I made a bad choice on the temperature sensors. When I received the thermocouples and digital meter from the coffee bean roasting place, I was able to read the detailed specs in the manual. Since the operating temperature range is so wide (several hundred degrees), the resolution is VERY low: +/- 4 degrees F! That's not nearly precise enough for this project.
Also, since the thermocouples generate a voltage in the microvolt range which is read by the very sensitive digital meter, any moisture around the sensor or the fabric-insulated wire or connector can throw the reading off by another 5 to 10 degrees!
And finally, now that I've decided to use extensions on the auger drill to get 6' deep, the 3' leads on these sensors won't be long enough to measure soil temperature at the bottom of the well. Extending the wires shifts the calibration by tens of degrees, so that's not an option.
Mind you, there is nothing wrong with these sensors, and they seem to be working within spec. The sensors aren't designed to be very precise or to work in high-humidity environments (let alone buried in wet soil). I probably should have discovered that before ordering the thermometer, but the detailed specs weren't posted on their website and I ordered them in a hurry.
So these are just not the sensors for this project, and now I'll have to move on to the 1-wire digital sensors I mentioned earlier, which, as you'll soon see, will prove to be a huge benefit to the project!
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