Calculation PSU and DENSITY(kg/l) do not match for (virtual)conductivity probe

Hello GHL,

I noticed something strange on my Profilux3 EX

I have 1 conductivity probe, and I have set it to show PSU.
I have set a second virtual conductivity probe and this one I have set to show density (kg/l)

But the 2 measurement values do not match.:confused:

The display shows 34,9 PSU and 1.0248 kg/l at a temperature of 26,1 Celsius. (see screenshot)
I would expect 34,9 PSU and something around 1.0231 kg/l at 26,1 Celsius.

I know that there can be a little bit of a difference, due to the calculation method you use but this is to much of a difference. This has nothing to do with the chosen calculation method. It almost seems that you somehow mixed up density and specific gravity.

Please give me some advice on this, which of the two values is correct?.... PSU or Density(kg/l), or is the density not density but specific gravity. But specif gravity is a dimensionless quantity is has no kg/l

Please advice...................

With kind regards,
Martin

This is what my P3 shows
Attachment 10948

This is what I would expect
Attachment 10947

Hello Martin,

Density and SG are two different units of measure.

Most reef hobbyists use the unit SG for measuring their saltwater, however the values shown by the ProfiLux in kg/L (Density) are not equal to SG. The second most widely used unit of measurement is PPT which is referred to by the ProfiLux as the unit PSU.
(PSU = PPT)
(Density ≠ Specific Gravity)

The difference shown by the ProfiLux could be due to the probe needing to be re-calibrated.

Hi Vinny,

Yes I understand al of this, It state the Density and SG switch just a "possible" reason for the problem I found.
But it think you don't understand exactly what I mean.

The display shows 34,9 PSU(the actual probe) and 1.0248 kg/l(the virtual probe) at a temperature of 26,1 Celsius. (see screenshot in first post)
I would expect 34,9 PSU and something around 1.0231 kg/l at 26,1 Celsius.

The two measurement values don't match...... 34,9 PSU at 26,1 Celsius can never be the 1.0248 kg/l, this should be much lower somewhere around 1.0231kg/l. This is pure physics, you can not change this. So 1 of the 2 values is right, If any.

Recalibration does not matter at all in this case, It is not the measurement value and the real value of the water itself which is questioned by me. It is that the PSU value and the Density value at a certain temperature for the real probe and the virtual probe do not match. But they should because the have the same input, the real probe. You can calculate PSU and Density at "any" temperature, they are not just random. The Profilux does not seem to calculate these values correctly. So my question stays, which of the 2 values is correct, PSU of Density(kg/l), if any... at this point they do not match...

My native language is Dutch and yours is German, I think that there may be some loss of meaning in each others translation/interpretation, I hope that I am more clear now by adding this remark.

Regards,
Martin

Quote:

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Originally Posted by Vinny

Hello Martin,

Density and SG are two different units of measure.

Most reef hobbyists use the unit SG for measuring their saltwater, however the values shown by the ProfiLux in kg/L (Density) are not equal to SG. The second most widely used unit of measurement is PPT which is referred to by the ProfiLux as the unit PSU.
(PSU = PPT)
(Density ≠ Specific Gravity)

The difference shown by the ProfiLux could be due to the probe needing to be re-calibrated.

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