A reminder to check your Refractometers

[Not_Now_John]

Test a standard and adjust the screw on your refractometer until it reads where it should

+1

Note, calibrate at the target salinity (35 ppt), not with RO/DI water (0ppt).

And ifs cooler where you store them, warm up your refractometer and calibration solution in your hand, or pocket. I put them in my pocket while doing other stuff and like 15 - 20 minutes later do the calibration.

Yes the commercial one I have says 77F. I imagine the closer you can get a homemade calibration fluid to the temp of your tank the better. Do you think it matters if the refractomer itself is warm?

 

[bondolo]

Do you think it matters if the refractomer itself is warm?

It sure does. Mine claims to have auto temperature compensation but that's mostly BS. I check it with RODI water every time I use it and it fluctuates wildly with ambient temperature fluctuations in the room (the RODI is also at ambient temperature). I've re-calibrated it to zero every time but this thread has gotten me worried that the 35ppt value might be off even when zeroed with RODI.

 

[BAYMAC]

Test a standard and adjust the screw on your refractometer until it reads where it should

+1

Note, calibrate at the target salinity (35 ppt), not with RO/DI water (0ppt).

And ifs cooler where you store them, warm up your refractometer and calibration solution in your hand, or pocket. I put them in my pocket while doing other stuff and like 15 - 20 minutes later do the calibration.

Yes the commercial one I have says 77F. I imagine the closer you can get a homemade calibration fluid to the temp of your tank the better. Do you think it matters if the refractomer itself is warm?

Yes, I have seen what it can do first hand after being told by a very reputable manufacturer to do it. I just had to test it once told :lol:

 

[Gomer]

The "auto temp correction" feature of the refract is a thermal thing on the refractive element. If the refract is at proper temp (see specs), then you are golden as the index is known. The refract glass has a large thermal mass relative to the small amount of water you add, so it really doesn't matter what temp the water is (it will equilibriate) just as long as the meter is at the right temp.

 

[BAYMAC]

"Thermal thing", that the technical term? Is it bi-metal?

I just toss em both in my pocket as they both live in a soft cotton bag.

 

[Gomer]

start with:
http://en.wikipedia.org/wiki/Gladstone-Dale_relation
then add the appropriate analog of:
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20070018851_2007019043.pdf

 

[Not_Now_John]

start with:
http://en.wikipedia.org/wiki/Gladstone-Dale_relation
then add the appropriate analog of:
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20070018851_2007019043.pdf

I like thermal thing better.

 

[Not_Now_John]

Do you think it matters if the refractomer itself is warm?

It sure does. Mine claims to have auto temperature compensation but that's mostly BS. I check it with RODI water every time I use it and it fluctuates wildly with ambient temperature fluctuations in the room (the RODI is also at ambient temperature). I've re-calibrated it to zero every time but this thread has gotten me worried that the 35ppt value might be off even when zeroed with RODI.

Guess I'll just have to start sticking it in my pocket. I was using RO to calibrate as well, didn't work out as well as I had hoped!

 

[Gomer]

or you can leave it next to your sump Under the stand is about the right temperature for me.