DeltaV PID parameters explained

Which direction makes the action stronger

On your system a HIGHER proportional number means MORE aggressive proportional action.

Reset is in minutes/repeat, so a LOWER number means FASTER integral action.

This is the single most consequential thing to get right. Proportional band and gain move in opposite directions, and so do repeats-per-time and time-per-repeat. An engineer who has moved from one system to another and carried the old habit across will make loops worse while believing they are improving them.

• Proportional term: gain
• Reset units: minutes/repeat
• Rate units: minutes
• Algorithm form: series interacting

The parameters you will see

On a DeltaV PID function block the tuning parameters appear as GAIN, RESET and RATE. GAIN is dimensionless. RESET is in seconds or minutes per repeat depending on how the block has been configured, so check rather than assume. RATE is in the same time unit as RESET.

The block also carries a structure parameter controlling whether proportional and derivative act on error or on the process variable. Derivative on PV is the usual choice and avoids a kick on setpoint changes.

Why the algorithm form matters

The algorithm form matters because the same three numbers behave differently in each. In the series (interacting) form the derivative term multiplies the proportional-plus-integral term, so changing rate also changes the effective gain and reset. In the ideal (non-interacting) form the three terms are independent of each other but all scaled by gain. In the parallel (independent) form even that scaling is absent — gain does not affect integral or derivative action at all. Moving a tuning set between systems without converting for form is one of the commonest ways a loop that worked on one plant fails on another.

Before you change anything

Confirm the units on the actual controller rather than trusting the platform default. Systems get configured in unusual ways, engineering units get changed during a migration, and a controller imported from another site may carry conventions from there.

The fastest check is to make a small deliberate change and watch which way the loop responds. If it gets more aggressive when you expected less, the convention is not what you assumed.

Questions that come up

Is DeltaV reset in minutes or seconds per repeat?

It depends on the block configuration — both are used in the field. Read the units off the faceplate or the block detail rather than assuming. A factor of sixty in the wrong direction is the difference between a stable loop and one that hunts continuously.

Does a higher DeltaV reset number mean faster integral action?

No. With reset expressed as a time per repeat, a higher number means the integral action repeats less often, which is slower. Lower is faster.

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