GB1249052A - Improvements in or relating to condition responsive apparatus - Google Patents

Abstract

1, 249, 52. Reading indicators photoelectrically. DRESSER INDUSTRIES Inc. Jan. 31, 1969 [April 12, 1968], No.5441/69. Heading G1A. The movement of a slotted vane indicating pressure, temperature, fluid-flow, motion, weight &c. is detected by a pair of photo-cells connected in a bridge circuit, imbalance of the bridge actuating a mechanism driving the slotted vane to a null position and simultaneously indicating the measured variable. The vane 150 is actuated by a Bourdon tube 13 and the driving mechanism comprises a D. C. servomotor 164 driving a lead screw 44 through a gear-train 46, 48, 47, 49, 53. On the lead screw is a block 43 which urges the vane to a null position by means of a spring 42 and simultaneously traces a record with pen 54. Further bevel gears 53 co-operating with gear 49 provide digital read-out on a counter 51 and printer 52. A frameless direct drive servomotor may be placed operatively around the lead screw, thus eliminating the gearing. A variable range span is achieved by coupling the spring 42 to the Bourdon tube through an arm 174, Fig. 3 supported by leaf springs 175, 176 and adjustable slides 180, 181 connected by a leaf-spring 186. Temperature compensation is provided by mounting the vane 150 on a bi-metallic strip 187, and by including a thermister in the bridge circuit. Non- linearity in the properties of spring 42 are compensated by angular adjustments in the position of block 43 caused by a pin 190 running in a curved slot 191.