrator Ladder Logic Control Program 1 0 0000 6 Bul 1764 EQU Equal Source A Source B 1 0 0001 4 Bul 1764 FQU Equal Source A Source B 0 0002 5 Bul 1764 EQU Equal Source A Source B 1 0 B3 0 0003 ONS I 0 Bul 1764 N9 6 0 lt I lt N9 4 0 lt 1 lt Time Base S 4 13 N9 5 0 lt 1 lt LAD 2 Total Rungs in File CPO Count Up Counter C5 1 Preset 32000 lt Accum 3350 lt ADD Add Source A Source B Dest O 0 4 Bul 1764 O 0 5 Bul 1764 O 0 0 Bul 1764 CU pee N7 1 3351 lt 335 1 lt 0004 0005 0006 0007 0008 Appendix A PLC Demonstrator Ladder Logic Control Program cont DN 1 0 2 Bul 1764 5 2 DN 1 0 3 Bul
4. 1 Edit the PLC Lab Sim2 RSS program to accomplish the following Selector switches 0 2 of the 1796 SIM 1500 Input Simulator must all be turned ON 1 e toggled in the UP position before the fan turns ON Exercise 2 Edit the PLC Lab Sim2 RSS program to accomplish the following Turn on the red light source output 0 O 0 0 without allowing it to blink only if output 4 2 120 VAC is ON OR input 4 Switch 0 is ON AND input 5 Switch 1 is not ON Exercise 3 Edit the PLC Lab Sim2 RSS program to accomplish the following When the count of gear teeth on the large gear is greater than the count of gear teeth on the middle gear turn on the red light source output 0 O 0 0 without allowing it to blink 5 0 Results of Using the PLC Platform in a Graduate Course A graduate course in manufacturing was recently taught by the author for seven students entitled Computer Control of Manufacturing This course covered topics in manufacturing ranging from numerical control and automation to sensors actuators control systems and the use of PLCs The topic of PLC s was covered as the eleventh of twelve three hour lectures given over the entire semester The lecture was quite extensive covering Chapter 8 in Reference 1 including the characteristics and elements of PLCs the use of truth tables Boolean algebra ladder logic and associated symbolism and examples demonstrating discrete process control using both logic event drive
5. 1764 C5 3 DN LAD 2 Total Rungs in File 10 MOV Move Source Dest 29 Count Up Counter 5 2 Preset 32000 lt Accum 4474 lt ADD Add Source A Source B Dest MOV Move Source Dest CTU Count Up Counter C5 3 Preset 32000 lt Accum 3079 lt ADD Add Source A Source B Dest MOV Move Source Dest CI RES 0 0 N7 1 3351 CU DN 1 lt N7 2 4474 lt 4474 lt C5 2 RES 0 lt N7 2 4474 lt Cu DN 1 lt N7 3 3081 N7 3 3081 lt C5 3 RES 0 lt N7 3 3081 lt
6. Development of a Programmable Logic Controller Experiential Learning Platform Richard B Mindek Jr Western New England College Springfield Massachusetts Abstract An experiential learning platform was recently developed to expose graduate engineering students as well as undergraduate junior and senior mechanical engineering students to the concept components operation and application of programmable logic controllers PLCs The platform consists of a programmable logic controller which can be programmed with a desktop PC in order to control several simple output devices The system allows students to write their own ladder logic programs and to experiment with the program structure needed to control particular output devices Student feedback to date suggests the availability of this platform which encourages self exploration has had a very positive impact on student learning in a recently run graduate course Plans for implementing an experiential learning approach using an updated version of the same platform in the undergraduate engineering curriculum are also discussed 1 0 Introduction A programmable logic controller PLC is a microprocessor based control system used by industry to communicate with other process control components It is used in process control for simple switching tasks proportional integral derivative PID control complex data manipulation arithmetic operations timing and process and machine control and coo
7. ay then energizes a second solenoid S2 opening a second valve to allow fluid flow out of the tank It also starts a timer T2 which provides a delay time of 90 seconds for the tank to drain After 90 seconds the timer de energizes the solenoid S2 which closes the drain valve When the START button is depressed again the timers are reset and the process begins again The ladder logic diagram for this control system reveals several checks and balances built into the system For example a normally closed float switch control is used in rung 1 which means that its output will be ON 1 when the float switch is open and the tank is filling The filling valve cannot be open unless this float switch is open At the same time rung 4 shows that the float switch must be closed and the contacts of the second timer must be open for second relay solenoid and first timer to be activated These cannot be activated otherwise which would obviously cause the tank to attempt to drain before reaching its maximum filled capacity The current plan is to incorporate this new system as an additional feature of the existing PLC platform This work will be completed during the coming summer and likely used in a manufacturing elective course the following spring More time will be devoted during the course to explaining the use of the RSLogix software and use of the rig In addition student surveys will be given twice during the semester to poll students regarding the
