Variable resistor with strain-reducing attachment means for the substrate

Claim 1

An adjustable electrical resistor device having a temperature coefficient of resistance within + OR - 3 parts per million per * C. over the range of -55* C. to +125* C., which resistor device consists essentially of: a substrate; an isolating layer of a dielectric on one face of said substrate, said isolating layer being substantially free of creep under normal operating temperatures; a metallic film 0.00002 to 0.0004 inches thick, made from resistive bulk metal held in place adjacent to one face of the substrate by the isolating layer which provides faithful strain transmission from the substrate to the metallic film, wherein said metallic film is provided with openings for restricting and rendering tortuous the conductive path therein and thereby impeding the flow of electrical current from one end of the metallic film to the opposite end thereof; a conductive strip held in place on one face of the substrate by the isolating layer adjacent to the metallic film without contacting the metallic film; a multifingered movable contact means for contacting the conductive strip and the metallic film and thereby establishing an electrical connection between the conductive strip and the metallic film at a variable distance from one end of the resistor device; a housing for the adjustable electrical resistor device; a shaft rotatably mounted in said housing, said shaft having a threaded section for engaging and moving the multifingered movable contact means; and nonconducting attachment means interposed between the substrate and the housing which minimizes strains induced in the substrate by differences of expansion characteristics of the substrate and housing, said nonconducting attachment means contacting only a small area of the substrate and said nonconducting attachment means being noncontinuous between the substrate and the housing.