Author Topic: Is hydrometer calibration linear?  (Read 1207 times)

Offline nateo

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Is hydrometer calibration linear?
« on: January 10, 2013, 05:35:36 PM »
My hydrometer (apparently) lost its calibration somehow. I know I checked it a year or two ago, and it was correct, but I checked it today in 60*F water and got 1.005. Do I just subtract 5 points off any measurement? Why/how would a hydrometer lose its calibration?
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Re: Is hydrometer calibration linear?
« Reply #1 on: January 10, 2013, 06:10:49 PM »
The only thing that can really go wrong is for the paper inside to slip up or down the tube. Check to see if the little bead(s) of glue are intact.

If that's the case, then the correction would be linear.
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Offline redbeerman

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Re: Is hydrometer calibration linear?
« Reply #2 on: January 11, 2013, 11:02:42 AM »
The only thing that can really go wrong is for the paper inside to slip up or down the tube. Check to see if the little bead(s) of glue are intact.

If that's the case, then the correction would be linear.

I have had this happen.  The correction is linear.
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Offline Titanium Brewing

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Re: Is hydrometer calibration linear?
« Reply #3 on: January 17, 2013, 01:43:31 PM »
My hydrometer (apparently) lost its calibration somehow. I know I checked it a year or two ago, and it was correct, but I checked it today in 60*F water and got 1.005. Do I just subtract 5 points off any measurement? Why/how would a hydrometer lose its calibration?

You use distilled water, correct?
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Re: Is hydrometer calibration linear?
« Reply #4 on: January 17, 2013, 02:49:19 PM »
You use distilled water, correct?

It doesn't matter. Tap water with a TDS high enough to be measured using a hydrometer is a couple orders of magnitude outside the EPA limits.
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Offline Titanium Brewing

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Re: Is hydrometer calibration linear?
« Reply #5 on: January 17, 2013, 02:58:04 PM »
I did not know that. Everything I have always read says use distilled. Thanks.
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Offline oregonianredbird

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Re: Is hydrometer calibration linear?
« Reply #6 on: May 06, 2013, 08:02:57 AM »
Old thread, but I wanted to point out that the calibration is not necessarily linear. Yesterday, I mixed solutions of known specific gravity using sugar and water. At low gravities (1-1.020) my hydrometer reads 0.004 too high. But at a gravity of 1.083, my hydrometer reads exactly 1.083. I suppose this can happen if the marking on the paper were printed a hair too far apart from each other.