From: robin_listas@es.invalid   
      
   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🇪🇺;   
      
   --- SoupGate-Win32 v1.05   
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