| 摘要 |
PROBLEM TO BE SOLVED: To ensure high accuracy measurement by providing a tubular electrode support placed on the outer circumferential surface of a tube concentrically thereto, and heat resistant conductors arranged spirally onto the inner circumferential surface of the holder and forming a source electrode, a sense electrode and a guard electrode. SOLUTION: A source electrode 3a, a sense electrode 4a and a guard electrode 5a comprising a heat resistant conductor, e.g. a thin stainless band, having a specified width are arranged spirally at an angle of 45 deg. and at a specified interval on the inner circumferential surface of an electrode holder 11. These electrodes 3a, 4a, 5a can be fixed constantly to the inner circumferential surface of the holder 11 through resiliency of the thin stainless band but they are secured, at the opposite end parts and the central part thereof, to the inner circumferential surface of the holder 11 through pins in order to deal with thermal elongation/shrinkage. Since the electrodes comprising heat resistant conductors are secured to elongate/shrink freely, each electrode elongates longitudinally depending on the temperature and constant positional relation is kept between opposite electrodes 3a, 4a.
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