PID hunting

What it means

Hunting is the field's word for a loop that will not sit still. It is used interchangeably with oscillating, cycling and swinging, and it dominates how the symptom is described in practice — an operator reports that a valve is hunting far more often than that a loop is exhibiting sustained oscillation. The same complaint is typed as pid hunting.

The word covers two mechanically different situations. A loop hunting because of tuning produces an oscillation that decays after a disturbance. A loop hunting because of stiction, backlash or another nonlinearity produces a limit cycle whose amplitude stays constant. The distinction determines whether anything you do at the faceplate will help.

Also called

On a plant you will hear this called cycling, oscillating, swinging. They mean the same thing.

Questions that come up

What is PID hunting?

PID hunting is a loop that will not settle around setpoint. If the cycle decays after a disturbance, the constants are generating it. If the amplitude holds, the valve is sticking and the faceplate will not fix it.

Is PID hunting the same as oscillation?

On a plant they are used interchangeably. Hunting is the word operators reach for; oscillation is the word on a trend. The useful split is whether the cycle decays — that, not the name, decides whether tuning can help.

Related

Where this comes up

• Why control valve hunting happens
• PID oscillation
• Flow loop unstable
• Cascade loop hunting
• Interacting control loops
• DeltaV PID parameters explained
• Honeywell Experion PID parameters explained
• How to tune a PID loop on a running plant
• As-found / as-left PID constants
• Tuning flow control loops
• Dead time
• Process gain
• Deadband
• Limit cycle
• Gain scheduling
• Quarter amplitude damping
• Bad actor loop