A low-power hypsometer-type barometer for remote weather stations

The paper describes a low-power barometer intended for remote weather stations, but also meeting the requirements for manned stations and airports, in which the condensation temperature of carbon disulphide (CS2) is used to determine the barometric 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 CS2migration on wetted surfaces and allow liquid and vapor to pass one another in the small diameter exit-condenser tube. A miniature Dewar flask gives thermal insulation and a 0.01-mm beryllium-copper diaphragm transmits the external pressure. The condensation temperature is read with a simple Wheatstone bridge and dc amplifier giving an outputV_{0} = 0.5(p- 100 Pa)V. 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 at20degC and indicated maximum drifts ofpm50Pa/year,pml0Pa/day, andpm2Pa short term.