What is direct acting and reverse acting control in PID controller?

Proportional, Integral, Derivative controller in control systemWhat is direct acting and reverse acting control in PID controller?
the output of a controller normally gives an output to a valve. Normally your output would be 4- 20mA. If you input increases you could have the output increase or decrease depending onyour conditions (also depending if your valve needs 4 mA to be fully close or 20mA). Direct is normaly increase in input to controller will give you increase in output and vise versa. Proportional band is the proportion to how much yr valve will open with respect to deviation of setpoint. eg if prop band setting is 10% then u will have full valve travel with a 10% deviation of set point. Derivative is used to correct offset of process to setpoint (rate of change).

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