Electric cartridge heater with a multiple thermocouple assembly

Claim 1

An elongate cartridge heater and thermocouple unit comprising an elongate normally cylindrical outer tubular metal sheath with open ends, an elongate normally cylindrical inner tubular metal tube with open ends concentric with and extending freely through the sheath in spaced parallel relationship therewith and defining an annulus, a plurality of axially aligned pairs of normally cylindrical thermocouple cables and spacer rods fixed to the exterior of the tube in circumferential spaced parallel relationship therewith and extending longitudinally through the annulus in interfering engagement with the sheath, plugs at and closing the ends of the tube and the sheath, an elongate resistance element substantially concentric with and extending longitudinally through the tube in spaced parallel relationship therewith and between the plugs, elongate conductor terminals at the ends of the element and each extending axially outwardly through and from a related plug and a filler of particulate dielectric material compacted in the tube about the element and in the annulus between the pairs of cables and rods, sheath, tube and plugs, the cables having outer end portions with thermocouple conductors accessible at free outer ends thereof extending axially through and from the plug at a related end of the annulus and having inner ends with thermocouple junctions, said cables being of different longitudinal extent and positioned with their junctions in contact with the sheath at spaced points longitudinally thereof, said rods being of different longitudinal extent and each having an inner end in close proximity with the junction of its related cable and an outer end terminating in close proximity with a related end of the annulus, said sheath being a strong substantially rigid supporting part, said tube being a relatively weak yieldable part orienting the cables and rods in the sheath.