hydrometer temp correction

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Bongo

Post by Bongo » Fri Sep 12, 2008 6:42 pm

Can't believe i missed this thread,good stuff.

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Jim
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Post by Jim » Fri Sep 12, 2008 7:04 pm

Jim wrote:
lockwood1956 wrote:Or better still (now who is bored?)

http://winesathome.co.uk/downloads/jims ... lator.html

if you like it Jim, ill email you it and you can use it (least I can do for the free info and guidance from your excellent site dude)

let me know if you would like colour scheme changing or whatever

regards
bob
Very kind of you Bob, yes I'd like that. 8)

I'll sort out the background colour when I get the page if you like - I think a paler green would fit in better. :wink:
I don't think I ever got the page, but I can link to yours if that's OK, Bob.

EDIT: Done
"Reality is that which, when you stop believing in it, doesn't go away" - Philip K. Dick

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MikeG
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Re: hydrometer temp correction

Post by MikeG » Tue Nov 18, 2008 9:59 am

I've written a spread sheet for hydrometer correction based on an article at http://hbd.org/brewery/library/HydromCorr0992.html and which I've attached as a zip file. I couldn't attach it as an xls file, I even tried changing the extension to spreadsheet and still it was rejected.

Sorry, there was a slight error in the x-axis the values should have been 0 - 20. I have now replaced it.

Sorry, apparently JBK has disabled attachments so I've put it on my bit of webspace.

Also, sorry edit1now for not replying before now but I don't know about OpenOffice. I created the spreadsheet with Lotus 123 (much better than Excel [-( ) and then exported it as a .xls file, I tried it under Excel and it looks fine there. Sorry I can't be more help.
Attachments

[The extension zip has been deactivated and can no longer be displayed.]

Last edited by MikeG on Fri Dec 16, 2011 7:48 pm, edited 1 time in total.

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edit1now
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Re: hydrometer temp correction

Post by edit1now » Sun Dec 28, 2008 7:49 pm

I just opened MikeG's file in OpenOffice and got a black spreadsheet with a lovely red curve. Should there be values or labels on the axes?

Thanks.

Rob Jones

Re: hydrometer temp correction

Post by Rob Jones » Sat Feb 28, 2009 3:47 pm

Many thanks I have just printed this out having just produced my first brew. Took a hydrometer reading at 70 ish paniced added sugar It seems to have turned out a bit stronger than I expected - lots to learn

Minger

Re: hydrometer temp correction

Post by Minger » Mon Apr 06, 2009 12:27 am

Am i reading that adjustment chart correct, If my brew was at 78 degrees and i got a hydrometer reading of 1038, i should be adding over 16 points? :?

Billy Hunt

Re: hydrometer temp correction

Post by Billy Hunt » Mon Apr 06, 2009 4:38 pm

I was taught all this temperature correction stuff when I did my print apprenticeship, shame I forgot it all. #-o

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towser
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Re: hydrometer temp correction

Post by towser » Mon Apr 06, 2009 5:48 pm

Does anyone have a formula that I can put into excel for Hydrometers calibrated to 20°C?

I have the excel formula for 14.3°C (58°C) as follows:

=1.313454-(0.132674*((TEMP*1.8 )+32))+(0.002057793*(((TEMP*1.8 )+32)^2))-(0.000002627634*(((TEMP*1.8 )+32)^3))

you need to take the spaces out of where it says 1.8 ) - the reason being i get a 8) if i leave the formula without spaces

where TEMP is a named range containing the temperature of the Specific Gravity (SG) reading

You then use =ROUND(SG+(COR*0.001),3)

where SG is the Specific Gravity and COR is the result from the correction formula above.

It would be great to get the same formula that works with 20°C
If that happens, I'm more than happy to share the spreadsheet on this site - which may suit people with no internet access in their brewhouse.

I do have sort of a formula that gets close, but not close enough:
=SG*(1+(0.00043*(TEMP-CALTEMP)))
where
SG = Specific Gravity
TEMP = TEMP is a named range containing the temperature of the Specific Gravity (SG) reading
CALTEMP = named range of the Hydrometer Calibration temperature.

