© 2018 Thorlabs
78
CLD101x
PID Tutorial
Temperature controllers are used to manage the temperature of thermoelectrically heated/cooled
components in experimental setups, independent of external influences. To adapt a controller to
different thermal loads, and to optimize the controller’s response characteristics, the controlling
parameters of the system’s feedback loop must be optimized. All Thorlabs temperature controllers
provide a PID control loop whose shares (P-, I- and D-share) must be matched to the thermal load
of the device under test. For an optimum adaptation, these parameters have to be adjusted
separately and independent of each other. This application note describes the PID parameters,
and how to set them to get optimum performance from your controller.
What is a ‘PID’ controller?
PID
is an acronym for
Proportional
,
Integral
and
Differential
. It describes a certain method, and the
parameters used to control it, for closed-loop circuits.
Principle setup of a temperature control loop
The figure above shows a standard laser diode setup with temperature control. The laser diode is
in thermal contact with a thermoelectric cooler (TEC, Peltiér element) and a temperature sensor.
The TEC is fed by a bipolar current controller which itself gets a signal from a comparator: The Set
Temperature (Tset) is compared to the measured temperature (Tact) at the laser diode. If the
difference between both signals is negative, i.e. the set temperature is higher than the measured
temperature, the current controller decreases the current to the TEC or even reverts the polarity to
change from cooling to heating, and vice versa.
Ideally this process should be continued until the difference between both signals is zero, the TEC
current stays constant, as well as the laser diode temperature.
The amplifier which processes the signal of the temperature sensor plays an important role for the
settling behavior of the complete system. There are different types of control circuits. One type is a
strictly linear amplifier. In this case we have a proportional or
P
-controller. Below is shown an
example of the settling behavior of a P-controller.
Settling behavior of a P-controller
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