Ovation PID parameters explained

Which direction makes the action stronger

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

Reset is in repeats/minute, so a HIGHER 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: repeats/minute
• Rate units: seconds
• Algorithm form: ideal noninteracting

Converting to and from other systems

The conversion is a reciprocal, not a scaling. Reset in repeats per minute and reset in minutes per repeat multiply to one — so a loop repeating four times a minute has an integral time of a quarter of a minute.

Because it is a reciprocal, the error you make by getting it backwards is not a constant factor. It grows as the numbers move away from one, which is why the mistake is sometimes survivable and sometimes catastrophic.

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

What does repeats per minute actually mean?

It is how many times per minute the integral action repeats the correction the proportional term has already made. Four repeats per minute means that if the proportional term is contributing a certain amount of output, integral action adds that same amount again four times in a minute while the error persists.

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