Programmable Controllers: Theory and Implementation

Introduction to PLC Programming and Implementation—from relay logic to PLC logicL1StartPB1StopPB2CR1L2CR1CR1TempTS3CR2PL1ReadyLevelFS4CR2 CR3SOL1OpenPL2LevelFS5CR2SOL2OpenCR3PL3CR1TempTS3H3HeatingorHFigure 7. Electromechanical relay circuit.Assume that the PLC used has a modularity of 8 points per module.Each rack has 8 module slots, and the master rack is number 0. Inputsand outputs can have any address as long as the correct module isused. The PLC determines whether an input or output module isconnected in a slot. The number system is octal, and internals start ataddress 1000 8 .SOLUTION(a) Figure 8 shows the circled real input and output connections. Notethat temperature switch TS3 is circled twice even though it is only onedevice. In the address assignment, only one of them is referenced, andonly one of them is wired to an input module.(b) Table 4 illustrates the assignment of inputs and outputs. It assignsall inputs and all outputs, leaving spare I/O locations for future use.Industrial Text & Video Company www.industrialtext.com 1-800-752-839812