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.
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.
