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
Distillation column control is a stack of coupled loops: reflux-drum level, sump, pressure, then composition. Why levels are easy, why pressure comes first, and why composition defeats naive tuning.
Ziegler-Nichols tuning: the 1942 method everyone still names
2026-08-23
The Ziegler-Nichols table from Ku and Pu, why both 1942 methods aim at quarter-amplitude damping, and why that is a poor default on a loop you intend to keep running.
Cohen-Coon, IMC and lambda: reaction-curve methods after Ziegler-Nichols
2026-08-23
Cohen-Coon for setpoint response, IMC and lambda for a loop you choose the speed of: the reaction-curve methods that followed Ziegler-Nichols, and when each is worth the extra effort.
Reset units: why a 30-second reset became 30 minutes
2026-08-18
Four reset-unit conventions — minutes per repeat, seconds per repeat, repeats per minute, repeats per second — two of them running in opposite directions. The conversion that catches the mistake.