Erroneous conductivity readings with ADuCM3029_demo_cn0428_cn0429

  • We are getting erroneous conductivity readings with ADuCM3029_demo_cn0428_cn0429.
  • This is with the latest hex file downloaded 4/1/2021.
  • We are using standard solution KCL-700, a 700 microsiemens solution.
  • We are using the recommended probes - Cole-Parmer 100-series Replacement Conductivity/Temperature Probe, K=1, 59200-06 probes
  • DIP switches are set to Z mode.
  • Mode is changed to conductivity.
  • We are getting a reading readings like 3e-07 S/cm (screenshot).
  • We should be getting readings like 7e-04 S/cm.

Reference: github.com/.../81

Thanks for your help.

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  • 0
    •  Analog Employees 
    on Apr 20, 2021 3:45 PM in reply to jpagliaccio

    Thanks for the results. The resistor values look correct to me within a percent or so. 1/1.5k ohms is 667 uS.

    So that tells me it's something about the sensor or the way it was connected to the board. A couple things to try:

    • Clean and rinse the sensor as recommended in the instructions sheet that came with the sensor
    • Make sure the contacts are fully submerged in the liquid (you might have to submerge it a little farther than you think because the contacts are sheathed by the plastic for protection)
    • Make sure the bnc is fully connected to the board
    • If that's not it, it may explain the readings if the standard solution is mislabeled and it's actually distilled water or something like that.

    By the way, Hi-Z mode shouldn't work with anything <200k ohms as mentioned in the user guide, so you wouldn't get a valid reading in Hi-Z mode. Essentially the gain of the TIA is too high so the amplifier saturates when there's a low conductivity present. Unfortunately, there's not a good way for the software to tell that the amplifier is saturated in that mode so we can't raise a flag.

    I hope it helps.

    Best regards,
    Scott

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