Confusing measurements from refractometer and hanna sanity tester (conductivity)

[gbroadbridge]

I still do not understand whether it uses its ATC during calibration or not,.

If you calibrate using the 35 ppt standard packet at, say, 20 deg C, and read that same packet at 25 deg C, does it read 35 ppt, or something else?

I thought I illustrated that in post #8 (although in reverse).

In the past I have calibrated with the solution at room temperature, and the device measures incorrectly at tank temperature.

I'll do it again shortly both with a new Hanna sachet and with your DIY 3.29%WT NaCl solution made with reagent grade NaCl for comparison.

 

[Randy Holmes-Farley Verified Community Expert]

I thought I illustrated that in post #8 (although in reverse).

In the past I have calibrated with the solution at room temperature, and the device measures incorrectly at tank temperature.

I'll do it again shortly both with a new Hanna sachet and with your DIY 3.29%WT NaCl solution made with reagent grade NaCl for comparison.

My proposed experiment would prove whether calibration at 25 deg C is needed, and I assumed they would use the known change in seawater conductivity as a function of temp to correct. It appears that your device did not do that correction correctly.

If I understand the pictures in post 8 correctly to be the same calibrated device reading at two different temps, in the same fluid, and getting two different answers, then the temperature compensation used is clearly incorrect. It is overcompensating for the lower conductivity as temp drops.

That leads me to conclude that one needs to calibrate at the sample temp and not allow any correction. As you indicated you do.