refractometer not reading

[fermjohnp]

Hi All,

We have a refractometer at our shop. I have calibrated it with water. It doesn't seem to be giving a reading on a coolant i am testing it with. The scale reads from 0-20%.

I figure it should read something on this coolant but it doesn't.
The coolant came from a cut-off unit that runs a white milky semi synthetic liquid.

Thanks all.

 

[MiketheEngineer]

Sorry - get it repaired or buy a new one

 

[IRstuff]

"I figure it should read something on this coolant but it doesn't."

Why should it? And why haven't you tested it against what the scale is calibrated for, which is typically something with sugar.

TTFN
faq731-376

 

[fermjohnp]

Hi The model is a AST from japan. It will read measurements from our shop water based oil solutions. I read 5% today on one of our grinding machine oils.

When i test the white milky liquid I see a light blue tint start near the upper 30% of the reading while looking through the eye glass. I do not know what this represents if anything.

What does this tell us about the fluid?

 

[IRstuff]

Probably that it's colloidal and diffracting the light

TTFN
faq731-376

 

[fermjohnp]

Colloidal?

 

[btrueblood]

"Colloidal? "

Look it up. My brain equates it to "milky". Refractometers work on clear, or nearly clear, liquids. Not so well when you have itty-bitty little droplets of oil knocking the photons around, or other crap in the fluid blocking the light path.

 

[IRstuff]

There are, supposedly, refractometers that can read cow milk, but that's water based. You could try diluting it to see what happens.

TTFN
faq731-376

 

[saberblue]

There are several possibilities-

1- that your fluid is so contaminated with tramp oil that your refractometer is over whelmed and can not read the fluid. A good quality digital refractometer will/may solve this problem.

2- If you are using an emulation (soluble oil) type fluid the emulsion may have become unstable and you are getting such a "dispersed" line that your instrument will not read.

3- the concentration of the fluid is in excess of the range of your refractometer. Try diluting the fluid. In fact run a series of dilutions both to confirm that the refractometer works with your fluid and that the refractometer factor that you are using is appropriate for the instrument in use (Brix, 10440, Blame etc.)) Do a series of dilutions record the refractometer reading calculate the slope of the line and use that (compare your results with the number supplied by your supplier) to convert your refractometer reading into % concentration.

4- there may be something on the prism of refractometer: oil, silaxane based anti foam, "hard water soaps" etc. etc.

Just some thoughts about using refractometers in general:

A- make sure that the unit and the fluid are with in the temperature range that it is designed and calibrated for (temperature has a major effect on refractometer accuracy

B- make sure that you have a good light source -- the frequency of the light can effect accuracy but not nearly as much as temperature does- as a practical matter shine a pocket flash light thru the prism gives very good results.

C- make sure that the all the parts of the unit are very clean - mild soap and water. If the prism or the cover is scratched or washed with solvent send the unit to the trash.

Attached is a link to a web site for a company that makes very good quality digital refractometers here in the US. I have used one of their hand held digital refractometers for more than 7 years both in the lab and in the field.

http://www.misco.com/

A.R. "Andy" Nelson
Engineering Consultant
anelson@arnengineering.com