Hello, 

I have a puzzling question or concern. I am still a bit new to Automation, but learning. 

Often operators at my plant will show me a control loop (flow, pressure, etc) and state the the valve is swinging (oscillating) all over the place. Then there is a request for me to tune the loop. 

One of my biggest concern is that, "what if there is some other instrument, I/O communication, valve, positioner, etc malfunction that causing the overshoot or instability in the loop". I don't want to just start tuning a loop without proper investigation of the entire loop to make sure maybe valve is not funcitoning correctly. 

Is there anything I can read related to proper diagnoistics of a valve assembly as it relates to tuning a loop?

Is there a program in DeltaV I can use to monitor the loop performance to see how the loop performs for all process conditions?

Like now, I have a loop with PV Scale of 0 - 3000 pph, loop is in manual, the PID out is 10% (and valve is showing 10% open), and the PV is 1600 pph. It doesn't make sense to me how the valve can be only 10% open while operating at 1600pph which is the mid range of the scale. maybe I am confusing my self. 

Thanks for the help.