Hello everyone! I have an application were we are controlling pH in a pipeline, the hard part is there are times when there is no flow in the pipe. I do not want the the metering pump to run and add chemical when there is no flow so we will shut it off automatically. I want the PID controller to hold its outputs and not change anything while there is no flow. I am worried when there is no flow the pH could drift causing the controller to increase error over time due to the I and D values, this would change the speed of the metering pump(it would be shut off) and when the flow comes back it may take a while for the controller to re-adjust itself. Thanks in advance to anyone who can help!!