How to tune a DeltaV PID

Before any constant moves

Put the loop in MANUAL. If the hunt continues, stop: it is not the PID. If you cannot transfer without the output jumping, fix tracking on the block before you touch GAIN. Write down the current GAIN, RESET and RATE. You will want them.

What to type, and which way

GAIN is dimensionless. Raise it for more proportional action, lower it for less. RESET is minutes per repeat on most blocks, sometimes seconds — read the faceplate. Lower RESET to speed integral action; raise it to slow. RATE is in the same time unit as RESET. Put derivative on PV (the structure parameter) so a setpoint change does not kick the output.

Change one parameter. Wait until the loop has finished responding. On a flow loop that is seconds; on temperature it is not. A second change before the first has settled is how DeltaV loops get a reputation for being mysterious.

Do not cycle it

Do not raise GAIN until the PV oscillates to find an ultimate gain. DeltaV will let you. The plant will not thank you. If you want a starting point from a bump in MANUAL, measure process gain, dead time and the time constant, then use the calculator — and treat the result as a number to try, not a number to trust.

Questions that come up

The RESET field looks like a large number. Is that minutes or seconds?

Read the units on the block. A RESET of 30 that is seconds is a different loop from a RESET of 30 that is minutes, by a factor of sixty. Confirm before you copy a number from another controller.

Should RATE be on a flow loop?

No. Set it to zero. Derivative on a noisy flow measurement chatters the valve. Temperature is the common case for RATE, on PV.

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