Patent GB-557765-A (GB)
Title: Improvements in or relating to electrical resistance elements
IPC: G01K1/14
Filed: 1942-08-08
Abstract: 557,765. Temperature variable resistances ; wire resistances; resistance casings and mountings;  couplings. SANGAMO WESTON, Ltd. Aug. 8, 1942, No. 11126. Convention date, Sept. 30, 1941. [Classes 37 and 38 (i)] A resistance bulb, particularly for a resistance thermometer, has a coupling tube 5, Fig. 1, which is telescoped into the tubular end of a protective metal shell 16 closed at one end and containing a resistance element 2, the junction of the coupling tube 5 and shell 16 and the space between the leadin wires 6 and the coupling tube 5 through which they pass being hermetically sealed. A thin metal tube 1 of aluminium or aluminium alloy has double threads pressed or rolled therein to form grooves in which the bare resistance wire 2, of nickel or alloy, is positioned. A depression 3 between adjacent grooves provides an anchor for the central portion of the resist. ance winding. An insulating layer of oxide is formed on the grooved tube 1 by anodizing, The upper end of the tube 1 fits over and is cemented to an insulat. ing bushing 4 of lava &c. which is counterbored from its opposite ends to reduce its thermal capacity. The lower end of the coupling tube 5 fits into the upper counterbore in the bush ing 4 and is sealed ir place, together with the lead-in wires 6, by insulating material 7 such as glass. The lead-in wires 6 pass through holes in the bushing 4 and are secured by screws 11 in transverse connectors 10. The other end of each connector is screwed to receive a nut 12, Fig. 4, which clamps one end of the resistance wire 2 between a spring washer 13 and a washer 14 formed with a projecting tongue which fits into a groove to prevent rotation. The protective metal shell 16 fits over the grooved tube 1 and the upper section of the coupling tube 5 and is outwardly flared at its upper end to receive solder or cement 17 to seal the joint. The shell 16 may be of aluminium anodized on its inner surface, or it may be formed of stainless steel, silicon bronze, or other corrosion-resisting alloy, in which case the resistance wire 2 is insulated by spraying with lacquer and baking. The outer ends of the lead-in wires 6 extend through and are soldered to tubular terminals 18, which are secured within a metal sleeve 19 by insulating material 20 moulded into grooves in the inner wall. The sleeve 19 has an enlargement 21 which is coned on its upper side and has a thin flange 22 at its lower end which is spun over the flared upper end of the shell 16. The lower end of the shell 16 is closed by a plug 23 which seats against a washer 24 and is sealed by solder or cement 25. An insulating sleeve 26 of glass fibre &c. is slipped over one or both of the lead-in wires 6 to prevent short circuiting. One terminal of the resistance winding may be grounded to the shell by embedding a loop of one of the lead-in wires 6 in the solder 17. Fig. 6 shows a mounting for the resistor bulb for measuring the temperature of free air adjacent to an aircraft. A mounting head 27 is counterbored from its outer end to receive the resistor bulb unit and a gland nut 28 is secured in to engage the outer conical surface of the enlarged part 21 of the sleeve 19 so as to clamp the unit in the head. A wind scoop and protective shell 29 is clamped between a shoulder on the head 27 and a bracket 30 by a nut 31. A double contact connector 33 on the end of a cable 34 is fitted over the terminals 18 and secured by a nut 35. A mounting head for screwing into a tapped hole in a container, such as the cooling jacket of an engine cylinder, is shown in Fig. 9. A central hole in the head has a coned portion against which the conical flange 22 of the sleeve 19 of the resistor bulb unit is clamped by a gland nut 41, rotation of the unit being prevented by a pin (not shown). Enclosed within the mounting head are a cable coupling member 48 and the cable end 49, which is held by a packing 50 of hemp &c. compressed by a gland 51 and nut 52. The portion 47 is hexagonal to take a wrench. In some applications, for example, a clinical thermometer, a mounting head is dispensed with and the connections to the measuring circuit are made directly to the lead-in wires 6.