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This is very useful feature, but I am wondering about the limitations of the internal thermometer. Is it a thermistor? How was the internal thermometer calibrated? I am wondering if we can modify it’s calibration manually. Also, what is the ultimate accuracy of the temperature reading?
When the logging feature is enabled, will it be possible to measure the thermometer’s temperature along with the two other channels, or does this temperature sensor use one of the meter’s channels?
David:
Sorry if James wanted to answer this….
I wondered the same and this was actually on of my proposed uses for the unit. (To log temperature in HVAC systems)
As it turns out the temperature sensor is internal to the chip and is mainly for temperature compensation of the readings.
As such it is not calibrated so can be a few degrees off of actual and it has a certain degree of self heating as the chip warms from sleep.
I think it is still a valuable tool as long as we are aware of the limitations and influences.
Tom
If possible, it’d still be nice to log the temperature so thermocouple readings can be recorded. I’ve got a build sort of working with thermocouple tables for Type-K and Type-T on the AUX input using the internal temperature for the cold-junction measurement. Once I get it to stop crashing when you try to go back to volts I’ll submit a pull request to James.
Thanks Adam! I’m very excited to see what you’ve come up with on thermocouple measurements. It’s high on the priority list, but stability and logging are top right now.
David and Tom: The temperature sensor is internal to the ADC, which is this model:
http://www.ti.com/lit/ds/sbas502b/sbas502b.pdf
The meter is calibrated to compensate for intrinsic offset in the ADC and gain errors in the ADS1292 PGA, but it’s not calibrated for any reference temperature. I hope this helps.
~James
@Adam Shea:
Post your code as a fork in git hub. I can try it out if it is android. I have a k type thermocouple.Really clean internet site , appreciate it for this post.
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