THORLABS CLD101 Series, Руководство по эксплуатации

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6 Appendix
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The higher the gain of the amplifier, the faster the system approaches a steady-state temperature.
With a simple P-controller, a small temperature error
D
t (this is the difference between the set
temperature and the steady-state temperature) will always be present.
To eliminate this control error the amplification must go to infinity. Doing this, however, will result in
the system oscillating around the set temperature, and the control system and temperature will
never stabilize. Consequently, the optimum setting of the amplification for a P-controller (the so
called P-share) is the maximum amplification that does not result in the system oscillating.
To further improve the settling behavior of the system two other kinds of amplifiers can be switched
in parallel to the P-controller: an amplifier with integrating capability (I-controller) and an amplifier
with differentiating properties (D-controller).
The I-controller enables the feedback loop to have greater amplification at low frequencies and less
amplification at higher frequencies. Because of this, the control error resulting from the P-controller
is eliminated.
When the I-share is high, the system response tends to overshoot (see figure below).
Temperature settling with different I-share settings of a PI control loop
Setting the P- and I-shares optimally means ensuring that the actual temperature does not oscillate
or overshoot. This setting for the P- and I-shares also results in the fastest system approach to the
set temperature. With the P- and I-shares chosen this way, however, the system cannot react
quickly to sudden changes in ambient temperature.
To allow the system to react more quickly to sudden changes in temperature an amplifier with
differentiating characteristic (D-controller) is added to the PI controller to establish a so-called ‘PID’
control loop. With the D controller the amplification is raised at higher frequencies associated with