Experimental work on thermocouple.
Here I have brazed a piece of enamelled copper wire on to a 100% nickel welding rod. The rod is 2.5mm diameter about a foot long. Heating the end tip with a soft oxy-acetylene flame directed only on the tip end produced an emf of 18 odd millivolts when red hot to the stage where I think the braze was about melt. I had the wire well separated from the rod (not wrapped as in photo) so I know there wasn't any shorting down at the end where the enamel could have been burning off the wire.
Next step is to make a new one with heavier wire and insulate the wire from the rod with high temp insulating cloth. I intend to then wrap high temp cloth around the lot except for about 8 mm (5/16"). Then I will cover the insulation with stainless tube or copper tube and crimp it lightly at the business end.
Later Experiments
The later experiments. I have now welded a heavier copper wire to the nickel rod. In boiling water I get 1.5 mV. When very hot almost to melting the weld I get 30.3 mV. When duller red hot the reading is 22.5 mV. I will test this set up in molten aluminium next before I proceed with any sort of covering.
Thermocouple Test continued--CLICK HERE
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Sunday, May 20, 2001