Explain less than (<) instruction using example

Explain less than (<) instruction using the example

Application:-Explain less than 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 an explanation of less than 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 than set temp, temperature indication will be ON.

If the set temperature is 200 degree and temperature read by temperature controller is 199 degrees, the lamp should be ON because 199degree is less than the set temperature.

PLC program:-

Write the ladder program for the 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 a digital output. Set temp is the input word.

Digital Output:-

Temp Lamp=Q0.0

M Memory:-

Set temp.:-MW10

Actual temp:-MW20

Table for an explanation, so the lamp will be ON if the actual temperature is less than the temperature.

Actual temp	Set temp	Result
199	200	1
200	200	0
202	200	0

PLC program Explanation:-

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

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