Test whether one value is greater or equal to a second value.
Let's say we have a HPU system that we are monitoring its oil temperature. When the temperature of the oil is greater than 120 degree Celsius, we want to send a warning and start the fan to cool down the oil. Now if the temperature is greater or equal to 125 then we want to stop the HPU cause it is getting very hot. We also want generate a fault to the operator to let him know why the HPU have stopped.
Ladder Logic Solution
- Temperature I:1.0
- Fan O:2.0/0
- HPU auxiliary I:3.0/0
- HPU Alarm B3:0/0
- HPU Fault B3:0/1
If the HPU is running and the temperature is above 124 degree then we start the fan to cool it down.
While the HPU is running, if the temperature is greater or equal to 125 degree then we energize a fault and we should eventually stop the HPU.
- HPU fault should de-energize the HPU start signal.
- HPU fault could be shown with a flashing light to inform the operator as to why the HPU have stopped.