Hello my dear automation friends, I work as an instrument maintenance in the factory. Additional scope has been made, there are 15 valves, 5 of these valves are fail open, and these 5 of them want 20-4 ma instead of 4-20 ma. Reverse is requested, I wonder what the purpose is, not many people know. Respects.
Hello,
there is nothing to be done to the control valve.
In PLC or DCS systems, you have the option to select the 'Reverse Acting" mode in the PID controller. It will take care of it.
In our facility we typically reverse the valve in the field. The reasoning is usually as simple as someone not wanting to do the work to reverse the action of the positioner.
okay.