Tuning Practice 10 — Temperature

The job

What you are looking at

A heated enclosure is cooled by outside air through a motorised louver. The controller output is how far that louver is open. Internal heat generation is the load. The measurement reads in degrees Fahrenheit.

This process is not linear. With the louver nearly shut, almost no heat escapes and the enclosure responds very slowly. With the louver wide open the same enclosure responds many times faster. In other words, the loop you are tuning is not quite the same loop at every operating point.

The controller is on factory defaults and the acting direction has not been commissioned. All three tuning terms are unlocked.

This is practice, not a test. Nothing on this page is scored and nothing is submitted anywhere. Judge your tuning by the trend in front of you: how quickly the measurement reaches the setpoint, how far past it goes, whether it settles, and how the loop behaves when the load changes. Change something, watch it, change it again.

How to work through it

Steps

Press Start. The loop begins balanced at setpoint, so nothing will move until you disturb it — move the setpoint, or change the load, and watch which way the measurement goes.
Set the acting direction for this loop.
Tune it at the load it is running at now, and get it holding setpoint.
Now move the Heat load a long way — well down, then well up — so the louver ends up in a very different position, and test your tuning again at each one. Settle on the numbers you would be willing to leave in the controller knowing it has to run across that whole range.
Before you call it tuned, change the load and confirm the loop brings the measurement back and holds it. A loop that only looks good on a setpoint move is not proven.

All three tuning terms are available on this exercise, including the derivative (rate) term.

Adjustment range available for each tuning term on this exercise
Tuning term	Lowest	Highest
Proportional gain (Kp)	0	8
Integral gain (Ki, 1/s)	0	0.5
Derivative gain (Kd, s)	0	12

These ranges are set for this loop only. Another exercise will have different ones, because a different process needs different numbers.

Simulator

For your own record

Commissioning notes

Nothing here is graded or sent anywhere. Write down what you settled on and why, so you have it to compare against the next exercise.

Which way did this controller have to act, and how did you work that out? What did you leave the tuning set to? Record the numbers themselves, in whichever form the controller was showing them. What did the loop do when you changed the load, and were you satisfied with the recovery?

Your notes stay in this browser, on this computer, and they belong to this exercise alone — each exercise keeps its own set. Open this exercise again on this computer and they will be here waiting for you. They are not sent anywhere and they are not graded, and they will not follow you to another machine, so copy anything you want to keep elsewhere.