THORLABS CLD101 Series, Руководство по эксплуатации

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2 Operation
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2.5.7 TEC Driver Setup
Use the arrow buttons to select a
parameter, then push EDIT button, or
push the selected topic a second time.
·
TEC Current Limit
:
The TEC
current limit must not exceed the
specified max. rating of the laser
diode. If the temperature set point is
close to environmental temperature, a
reduced TEC current limit may be
helpful to decrease the temperature
settling time (reduce number of
overshoots during settling time). The max. TEC current limit of the CLD101x is 3.0 A.
·
Output Voltage Protection : If the TEC current is interrupted (TEC open), the output voltage
exceeds the TEC compliance voltage and the TEC output is switched off (default setting). The
same may happen if a TEC with a high resistance is driven by a high current - in such cases the
TEC output voltage protection can be switched off: Choose EDIT to select between "Switch off"
and "None".
·
Switch TEC on when starting device : By default, the TEC is switched off. If required, the TEC
can be switched on at power up. Check the appropriate box if required.
·
Temperature Set Point : Edit this value to set the target temperature to the desired value. In
certain cases (e.g. DFB laser diodes) it is recommended to set this value to the reference
temperature as stated in the individual test report of the laser.
·
Lower / Upper Set Point Limits : To avoid unwanted operating temperatures of the laser, the
set point interval can be limited. The absolute limits depend on the thermistor parameters and
are given by the measurement limits of the CLD101x .
2.5.8 PID Control Loop
The temperature controller in the CLD101x is using a digital proportional-integral-
derivative controller (PID controller) to correct the difference between a measured
temperature and a desired temperature set point. The temperature can be adjusted
accordingly by calculating and then outputting a corrective current.
The PID controller calculation (algorithm) involves three separate parameters; the Proportional, the
Integral and Derivative values. The Proportional value determines the reaction to the current
temperature error, the Integral value determines the reaction based on the sum of recent
temperature errors, and the Derivative value determines the reaction based on the rate at which the
temperature error has been changing. The weighted sum of these three terms is used to adjust the
temperature via the current supply of a cooling/heating element (Thermo-Electric Cooler (TEC),
aka Peltier Element).
By tuning the three constants in the PID controller algorithm, the control loop properties can be
optimized in order to get a maximal stable temperature as close as possible to the target
temperature and with a minimum settling time.
Every constant (P, I, D) can be set to zero to disable it. For example, by setting the Derivative value
to zero, the PID controller will operate as PI controller. This may be useful in an noisy environment
since derivative action is very sensitive to measurement noise.
On the other hand, the absence of an integral value may prevent the system from reaching its target
temperature and is not recommended. A short PID Tutorial can be found in
appendix .
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