Howto: Calibrate Temperature Probes

Describe your system and processes, and post your config file.
TrickyDick
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Re: Howto: Calibrate Temperature Probes

Post by TrickyDick »

I tried using the utility written by BBrally but didn't really understand how to use it properly. There were several tabs, and I wasn't entirely sure which to use. I think there was one called calibration of coefficients or something similar with some "buttons" marked active/inactive and locked/unlocked.

I prepared three water baths. My probes are welded or otherwise permanently attached to triclover fittings. I tried to get as close as possible to 32, 104, 154 degrees or whatever the default temps were in the utility. The top of the TC plate was resting on the edge of the water glass I used to hold each water bath. One had ice, one was on a countertop, and one was on a heated stir plate.

There seems to be a numerical value on the probe readout table, that would progressively increase with time while the probes were in the bath.
As I let the probes dwell in each bath, all four probes at once, sequentially activating, and then unlocking/locking the buttons which seemed appropriate, I ultimately ended with the probes in the hottest of the three baths, and had an error message next to each probe that said negative coefficient value was not permitted. I feared I had done something wrong, and aborted.

Where did I go wrong?
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bbrally
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Re: Howto: Calibrate Temperature Probes

Post by bbrally »

The instructions I wrote are a little lacking, but it sounds like you figured out how to use the program.

The idea behind the locked/unlocked and active/inactive buttons, was to make it difficult to accidentally overwrite values you had previously acquired.

The coefficients are required to be positive, I'm not a mathematician, so can't explain why. But if the values of resistance/temperature are far off the correct values, negative coefficients can be created.

I can think of three posible problems. You have control over two, and one is outside of your control.

One problem could be that the temperature you are sensing is different than the temperature used in the calculations, sometimes only a few degrees can make all the difference. This is where a good calibrated thermometer is needed.

A second problem could be that the program averages the temperature readings from the moment the unlocked button is clicked. If your probes haven't had a chance to stabilize, the average temperature will include values far outside of the actual temperatures. Give the probes a minute or more in the bath to thoroughly aclimate to the new temp.

The problem outside of your control is the sensitivity/accuracy of the BCS to record resistance values isn't the best for this function. It works fine to measure temperatures to a tenth of a degree, but the resistance measurement is probably barely accurate enough to perform this calculation.

For this reason I had thought to not include it in the utilities, but then did anyways.

I've found that the easiest way to get my probes to where I wanted them was to set them all to default (this can be done on the 'coefficient calculator' tab and then in the settings menu). Then stick them in a bath at the temperature I'm most interested in being accurate and using the 'offset calculator' tab to set all probes to that temperature.

None of my probes are the original EEC probes or the brewers hardware probes, and this method works fine for me to get my mash temperatures right where I want them. When my probe reads 152.0 degrees, I know I'm within 0.1 of that. The fact my water boils at 214 degrees doesn't worry me, I don't use anything other than duty cycle during my boil.
mahleywc
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Re: Howto: Calibrate Temperature Probes

Post by mahleywc »

Doing the initial setup of my new BDS 460. I have Brewer's Hardware BCS temperature probes. I thought I would start testing by updating the probe coefficients with those from the Brewer's Hardware site for the probes I have:
A= 0.001137155
B= 2.3259496e-4
C= 9.540003e-8

In Settings I entered the A coefficient okay but coefficients B and C could not be changed, reverting back to the original values after entry of the changes. Is there a lock on these fields that needs to be unlocked? I have not activated Authentication so no Admin logon is needed.

A few more dumb questions and I may have this under control...
mahleywc
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Re: Howto: Calibrate Temperature Probes

Post by mahleywc »

Never mind...e-x..., my last math class was 1972...
ercousin
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Re: Howto: Calibrate Temperature Probes

Post by ercousin »

I'm using 4.0 software on my BCS-460 and for the life of me, I can't figure out where to go in the GUI to find the thermotest page that lets me measure resistances....

Any help?

"Thermo Test page in the BCS-460"
JonW
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Re: Howto: Calibrate Temperature Probes

Post by JonW »

The resistance values are not in the BCS GUI, you need to either use a utility like that written by bbrally, or use the BCS API to read the value.

bbrally utility: http://calculator.from-ca.com/

BCS API: http://192.168.1.100/api/temp/0
Example above is to read temp probe 0.
mellman
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Re: Howto: Calibrate Temperature Probes

Post by mellman »

Hello!

I've been having some issues calibrating my BCS temp probes. One of my probes seems to read great, the other two I'm trying to calibrate are 8-10 degrees off.

Is it safe to just use the offset tool in the bcs utility? or should i tweak the resistance coefficients until the temps are read accurately?

I have about an additional 12 ft of wire by temp probes are going through (Cat6e) to get from my panel to where and how I want my probes run. Here are my temps (as measured with a thermapen) and then the outputs from the BCS for resistance values.

