Temperature Probe Coefficients

[391dave]

So I am perplexed with the temperature coefficients. I got a new probe from Ebrewsupply and they use the brewers hardware probes so the coefficients should be the same. My water was boiling at 206.5. At my elevation and pressure it should be around 210.5 to 211.

So I followed the instructions on the forum to determine the coefficients and they were different than what was in there. My procedure was to use a calibrated thermometer and ice water, a 104 F bath, and a 158 F bath. The warmer temps were maintained with my sous vide device and verified with the calibrated thermometer.

After I measured the resistance of each probe at each temperature I used the cargo site listed on this forum and a Stanford research system (http://www.thinksrs.com/downloads/progr ... ulator.htm) calculator. Both of them give different coefficients for the same resistances and temperatures. The colors are just the different probes. All were purchased from ebrewsupply. Any thoughts?

Temp Yellow Green White Red/black Red
32 32310 32463 32513 32246 32380
104 5330 5320 5350 5310 5310
158 1744 1759 1784 1749 1742

Cargo Calc Yellow Green White Red/Bl Red Brewers Hardware
a 0.0011271357 0.0011132912 0.0010773953 0.001141966 0.0011534689 0.001137155
b 2.341354E-04 2.3643795E-04 2.4174083E-04 2.3165571E-04 2.3004042E-04 2.3259496E-04
c 9.1832916E-08 8.1733525E-08 6.425385E-08 1.0205388E-07 1.0578107E-07 9.540003E-08



Stanford Calc
1.176888875E-03 1.113291284E-03 1.077395246E-03 1.141966029E-03 1.153468858E-03
2.258216424E-04 2.364379497E-04 2.417408179E-04 2.316557057E-04 2.300404225E-04
1.245018526E-07 8.1733521870E-08 6.4253848850E-08 1.020538806E-07 1.057810675E-07

[391dave]

Well that formatting is not good. Here is a pdf

[bbrally]

It's impossible to manufactured two sensor with exactly the same properties. So the coefficients that Brewers hardware and others give you is just the sensor manufacturers average for the sensor part number in question. There will always be some deviation between "identical" sensors.

There are also different formulas used to calculate the coefficients. And all of these formulas only provide approximations to the actual values of the resistance and temperature.

If you plug the different coeficients into your BCS, you should see only a small difference in temperature displayed.

[clearwaterbrewer]

Also, there are notes in the forum on how to tweak the probes on the fly to get them to read the same at a certain temperature...

FYI - for my distillery, I needed one tenth of a degree accuracy during proofing before bottling... I got one of these $70 thermometers from www.novatech-usa.com and very happy with it.. (you do not realize the lack of precision in a standard homebrew floating thermometer until you use one of these!)

B60730-1300
30 to 124°F DURAC Plus Precision Glass Thermometer (each) [ H-B Instrument # 6/1124 ]
$68.06


Not really on topic, but the TTB also requires NIST traceability, so I had to get that on one thermometer and only bring it out of the packaging to verify the other thermometer, it added a couple hundred bucks, but they calibrate it to a hundredth of a degree and give you a laminated certificate of calibration to the serial number of the thermometer.

B60205-0700
30 to 124°F DURAC Plus Partial Immersion Liquid-in-Glass Thermometer, with a NIST Traceable Calibration Certificate (each) [ H-B Instrument # 3/4124 ]
$261.20