Erroneous conductivity readings with ADuCM3029_demo_cn0428_cn0429

Hello,

Thanks for the details about the configuration and measurement. Regarding the DIP switches, I'm confused by your statement that they're set to Z mode. For the software configuration shown in the screenshot, S1 should be set to 'Z' and S2 should be set to 'INT'. Can you confirm that's the case?

Thanks,
Scott

S1 and S2 match this from your documentation. S2 is INT.  

from the setup doc ... wiki.analog.com/.../cn0428

"The options available on S1 are 'pH' and 'Z'." We are on Z (switch S1). 

Thank you. That is clear. To isolate the problem further, do you have a BNC-to-miniclip cable where you could clip a resistor in the 1.5kΩ range to see what reading you get?

Results from Evaluation board 1 with a 1% 1.5K ohm resistor

Results from Evaluation board 2 with a 1% 1.62K ohm resistor

Here too - easier to see the screenshots https://github.com/analogdevicesinc/EVAL-ADICUP3029/issues/81

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