GB715388A - Improvements in or relating to electrical measuring and like instruments in hermetically sealed casings - Google Patents

Abstract

715,388. Indicating-apparatus. SANGAMO WESTON, Ltd. April 18, 1952 [June 2S, 1951], No. 15060/51. Class 106 (4). [Also in Groups XXII and XXXVI] A method of making an hermetic seal between the parts of an instrument casing in such a way that the parts may be easily separated for e.g. servicing, comprises shaping the parts to be sealed to present a narrow groove into which is placed a loop of thin wire which is buried in solder, the parts being separated by tearing out the wire by an exposed end. The back plate 3, Fig. 1, of an instrument with a cylindrical body 1, is dished at its periphery to provide a lip 3a, leaving a circumferential groove into which is placed a thin steel wire 8, Fig. 3, and the groove filled with soft solder 10, one or both ends of the wire being brought out through a narrow slot in the lip 3a. Other forms of lap joint between the casing and end plate are described. The internal functional parts of the instrument may be mounted on a plate 15 having a spring expanding wire 15a in a circumferential groove. Electrical connections are provided by ceramic terminals comprising a threaded portion 4 and a conducting flange 6, one terminal being hollow, for testing the hermetic seal. A socket for connecting external leads to the terminals 4 consists of an insulating block 20, Fig. 8, containing sleeves 22, captive female screws 21, and lugs 23 to which the external leads are soldered. The sleeve 22 is free to move axially and is screwed down on terminal 4 by the: screw 21. A cable entry block 28, Fig. 10, is provided on the socket wherein the cable 29 is gripped by a saddle 30 and grub screws 31. In an alternative socket and terminal arrangement a metal plug body 67, Fig. 17, is soldered to a hole in the back plate 3, thereby securing a clip 66 with two spring prongs 65. A glass-metal terminal seal 69 is then soldered into the plug body 67, reinforced by a backing ring 71. The socket comprises a fixed metal ferrule 74 secured on a rubber covered connecting cable 73 terminating in sockets 76, leaving a small flange 75 of rubber at the end, and a ferrule 77, which is loose on the cable 73, is screwed to the plug body 67. A clamp for fixing the instrument to a panel 49, Figs. 11, 12, comprises a metal strip 50 carrying a threaded block 51 permanently held by a screw 58, and a threaded block 52 taking a screw 53, subsequently locked by a nut 55 and washer 54. The ends of strip 50 are adjustably secured to block 52 by rivets 56, Fig. 13, sliding in inclined slots 57, to exert a wedge action as screw 53 is tightened. A fixing flange may alternatively be connected to the expanded rim la of the casing.