Adjusting probes and resistance


 
E

EdwinH

New member
Ik have four probes on my HM4.1, two Maverick ET-72 6" high resistance hybrid probes, a ET-72 standard food probe and a ET-72 pit probe. Compared to my Maverick ET-733 (which I believe is accurate) there are differences, sometimes more then 5 degrees Celcius, between them.

A quick test shows the following results:

[table="width: 500, class: grid"]
[tr]
[td][/td]
[td]Temp1[/td]
[td]Temp2[/td]
[td]Temp3[/td]
[td]Temp4[/td]
[td]Temp5[/td]
[/tr]
[tr]
[td]ET-733[/td]
[td]13[/td]
[td]29[/td]
[td]53[/td]
[td]80[/td]
[td]100[/td]
[/tr]
[tr]
[td]Probe 0[/td]
[td]12,7[/td]
[td]28,4[/td]
[td]53[/td]
[td]81[/td]
[td]100,4[/td]
[/tr]
[tr]
[td]Probe 1[/td]
[td]11,1[/td]
[td]27,7[/td]
[td]51,2[/td]
[td]78,9[/td]
[td]98,4[/td]
[/tr]
[tr]
[td]Probe 2[/td]
[td]11,1[/td]
[td]27,9[/td]
[td]52,2[/td]
[td]77,8[/td]
[td]98,3[/td]
[/tr]
[tr]
[td]Probe 3[/td]
[td]11,2[/td]
[td]27,9[/td]
[td]53[/td]
[td]78,3[/td]
[td]98,3[/td]
[/tr]

[/table]

For higher temperatures, the differences can be greater, but I haven't tested this yesterday. I only went up to 100 degrees C (boiling water)

So I went on finding the resistance of the ET-72 probes using the 'R'-setting in HM. For one of the probes the following results:

Temp C Resistance
Low 4 543445
Mid 24 215647
High 99 18700

This leads to the following Steinhart-Hart values:

a= -0,000369703
b= 0,000322661
c= -0,000000123

When I enter these values in HM, and click save&apply, the entire probe is disabled. So it seems that the values are not accepted? What am I doing wrong?
 
Last edited:
It if shows as "disabled" then that means the calculated value is below -20C or above 500C so is most likely invalid. This assumes the number was properly accepted by HeaterMeter (and that you used '.' as the decimal separator and not ',').

Also note that HeaterMeter's resistors are set to optimize precision at temperatures around 120C so low temperatures will likely show low precision (but probably shouldn't be off by 2C at 13C).
 
Ah, thanks, the '.' did the trick. However, the probes are now completely off at a 2 degrees difference between them at room temperature, so I have to recalculate the values :(
 
Last edited:
Yeah sorry about that. The input is actually parsed on the microcontroller, which doesn't know anything about localization. :)
 
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