THORLABS ITC4000 Series Operation Manual page 44

ITC4000 Series
Note
The settling behavior may be additionally observed at the DEVIATION OUT jack (R14, section
Operating elements at the rear panel ) by means of an oscillo-scope (please refer to section
12
TEC control outputs ).
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Switch on the TEC output with the switch " TEC ON" (F6, see section Operating elements at
the front panel ). Watch the course of the actual measured temperature. If it oscillates con-
11
tinuously, or even builds up to increasing amplitude, switch the TEC output off immediately.
Further decrease the Proportional parameter before switching the TEC output on again.
Proportional (P) parameter:
Repeatedly increase and decrease the Temperature set point about 1...2C around your desired
target temperature with the adjustment knob (F8). Watch the settling behavior of the actual
measured temperature.
Increase the P parameter gradually by turning the adjustment knob clockwise. Higher values
will increase the settling speed. Too high values will increase the amplitude and number of
overshoots. This may lead to an unstable system (continuous oscillation or even increasing
amplitude), which should be avoided. The P parameter is set correctly when the oscillation is
recognizably damped, this means the actual temperature approaches the set point with each
overshoot having about half the amplitude of the previous overshoot. Due to the disabled Integ-
ral constant, a temperature deviation may remain. Please evaluate the time span between the
maximum temperature of the positive overshoot and the minimum temperature of the following
negative overshoot (i.e., half a period); doubling this value will be approximately equal to the full
period of a continuous, undamped oscillation. You will need this data to set the "oscillation
period" value as described below.
Oscillation period:
The oscillation period value corresponds to the resonance frequency of the temperature control
setup. The value entered here impacts the control cycle period of the digital PID control, which
is determined as one-hundredth of the oscillation period. Enter the time span recorded in the
previous section when you adjusted the P parameter and observed the settling behavior of the
temperature.
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