8. diameter of the large gear a small red LED on the sensor illuminates and input 1 1 0 1 is activated on the PLC by completion of the 24 VDC circuit see Figure 3 Thus the voltage in the circuit changes from 0 to 24 VDC when this happens Rung 3 of the ladder logic program Appendix A shows that this closes the 0 1 switch contact and then sends a 1 bit to the binary location B3 0 0 This resets the PLC so that the counter load on the right side of rung 3 makes only one count for each rise in voltage from 0 to 24 VDC If this were not included in the ladder logic the scanning frequency of the PLC would cause the counter to register a very high number of counts corresponding to the scanning rate of the PLC Rung 3 of the ladder logic program shows that the counter counts UP each time it sees a rise in the voltage signal of the circuit from 0 to 24 VDC and stores it in location C5 1 In addition this count is stored in an integer location N7 1 which is included so that this number can be accessed by other control programs e g Visual Basic which could use the stored number to perform so other task This is done because the counter location C5 1 s not accessible by external programs Rung 4 is used to reset the counter once it gets to a preset value In the current case the preset value is set to 32000 counts This is shown in the counter function on the right side of rung 3 as Preset while the accumulated number of counts up to the cur
9. e various component loads that the PLC controls Note from Figure 3 that a 1796 SIM1500 Input Simulator is used to turn the fan red blinking light and 120 VAC powered incandescent bulb not shown on and off using simple toggle switches In addition the gear teeth of three separate gears are counted as they are rotated through 24 VDC sourcing connections Sourcing means that the common side of the 24 VDC circuit is connected to ground and voltage in the circuits changes from 0 VDC to 24 VDC every time a tooth passes by each of the frequency counters This in turn triggers the input side of the PLC connected to each gear to turn to the 1 ON position which increases the total count number for each gear every time a tooth passes by the frequency counter Also note from Figure 3 that the part counter shown is wired in a manner similar to the gear frequency counters At present the part counter is not wired completely into the PLC circuit and is not included in the ladder logic control program Micrelogige S05 Xa 4 Q Y 179 b Sim 1560 2 2 4 6617 zavpclelel e go io co 4 001 a Se 1 7 v 2 roe 3 1 a ET 11 Fra 767 oc ae oe A CJE IN coms 9 J 2 i I EI Vo Way we EAR i d MU cm m gon V Msc 5 7 HH m s ww 4 CPi Figure 3 Schematic Diagram of PLC System Components and Wiring
10. ents rated the usefulness of the projects run in the course the PLC project was one of three given as a 4 6 out of 5 It is the author s interpretation of this feedback that students found the PLC project helpful especially the ability to learn through exploration of a hands on platform but that more time and a broader range of exploration are needed These issues are currently being addressed and will be incorporated into an updated PLC platform as described in the following section 6 0 Incorporation of the PLC Platform in the Undergraduate Curriculum Figure 5 shows a more complex control system relative to the existing system a storage tank and its corresponding ladder logic control diagram which is planned to be incorporated into the PLC platform before it is used in a new undergraduate manufacturing elective course Note that this control system employs the use of both timers and counters in addition to relays switches and loads Its operation can be described as follows When the start button is activated the control relay C1 is energized which then activates the solenoid S1 opening a valve to allow fluid flow into the tank When the tank fills to maximum capacity the float switch FS closes opening relay Cl and causing the solenoid S1 to de energize thus closing the valve to stop fluid flow into the tank At the same time the float switch FS activates the timer T1 which activates a second relay C2 after a 120 second delay This rel
