Abstract: A catalytic combustion-type, gas sensing, resistive element and the method of making it by forming an electrical conductor, whose electrical resistance varies with temperature, into a helical coil, coating the coil with a refractory material whose coating matures at a temperature in the range of 1200.degree. C to 1400.degree. C, and heating the coated coil at that temperature range until the coating matures and shrinks into a dense, gas-tight sheath about the helical coil. The coating on the helical coil is integral between adjacent loops and there is a hollow space along the longitudinal axis of the coil. The exterior of the sheath coating may then be further coated with a catalyst, catalytic wash coating, or in some embodiments the hollow space is filled with a porous catalytic material such as platinum and the ends of the hollow space are capped with a porous refractory ceramic material.

Abstract: A catalytic combustion-type, gas sensing, resistive element and the method of making it by forming an electrical conductor, whose electrical resistance varies with temperature, into a helical coil, coating the coil with a refractory material whose coating matures at a temperature in the range of 1200.degree.C to 1400.degree.C, and heating the coated coil at that temperature range until the coating matures and shrinks into a dense, gas-tight sheath about the helical coil. The coating on the helical coil is integral between adjacent loops and there is a hollow space along the longitudinal axis of the coil. The exterior of the sheath coating may then be further coated with a catalyst, catalytic wash coating, or in some embodiments the hollow space is filled with a porous catalytic material such as platinum and the ends of the hollow space are capped with a porous refractory ceramic material.