A Low-Power, Hypsometer-Type Barometer for Remote Weather Stations

A low power barometer for remote weather stations but meeting the requirements for airports and manned meteorological stations uses the condensation temperature of CS₂ to determine the baro- metric pressure (P). A heated cylindrical bulb with a re-entrant well for a thermistor through the bottom and an internal radiation shield is 1/3 filled with CS₂. Helical springs assist CS migration on wetted surfaces and allow liquid and vapour to pass one another in the small diameter exit-condenser tube. A miniature dewar gives thermal insulation and a .01 mm. beryllium copper diaphragm transmits the external pressure. The condensation temperature is read with a simple Wheatstone bridge and dc Amplifier giving an out- put V₀= .5(P-100Pa) volts. Pulsed power with the pulse length controlled by a second thermistor on the outlet tube is used for efficiency. Long term tests of a number of barometers have given power levels around 40 mW at 20°C, and indicated maximum drifts of ±50 Pa/yr.,±10 Pa/day and ±2 Pa short term.