Without control (MAN), the PV swings across this band. In AUTO, watch how much the controller reduces it.
Disturbances the controllers must fight.
Each resets the plant, sets the tuning and plays timed events with explanations.
Set each loop's units, range and PV fluctuation in its faceplate (Units, range & PV fluctuation), add timed events here, then run. Save a scenario to use it again; everything is stored on this device.
A saved scenario keeps the units, ranges, setpoints, PV fluctuations, tuning and events of all four loops.
Each loop compares the process variable (PV), what the transmitter measures, with the setpoint (SP), where you want it. From the difference (the error) the controller calculates the manipulated variable (MV): the valve opening.
MV = Kc · [ e + (1/Ti)·∫e dt + Td · de/dt ]
| Term | What it does | Too much | Too little |
|---|---|---|---|
| P: gain Kc | Moves the valve in proportion to the error, right now. | Overshoot, oscillation, a jittery valve on noisy loops. | Slow, sluggish response. |
| I: integral time Ti | Keeps moving the valve while any error remains, so it removes the offset. Smaller Ti = stronger integral. | (Ti too small) slow rolling oscillation and overshoot. | (Ti too large or 0) slow recovery or a permanent offset. |
| D: derivative time Td | Reacts to how fast PV is changing and brakes early. Useful on slow loops with lag, like temperature. | Amplifies sensor noise. | More overshoot on slow, lagging loops. |
Loop types: flow is fast and noisy (low gain, short Ti, no D). Level here is integrating, because the outflow is held by the flow controller, so it needs integral but no D. Pressure is moderately fast. Temperature is slow with lag and dead time, which is where derivative helps.
Action: level, temperature and flow are reverse acting (PV below SP → open the valve). Pressure is direct acting (PV above SP → open the vent).
This is a teaching model: the behaviour carries over to real plants, the exact tuning numbers don't.
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