aaaaaaaaarg New Refractomer

[lillibirdy]

I just got my new refractometer w/ automatic temp control. It says it MUST be calibrated in a room with a temp of 68 degrees. Well hmmmmm, am I sposed to just watch the thermometer all morning and eve trying to catch it when the room is just exactly 68? It seems to rush past that point quite quickly.... I called them, and the techs said they checked with two sources and indeed I do need to calibrate in a room thats exactly 68 degrees. I spose I can set my thermostat to 68 tonight, but it isn't even accurate to the nnnnnth degree. Now will I be back to wondering if calibration is off a tad, and still can't trust accuaracy.
How have some of you others dealt with this?
Thx

 

[birdy]

Interesting, I have always just calibrated mine to room temp, which in my basement is probably pretty close to 68, maybe around 70. I don't know what to tell you, probably just get as close as you can, I doubt it is going to make the refractometer to be off enough to make a difference. Even if it is off a smidge it is probably still more acurate than a hydrometer. I am interested to see what others think.

 

[benj2112]

I live in a pretty old place and just calibrated mine as close to 68 as I could. The thermostat said it was 68; my outside thermometer said it was 68 and so did the weather channel.
The interesting thing is that for about a year and a half now my cheap plastic hydromoter and refractomoter still tell me the same thing...guess I got a good hydromoter.

 

[ophiura]

You know, I'll be the first to admit I tend to just 0 it at room temperature...and always did so in school, and elsewhere. It introduces some error, for sure. Its not ideal. I looked into trying to get a feel for the actual error (eg, would it be off .2 of a point or 1 point or what?), but had little luck.

 

[ophiura]

Huh, this is an interesting thing - I'm still doing some reading on it.
"Boomer" posted this on another board, and generally if you search for Randy Holmes Farly refractometer...or similar terms some of these things should come up.
The same amount of salt in different temp. waters will give 2 different salinity readings.
No, on a refract or conductivity meter, they will be the same.
Salinity is salinity it is not affect by temp. 35 ppt =35 ppt no mater what the temp is. What is affected by temp is Specific Gravity and hydrometers measure SG. A refract or conductivity meter that does not have ATC (Automatic Temp Comp) will be affected by temp. However, I know of no one in this hobby that uses one without ATC for seawater mixing. So we are really only left with the hydrometer. However, some hydrometers, i.e SeaTest use thermal expansion plastic, so they too are ATC in a sense.
I think part of a take home message is that the error introduced is fairly minimal when you consider all of the possible sources of error. These are not high end scientific instruments...but they are more consistent and less sketchy than hydrometers.
Another idea - and it is so true yet I admittedly didn't think much about it - is to use a known salinity to calibrate it. So there are "recipes" if you will for 35ppt mixtures to test. Might do that some day!

 

[lillibirdy]

OMG I just went into the garge for something and thought...hmmmm, it is a few degrees chillier in here, and so I put a thermometer in there and it was RIGHT ON 68!!! Can't believe it, must be my lucky day! So I calibrated it with my distilled water, and checked it against my TWO diff hydrometers which I had calibrated to my LFS refracto, and both where off from where he had said they where. I had begun to not trust his refractometer, or rather whether he would properly calibrate and maintain it, so finally broke down and bought my own. I had done hypo with a swing arm early on, and was a nervous wreck. This was a very reasonable $42. so now I feel much relieved. Now to figure out the easiest way to rid the little plate of air pockets as it says it should be before reading it...gotta keep playing with it before it is clear.