Output PWM Control
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Firmware v2.0 and later implement full pulse width modulation (PWM) control of the outputs. The behavior can be controlled with these three parameters for each output:
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[edit] Output Period
This is the period of the PWM. The output will be updated as a percentage of this period. For example, if an output controlled to 20% and the Output Period is 10 seconds, it will be on for 2 seconds and off for 8 seconds. The minimum granularity of the pulse is 0.1 seconds.
[edit] Min Pulse Percent
The minimum pulse percent is the smallest pulse that the system will produce. This is normally defaulted to 0% (which is technically 0.1sec, the minimum granularity of the system). For example, if the Min is set to 20%, and the output of the PID or Duty Cycle is 4%, the output will not turn on. It will only turn on when controlled above this point. This setting is used to limit the amount of switching, it is NOT a floor.
[edit] Max Pulse Percent
This is a cap on the maximum pulse. Normally defaulted to 100%. If an output is controlled by PID or Duty Cycle, this limits the amount of time that the output can be asserted within its period. Can be used to effectively reduce the wattage of heating elements, as well as other applications. For example, setting the Max Pulse Percent to 90% will limit the maximum On time of an output to 90%, even if the PID is commanding 100% On.
[edit] Examples
In the example below, we have two outputs, both with unique settings. Both outputs are set to 90% (either from the PID, or Duty Cycle control).
Output1, which is red in the plot below, has an Output Period of 20sec. This yields a 90% output of 18sec On and 2sec Off.
Output2, grey in the plot, has its Output Period set to 40sec. This yields a 90% output of 36sec On and 4sec Off.
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