Abstract
Fine K-type thermocouple is fabricated by the non-contact discharge welding, which is developed by our group, and is examined comparing with a K-type thermocouple of 0.65mm in diameter. An alumel wire and a chromel wire of 50μm diameter are fixed to butt their tips with the crossing angle of ca. 0.35rad. A tungsten needle is positioned about 50μm above the tips. High voltage of 5kV is repeatedly applied to the needle for 0.5s to generate discharge between the needle and the tips. The tips are welded after the end of 7th discharge. Three different kind of discharge are observed by the completion of welding. Thermoelectromotive force (EMF) of the fine thermocouple is almost the same with that of the thermocouple of 0.65mm diameter in the temperature range below 643K, though EDX analysis indicates that hot junction and wires near the hot junction are partly oxidized. Hot air heated at 354K is blew to the hot junctions of fine thermocouple and 0.65mm thermocouple at the same time, and variation of their EMF is recorded with a digital oscilloscope. The heat response rates, which is defined by the initial increasing rate of EMF, of the fine thermocouple and the 0.65mm thermocouple are 870K/s and 22K/s, respectively.
