iGrill probes with HM


 

Steve_M

TVWBB Guru
Since it looks like I might finally have my iGrill probes calibrated for use with the HeaterMeter, I figured I'd post this info to see if it might help others out as well.

After taking some initial resistance readings with the iGrill probes and plunking the data into a couple of online utils that are supposed to calculate the Steinhart-Hart model coefficients for the probes, I wasn't getting what I would consider valid coefficient data.

I then came across this little gem of a Thermistor Calculator that does both the Steinhart-Hart model coefficients and β model coefficients, and I'm feeling confident that I've got the correct coefficients for use with the HM now.

Link to Thermistor Calculator Here


I used the following data in the calculator that I gathered by using the iGrill to measure the temp and then took resistance readings based on those temps.

R1: R: 248000 T: 5.5
R2: R: 100000 T: 25
R3: R: 5630 T: 104

Which gave me the following Calculated Steinhart-Hart model coefficients:

Use the RED numbers for the Probe Coefficients data in the HM config

A = 0.7739251279e-3 ( 0.00077392512 )
B = 2.088025997e-4 ( 0.00020880259 )
C = 1.154400438e-7 ( 1.15440044e-7 )

One of the big "ah-ha!" moments was when I realized that the the iGrill probes are 100k, not 10k thermistors, meaning their resistance at 25C is 100k ohms, not 10k ohms. 10k thermistors seem to be far more common.

I also ran some additional testing tonight, taking the probes up to 200C ( 392F ) and using the Model Calculator function on the right side of the Thermistor Calculator website I posted, I was able to punch in the resistance values and it was consistently matching what the iGrill was reporting.

So that takes care of the indoor work, time to see how this performs during a real cook!
 
Update:

I placed my probes in my super scientific egg carton holder, fired up the far right burner on my gas grill, placed the holder + probes on the far left side of the grill on the top warming rack and waited about 10 minutes for temps to stabilize.

YdYsG2Hl.jpg


The good news:

When quick swapping the probe jacks between the actual iGrill base unit and the HeaterMeter, the temps were reading no more than 2 degrees difference, which I'm ok with and would have no problems cooking with.

The bad news:

All 3 probes were reading different temperatures, even though they were all within a close area and had 10 minutes to stabilize. On the upside, the difference in temp was noticed on both the iGrill and the HM

ie:

Pit Probe : HM = 262, iGrill = 264
Meat 1: HM = 247, iGrill = 249
Meat 2: HM = 256, iGrill = 258

So, I feel confident that I've got decent Steinhart-Hart coefficients calculated for the iGrill probes, but I don't feel confident in using the iGrill or its probes any longer as I'm seeing a difference of 15 degrees between the lowest and highest probes on both the iGrill and HM.

Perhaps I'll just sell the iGrill and probes to fund some new ET-72/73 probes.
 

 

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