Programmable Controllers: Theory and Implementation

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Introduction to PLC Programming and Implementation—from relay logic to PLC logicL1123StopTR1StartTR1TR1S1TR1M1L2OL4M1TR1S156S1S2S2(a)L1S265%S1M1T1L2S2S1M1T2ML3S2S1M1T3(b)Figure 36. (a) Hardwired relay circuit and (b) wiring diagram of a reduced-voltage-startmotor.Figure 37 illustrates the hardwired circuit with the real inputs and outputscircled. The devices that are not circled are implemented inside the PLCthrough the programming of internal instructions. Tables 13, 14, and 15 showthe I/O assignment, internal assignment, and register assignment, respectively.Figure 38 illustrates the PLC implementation of the reduced-voltagestartcircuit. The first line of the PLC program traps the timer with internaloutput 1000. Contacts from this internal replace the instantaneous timercontacts specified in the hardwired control circuit. This PLC circuit implementationdoes not provide low-voltage protection, since the interlockingdoes not use the physical inputs of M1, S1, and S2. If low-voltage protectionis required, then the starter’s auxiliary contacts or the overload contacts canbe programmed as described in the previous examples. If the auxiliarycontacts or the overloads are used as inputs, they must be programmed asIndustrial Text & Video Company www.industrialtext.com 1-800-752-839838
Introduction to PLC Programming and Implementation—from relay logic to PLC logic1L1StopStartTR1L2OL23TR1TR1TR1S1M14M1TR1S156S1S2S2Figure 37. Real inputs and outputs to the PLC.I/O AddressModuleTypeRackGroupTerminalDescriptionInput0 0 0 Stop PB (NC)0 0 1 Start PB (NO)Output0 3 0 Motor Starter M10 3 1 S10 3 2 S2Table 13. I/O address assignment.DeviceInternalTable 14. Internal address assignment.Description— 1000Trap timer circuitTimer1001TimerRegisterDescription4000Preset register value 53, time base 0.1 sec for 5. 3sec (timer output is 1001)4001Accumulated register for timer output 1001Table 15. Register assignment.Industrial Text & Video Company www.industrialtext.com 1-800-752-839839
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Programmable Controllers: Theory and Implementation

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