Question about Digital Refractometers

[sodeen]

So I've been tasked with coming up with controls for a stainless steel passivation line, and one of the requirements is a weekly check of the concentration in a tank of alkali cleaner/degreaser.

Our machine operators have digital refractometers that they use to check the concentration of their aqueous quench solutions. Put a drop on the meter, get a reading, multiply by some coefficient (I think it's roughly 3) based on identity of the solution, and boom, you have your value.

The problem I'm having trouble with is determining where the co-efficient in part 2 is drawn from. It was handed down via OTJ training to the workers, and the ones who are in charge of the procedure that calls it out aren't really sure, either.

Does anyone know where to find this value? Is it based on something you can find in the MSDS? Any help would be appreciated, as I an a materials guy - not a chemistry guy.

 

[60degrees]

Try the TDS or MSDS. Maybe you are lucky. But why don´t you make a calibrating set yourself? E.g. 1. 100% cleaner > measure the refraction index, 95% cleaner + 5% water > measurement and so on.
When you get a reading you can check your table and you are done.

 

[ash9144]

You should consult the manual of the manual. Although it probably doesn't really matter as long as they all record the same value. My guess would be they have a scale from some old method that was used and rather than change the scale to get concentration they just determined the correlation that would match their old chart.