Differential threshold switch
This function block checks an analogue input on whether it is inside a measuring range.
Connect the sensor to be monitored to the AI input on the block, then set the parameters for the threshold V and differential value D.
If the differential value D is greater than 0 then the output Q is on when AI is within the allowed range (V+D), and off as soon as AI is outside of the range. If D is 0 then Q will be on when AI is the same as the threshold (V), and off as soon as AI is different from V.
This function block can be used for level control, climate monitoring and flow control as well as other uses.
In this example a 1000 litre rain water tank is being used to supply water to an irrigation system and also to the house. The range is from 400 (parameter V) to 700 (V + D). In this range Q will be on so the irrigation pump is allowed to run, less water than that and the pump won't run, more water and the pump will also not run (in the config with more water the house supply is fed from the tank).