On 2026-03-04 21:59,
peter@easthope.ca wrote:
Anyone worked with copper-constantan thermouples? How are the two
wires joined?
Good thermocouples use special cables that have wires made of copper and constantan, to avoid having extra joints in the way to the electronics.
You don't need to weld them, even twisting together the wires of the
cable creates a sensor, and it works.
A dry bath heats a block of aluminum which has holes to receive test
tubes. Temperature is controlled by a Cal Controls # 3200. The
heating pad heats when power is applied but the relay in the 3200
never switches. So I wonder whether the fault is in the 3200 or the thermocouple.
Can heat the thermocouple and measure voltage across the two wires. https://its90.nist.gov/downloadFiles/type_t.tab.txt
Not sure a common multimeter has the precision to detect a faulty thermocouple.
Some multimeters have a scale to measure temps with a thermocouple, and
the proper socket.
Notice that the setup actually has two joints, one at the sensor and
another (same loop) at the electronics board. The thing measures
temperature differences between the two joints, so there is another type
of sensor (ex.: thermistor) near the second joint. Think that the
constantan wire has to join the electronic board metals at some point.
Ideas?
My experience (old) is with sensors and measurements. The setup used in heaters is different.
Sometimes we had failures and the answer was to replace sensor or
cables. We did not study why they failed. We just tried a spare sensor,
and if it worked, problem solved. We had a bunch of them. Once we had
the vendor give us a lecture :-)
Thx, ... P.
--
Cheers, Carlos.
ES??, EU??;
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