Test whether one value is less than or equal to a second value.
Example
Let say we have a HPU system that we want to monitor the temperature of the oil. When we start the HPU system, we want to check If the temperature of the oil is less than or equal to 50C(Celsius) then we will run Heater 1 on. If the temperature is less than 70C then we want to run Heater 2. We should also disallow the HPU to run if the temperature is less or equal to 50C.
Ladder Logic Solution
- Temperature element I:1.0/0
- Heater 01 O:2.0/0
- Heater 02 O:2.0/1
- HPU no permission B3:0/0
- HPU start O:2.0/2
The start button is pushed then we check to see if the temp <= 50c is true. If it is true then we energize Hearter1 and we disallow to run the HPU.
While the start is still on we check if the temperature is below 70c if it is then we run the second heater to accelerate the heating process.
As long the as the temperature is below 50 then we will not allow the HPU to start.
Note
- For simplicity reasons, we are assuming that the push buttons are maintained signals.
- Notice that the temperature value is passed via an analog input (16 bit word).
