Beyond the single loop: ratio, override and split-range control
2026-08-23
Three control structures that go beyond one controller and one valve — ratio for blending, override for protection, split-range for two valves sharing one output.
Blog
Notes on the mistakes that keep recurring in loop tuning, and the checks that catch them.
P vs PI vs PID: what each controller form is for
2026-08-23
Proportional-only, PI and PID compared — what each form can and cannot do, and why the full PID is a minority taste on a real plant.
Three-element boiler feedwater control: what the third element is for
2026-08-23
Drum level, steam flow and feedwater flow. Why the third element exists, what shrink and swell do to the level signal, and when single-element control is the honest answer.
Distillation column control: the loops and what actually needs tuning
2026-08-23
A column is a stack of coupled loops. Why the level loops are easy, why pressure comes first, and why the composition loops defeat naive tuning.
Ziegler-Nichols tuning: the 1942 method everyone still names
2026-08-23
How the two Ziegler-Nichols methods work, why both aim at quarter-amplitude damping, and why a method from 1942 is a poor default for a loop you intend to keep running.
After Ziegler-Nichols: IMC, Cohen-Coon and the reaction curve
2026-08-23
The reaction-curve methods that followed — Cohen-Coon for setpoint response, IMC and lambda for a loop you choose the speed of — and when each is worth the extra effort.
Why a 30-second reset became 30 minutes
2026-08-18
Four ways to express integral time, two of them running in opposite directions, and the single conversion that catches the mistake before it reaches a live loop.