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Hydrometer inaccuracy ?

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AJP

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I'm posting this in the Beginners section because I have to be missing something.

I have 2 hydrometers, both are marked as calibrated at 60F

I decided to verify that they were accurate, so I grabbed some distilled water (recently purchased), rinsed the test tube out with distilled water, filled it up, measured the temp with a Thermopen (72F). Dropped the Hydrometer in, let it settle and it read 1.003, looked up the temp adjustment of .001 for a reading of 1.004.

So I grabbed the other Hydrometer and it read the same value!

I immediately figured that the water wasn't really distilled water, so I grabbed some DI water that I made downstairs. It read nearly the same, maybe 1.003 corrected.

I decided to check my thermapen against my backup thermapen, no difference!

I thought about barometric pressure but decided that wouldn't impact it enough to see.

I even cooled some of the distilled water to 60F and it still measured 1.002.

So, what am I missing? :a1

The only thing I can think of is that the Hydro's are not calibrated correctly, I bought them at the same time, at the same store.

Thanks,
AJ
 

Kraffty

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I would just allow for .004 difference, it's really not off by very much. I don't think my three are any more accurate and not even sure I can read the difference between .002 or .004 accurately myself.
Mike
 
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AJP

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I would just allow for .004 difference, it's really not off by very much. I don't think my three are any more accurate and not even sure I can read the difference between .002 or .004 accurately myself.
Mike
That makes sense.

Thanks,
AJ
 

ibglowin

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Remember this is a $5 tool that you are expecting to read accurately to 3 decimal places. Not gonna happen.

You have done all the right things. So now you just remember it reads off by 0.xxx and subtract that amount each time you make a measurement.

Still the best $5 tool in a winemakers toolbox.


So, what am I missing? :a1

Thanks,
AJ
 

NorCal

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I have a set of precision hydrometers, where one very large hydrometers measures 0-5 brix, 5 or 6 times more definition than the $10 one.

What is funny is that I rarely use them and reach for the $10 one. I need to know starting, and know that it's dropping steadily, but if it's within a 1/4 of a brix, don't really care. As it nears completion it is nice to have more accuracy to see that there is no residual sugar, but not really a necessity to me.
 

balatonwine

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A few things to consider:

- Every tool has a tolerance. That is, no reading is perfect, but will be within +/- some value.

- Every reading will have a least significant value (i.e. the last one) that you can only rely up to within the given range marked on the tool. So if a tool has demarcations in the range of 1 value, then your reading uncertainty is always within +/- 1 of that value.

- You seem to be using one thermometer to check the accuracy of two tools. How do you know the thermometer is correct? This is the circular issue of testing tools: you have to also test the testing equipment.

- Distilled water can vary in quality. So it will also add a degree of error to a measurement.

So if you are off by 0.002, that is probably withing tolerance, not unexpected, and nothing to worry about. But in the end, you do not really measure complete dryness simply by a reading the absolute value of hydrometer, but rather taking multiple measurements over time. If the value does not change, you are dry (assuming no stuck fermentation and taking into account any know bias in the measuring instrument).
 
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Redbird1

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He did use two thermometers.

Even if both were wrong, the temperature correction factor is negligible considering all he was doing was measuring room temperature water. Temperature correction is the same from 67F -75F at 1.003.
 

AJP

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A few things to consider:

- Every tool has a tolerance. That is, no reading is perfect, but will be within +/- some value.

- Every reading will have a least significant value (i.e. the last one) that you can only rely up to within the given range marked on the tool. So if a tool has demarcations in the range of 1 value, then your reading uncertainty is always within +/- 1 of that value.

- You seem to be using one thermometer to check the accuracy of two tools. How do you know the thermometer is correct? This is the circular issue of testing tools: you have to also test the testing equipment.

- Distilled water can vary in quality. So it will also add a degree of error to a measurement.

So if you are off by 0.002, that is probably withing tolerance, not unexpected, and nothing to worry about. But in the end, you do not really measure complete dryness simply by a reading the absolute value of hydrometer, but rather taking multiple measurements over time. If the value does not change, you are dry (assuming no stuck fermentation and taking into account any know bias in the measuring instrument).
BTW: I used 2 thermometers (both were calibrated and checked when purchased), I also used both distilled water and RO water (2 different sources).

Thanks,
AJ
 

drainsurgeon

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Mine is off a bit too. It shows .998 with distilled water so I add .002 to each reading I take. For a while I couldn't figure how my wines were going so dry. :r If I want to start a batch at 1.1, I push it to 1.098. Or, more often, I just don't worry about it. I think even commercial wines have an except-able "range" when claiming ABV.
 

Smok1

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I have a set of precision hydrometers, where one very large hydrometers measures 0-5 brix, 5 or 6 times more definition than the $10 one.

What is funny is that I rarely use them and reach for the $10 one. I need to know starting, and know that it's dropping steadily, but if it's within a 1/4 of a brix, don't really care. As it nears completion it is nice to have more accuracy to see that there is no residual sugar, but not really a necessity to me.
Where did you pick up the percision hydrometers? Im looking for a set
 
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