164.2 {"name":"HLT Temp" temp:1641 setpoint:null resistance:1559
129.5 {"name":"HLT Temp" temp:1295 setpoint:null resistance:3089
104.1 {"name":"HLT Temp" temp:1041 setpoint:null resistance:5311
32.2 {"name":"HLT Temp" temp:304 setpoint:null resistance:31792
164.2 {"name":"MLT Temp" temp:1527 setpoint:null resistance:1939
129.5 {"name":"MLT Temp" temp:1256 setpoint:null resistance:3337
104.1 {"name":"MLT Temp" temp:952 setpoint:null resistance:6503
32.2 {"name":"MLT Temp" temp:352 setpoint:null resistance:29728
164.2 {"name":"BK Temp" temp:1536 setpoint:null resistance:1844
129.5 {"name":"BK Temp" temp:787 setpoint:null resistance:9674
104.1 {"name":"BK Temp" temp:990 setpoint:null resistance:5968
32.2 {"name":"BK Temp" temp:364 setpoint:null resistance:28787

All probes were bought from Brewers Hardware, probe 0 (HLT) is configured with the Brewers Hardware settings, the rest were as well but for whatever reason its accurate for that probe but not the other two. AFter calibrating with the utility they went from being 10+ degrees under to being about 10 degrees over.

Can I simply split the difference on the resistance change? Do I need to manually tweak things?
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bbrally
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Re: Howto: Calibrate Temperature Probes

Post by bbrally »

The BCS sensitivity to resistance measurement is very course. Thus it doesn't provide the most accurate coefficients. But, using the Sampling tab from the Coefficient calculator you should be much closer than 8 degrees. 1 or less is normal.

I don't suggest 'tweaking' the resistance values to get the correct temps. It would be taking a shot in the dark, and take forever as you'd have to test all three temps after a change to confirm it had the proper affect at all temps.

I would suggest double checking your measurements. If you are sure of your measurements, then I would change the coefficients back to the brewers hardware defaults and then use the offset calculator to bring the other two inline with the one you feel is accurate. this should provide accurate results for the temperature at which you do the adjustment. The farther away from this temperature the more uncertain the accuracy will be, especially if the coefficients were inaccurate to begin with.

My experience with brewers hardware probes is that they have always been within a degree or so of accurate with the default coefficients. Using the offset calculator at the temperature I consider critical has been the easiest for me to bring them inline and is all I now do for any probe I set up from Brewers Hardware.
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Re: Howto: Calibrate Temperature Probes

Post by mellman »

I'm still getting pretty frustrated...I hadn't tried the sampling page before, i was just manually refreshing the resistance values from the BCS directly. The Sampling tool certainly makes that job easier, however I'm not even getting usable results now.

(Probe 0) HLT Temp
30971.8229

4759.3934

2220.4286

-3.5060519248e-4

4.8592205771e-4

-9.2502245083e-7

Negative values not allowed. Confirm temperature/resistance values.
(Probe 1) MLT Temp
26908.4688

4704.1148

2273.2857

-4.9559846383e-4

5.0492620195e-4

-9.4545325362e-7

Negative values not allowed. Confirm temperature/resistance values.
(Probe 2) BK Temp
28391.8750

4866.5902

2320.8571

-4.0511449414e-4

4.8881574009e-4

-8.8652169898e-7

Negative values not allowed. Confirm temperature/resistance values.
(Probe 3) Chiller Out Temp
31248.0417

4773.5410

2231.4286

-3.8086932776e-4

4.9083530731e-4

-9.4510496959e-7

Negative values not allowed. Confirm temperature/resistance values.


Run through twice, and not having any luck - one time i could have calibrated one of my probes but its the one that's already fairly accurate so i didnt feel it was worth potentially screwing it up.

Here is my process:

Heat a few quarts of water in the microwave to ~168* F (measured with thermapen.
Prepare a second vessel of ice + water, thermapen reads 32-33 * on this depending on where its placed.
place probes in hot water, allow to sit for a few minutes to acclimate and when water has settled to 146.3 (was cooling faster than I expected) lock the 3rd column
place probes in ice water, allow to sit for several minutes to acclimate, take reading on that temp and input read temp in 1st column
mix ice water into hot water until it is around 104*, put set this in the second column.

Then all the probes show negative coefficients so, I can't save anything. I've done this twice now. What am I missing? is the fact that i've got additional cable lengths on my probes impacting the resistance values that it should be within, and therefore i'm SOL?
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Re: Howto: Calibrate Temperature Probes

Post by JonW »

You mentioned extending the wires on the temp probes. Have you also placed a jumper between earth ground and the BCS ground? Without that, your temps are going to be bouncing. If you look at the temps, are they fluctuating quite a bit? If so, this could be why your attempt to calibrate them is off.
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