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DL05 PID for Simple Hydraulic System

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  • DL05 PID for Simple Hydraulic System

    I am looking to improve the control on a simple hydraulic test unit that utilizes a DL05 with analog input and output (12 bit).

    The typical test ramps from 0 to a couple hundred PSI (+/-), then drops back slightly (+/- 50 PSI), then ramps up to 2000-3000 PSI. Currently the application uses a PID (PI) loop and works fairly well except that it overshoots at the 1st pressure, which is critical in the application as opposed to the higher pressures.

    I am looking for potential methods of eliminating/reducing the initial overshoot (Feed forward, Cascade, etc.). Can 2 non-cascaded loops be used (one for low and the other for high pressure)?

  • #2
    I'd consider having two sets of variables for the Gain, Integral and Derivative. Load the first set until it hits the first setpoint, switch to manual and load the second set, then set it back to auto after one scan to get the PID to notice the change to take it to the finale.
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    • #3
      You could also use a RAMP/SOAK profile that "nudges" the SP up slowly to a desired "target" SP, so that your error term stays relatively small. When I say "slowly", I mean just a little slower than as fast as the system can handle.

      Obviously, there would be no SOAK step, just this one RAMP step.
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