Calibrating Hydrometers

[Brad W Wi]

Is there a way to calibrate hydrometers on your own, or do you send them out? If sending out, to who?

[Sunday Rock Maple]

A sap hydrometer should read zero in distilled water. Not sure what to do for syrup hydrometers, but there isn't much that can go wrong (other than breaking the glass of course).

[Brad W Wi]

If not much can go wrong, why do some supply houses offer checking the calibration? I'm not being a smart azz, just wondering.

[PerryFamily]

The paper inside will tend to slide down if you are not careful, thus giving you an inaccurate reading.

Had a draw last year that was right on according to the thermometer but could not get it to density,checked a couple more times as the needle climbed over seven. Grabbed a new hydrometer and it was super heavy. Drew off a big batch. Thats what happened, the paper slid. Too rough putting it in the cup empty I guess. Chucked it and always have a few spares.

my opinion only

[jimsudz]

I have a Leader hydrometer from early 90's,always had problems with crystals forming.After being DQ at state fair for being over dense decided to get an new hydrometer. Also use a refractometer.

[Dennis H.]

The glue that holds the paper scale inside and come loose and alow the paper to side up and down.

I have 3 hydrometers and I check them all at least once in the beginning of the season in the same batch of syrup to see if they are the same.

[Brad W Wi]

I do have one for a spare as well. But I'm a belt and suspenders type of guy and would like to check them both. I'm thinking that with the replies so far there isn't a way to check on my own. I hate to send in the mail. I figure it will get bounced around and possibly off zero.

[nymapleguy607]

There really wouldn't be a way to recalibrate a hydrometer. If the paper slides then your toast, best thing is to just have a spare.

[Timberwolf]

You could make a 'calibrated test solution' with distilled water and sugar based on this article: http://en.wikipedia.org/wiki/Syrup then compare your hydrometer reading to the 66 Brix value it should read.

[Dennis H.]

What do they use to test hydrometers?
I hear from time to time at Association meetings they have a guy who will test hydrometers, what do they use?
It would be nice to find ou twhat it is and if we as producers can get it or make it.

[maple maniac65]

they use real maple syrup here in NH. The state inspector checks your hydrometer against theirs.

[happy thoughts]

You could make a 'calibrated test solution' with distilled water and sugar based on this article: http://en.wikipedia.org/wiki/Syrup then compare your hydrometer reading to the 66 Brix value it should read.

I've always wondered about calibrating those things myself. If you just compare a bunch of hydrometers how do you pick which one is the "accurate" one as someone else suggested. I think you're probably closer to the right track but you'd also need to know the temp of the solution to accurately calibrate. You might also want to check a reading in distilled water at a specific temp. Getting an accurate temp to do the calibration is a whole nuther ball of wax. A lot of common thermometers are themselves inaccurate. Somewhere there must be an easier answer.

[Brad W Wi]

There you go Dennis, You said and asked what I should have. Thank you!
Brad

[DrTimPerkins]

What do they use to test hydrometers?

Typically it is a calibrated gylcerin solution.

[Thad Blaisdell]

they use real maple syrup here in NH. The state inspector checks your hydrometer against theirs.

Ive heard that in NH they use real Vt Srup.... lol

[gmcooper]

In Maine Kathy Hopkins with Somerset Extension can check hydrometers. I know some days she has found some to be quite a bit off and many just a little off. Anyone who checks their thermometers will likely find a significant difference between some of them. Last year we had two new Taylor thermometers from a maple supply dealer that were 10 degrees different side by side. One needed a bit of adjusting.

[Beweller]

Use a 100 or 250 ml volumetric flask and a digital scale good to 100 mg. Check the scale with new U.S. Coins. Tare the flask. Carefully fill the flask with 68 degree syrup or test solution. (Use a dropper to avoid getting syrup/solution on the wall above the reference.) Weigh the filled, tared flask. The weight of the syrup divided by the flask volume is the syrup density. Consult a conversion table to determine the density in Brix. Done.

[PerryFamily]

this sounds like a lot of work. For the $25, i would chuck it and get a couple new ones.

[Tweegs]

For the sake of the discussion and out of simple curiosity…

Could you boil a pan of water and measure the temperature with a good digital thermometer. Adjust the thermometer (or use an offset) to trim the thermometer to exactly 212.0 degrees (elevation and barometric pressure shouldn’t matter for this purpose).

Now, bring a pan of syrup to boiling adjusting sap/water content to boil at exactly 219.1 degrees using the thermometer as calibrated above.

Could you not, then, use this syrup to test the accuracy of your hygrometer?

[happy thoughts]

For the sake of the discussion and out of simple curiosity…

Could you boil a pan of water and measure the temperature with a good digital thermometer. Adjust the thermometer (or use an offset) to trim the thermometer to exactly 212.0 degrees (elevation and barometric pressure shouldn’t matter for this purpose).

Now, bring a pan of syrup to boiling adjusting sap/water content to boil at exactly 219.1 degrees using the thermometer as calibrated above.

Could you not, then, use this syrup to test the accuracy of your hygrometer?

I don't think so because pressure/altitude matter when trying to arrive at the correct syrup density. Also, this then uses a thermometer as the basis for your standard. At that point you might as well just skip the hydrometer.

It seems to me that the simplest solution would be finding the glycerin based test solution Dr Tim mentioned.

[Beweller]

Glycerine seems a little light to me if you intend to have the test solution the same density as 66 percent syrup at 210 deg or so.

In all of this you need to think about the sensitivity and accuracy of your measurement(s). You can calculate the sensitivity of your hydrometer from the relation
A*rho^2/M,
where A is the cross sectional area of the stem, M is the mass of the hydrometer and rho is the density of the test solution (consistent units). The calculated value is the change in density per unit change in height along the stem. Note that a syrup temperature difference of 10 deg causes an error of about 0.6 Brix, and my guess is that most hydrometers have a resolution of about 0.6 Brix per millimeter. If so, you need good eye sight.

[Tweegs]

You know, in this age of cheap, sophisticated electronic gadgetry, you’d think someone would come up with an affordable, reliable, easily calibrated substitute for this antiquated instrument that is the bane of the sugar making world.

With microcontrollers costing no more than what you can scrounge from between your sofa cushions, we rely on a piece of paper stuffed in a glass tube? Really?

Someone jump on this, there’s a fortune to be made here!

I’d do it, but I have to go cut firewood. :lol:

[Beweller]

Those fancy electronic instruments are convenient to use. But they seem to have a habit of going wrong in unobvious ways. Whereas the simple physical instruments seem to either read correctly or be obviously wrong. The hydrometer functions by determining the volume of a specified weight of fluid, with the density being the specified weight divided by the determined volume. Every aspect of the instrument can be determined by a simple measurement of mass or dimension. You can hardly get more fundamental.

When you buy a hydrometer, was that particular hydrometer "calibrated"--"hand made"-- with divisions specific to that hydrometer and with the scale located in the exactly correct position--or was everything standardized on the nominal mass and dimensions of the production run. And how big was the spread of the mass and dimensions about the nominal. Does the manufacturer do spot checks of the accuracy of its hydrometers, and if so at what sampling rate and with what acceptance window.

Calibrate. Or buy three or more hydrometers from different manufacturers (or at least different production runs) and assume that average is correct provided the spread is less than some maximum acceptable value.

And check the law/rule that specifies the legal density. What are the maximum/minimum values that define the acceptable window. If a simple "66 Deg Brix" is specified, take the specification to court. It is quite impossible to meet. No measurement can be exact.