GB596993A - Compensating system for a condition-responsive measuring instrument - Google Patents

Abstract

596,993. Pressure gauges; indicating-apparatus. WEINGART, R. I. N. May 31, 1945, No. 13661. Convention date, April 21, 1943. [Classes 106 (ii) and 106 (iv)] In an instrument movement having rotary driving and driven members, incorporating a helix and spring means to maintain contact during return movement, the driving member is rotated by a condition-responsive element influenced by the quantity to be measured and the driven member is displaced axially by a condition-responsive element influenced by a qualifying factor to produce a compensating effect. In a pressure gauge as shown in Fig. 1, the pressure to be measured is communicated to the inside of a capsule 28, exposed externally to atmospheric pressure, and the resultant movement, due to any change of pressure, is transmitted to a pivoted driving arm 21, slotted to engage a helix 12 on a driven indicator shaft 11, which is under the action of a spring 18. Atmospheric pressure acting on a second capsule 38 causes a compensating movement of the indicator by transmitting an axial thrust to the indicator shaft 11 through a pivoted arm 43 and so eliminates the effect of changes in atmospheric pressure from the indication. Similarly, changes in ambient temperature can be eliminated from the indications of a thermometer as shown in Fig. 2, wherein a bulb 64 is exposed to the temperature to be measured and is connected through a capillary tube 63 to a Bourdon tube 60 which supplies a drive to the indicator while a capillary tube 80 is exposed to the ambient temperature and influences a capsule 82 which supplies the compensating drive. Alternative linkwork between capsule and driven shaft, incorporating an extensible driving arm, is described. To compensate for the temperature of an instrument casing alone, a bimetallic strip may be substituted for capillary tube and capsule. As shown in Fig. 5, the helix may be formed on a cylinder 127 keyed to the indicator shaft to allow longitudinal, but not rotative, relative movement, the axial thrust from the driving arm 132 of the compensating device being applied to the cylinder 127. The system may be used to show, in a measuring instrument, the differential in movement of two separate elements responsive to changes in conditions, as, for example, in maintaining equal pressure in two boilers and the system may be used to indicate the sum of two movements. Specifications 557,617, 557,639 and 583,901 are referred to.