Patent GB-702636-A (GB)
Title: Improvements in or relating to instruments for detecting, indicating and/or measuring linear displacements
Inventor: THIRKELL VICTOR WILLIAM
IPC: G01L7/00
Filed: 1952-03-21
Abstract: 702,636. Pressure gauges ; indicating-apparatus. EDWARDS & CO. (LONDON), Ltd., W. March 21, 1952, No. 7432/52. Classes 106 (2) and 106 (4) Apparatus for indicating linear displacements comprises a tilting element movable with a roller, mounted for rocking movement about its axis, by a taut thread coiled around the roller and secured at its ends to limbs of a resiliently movable frame carrying a feeler part in contact with a diaphragm or other displaceable element, the thread effecting movement of the tilting element in response to movement of the diaphragm or displaceable element As shown, the displacement of a diaphragm structure 6 in an optical manometer is indicated as a measure of the difference between pressures communicated through passages 10, 11 to two chambers 8, 9 respectively formed in a body composed of two halves 1, 2 which fit together and form therebetween an annular groove 3 within which is disposed two sealing rings 4, 5 for the diaphragm 6 which is located between the part 2 and a ring 7 seated on a shoulder of part 1 The chamber 9 is closed by a cover 12 sealed by a ring 13 in a groove 14 and held by screws 15. Movements of the diaphragm 6 in response to pressure differences in the chambers 8, 9 are communicated by a feeler 16 to a small mirror 17 mounted on a roller in the form of a short length of tinned copper wire 18, whose ends are flattened and soldered to a suspension strip whose outer extremities are connected to the short limbs 20 of a yoke 21 seated on an annular shoulder 22 of the part 2 The suspension is joined to the limbs 20 through the medium of U-shaped strips of phosphor bronze Movements of the feeler 16 are transmitted to the roller 18 by a thread 24 of silk, nylon or other suitable material whose ends are secured to the limbs 26 of a bow 25 after being coiled round the roller 18 The bow 25 may be of thin hard brass wire and it is formed with a coiled spring 27 with one end soldered to the yoke 21 The feeler 16 conveniently forms a continuation of the bow 25 a beam of light incident on the mirror 17 is reflected and focused on a scale by a lens 29 clamped in the centre of the cover 12 In order to be highly sensitive to small pressure variations the diaphragm structure 6 comprises two parts, a thin pliable membrane 32 and spiral spring 33, e.g. of phosphor bronze, hard brass, steel or beryllium copper wire, the membrane being of polyethylene, polytetrafluorethylene, rubberized silk or oiled silk, mica, steel or beryllium copper. The spring 33 tends to restore the membrane to a position of equilibrium, the outer convolution being soldered to a ring seated on a shoulder 34 of the ring 7 and the inner convolution secured to a metal diaphragm 35. If desired, the spring 33 may be disposed between a pair of membranes 32 or the membranes 32 may be disposed between a pair of spiral springs 33. If it is desired to support more than the outer turn of the spring 33 the shoulder 34 of ring 7 may be extended. The resilient part of the diaphragm may comprise a plurality of hairpin springs disposed in the diaphragm plane for contact with the membrane 32 or it may comprise resilient strips resembling spokes or the membrane may be in contact with a thin resilient sheet formed with spiral or other shaped slots. The invention may be applied to a comparator or to electrical measuring instruments.