Graham

Re: hydrometer temp correction

Post by Graham » Mon Apr 06, 2009 8:12 pm

As with many home brewing "techniques", it is an upside-down approach. If you are going to mess around with polynomials to derive temperature correction, it is better and more flexible to use a polynomial that provides the density of water at different temperatures, and derive temperature correction from first principles. That way you can obtain a correction figure at any temperature you wish. Figures for the density of water vary depending upon whose reference you look at, but there are polynomials out there on the web to match any of them. Here is the polynomial that I use for water density.

1-(T+288.9414)/(508929.2*(T+68.12963))*(T-3.9863)^2

Where T is temperature in °C.

The simplest way of deriving a correction figure is:

(Density_of_water@reference_temp / Density_of_water@sample_temp) -1

Basically divide one by t'other and subtract 1

Where reference temp is the temperature written on the hydrometer and sample temp is the temperature of your wort.
That polynomial will give:
0.9982337 @ 20°c
0.9956783 @30°C

Therefore the correction for a 20°C hydrometer, at 30°C wort temperature will be (0.9982337/ 0.9956783)-1 = 0.002566.
Depending upon how you want the figure expressed you may need to multiply it by 1000 giving 2.6.

That method is accurate enough for our purposes, but correction is also affected by specific gravity. There is a variation on that formula, this is not much more complicated, that takes specific gravity into account and gives more accurate figures, which I will elaborate on if you wish. However, there is a limit to how accurate we can get because the glass of the hydrometer also expands with temperature and it makes a significant difference, but I have never seen home brewers take that into account yet.

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towser
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Re: hydrometer temp correction

Post by towser » Mon Apr 06, 2009 10:12 pm

Many many thanks Graham!

You wouldn't believe how many hours I've spent trawling the internet to get that formula.
I've developed a spreadsheet that looks at this and also estimates ABV from OG. Maybe its useful for others.
http://dl.getdropbox.com/u/889761/ABVCalculator.xls

Graham

Re: hydrometer temp correction

Post by Graham » Mon Apr 06, 2009 10:25 pm

towser wrote:Many many thanks Graham!

You wouldn't believe how many hours I've spent trawling the internet to get that formula.
I've developed a spreadsheet that looks at this and also estimates ABV from OG. Maybe its useful for others.
http://dl.getdropbox.com/u/889761/ABVCalculator.xls
Looks as if you have already incorporated the above into your spreadsheet.

Do you want the more accurate version?

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towser
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Re: hydrometer temp correction

Post by towser » Mon Apr 06, 2009 10:28 pm

I can certainly give it a try!
Why didn't they make students interested in Chemistry by brewing beer?
It would have gained 100% attention :-)
What a great hobby this is turning out to be!

Graham

Re: hydrometer temp correction

Post by Graham » Mon Apr 06, 2009 10:39 pm

Here it is - It isn't much different - almost the same. The density polynomial is the same, but the other bit becomes:

(SG*density@hydtemp/density@sampletemp)-SG

The brackets are superfluous.

In this case SG probably must be in the 1.050 form, which your spreadsheet already is, so it doesn't matter

[edit]
There is a gotcha with this version inasmuch as you need an SG to begin with. No good for a general purpose table for instance. If you do not have an SG, set SG to 1.000 and it'll give the same figures as the old formula. You made need to put a test in to ensure that SG is 1.000 in the absence of a proper SG (if that makes sense).
[/edit]
Last edited by Graham on Mon Apr 06, 2009 10:55 pm, edited 1 time in total.

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towser
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Re: hydrometer temp correction

Post by towser » Mon Apr 06, 2009 10:53 pm

Well I think I've got it in there ok. Hopefully I've interpreted your formula in excel language ok.
I really hope this tool is useful. I've certainly learned something making it.
Once again, many thanks for your help:

http://dl.getdropbox.com/u/889761/ABVCalculator.xls

Graham

Re: hydrometer temp correction

Post by Graham » Mon Apr 06, 2009 11:00 pm

towser wrote:Well I think I've got it in there ok. Hopefully I've interpreted your formula in excel language ok.
I really hope this tool is useful. I've certainly learned something making it.
Once again, many thanks for your help:

http://dl.getdropbox.com/u/889761/ABVCalculator.xls
Your figures match mine, so if you are wrong, we are both wrong.

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