Calibrating conductivity probe [Archive]

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Mo.

26-12-08, 01:43

HI

I just calibrated my GHL conductivity probe with the 50mS solution.
I used the GHL temp probe as the temp compensation.

When checking in air, I get 0.01 mS
When checking in the 50mS solution, I get 48mS. I have calibrated 3 times and keep getting the same results.

My salinity measures 1.021 on the GHL and 1.026 on the refractometer. I checked the refractometer with RO and it seems fine.

I can't work this one out. I have had no top up running for 2days and have about 10L loss, so I can't believe that my salinity is 1.021.

I usually get 1.025 on the refractometer, so it fits with that.

What next, to get this sorted?. Is 48mS a significant difference from calibration values?.

My tank runs at 26.5/ 27.0 C

I calibrated with the solution in the supplied probe reservoir at room temp and at tank temp. This doesn't show much if any difference.

Thanks
Mo

stevew@reefdreams

28-12-08, 21:17

Mo.

30-12-08, 01:42

Hi Mo,

What firmware and software versions are you using?

There was a change made to the specific gravity / salinity calculation in one of the versions, I'll check which one and get back to you when I am back at work tomorrow.

Steve

HI Steve

Software version 4.0.4.0.
How do I tell which firmware I have?.
I only downloaded the software about 10 days ago.

Thanks
Mo

Mo.

30-12-08, 01:50

It seems there is an offset in the software, but this is greyed out.
It shows 1.0219 which is well off.

I don't know if the offset can be used to bring it in line?

Thanks
Mo

Mo.

30-12-08, 17:29

stevew@reefdreams

31-12-08, 10:57

Hi Mo,

The first thing to do is to soak the probe in vinegar for an hour as the platinum surface may have tarnished since manufacture, then clean thoroughly in fresh water with a soft brush.

The temperature of the solution should be as close to the probe temperature as possible for calibration. Floating the solution in the sump in a sealed bag will take about an hour to bring the temperature in line.

There is only one true value with the probe and that is the conductivity measured in ms. The salinity is a calculated value from the conductivity and can be influenced by the different salts used in the original conversion. For this reason an offset function was introduced and you can adjust the salinity reading to compensate.

In your case this box is greyed out, that is because you are running an earlier firmware where this function wasn't available.

If you check on the general page in the software it will show you the firmware running on the Profilux. I would suggest you upgrade the firmware to match the version of software you are using. Please remember to save your settings and sensor data before doing this.

You will then be able to adjust the salinity reading.

Steve

Mo.

01-01-09, 13:09

Hmm!

I tried updating the firmware.

"Error while transmitting firmware".

I tried this with my old PC and serial cable!.

I tried through WLAN.

I tried about 20 times!!!. Erros while transmitting firmware.

I'd better go and get the probe out of the vinegar now and give it a wash down.

What next?!. I can't get the firmware upgrade to 404. The software is compatible with that version.

Mo

Mo.

01-01-09, 15:33

Recalibrated..... no change

Reads 1.0214. Should be 1.025

I can't get the Firmware update to load......

:confused:

Mo

marinemanager

05-01-09, 16:41

Hi Steve

I wonder if we have the same problem? My GHL is a couple of months old and the conductivity was drifting downwards compared to my refractometer.

I thought it was time for a recalibration. I followed all the instructions and when the sensor was placed in the 50ms fluid I could see the reading rise and stabilise at 50ms on my external display. Calibration completed and I saved the results, but left the sensor in the fluid. The reading then dropped to 45ms. In the tank the current value is 50.2, compared to refractometer value of 1.026.

Could you explain the relevance of the unit asking for the temperature of the calibration fluid? Why do I need to equalise the temperature of the fluid with the tank? Why can't I just enter room temperature (say 20) when it prompts for the fluid temperature?

Regards
John

Mo.

05-01-09, 22:37

Steve

I managed to get mine working, by adding an offset. Thanks for the info on upgrading firmware. You were right in that I was clicking ok on the PC before accepting the download on the box!.

I updated the firmware and added an offset to ensure it was reading the same as my refractometer. So far so good....

I don't know why the probe was reading low after using the calibration fluid. it seems to be reading fine now...

Thanks
Mo