Calibrating refractometer

[WaterKeeper]

Your asking for it. I banned Boomer to the Chemistry Forum for life and you're next buddy.

 

[jdieck]

<a href=showthread.php?s=&postid=9593555#post9593555 target=_blank>Originally posted</a> by WaterKeeper
Your asking for it. I banned Boomer to the Chemistry Forum for life and you're next buddy.

Now I finally know why you do not post this things there!

 

[EvilE]

<a href=showthread.php?s=&postid=9587161#post9587161 target=_blank>Originally posted</a> by vessxpress1
If you read that article, you'll see that some are pretty bad. They tend to get worse with age as stuff builds up on them and I always hated trying to get all the microbubbles off the arm. Some are decent though. They can be hit or miss.

BTW, I'd trust Randy before the LFS.

someone on here posted a study on refractometers vs. swing arms, and when properly used (and yes new) the swing arms read the same as the refracts EVERY time!! Of course, I still trust a properly calibrated Refract more then a swing arm, but it is still interesting.

BTW--I never once said I didn't trust Randy, I just dont have the proper solution to properly calibrate my refractometer, and my LFS does. He used their calibration solution, compared it to their refractometer, and he he then tested different SW tank water with mine and theirs, and RO water with mine and theirs. He tuned it for about 10 minutes, till he felt it was accurate.

 

[crumbletop]

<a href=showthread.php?s=&postid=9592611#post9592611 target=_blank>Originally posted</a> by jdieck
The zero will be off not only because you shift the chart but also because the slopes are different.

I found the data... From the 87th edition of the CRC handbook of chemistry and physics. It took a bit of manual calculating to match things up with another table of refractive indexes of seawater, but through the range of useful salinities for marine aquarian (10 ppt - 40 ppt), including hyposalinity, the slope is exactly the same for NaCl and seawater. They are offset by approx 1.1 ppt. I cross-checked the #'s with various tables in Randy's articles, and other tables on saltwater I found.

 

[jdieck]

:thumbsup: Note that if they are parallel between 10 and 40 ppt but not between 0 and 10 then they are not linear which may be an inconsistency. What I think is that the diference in slope is small enough to not show withing the accuracy range and small enough at that range that it may not even show after the third significant digit on the tables.
In any case as WK mentione the source of error is well within the acceptable for our purposes.

 

[EvilE]

my head is still spinning.......

 

[vessxpress1]

<a href=showthread.php?s=&postid=9593831#post9593831 target=_blank>Originally posted</a> by EvilE
someone on here posted a study on refractometers vs. swing arms, and when properly used (and yes new) the swing arms read the same as the refracts EVERY time!!

I didn't mean to completely trash swing arms. They'll do the job. I don't prefer them (don't like getting wet if I don't have to) and I wouldn't want to still be using one that is 5 years old.

My IO swing arm matches my refractometer very close if not exactly. I have seen some that were way off though.

 

[crumbletop]

<a href=showthread.php?s=&postid=9594400#post9594400 target=_blank>Originally posted</a> by jdieck
:thumbsup: Note that if they are parallel between 10 and 40 ppt but not between 0 and 10 then they are not linear which may be an inconsistency. What I think is that the diference in slope is small enough to not show withing the accuracy range and small enough at that range that it may not even show after the third significant digit on the tables.
In any case as WK mentione the source of error is well within the acceptable for our purposes.

Gotcha. I didn't calculate lower than 10 because 10 is already lower than 1.009. Likewise above 40.