J
Jim Wilkins
Curbie said:Hi Jim,
Good stuff as always.
I did tried multiple thermocouples to even out the variations in their
alloy compositions and statistical averaging to average out noise on
the wires, then calibrated with temperature sensors, and was never
able to get the thermal couples to maintain <1C in relation to the
temperature sensors. Probably just me, through I got 2 batches a 3
DS18B20 temperature sensors from 2 two different sources and they read
<.5C between all senses between both batches, just cheapo
thermocouples I guess.
Curbie
I've done a lot of temperature testing of the environmental test chambers I
built and always had a hard time with the thermocouples. The twisted wires
don't make good contact with flat hot surfaces so some of the heat leaks
away to the air or down the wires. Tying them down under insulation helps
somewhat. I have the best results with thermocouples tightly jammed into
drilled holes that are deep enough to heat the lead wires. The thermowell I
made yesterday to measure flue temperature is a 3/4" long bolt drilled down
the center from the head end 0.500 deep at 0.140" to clear the insulation,
then a further 0.200" at 0.075" diameter to jam in the bare twisted 20AWG
wires.
The ones I checked with boiling water didn't agree until I stuck them all in
about four inches through the teapot's whistle vent, in the steam above the
water. The bottom of the kettle read about 101C.
I use all type K because my most demanding use is checking the annealing and
hardening temperatures of tool steel. Other types like E, J or T may be
better for you.
http://www.omega.co.uk/temperature/pdf/Thermocouple_Tolerance.pdf
After welding the wires together you can hammer them flat.
jsw