GB2034478A - A pressure gauge having an aneroid capsule - Google Patents

Abstract

A pressure gauge comprises an aneroid capsule 10 having two spring facing membranes (11 and 12). A first capacitor plate (17) is disposed inside the capsule (10) facing a portion (18) of the second membrane (12) which portion (18) constitutes a second capacitor plate. An insulated conductor (16) is secured to and passes through the first membrane (11) at or near the point where the amplitude of movement of a first membrane (11) is at a maximum. The first capacitor plate (17) is fixed to the inner end of the conductor (16). The pressure gauge is suitable for use in radiosondes. <IMAGE>

Description

SPECIFICATION A pressure gauge having an aneroid capsule The present invention relates to a pressure gauge having an aneroid capsule particularly for radiosondes, in which the relative displacement of the aneroid capsule 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 fix one membrane of the aneroid capsule on the chassis of the instrument and the other membrane of the aneroid capsule on the moving condenser plate against which there is a fixed condenser plate.

With this arrangement the movements of the aneroid capsule membranes can be made movements of the condenser plates and thence to a capacitive signal, which is the measuring unit for pressure measurement. Pressure gauges of this type are particularly used in radio-sondes.

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

According to the present invention there is provided a pressure gauge comprising an aneroid capsule having first and second facing membranes, a first capacitor plate disposed inside the capsule facing a portion of the second membrane, said portion constituting a second capacitor plate, and an insulated conductor which is secured to and passes through the first membrane at or near the point where the amplitude of movement of the first membrane is at a maximum and to which the first capacitor plate is fixed.

The capacitance between the capacitor plates is dependent upon, and may be proportional to the pressure.

This invention can provide a pressure 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 condenser. In pressure gauges known so far this influence has caused non-linearity and measuring errors.

This invention can provide a construction in which temperature dependence based on the construction itself can be controlled more easily than in construction known so far.

An embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure lisa plan view of a pressure gauge in accordance with the invention; and Figure2 is a sectional view along line ll-ll of Figure 1.

The pressure transmitter shown in the Figures is based on the use of an aneroid capsule 10. The construction of this aneroid capsule in itself is of an ordinary type and comprises two spring membranes 11 and 12 pressure-tightly interconnected at their edges. The spring constant of spring membranes 11 and 12 determines the behaviour in aneroid capsule 10 as a pressure gauge.

In aneroid capsule 10 there is a vacuum space 20, in which space there is, a condenser plate 17, that is preferably a circular disk. Condenser plate 17 is, at its centre 19, resistance butt-welded on an inlet pin 16.

In said inlet assembly there is a sleeve 14 attached in the opening of the centre part of the spring membrane 11; in the interior of this cylinder 15 there is an insulator cylinder 15, through which cylindrical inlet pin 16 extends.

Thus, condenser plate 17 is rigidly connected, by means of inlet pin 16, with spring membrane 11. In the other membrane 12 there is, opposite to condenser plate 17, a plane-formed section 18 of similar size and shape to the condenser plate 17.

The distance d(p) between condenser plates 17 and 18 is essentially linearly dependent on pressure p influencing on aneroid capsule 10 in such a way that the higher is pressure p the smaller is gap d(p).

The sensitivity range of the gauge can be selected by choosing radius r of condenser plates 17 and 18 suitably and by locating condenser plate 17 at a suitable distance from counterplate 18.

As shown in Figure 2, the capacitance C to be measured can be read between the inlet pin 16 and membrane 12 of the aneroid capsule.

As the "hot" condenser plate 17 is protected in the aneroid capsule, the stability and mechanical solidity of the structure is good. The "air gap" of the condenser is further formed inside the aneroid capsule vacuum, which makes ambient temperature and pressure have no influence on the results of measurements.

The invention is by no means restricted to aforementioned details which may vary within the framework of the invention.

1. A pressure gauge comprising an aneroid capsule, having first and second facing membranes, a first capacitor plate disposed inside the capsule facing a portion of the second membrane, said portion constituting a second capacitor plate, and an insulated conductor which is secured to and passes through the first membrane at or near the point where the amplitude of movement of the first membrane is at a maximum and to which the first capacitor plate is fixed.

2. A pressure gauge in accordance with claim 1, wherein the first capacitor plate is generally circular, the said portion of said second membrane is generally circular, and said conductor is secured to and passes through the centre of the first membrane.

3. A pressure gauge in accordance with claim 1 or claim 2, wherein a sleeve is attached to an opening in the middle of the first membrane, an insulator cylinder is disposed within said sleeve, and the conductor is constituted by a pin which passes through the insulator cylinder and to whose inner end the first capacitor plate is fixed.

