Salinity convertion - confused on numbers.

[kilnakorr]

Help - have you read the links that explain the science behind salinity measurements at all? The correction factor is not always 0.0013 - its differ between different water mixes - in my case 0,0013 did the job. I had to calculated it from my real measurements and the tables. There is many different ways to calculate the density from the conductivity measurements - as I understand GHL use the most accepted reference salt water mix.- the Copenhagen Standard Sea Water.


I do the same but use a refractometer that I have as correction tool. But the normal calibration is important because it gives you the slope coefficient for the curve (or line) from 0 to 50 mS. However - iME - the probes is rather good after the first calibration and if you now and when gently use a tooth brush on the plates in the gap in the electrode - it will work for very long time. My last worked for 5 years before I dropped it into the floor

Here is my salinity in PSU for the last week (sample period 5 min) The rise around 16:00 today is caused of an adaption to my refractometers readings. After this I had to take out a little amount of aquarium water and replace with RO water (og other reasons than salinity). The probe readings answered directly

Sincerely Lasse

The point is, that it seems there is already a widely used formula to convert mS/cm to kg/L.
This is showed by every online convertion tool and @Randy Holmes-Farley table.
So why would GHL not simple use this, but make there own, that so far, has proven to be inaccurate?
We only have three value sets so far, but they do show an obvious picture:

Your offset is -0.0013

My readings.
GHL: 50.1 mS / 1.0230kg/l
Calculated:1.0217kg/l
Difference/offset: -0.0013

@arking_mark
GHL: 52.7mS / 1.0245kg/l
Calculated:1.0231kg/l
Difference/offset: -0.0014

 

[Lasse]

Conclusion

1) The real value - the one you measure is mS - conductivity. If it is right or not depends on calibration and how exact your temperature compensation is. sometimes it is a need to manipulate the compensation values. as an example - I need to use a manual compensation that is around -2.6 degree C
2) The inbuild conversions from mS to PSU is inline with most calculation tools online and can be used without any more changes
3) The inbuild conversion from mS to density (kg/L) may need use of a correction factor ( there is a possibility in the program to do that) in order to show the same density (Kg/L) as many of the online calculators. the factor is different from case to case
4) GHL gives no option to read specific gravity
5) Density and specific gravity is not the same at temperatures over +4 degree C. In 25 degree C specific gravity is around 0.003 higher than the density.
6) Density has an unit (kg/L) - specific gravity is unitless. Probably why countries not using the metric system love to use this.

In general - IMO - it is much better to use PSU than specific gravity (or density) in the hobby.

Sincerely Lasse