Controll loops for non temperature sensors

  • Hello Duet team and Co users,

    I am currently building a fuildhandiling robot with a duet Wifi and a DUEX5.

    There are serveral cases here where it would be nice to controll air flow and air pressure with the duet.

    It should be possible to use the M308 with Y parameter Y"linear-analog" to define any kind of sensor that has a 0 to 5v output.

    But is it also possible to couple an PWM output controll loop to this?

    For example using a simple on/off controll to keep a pressure in a certain range.
    Or using PWM on an air pump to maintain a certain flow measured form a gas flow sensor.

    Is this possible? And how do i set it up?

    Thanks in advance for your responses!

  • administrators

    Currently the way to do this would be to use "temperature" as a analogue for either "pressure" or "flow rate" (depending on what you were sensing/controlling) then you would set the pump control as a heater. You would then need to work out what linear analog sensor "temperature" related to what pressure/flow and then set that temperature. No doubt you would need to adjust the PID parameters so that the POID loop worked properly.

    @DC42 mentioned that an additional complication is that "temperatures <40C are counted as "off" by RRF so you would need to scale your sensor to be working at a higher temperature.

    I am going to move this into the firmware wishlist category as something to consider for the future.

  • Hello Tony, Thanks for your reponse. Any idea how the firmware would react to very high values like displaying pressure in pascal (1bar is 100000 pascal) or Kpascal. If i use absolute pressures the values that i need should be in the range of 50 to 150 kpascal. I assume that this should be fine for the firmware?

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