36 lines
1.5 KiB
ReStructuredText
36 lines
1.5 KiB
ReStructuredText
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.. _pid_controller:
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PID Controller
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==============
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The PID controller is the main element of the oven. It controls the output of the solid state relais in order to achieve the desired temperature.
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The PID controller is implemented in the ``pid-controller.c`` file. See the :ref:`pid_code_api` for details.
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Functional Description
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----------------------
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The following figure shows the PID controller's structure.
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.. drawio-image:: pid.drawio
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The controller is composed of 3 paths. The proportional, the derivate, and the integrator path.
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Compared to a textbook PID controller, this version contains a few additional features.
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The integrator has a configurable maximum limit of :c:var:`pid_controller.integral_max`. Once this value is reached (plus or minus), the integrator freezes.
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The integrator is also frozen in case the output value is in saturation. This serves as an anti-windup protection.
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The output value saturates at configurable high and low limits (:c:var:`pid_controller.output_sat_max` and :c:var:`pid_controller.output_sat_min`). The controller instance used for the
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reflow oven's solid state relais output is saturated by software to a limit of 0 to 100.
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In addition to the above features, the derivate term contains an additional first order low pass filter in order to prevent coupling of high frequency noise amplified by the derivate term.
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The low pass filter is charcterized by its time constant :math:`k_{d\tau}`.
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.. _pid_code_api:
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PID Controller Code API
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-----------------------
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.. doxygengroup:: pid-controller
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:project: Reflow Controller Firmware
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