Sensitive aneroid diaphragm capsule with no deflection above a selected pressure

Abstract

A sensitive diaphragm capsule has been designed in which the two corrugated diaphragms nest into each other at external air pressures above a desired value. Evacuated capsules of this type have particular application in measuring pressure with radio sondes of the Diamond-Hinman-Dunmore type, where the deflection of the contact arm is fixed. At the ground level the diaphragms are designed to nest into each other and deflection does not begin until the air pressure is reduced to the value called the cut-off pressure. Several elements of two capsules each were constructed .with a cut-off pressure of 140 millibars. When installed in a radio sonde in place of the usual t ype, which is responsive over the entire range of pressures, a sevenfold increase in sensitivity in pressure measurement was obtained at altitudes above 46,000 feet.In measuring air pressure with radio sondes of the DiamondHinman-Dunmore type, l where the motion of the pressure contactor is a fixed distance, it IS desirable, in some cases, to increase the sensitivity at high altitudes. To secure this increase in sensitivity, a disphragm capsule has been des~ned at the National Bureau of Standards, the two diaphragms of whIch, when evacuated and sealed off in accordance with the usual practice for capsules used to measure atmospheric pressure, nest into each other at air pressures greater than a selected value. At pressures less than this cut-off value, the capsule deflects normally. The nesting of the diaphragms prevents damage to the relatively sensitive diaphragms, which might be caused by excessive differential pressures. The new diaphragm element is designed so that the contact arm of the radio sonde deflects over the same distance for the pressure interval from the cut-off to zero pressures, as does the ordinary element from sea level to zero pressures.The capsule, at zero pressure, is shown diagrammatically in figure 1. The connections needed for evacuating the capsule and for attachment to the radio sonde are not shown in figure 1. It is apparent from the form of the capsule that, as the air is evacuated from its interior, it will gradually collapse and finally, at a definite differential pressure, the two diaphragms will nest into each other and remain nested for larger external pressures. The evacuated capsule starts deflecting when the air pressure is reduced to a pressure equal to the differential pressure at which nesting took place during evacuation. This is known as the cut-off pressure.A pressure element of this type, consisting of two diaphragm capsules installed in a Diamond-Hinman-Dunmore radio sonde made by I Harry Diamond, Wilbur S. Hinman.Ir., Bnd Francis W. Dunmore, A method/or the inot8tigatiMI o/upper· air phenomena and it. application to radio meteorographl/.

An improved radio sonde and its performance

“…Thus, for the pressure element, the arrangment devised by Brombacher, Goerke, and Cordero [6] may be used, giving measurements …”