108 C4 Manual Rev 7.5.2
Proportional term Setup parameter F0
Integral term Setup parameter F10
Differential term Setup parameter F11
Note that you will also find the in setup section of this manual a reference to the
Integral Wind-up Limiter Term (Setup parameter F12). Do not alter this field. It
is set once at the factory for the C4 model controller and never requires
adjustment.
Adjusting for changing needs.
When you C4 was shipped from the factory, it was optimized, or “tuned”, for
normal operation of the chamber or platform to which it was attached, or for
which it was intended. It was presumed that the load that you would test would
not have great mass, that some overshoot of the setpoint was acceptable when
going to a new temperature, and that the cryogenic coolant available (if used)
would be delivered from a supply source that indeed delivered liquid, not just
compressed gas.
Your needs may not match the original settings, or your controller may have had
it’s settings changed for other reasons. If the controller is settling a little short of
the setpoint, or is oscillating, you can probably make a few changes in the PID
settings and improve things considerably.
You need to be aware that very precise control requires a stable environment. The
C4 is an excellent and accurate controller. However, it is not magic. For example,
if you tune your C4 to provide fast ramps with conservative approaches to
setpoints with liquid nitrogen cooling a static load, and then run the unit using a
nitrogen source that delivers gas instead of liquid a good part of the time, and
then you add a substantial live load as well, your system performance will not be
what you expected. Before you start the tuning process, we suggest that you do
what you can to be sure that you are tuning for the actual loads that you will be
testing using the coolant that will be available at test time.
If you are using cryogenic coolant, be certain that the coolant delivery is
consistent. It is not possible to provide a stable environment in your chamber or
on your platform if the supplied coolant’s ability to absorb heat keeps drastically
changing as the supply vacillates between liquid and gas. Likewise, if you will
have live loads that turn on and off during the test, optimize the performance of
the system with the load at the point that is most critical to you. If the live
loading is small, it should make little difference. However, if the live load is
substantial, the performance of the system will be adversely affected when it is
operating with a load substantially different than the load for which it was tuned.