View Full Version : conductivity Meter

10/13/2011, 07:01 AM
Question on the conductivity meter? I have the lab grade meter, and I'm disturbed by the range in readings. I calibrated it and calibrated my refrac with 1.026 053ms calibration solution.

The refrac and conductivity meter matched exactly. However. As the temp changes into the night / lights off, the salinity also changes. Then back into mid - day at the warmest temp it has the right reading. It ranges from 33 to 35.5.

My salinity is right at 35 or 1.026 based on the calibrated refrac. I believe I have temp compensation turned on. I'm not sure what else to do or is that just how it's always going to be. As temp goes down the salinity goes down and as it rises the salinity rises?

10/13/2011, 08:28 AM
With respect to temperature calibration, do you have a temperature probe plugged into the PM2 module?

10/13/2011, 08:53 AM
I have the temp probe plugged into the main unit, not in the break out box. for conductivity to work right does the temp probe need to be in the conducitivity break out box?

10/13/2011, 09:01 AM
Yes, it must be plugged into the PM2 for the compensation feature to function properly; the PM2 module doesn't reference the temperature probe in the in the main module.

One common solution is to just move the probe from the base unit to the PM2; this is what I've done in my setup. Alternately, the temperature probes are inexpensive, so running two of them is also an option.

10/13/2011, 09:31 AM
I'll move it over. So, the reading should remain relatively steady other than evaporation. Is that a proper assumption if the temp probe is working right in the right spot?

10/13/2011, 09:47 AM
On my setup, I see typically +/- 0.10, with infrequent +/- 0.25 variance throughout the day, typically correlated with the ATO , so yes, you should see a relatively steady reading. You might benefit from a recalibration with the temperature probe in place and with the calibration fluid at tank temperature if you still see problems after the move.

Note that probe names can be renamed (assuming current firmware on the Apex); thus, if you move the probe, you can rename it to something like Temp instead of the Tmpx4 or similar that's the default name for the PM2 temperature port.

10/14/2011, 12:02 PM
You would need a pretty big temperature swing to account for a 2.5ppt change in salinity. It's likely something else. Here's calculator.


10/15/2011, 01:41 AM
You would need a pretty big temperature swing to account for a 2.5ppt change in salinity.


I use temp calibration, have it set to .8 and I get ~.4 swing throughout the day.