Flintloop – tune a PID loop without guessing

Flintloop is a small desktop program that reads a step response off a real controller, fits a first-order-plus-dead-time model to it, and hands you gains that hit a stability margin you choose. It is not a dashboard and not a cloud service – one window, one loop at a time, everything on your machine.

• Reads the loop where it lives. Modbus TCP, Modbus RTU over RS-485, OPC UA, a plain ASCII serial mode, or a CSV/historian export when you cannot touch the controller.
• Shows its work. The fitted model, the gain and phase margin, and the predicted response are on screen before you write a single number back.
• Writes gains in the controller's own units. Seconds-per-repeat, repeats-per-minute, or a parallel form – picked per controller, not forced into one convention.

What's new in 3.2.1

A maintenance build hardening the Modbus float decoder and the noise-band measurement. See the full version history.

Three steps, roughly

1. Connect to the loop or load a capture, bump the setpoint, and let Flintloop watch the response.
2. Check the fit. If the model does not sit on the data, the loop is nonlinear or noisy and no gains will save it – Flintloop says so rather than fitting anyway.
3. Pick a rule (lambda/IMC or a damped-response rule), read the gains, write them back or copy them by hand.

Longer version on the workflow page; the maths is on the theory pages if you want to check it.