Copyright © 2017 Thorlabs
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TED4015
3.7 PID Auto Tune
A very simple method to adapt the PID parameters to the characteristics of your thermal setup
is the use of the implemented PID Auto-Tune function. It is easy to use and gives good results
after relatively short time (depending on the time response of your thermal setup).
The implemented PID Auto-Tune algorithm is using the Ziegler-Nichols method. That means
the I and D shares are set to zero and the algorithm is looking for the “critical gain” KC at which
the output of the control loop starts to oscillate. The algorithm is optimized for finding good PID
parameters as quick as possible.
The new parameters are displayed and you can set them active or discard them.
This gives a good transient oscillation to a new temperature set point, but it is more optimized
to avoid influences of disturbances from outside, such as changes in ambient air temperature,
changes in heat sink temperature, laser diode power (lost heat) and so on.
Strictly speaking, a set of PID parameters is valid only for the temperature set point active dur-
ing PID Auto-Tuning. However, a new temperature set point not too far away will also lead to an
adequate transient response. Therefore you will be able to control the temperature of your sys-
tem effectively in a certain temperature range of many degrees (depending on your thermal
setup).
If the system behavior for another temperature set point is not good enough, you can start the
PID Auto-Tune function at the new temperature set point again. In this case, a quick 5 step
Auto-Tune procedure is started under the following conditions:
- You already finished a PID Auto-Tuning successfully before
- You didn’t change the PID parameters by hand in the meantime
- You didn’t unplug the cable between the TED4015 and your thermal setup (e.g. changing
the mount).
To save time, the new quick PID Auto-Tune process tries only to readjust the PID parameters
calculated before. It starts without changing the KP value and the oscillation period value.
Normally you will get better PID parameters for the new temperature set point after a shorter
time. If the KP tuning has to be greater than the allowed range the re-adjusting fails and the
complete PID Auto-tuning over the whole KP range is started automatically, giving you a better
tuned PID-Controller at the end.
Sometimes the PID Auto-Tune function may not finish successfully. In that case, the KC of your
system may be outside the possible tuning range (smaller than 0.1 or greater than 100). Please
try it out by manually tuning the PID-Controller.
If the PID Auto-Tune function finishes very fast but gives bad results, your system might be too
noisy, and the noise (maybe 50 or 60 Hz) could be interpreted as oscillations of your system.
Eliminate the noise and try the PID Auto-Tune function again.
If you don’t like the system performance given by the PID Auto-Tune function, you can tune the
parameters manually (see section
).
