GB842037A - Improvements in and relating to pressure measuring apparatus - Google Patents

Abstract

842,037. Pressure gauges. VICTORY ENGINEERING CORPORATION. Dec. 17, 1957, No. 39157/57. Class 106 (2). [Also in Group XXXVIII] In a pressure measuring device of the hypsometer type, two thermistors 15, Fig. 1, are located at one end of a fibreglass wick 13, the other end of which extends into a mass 12 of glass wool packing saturated with a liquid having a stable high boiling point, e.g. methylcyclopentane, and a heater element 14 around the wick is energized from a D.C. source 26 to boil the liquid, a control thermistor 20, disposed around a constricted portion 18 of the elongated container 10 which holds the saturated glass wool, being connected in the heater circuit to vary the heater output in accordance with changes in the temperature of the liquid. Liquid without glass wool packing may be used in suitable cases. The lower portion of container 10 is encased in a housing 21 and surrounded by a heat-insulating material; if the latter is selfsupportingly rigid, as is e.g. " Styrofoam " (Registered Trade Mark), the housing 20 may be dispensed with. The upper portion of container 10 provides a cool surface on which the vapour from the wick 13 may condense. A shunt resistor 24 for connection to the control thermistor is fixed to the housing 20 or the insulation 22; alternatively, several control thermistors, with or without shunts, may be used. Fig. 3 shows a D.C. bridge circuit into which either thermistor 15 may be connected by a switch 30, the bridge output being applied to a modulation circuit 32. Alternatively, the thermistors may be connected directly into a suitable modulation circuit.