Programmable Controllers: Theory and Implementation

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Introduction to PLC Programming and Implementation—from relay logic to PLC logicModuleTypeRackI/O AddressGroupTerminalTable 12. I/O address assignment.DescriptionInput0 0 0 Stop PB (wired NC)0 0 1 Forward PB (wired NO)0 0 2 Reverse PB (wired NO)0 0 3 Overload contactsInput0 0 4 Acknowledge OL/Reset PB• • •• • •• • •Output0 3 0 Motor starter M1 (FWD)0 3 1 Forward PL10 3 2 Motor starter M2 (REV)0 3 3 Reverse PL2Output0 3 4 Overload condition FWD0 3 5 Overload condition REV0 3 6 —0 3 7 —L1Stop000ForwardReverse001L2OL003ACK OL004OL003ACK OL004Stop000Stop000M1030M2032Rev002Rev002Fwd001M1030Fwd001M1030M2032L1OL Fwd034LOL Fwd034UOL Rev035LOL Rev035UOL M1003 030030PL1031031ML2Fwd PL1002OL003ACK OL Reset004Stop000Stop000Fwd001Fwd001Rev002M2032Rev002M2032M1030OL003M2032PL033032033M2RRev PL2OL FaultFwd034OL FaultRev035Figure 34. PLC implementation of the circuit in Figure 31.Industrial Text & Video Company www.industrialtext.com 1-800-752-839836
Introduction to PLC Programming and Implementation—from relay logic to PLC logicto the overload. An additional normally open acknowledge overload resetpush button, which is connected to the input module, allows the operator toreset the overload indicators. Thus, the overload indicators will remainlatched, even if the physical overloads cool off and return to their normallyclosed states, until the operator acknowledges the condition and resets it.Figure 35 illustrates the motor wiring diagram of the forward/reverse motorcircuit and the output connections from the PLC. Note that the auxiliarycontacts M1 and M2 are not connected. In this wiring diagram, both theforward and reverse coils have their returns connected to L2 and not to theoverload contacts. The overload contacts are connected to L1 on one side andto the PLC’s input module on the other (input 003). In the event of an overload,both motor starter output coils will be dropped from the circuit because thePLC’s output to both starters will be OFF.L1 L2 L3FWDREVL1L1L2L1M1M23232FROLTo PLCInput 003MFigure 35. Forward/reverse motor wiring diagram.REDUCED-VOLTAGE-START MOTOR CONTROLFigure 36 illustrates the control circuit and wiring diagram of a 65% tapped,autotransformer, reduced-voltage-start motor control circuit. This reducedvoltagestart minimizes the inrush current at the start of the motor (lockedrotorcurrent) to 42% of that at full speed. In this example, the timer must beset to 5.3 seconds. Also, the instantaneous contacts from the timer in lines 2and 3 must be trapped.Industrial Text & Video Company www.industrialtext.com 1-800-752-839837
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Programmable Controllers: Theory and Implementation

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