11. he gear teeth of the smallest gear which has 13 teeth per revolution Rung 9 is a Program End rung not shown in Appendix A To exercise the components of the system using the RSLogix software the following steps are performed 1 Begin by turning on the PC and double clicking the icon on the desktop titled RSLogix 500 2 Using the File command at the top of the toolbar open the file in the documents folder entitled PLC LAB Sim2 RSS ladder logic program This will bring up the screen as shown in Figure 4 The opened ladder logic program is shown in the right window while the program currently downloaded to the PLC as well as access to its various PLC functions is shown in the left window PLC LAB SIM1 ON File Edit View Search Comms Tools Window Help WD e x melo Jae B m le Q m e gt i 777777777 Node 14 Ll I User TimeriCounter Input Output A Compare 10 x Put E13 Project E rv le xl s EZ Help Eig Controller Shan Eos i Controller Properties AS Processor Status d CS Function Files 4l io Configuration x pt Channel Configuration H Program Files 0B svso Source B 0B svst t LAD 2 2 2 Data Files LP d Cross Reference I oa OUTPUT 0 n INPUT BJ s2 STATUS E B3 BINARY ED T4 TIMER B cs COUNTER BE RE CONTROL L G N7 INTEGER ll F8 FLOAT Le B E Data Logging E Configuration gt 4 2
12. ing rung 1 of the ladder logic diagram in Appendix A it is seen that O 0 5 portrayed as a load on the right side of rung 1 of the ladder logic diagram is activated when input 4 1 0 4 a ladder logic switch 15 activated to 1 ON This is done by physically moving toggle switch of the 1796 SIM1500 Input Simulator in the up position completing the 24 VDC circuit The wiring diagram of Figure 3 shows how all this is accomplished via hardware Here it is seen that 120 VAC is brought in to power the fan through a relay left side relay This relay acts as a switch which is activated only when the other side 24 VDC side of the relay closes the contacts to the 120 VAC circuit via a 24 VDC signal from the PLC This 24 VDC signal is activated only when output 5 O 0 5 on the PLC is given a value of 1 And of course as stated earlier this output is activated through input 0 4 The input 1 0 4 is physically connected to the high plus side of the 24 VDC circuit via switch 0 of the 1796 SIM 1500 Input Simulator The ground side of this circuit is connected to the DC COM common of the PLC on the input side as shown in Figure 14 The fan can also be turned on by entering a value of 1 directly into the ladder logic program for location N9 4 Source A at Rung 1 This can also be done by opening the N9 folder lower left window of the RSLogix 500 software and entering a value of 1 in location 4 The fan can be turned off by entering a va
13. l and remote VO Today PLC s are used in all facets of industry provide a broad range of functions can be programmed using a desktop personal computer and can be purchased for as little as several hundred dollars With such broad use in industry wide ranging application in engineering related fields and availability to users at all levels it is imperative that engineering educators provide young engineers with a fundamental understanding of the operation and capabilities of PLCs This task has recently been undertaken within the Mechanical Engineering Program at Western New England College through the building of a PLC platform and development of a PLC laboratory This laboratory is unique in that it is designed to allow students to self learn fundamental PLC operation The purpose of this paper to describe the work recently completed in this area at Western New England College report on the use of the platform at the graduate level as well as present future plans to incorporate it within the undergraduate engineering curriculum 2 0 Basic Components of the PLC Platform In order to give students an opportunity to experience how computer automation and control is accomplished in a manufacturing environment a demonstration apparatus was built containing actuation and sensing devices a computer interface feedback control and an Allen Bradley MicroLogix 1500 programmable logic controller This platform can be utilized by the instructor in a cla
14. lay acts as a switch which is activated only when the other side 24 VDC side of the relay closes the contacts to the 120 VAC circuit via a 24 VDC signal from the PLC This 24 VDC signal is activated only when output 4 O 0 4 on the PLC is given a value of 1 As stated earlier this output is activated through input 1 0 6 The input 1 0 6 is physically connected to the high plus side of the 24 VDC circuit via switch 2 of the 1796 SIM 1500 Input Simulator The ground side of this circuit is connected to the DC COM common of the PLC on the input side as shown in Figure 3 The 120 VAC load can also be turned on by entering a value of 1 directly into the ladder logic program for location N9 6 Source A at Rung 0 This can also be done by opening the N9 folder lower left window of the RSLogix 500 software and entering a value of 1 in location 6 The load can be turned off by entering a value of 0 in location N9 6 using either of these methods Again it is important to note that activating the 120 VAC load using a 24 VDC relay switch isolates the 120 VAC circuit from the PLC and switching functions making the operation of turning the load on safer 7 Frequency counting of the teeth on the large gear is performed using rungs 3 and 4 of the ladder logic program as shown in Appendix A as the gear is rotated using the crank handle shown in Figure 2 When a gear tooth of the large gear passes by the sensor located on the outside
