Lab 1, PID control of water tank named LM900

Time and place

  • HVL Robotics Lab, Øyrane 12, 6800 Førde, 2. floor (under Reodorklubben).
  • Time: TBD.

Equipment

  • LM900, the red model with two water tanks, a manual valve between the tanks and some sensors.
  • Beckhoff CX and IO`s
  • Some device with a browser, connected to lab WiFi
  • If you need to debug, or you`re just interested, take a look thru the IO list and System Control Diagram on GitHub

Description

In this lab you will tune a PID to control the water level in a tank. Software is done, you will do the tuning.

Your PID will be given a score, less is better. Take a screen dump of your score and PID gains, send it to me, and receive a thumbs up for completing the lab.

The LM900 model can be a fun, practical challenge for three reasons

  1. The manual valve is an un-measured disturbance (but you can estimate it)
  2. The outflow of tank 1 is dependant of the square root of its water level (non-linear, can be compensated for)
  3. The pump should not run dry, and tank 1 should not overflow (interlocks are in place to prevent this)

The overall workflow for you to do is

  1. Turn on stuff
  2. Get to the user interface thru a browser
  3. Have fun
  4. Tune the PID manually (feel free to use the auto tuner, but do some additional tuning)
  5. Get a score
  6. Win

Steps

  1. Connect to the local lab WiFi with your device (PC, smartphone, tablet) and go to http://172.31.1.142/Tc3PlcHmiWeb/Port_851/Visu/webvisu.htm. If all is well, go to the next step, else:

    1. Check that the LM900 IO is connected to Beckhoff IO modules
    2. Check that IO`s are connected to Beckhoff CX.
    3. Check power supply to LM900, IO, CX, router. Turn these on.
    4. Wait for green lights. Else, call for help.
    5. Connect compressor, start compressor, wait for compressor to fill up, turn off compressor.
    6. Open and let the bubbles out of the purge meter using the black knob on the glass thingy on the LM900, then close again.

  2. The LIC01 (level indicator and control) CA is a NORSOK I-005 (IEC PAS 63131) template for control of analogue signals (PID). Select manual, internal mode, play around with the manual output Y.

    1. Open the manual valve completely
    2. Set your manual output Y to something that gives a steady water level YX (maybe 50%).
    3. What is the resulting level? What is the ratio between manual output and resulting water level?

  3. Set your internal mode gains from the options pane on the LIC01. This PID is in standard form, so I and D are in units of seconds. Maybe try Kp,Ti,Td as 1,10,0.

  4. Try your PID

    1. Set a desired level YR as 50%

    2. Switch to auto (still internal)

    3. Observe your PID.

      1. Move the YR around
      2. Move the manual valve around

    4. Adjust tuning until you get a smooth running pump, the level reaches it`s reference smoothly and the manual valve disturbance is handled ok.

  5. Open the manual valve fully, run the test, get a score.

    1. Happy? Done. Else, keep tuning, ask questions, take the opportunity to understand control theory.

Reg tek rulez!