Calibrating Conductivity probe

[keener]

I'm having the exact same problem with my Salinity probe. After calibration and or cleaning it works great.. but then drifts during the course of the day and settles at something much much lower than it should be.. right now it is reading 1.0214 when it should be reading 1.026 and I just cleaned and calibrated it yesterday!? Is this normal?? Did you resolve your issue?

[Matthias]

is the measured value stable after settling?

if yes - then enter a reasonable "offset" and it should be fine

[keener]

is the measured value stable after settling?

if yes - then enter a reasonable "offset" and it should be fine

It is stable for a time but then fluctuates downward quite quickly and frequently.

For example, yesterday evening I did as you suggested and set an offset of 0.001 to get the correct reading of 1.0265 (where it was reading 1.0255 previously). It was fine and now I just received an email from my profilux that says the salinty is 1.0243. I'm pretty sure the salinity hasn't dropped that much from yesterday evening to this morning. Again, I have an auto top off and the fresh water is not in contact with the probe. Last night I also cleaned and calibrated the probe and placed it in a higher flow area (under the outlet of a very slow flowing powerhead to reduce the chances of junk getting on the contacts). So frustrating.. Is it possible the probe is defective? Or what am I doing wrong? Do I really need to clean this $300 probe once a day ??

edit: this evening I will try changing the offset to 0.002 to bump that value up again but I've done this before..

[Matthias]

I can't imagine that the probe is defective - was the calibration successful?

I think this is a problem with temp. compensation. Is the temp. probe nearby the cond. probe?
Is the compensation activated? Was everything regarding temp. set correctly during calibration.

Are you using the correct cond. probe (with Platinum)?
What are the both ADC calibration values?

[keener]

It seems to have stabilized more now that I've put it closer to my return pump. It seems to need quite a bit of flow near it.