2 Position controller
With this function block you can control an analogue signal with a variable hysteresis value.
The analogue signal is connected to the input AI. The setpoint of the block can be defined by setting the parameter T. The hysteresis value is specified by the parameter H.
Hysteresis is used to prevent frequent switching of an output - for example a pump or a boiler. Neither are designed to handle this kind of switching unlike diverting or mixing valves.
The output Q is active if the actual value is less than the setpoint - hysteresis value. Then only when the analogue value is higher than the setpoint + hysteresis value is the output Q switched off.
If the input Dis is enabled then all the inputs are disabled and the output Q is switched off.
In this example, the pump would be turned on when the level is less than 9 (TH). The pump will then remain on until the analogue value has reached the value 11 (H + T) and then turns off.
Boiler control, level control, heating systems etc.