15. lue of 0 in location N9 4 using either of these methods Finally it is important to note that activating the fan using a 24 VDC relay switch isolates the 120 VAC circuit from the PLC and switching functions making the operation of turning the fan on safer 5 Next flip the toggle switch 1 of the 1796 SIM1500 Input Simulator to the up position Note that the blinking red light turns on This occurs because output 0 O 0 0 of the PLC is activated from 0 OFF to 1 ON Referencing rung 2 of the ladder logic diagram in Appendix A it is seen that O 0 0 portrayed as a load on the right side of rung 1 of the ladder logic diagram is activated when input 5 I 0 5 a ladder logic switch is activated to 1 ON This is done by physically moving toggle switch 1 of the 1796 SIM1500 Input Simulator in the up position completing the 24 VDC circuit The ladder logic also shows a time base switch or timing delay S 4 13 in line with the 1 0 5 input and I 0 O output This software delay is actually what causes the red light to turn on and off at regular intervals that is to blink The wiring diagram of Figure 3 shows how the red blinking light is activated via hardware Here it is seen that 24 VDC power is brought from the input side of the PLC over to the output side through output 0 common VDC 0 The 24 VDC connection is completed through VDC 0 and O 0 0 when I 0 5 is turned ON The 24 VDC common side is connected from the 24 VDC common screw ter
16. minal COM on the input side of the PLC through the 24 VDC screw connector see Figure 14 and then to the ground side of the red blinking light The red blinking light can also be turned on by entering a value of 1 directly into the ladder logic program for location N9 5 Source A at Rung 2 This can also be done by opening the N9 folder lower left window of the RSLogix 500 software and entering a value of 1 in location 5 The red blinking light can be turned off by entering a value of 0 in location N9 5 using either of these methods 6 Toggle switch 2 of the 1796 SIM1500 Input Simulator activates the 120 VAC powered incandescent light bulb not currently installed The activation of this 120 VAC load is accomplished in a manner analogous to the fan activation In this case the 120 VAC load is energized because output 4 O 0 4 of the PLC is activated from 0 OFF to 1 ON Referencing rung 0 of the ladder logic diagram in Appendix A it is seen that O 0 4 portrayed as a load on the right side of rung 1 of the ladder logic diagram is activated when input 6 1 0 6 a ladder logic switch is activated to 1 ON This is done by physically moving toggle switch 2 of the 1796 SIM1500 Input Simulator in the up position completing the 24 VDC circuit The wiring diagram of Figure 3 shows how this is accomplished via hardware Here it is seen that 120 VAC is brought in to power the load through a relay right side relay This re
17. n and sequence time driven system changes Students were then asked to read the corresponding material in the text 1 for homework given instruction for about 15 minutes on the use of the PLC platform and its associated software as described above and then given a PLC project to complete The project required students to complete the exercises as outlined in section 4 0 of this paper and then summarize their results in a brief technical memo It should be noted here that only one of the seven graduate students in the course had any previous experience using PLCs and none had any experience using the RSLogix software Although not conclusive the results of the project were very encouraging The students were able to explore some of the capabilities of PLCs within the design limitations of the platform and required very little external input On the project itself students scores averaged 86 indicating they generally understood the basic operation of the PLC as they completed the project And feedback on the project was also very good from the students as reflected in their end of semester evaluations Positive comments included course fills a need that addresses automation in manufacturing and liked the hands on nature of the course Negative comments included the use of software programs with little knowledge of them was a struggle Students suggested that more time be devoted to topics such as PLCs and PID control Overall stud
18. rdination Groover 1 defines a PLC as A microcomputer based controller that uses stored instructions in programmable memory to implement logic sequencing timing counting and arithmetic functions using digital and analog input output I O modules for controlling machines and processes Although PLC s are used in the process industries e g processing mined materials and oil refineries they are more commonly found in discrete manufacturing industries such as in machine control transfer lines and material handling equipment First conceived in 1968 by Richard Morley the PLC was originally developed as a device to overcome the inflexibility and high cost of hard wired controllers made of relays coils counters timers and similar mechanical components GM Corporation subsequently developed a set of specifications which included that the PLC be 1 programmable and reprogrammable 2 capable of being used in a rugged industrial environment 3 able to accept 120 VAC I O 4 have output capability needed to continuously run devices motors relays etc of a 2A rating and 5 competitively priced relative to mechanical devices As technology has advanced over the years especially microprocessor technology PLC capability has grown from primarily on off control to include operator interfaces performing arithmetic operations and data manipulation computer communications supplemental computer memory analog and positioning contro
