To measure temperatures in the biomeiler, I buried thermocouples in strategic locations. This is an ideal way to measure temperatures in such a situation.
The way a thermocouple works is that two types of metal are welded together and that junction is placed at the location where the temperature is to be measured. At different temperatures, the metals react in a way that produces different voltages across the junction.
If the voltage at the measurement junction is combined with the voltage of another junction at a known temperature (usually an ice-water bath) the net voltage corresponds to a specific temperature. Thus, you have an electronic thermometer with a large operational range and no moving parts.
I would like to collect my readings indoors, where I could set up my voltmeter and reference junction in a convenient manner and collect data without wearing gloves and without my breath frosting over my glasses and the voltmeter screen. The fact that LCD screens and small batteries don’t work well in Alaskan winter temperatures adds more hassle. Unfortunately, one of the difficulties with using thermocouples is that any connection with a different type of metal can cause a problem with the reading. So, I cannot extend the thermocouples with ordinary copper wire. I would have to use the same kind of wire the thermocouples are made of. An internet search tells me that buying enough of that wire would not be affordable.
Once I learned that I will have to collect measurements outdoors, I resolved to make the data collection process as simple as possible.
One improvement I made was to make a better set of probes for my voltmeter. I had some leads from a burned out voltmeter that are compatible with my remaining voltmeter. I cut the probes off the ends and soldered on some alligator clips.
I used a short length of old lamp wire to make a double-alligator jumper wire. Now I can clip together the leads from the reference junction and measurement junction and have fewer things to hold while I collect the data.
I have tested out the new meter leads and jumper wire with the thermocouples. When both thermocouples are at the same temperature, the net voltage should be zero – and it is. Nice! Interaction with the jumper wire metal is not adding any significant voltage to the system. I figured that any voltages created would be symmetrical and cancel, but the real world does not always meet my expectations.
