Explain less or equal (<=) instruction using example

Application:-Explain less or equal instruction in the PLC. Write PLC program for explanation using ladder diagram language in the Programmable Logic Controller (PLC).

Components:-Programmable logic controller, HMI panel, wires, 24 VDC lamp, 24 VDC power source, 24VDC temperature controller.

Diagram:-

Explanation:-

Consider a simple temperature controller example for explanation of less equal instruction in the PLC. Here we have taken simple HMI (Human Machine Interface) for display and programmable Logic Controller (PLC) for programming. Consider one temperature control which is displaying the temperature given by temperature sensor, here we haven’t considered analog signal calculation and scaling so we can directly consider actual temp value in the PLC. Here if the actual temp value in the actual temp box is less or equal than set temp, temperature indication will be ON.

If set temperature is 50 degree and temperature read by temperature controller is 45 0r 50 degree, lamp should be ON because 45 degree is less than 50 degree.

PLC program:-

Write the ladder program for above application using ladder diagram language. Here for ladder logic we can use any supported PLC system like S7-1200, S7-300, S7-1500 or any other PLC which can support this instruction. For PLC logic we need digital inputs and outputs.

For our application lamp is digital output. Set temp is the input word.

Digital Output:-

Temp Lamp=Q0.0

M Memory:-

Set temp.:-MW10

Actual temp:-MW20

PLC program Explanation:-

In network 1, actual temperature (MW10) will be compared with set temperature (MW20). So if the measured temperature (MW10) is less or equal than set temperature (MW20), low temperature indication lamp (Q0.0) will be ON.

In less or equal (<=) instruction, two operands are compared, we can set data type in comparator instruction.