19. rent time is shown just below it as Accum Rung 4 shows that when the current count value stored in C5 1 reaches the preset value of 32000 the counter is reset to zero That reset value is also reset in the N7 1 location whenever a reset occurs 8 The counting of gear teeth on both the medium and small size gears is accomplished in the same manner as used for the large gear Rungs 5 and 6 of the ladder logic are used to count gear teeth of the medium gear which uses input 0 2 binary location B 0 1 counter location C5 2 and integer location N7 2 in performing the same tasks as rungs 3 and 4 in the ladder logic for the large gear Rungs 7 and 8 of the ladder logic are used to count gear teeth of the small gear which uses input 1 0 3 binary location B 0 2 counter location C5 3 and integer location N7 3 in performing the same tasks as rungs 3 and 4 in the ladder logic for the large gear 9 The part counter shown in Figure 2 is currently not completely wired into the PLC hardware and 15 therefore not included in the ladder logic program of Appendix A It will be added at a latter time 4 0 Suggested Exercises for Exploration of PLC s There are many exercises that can be performed to gain a deeper understanding of ladder logic and how it can be used together with a PLC to accomplish control of a system The following exercises are suggested to be completed by students wishing to investigate the capabilities of PLC operation Exercise
20. ssroom environment for demonstration purposes as well as by students as part of an active learning environment within or outside of the classroom The apparatus is flexible so as to allow students to investigate how a basic control system works to perform an automated task including the basics of how the various components of the system function and communicate with each other and to investigate the theory associated with proportional integral derivative control and associated techniques Figure is a photograph of the basic PLC system used in this laboratory It consists of a personal computer which is loaded with both RSLinx and RSLogix 500 software used for PLC communication and programming the PLC an Allen Bradley MicroLogix 1500 PLC and a series of relays switches and power sources which are used as representative I O components that a typical PLC would control A description of each of the components of the system follows iH HS SIN Figure 1 PLC System Used in this Laboratory Figure 2 PLC System Components Personal Computer and Software The personal computer used in this laboratory see Figure 1 is a Dell computer with Pentium II processor operating at a speed of 996 MHz and 256 MB RAM Itis equipped with a CD ROM drive not writeable a zip drive 100 MB and a floppy disk drive The computer is loaded with a Windows XP operating system Other software loaded on the PC to support this laborator
21. y includes both RSLinx rev 2 43 and RSLogix 500 ver 6 30 written for Rockwell Automation Inc networks and devices The purpose of RSLinx software is to provide communication between the programmable controller and the PC RSLogix 500 software is the application software used in the laboratory in conjunction with the MicroLogix 1500 PLC This software allows the user to configure the PLC and to upload and download control programs more commonly known as ladder logic programs 2 Programmable Logic Controller The PLC used in this laboratory is an Allen Bradley MicroLogix 1500 1764 24BWA It contains a base unit with a power supply input and output circuits and a 1764 LRP Series C processor It has a line power of 120 240 VAC 8 standard 24 VDC inputs 4 fast 24 VDC inputs 12 relay outputs 2 isolated relays per unit and 4 high speed I O 20 kHz 3 VO Components Several inputs and outputs are connected to the PLC to demonstrate some of its capability as shown in Figure 2 Inputs include an array of ON OFF switches Outputs include a cooling fan an emergency blinking light a part counter and a set of three frequency counters using three different gear diameters And because not all I O on the PLC are utilized the number of I O components is easily expandable Figure 3 is a schematic of the wiring diagram for the PLC system components shown in Figure 2 This figure shows the physical wiring connections made to and from the PLC to th
Download Pdf Manuals
Related Search