When transport delay exceeds the process time constant, plain PID will disappoint.
The controller acts on stale information and over-corrects. Reach for feedforward, a Smith predictor, or fixing the delay itself.
Not if you compensate for it. A Smith predictor models the delay explicitly and restores useful control well past the point plain PID gives up — the rule is about the limits of PID, not about the limits of control.
Estimate with the rule, then check it against the calculator that models it properly.
Open PID Control →When transport delay exceeds the process time constant, plain PID will disappoint. The controller acts on stale information and over-corrects.