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Home Brew Forums > Home Brewing Beer > Brew Science > single junction vs. double junction
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Old 03-18-2012, 03:07 AM   #1
zazbnf
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Default single junction vs. double junction

Is there any accuracy advantage to double junction electrodes over single junction electrodes in brewing applications, or is it just a longevity issue?

I can get 2 of these:

http://www.coleparmer.com/Product/Oa...or/EW-35801-00

for the about the price of a low end double junction. Assuming the single junction lasts 6 months and a double for 12 months; if accuracy is similar the cheaper single junction seems to make sense.

I will be using it with this meter, and will brew at most 2x per month:

http://www.coleparmer.com/Product/Me...ServiceSupport

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Old 03-18-2012, 12:55 PM   #2
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The theory behind the double junction design is that it is harder for things from the solution being tested to make their way to and contaminate the reference electrode. Beer has stuff in it (proteins) that are tough on electrodes. They coat the bulb and I seem to recall something about precipitating silver salts which could potentially be a problem for a Ag/AgCl reference especially in a single junction design.

Electrodes seem to have improved a lot over the last 10 - 15 years. I used to get 6 mos to a year of service but now am regularly getting over 2 usually in liquid or renewable junction electrodes but even in some conventional gel filled ones. These are not $45 electrodes though. Most are over $200. I always thought such electrodes were out of reach for home brewers but if indeed 6 mos. is all that can be expected from a $50 electrode then $250 for one that has been going 2.5 years and still has slope of over 98% does not seem so unreasonable.

OTOH even the little Hanna pen I bought over a year ago seems to be hanging in there though I almost never use it except to see if it is still working. It drfits some after cal but not randomly.

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Old 03-18-2012, 02:07 PM   #3
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Thanks AJ,

The meter came with this electrode:

http://www.coleparmer.com/Product/Th...or/EW-05719-14

however it was dried out according to the manual for this electrode it says to NEVER let it dry out. Since the fill solution recommended for this electrode was going to cost me almost 100 bucks, I figured I should just replace it instead of buying the solution and hope it could be revived and being out the 100 bucks for the fill solution.

If I were to invest in a higher end electrode, what are your thoughts on this one:

http://www.coleparmer.com/Product/Ac...NC/EW-55502-02

or do you have something else you would recommend? I don't know that I need one with built in ATC as the meter came with a separate temp probe that seems very accurate compared to my digital thermometer.

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Old 03-18-2012, 02:53 PM   #4
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The first thing that catches my eye is that the first electrode has an 8 pin mini DIN connector and the second a BNC connector. Obviously, you want a connector which matches your meter.

If your meter has a separate temperature probe which plugs into a separate connector then you would need to be sure first that the cabling and connectors on the electrode matched those of the meter and that the RTD was of the type expected by the meter. If possible it is best to buy electrodes that are specified to work with the particular meter you have.

That's what I do - i.e. when I replace an electrode it is a direct P/N replacement for the electrode that came with the meter or it is made by the meter's manufacturer and is recommended for use with the particular meter I have. Thus I can't really recommend anything in particular to you unless you wanted to buy a Hach meter.

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Old 03-18-2012, 03:41 PM   #5
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Quote:
Originally Posted by ajdelange View Post
The first thing that catches my eye is that the first electrode has an 8 pin mini DIN connector and the second a BNC connector. Obviously, you want a connector which matches your meter.
Well the eletrode that came with the meter is obviously not original to the machine. There is no 8 pin din connector on the meter, the electrode was just connected via it's bnc connector. The temp probe plugs into a jack that looks like an old large headphone jack.

Since I do not have a manual for this model, and am not sure what electrode it would have shipped with, I just e-mailed cole-parmer to ask if they can recommend an electrode for use with this meter.

And as much as I would like to buy a new Hach meter, just isn't in the budget at this time

Thanks
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