4. A pressure gauge in accordance with claims 1, 2 or 3, wherein the construction of the pressure gauge is generally circular and symmetrical as to the centre line of aneroid capsule.

5. A pressure gauge substantially as hereinbe

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

Claims (5)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION A pressure gauge having an aneroid capsule The present invention relates to a pressure gauge having an aneroid capsule particularly for radiosondes, in which the relative displacement of the aneroid capsule 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 fix one membrane of the aneroid capsule on the chassis of the instrument and the other membrane of the aneroid capsule on the moving condenser plate against which there is a fixed condenser plate. With this arrangement the movements of the aneroid capsule membranes can be made movements of the condenser plates and thence to a capacitive signal, which is the measuring unit for pressure measurement. Pressure gauges of this type are particularly used in radio-sondes. An object of this invention is to provide a pressure gauge construction that is simpler, cheaper, is mechanically more stable and has fewer partsthan earlier pressure gauge types. According to the present invention there is provided a pressure gauge comprising an aneroid capsule having first and second facing membranes, a first capacitor plate disposed inside the capsule facing a portion of the second membrane, said portion constituting a second capacitor plate, and an insulated conductor which is secured to and passes through the first membrane at or near the point where the amplitude of movement of the first membrane is at a maximum and to which the first capacitor plate is fixed. The capacitance between the capacitor plates is dependent upon, and may be proportional to the pressure. This invention can provide a pressure 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 condenser. In pressure gauges known so far this influence has caused non-linearity and measuring errors. This invention can provide a construction in which temperature dependence based on the construction itself can be controlled more easily than in construction known so far. An embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure lisa plan view of a pressure gauge in accordance with the invention; and Figure2 is a sectional view along line ll-ll of Figure 1. The pressure transmitter shown in the Figures is based on the use of an aneroid capsule 10. The construction of this aneroid capsule in itself is of an ordinary type and comprises two spring membranes 11 and 12 pressure-tightly interconnected at their edges. The spring constant of spring membranes 11 and 12 determines the behaviour in aneroid capsule 10 as a pressure gauge. In aneroid capsule 10 there is a vacuum space 20, in which space there is, a condenser plate 17, that is preferably a circular disk. Condenser plate 17 is, at its centre 19, resistance butt-welded on an inlet pin 16. In said inlet assembly there is a sleeve 14 attached in the opening of the centre part of the spring membrane 11; in the interior of this cylinder 15 there is an insulator cylinder 15, through which cylindrical inlet pin 16 extends. Thus, condenser plate 17 is rigidly connected, by means of inlet pin 16, with spring membrane 11. In the other membrane 12 there is, opposite to condenser plate 17, a plane-formed section 18 of similar size and shape to the condenser plate 17. The distance d(p) between condenser plates 17 and 18 is essentially linearly dependent on pressure p influencing on aneroid capsule 10 in such a way that the higher is pressure p the smaller is gap d(p). The sensitivity range of the gauge can be selected by choosing radius r of condenser plates 17 and 18 suitably and by locating condenser plate 17 at a suitable distance from counterplate 18. As shown in Figure 2, the capacitance C to be measured can be read between the inlet pin 16 and membrane 12 of the aneroid capsule. As the "hot" condenser plate 17 is protected in the aneroid capsule, the stability and mechanical solidity of the structure is good. The "air gap" of the condenser is further formed inside the aneroid capsule vacuum, which makes ambient temperature and pressure have no influence on the results of measurements. The invention is by no means restricted to aforementioned details which may vary within the framework of the invention. CLAIMS

1. A pressure gauge comprising an aneroid capsule, having first and second facing membranes, a first capacitor plate disposed inside the capsule facing a portion of the second membrane, said portion constituting a second capacitor plate, and an insulated conductor which is secured to and passes through the first membrane at or near the point where the amplitude of movement of the first membrane is at a maximum and to which the first capacitor plate is fixed.

2. A pressure gauge in accordance with claim 1, wherein the first capacitor plate is generally circular, the said portion of said second membrane is generally circular, and said conductor is secured to and passes through the centre of the first membrane.

3. A pressure gauge in accordance with claim 1 or claim 2, wherein a sleeve is attached to an opening in the middle of the first membrane, an insulator cylinder is disposed within said sleeve, and the conductor is constituted by a pin which passes through the insulator cylinder and to whose inner end the first capacitor plate is fixed.

4. A pressure gauge in accordance with claims 1, 2 or 3, wherein the construction of the pressure gauge is generally circular and symmetrical as to the centre line of aneroid capsule.

5. A pressure gauge substantially as hereinbe fore described with reference to the accompanying drawing.