GB2035567A - A pressure gauge - Google Patents

Abstract

A pressure gauge is based on the use of an aneroid capsule (10) and has membranes (11, 12) of the insulating material e.g. glass or a plastics material. Opposed capacitor plates (21, 22) are provided on the outer surfaces of the insulating membranes (11, 12). The capacitance to be measured is that between the capacitor plates (21, 22).

Description

SPECIFICATION A pressure gauge The present invention relates to a pressure gauge based on the use of an aneroid capsule particularly for use in radiosondes, which gauge the relative positions of the aneroid gauge membranes is transformed into a capacitance dependent upon the pressure to be measured.

A previously known system is to use an aneroid capsule as a pressure gauge in such a way so as to fasten one membrane of the aneroid capsule to the chassis of the instrument and the other membrane of the aneroid capsule to the moving capacitor plate facing which there is a fixed capacitor plate. With this arrangement the relative movements of the aneroid capsule membranes can be made relative movements of the capacitor plates. An output signal is derived and representative of the capacitance and therefore of the pressure. This kind of pressure gauges are particularly used in radiosondes.

An object of this invention is to provide a pressure gauge construction that is simpler, cheaper, and mechanically more stable, and has fewer parts than earlier pressure gauge types.

An additional object is to provide such a gauge in which it is possible to eliminate the influence of ambient moisture and pressure on the dielectric coefficient of the air gap of the measuring capacitor.

In pressure gauges known so far this influence has caused non-linearity and measuring errors. Another object is to provide a construction in which temperature dependence e.g. heat expansion based on the construction itself can be controlled more easily than in constructions known so far.

According to this invention there is provided a pressure gauge comprising an aneroid capsule having first and second membranes of insulating material, and first and second capacitor plates secure on the outer surfaces of the first and second membranes respectively, the capacitance to be measured being that between said capacitor plates.

An exemplary embodiment of this invention will now be described with reference to the accompanying drawings, of which: Figure 1 is a plan view of a pressure gauge in accordance with the invention; and Figure 2 shows sectional view ll-ll in Figure 1.

Aneroid capsule 10 of a pressure gauge in accordance with the invention is made of insulating material, for instance plastic or glass, but preferably glass due to its favourable temperature dependence prop erties.

Aneroid capsule 10 comprises two spring mem branes 11 and 12 made of glass; these spring mem branes 11 and 12 being fastened at their edge sections pressure-tightly to each other so as to leave a vacuum chamber 14 between them. On the outer surfaces of glass membranes 11 and 12 there are provided capacitor plates 21 and 22 made, for instance, by vacuum i.e. vaporating metal on the glass membranes 11 and 12. These plates form capacitance C on which the pressure measurement is based. As the pressure influencing on aneroid capsule 10 changes, the distance d(p) between capacitor plate 21 and capacitor plate 22 also changes thus making it possible to measure the pressure by measuring capacitance C of the capacitorformed by plates 21 and22.

A particular advantage of the construction of a pressure gauge in accordance with the invention is, forinstance,that no inlets are required. Another advantage is the very low temperature dependence of glass.

The invention is by no means restricted to aforementioned details described only às an example; they may vary within the framework of the invention as defined in the following claims.

1. A pressure gauge comprising an aneroid capsule having first and second membranes of insulating material, and first and second capacitor plates secure on the outer surfaces of the first and second membranes respectively, the capacitance to be measured being that between said capacitor plates.

2. A pressure gauge in accordance with claim 1, wherein the first and second membranes of the aneroid capsule (10) are of glass.

3. A pressure gauge substantially as hereinbefore described with reference to the accompanying drawings.

The drawing originally filed was informal and the print here reproduced is taken from a later filed formal copy.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (3)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION A pressure gauge The present invention relates to a pressure gauge based on the use of an aneroid capsule particularly for use in radiosondes, which gauge the relative positions of the aneroid gauge membranes is transformed into a capacitance dependent upon the pressure to be measured. A previously known system is to use an aneroid capsule as a pressure gauge in such a way so as to fasten one membrane of the aneroid capsule to the chassis of the instrument and the other membrane of the aneroid capsule to the moving capacitor plate facing which there is a fixed capacitor plate. With this arrangement the relative movements of the aneroid capsule membranes can be made relative movements of the capacitor plates. An output signal is derived and representative of the capacitance and therefore of the pressure. This kind of pressure gauges are particularly used in radiosondes. An object of this invention is to provide a pressure gauge construction that is simpler, cheaper, and mechanically more stable, and has fewer parts than earlier pressure gauge types. An additional object is to provide such a gauge in which it is possible to eliminate the influence of ambient moisture and pressure on the dielectric coefficient of the air gap of the measuring capacitor. In pressure gauges known so far this influence has caused non-linearity and measuring errors. Another object is to provide a construction in which temperature dependence e.g. heat expansion based on the construction itself can be controlled more easily than in constructions known so far. According to this invention there is provided a pressure gauge comprising an aneroid capsule having first and second membranes of insulating material, and first and second capacitor plates secure on the outer surfaces of the first and second membranes respectively, the capacitance to be measured being that between said capacitor plates. An exemplary embodiment of this invention will now be described with reference to the accompanying drawings, of which: Figure 1 is a plan view of a pressure gauge in accordance with the invention; and Figure 2 shows sectional view ll-ll in Figure 1. Aneroid capsule 10 of a pressure gauge in accordance with the invention is made of insulating material, for instance plastic or glass, but preferably glass due to its favourable temperature dependence prop erties. Aneroid capsule 10 comprises two spring mem branes 11 and 12 made of glass; these spring mem branes 11 and 12 being fastened at their edge sections pressure-tightly to each other so as to leave a vacuum chamber 14 between them. On the outer surfaces of glass membranes 11 and 12 there are provided capacitor plates 21 and 22 made, for instance, by vacuum i.e. vaporating metal on the glass membranes 11 and 12. These plates form capacitance C on which the pressure measurement is based. As the pressure influencing on aneroid capsule 10 changes, the distance d(p) between capacitor plate 21 and capacitor plate 22 also changes thus making it possible to measure the pressure by measuring capacitance C of the capacitorformed by plates 21 and22. A particular advantage of the construction of a pressure gauge in accordance with the invention is, forinstance,that no inlets are required. Another advantage is the very low temperature dependence of glass. The invention is by no means restricted to aforementioned details described only às an example; they may vary within the framework of the invention as defined in the following claims. CLAIMS

1. A pressure gauge comprising an aneroid capsule having first and second membranes of insulating material, and first and second capacitor plates secure on the outer surfaces of the first and second membranes respectively, the capacitance to be measured being that between said capacitor plates.

2. A pressure gauge in accordance with claim 1, wherein the first and second membranes of the aneroid capsule (10) are of glass.

3. A pressure gauge substantially as hereinbefore described with reference to the accompanying drawings.

The drawing originally filed was informal and the print here reproduced is taken from a later filed formal copy.