GB2370638A

GB2370638A - Pressure-measuring device

Info

Publication number: GB2370638A
Application number: GB0126984A
Authority: GB
Inventors: Juergen Biskup
Original assignee: ABB Patent GmbH
Current assignee: ABB Patent GmbH
Priority date: 2000-11-09
Filing date: 2001-11-09
Publication date: 2002-07-03
Anticipated expiration: 2021-11-09
Also published as: GB0126984D0; DE20019067U1; GB2370638B

Abstract

A pressure-measuring device has the pressure to be measured, in a connection 9, act on a piezoresistive sensor 3 through a separating diaphragm 14 and a hydraulic fluid in spaces 16, 19, 13 and 18. The sensor 3 is protected against excess pressure by a preloaded overload diaphragm 2, on which it is mounted, which deflects on the occurrence of the excess pressure to increase the space 16 available for the hydraulic fluid. The movement of the separating diaphragm 14 under excess pressure is limited by contact with the end face of the body 1.

Description

Pressure-measuring device

The present invention relates to a pressure-measuring device having a piezoresistive pressure sensor and hydraulic force transmission.

Piezoresistive pressure sensors are distinguished by a high long-term stability, a wide deployment temperature range and a large measuring range in conjunction with low temperature dependence and high measurement dynamics. However, particularly in the case of high pressures or differential pressures, piezoresistive pressure sensors exhibit an unsatisfactory resistance to overload.

Amplifying the sensor element in order to improve the resistance in the case of overload compromises the measuring range and the measurement dynamics.

Aspects of the present invention seek to provide a pressure-measuring device having a piezoresistive pressure sensor and hydraulic force transmission, in which the piezoresistive pressure sensor is protected against impermissible overloading in the event of a high pressure load in the measuring range.

According to the present invention there is provided a pressure-measuring device having a pressure sensor and hydraulic force transmission, in which the pressure of a measuring medium is transmitted to the pressure sensor with the interposition of a separating diaphragm with the aid of a fluid pressure transmission medium, wherein the deflection of the separating diaphragm is mechanically limited to an amount prescribably exceeding a measuring range, and the pressure sensor is arranged such that it can move on a mechanically pretensioned overload diaphragm, which limits a volumetrically variable equalizing space for accepting excessive pressure transmission medium.

Embodiments of the present invention are based on a pressure-measuring device having a piezoresistive pressure sensor and hydraulic force transmission, in the case of which the process pressure of the measuring medium is transmitted to the pressure sensor with the interposition of a separating diaphragm with the aid of a fluid pressure transmission medium or transmitter.

In embodiments of the present invention, the deflection of the separating diaphragm, which is a function of process pressure and displaces the pressure transmitter, is mechanically limited to an amount prescribably exceeding the measuring range, and the pressure sensor is arranged in the pressure-measuring device such that it can move on a mechanically pretensioned overload diaphragm which, as a function of process pressure exceeding the measuring range, limits a volumetrically variable equalizing space for accepting excessive pressure transmitter.

Upon the occurrence of a process pressure exceeding the measuring range of the pressure-measuring device by the prescribed amount, the separating diaphragm is deflected up to its mechanical limitation. The force exerted by the displaced pressure transmitter in the process effects the deflection of the overload diaphragm against its pretensioning, the equalizing space being released for acceptance of the displaced pressure transmitter. As a result, the pressure sensor is loaded at most with the pressure of the upper value of the measuring range plus the prescribable excessive amount. It is possible thereby, in the case of overload, to dispense with amplification of the sensor element in order to improve the resistance. Wide measurement dynamics in conjunction with overload resistance is thereby achieved. The invention furthermore permits high static and dynamic overload factors which exceed the measuring range by a multiple.

The invention is explained in more detail below with the aid of an exemplary embodiment. Figure 1 illustrates in section a pressure-measuring device with a piezoresistive pressure sensor 3 and hydraulic force transmission. The pressuremeasuring device is constructed from a rotationally symmetrical, substantially cylindrical central body 1 which has an axial bore 13 and the first end face of which has a concentrically corrugated surface. The bore 13 is partially filled by a filling piece 17.

The first end face is connected, with the interposition of a concentrically corrugated separating diaphragm 14, to a connecting piece 8 by a weld 11. The position and the shape of the concentric corrugations of the separating diaphragm 14 and of the central body 1 correspond in such a way that the interspace 18 between the separating diaphragm 14 and the central body 1 can be evacuated as far as possible.

The connecting piece 8 is provided with an axial process pressure connection 9 which is designed with an internal thread for connection to a pipeline and opens into a chamber 10 which is formed by a flat, conical cutout in the side of the connecting piece 8 facing the central body 1.

The pressure-measuring device is fitted with a mechanically pretensioned, annular overload diaphragm 2 which is fastened on the second end face, remote from the connecting piece 8, of the central body 1 by means of a weld 7. The opening in the annular overload diaphragm 2 is sealed by a glass bushing 5 in a pressure-tight fashion by means of a weld 6. An axially arranged central tube 4 and connecting wires 12 insulated electrically from one another are led through the glass bushing 5.

The piezoresistive pressure sensor 3 is connected to the central tube 4 on the side of the glass bushing 5 facing the central body 1. The piezoresistive pressure sensor 3 can be loaded with a reference pressure by the central tube 4. The pressure sensor 3 is covered by a cap 15. The cap 15 forms an electrical and hydraulic protection for the sensitive pressure sensor 3.

On its side facing the overload diaphragm 2, the central body 1 has, while forming an equalizing space 16, a large-area, flat cutout and, while forming a sensor space 19 for holding the pressure sensor 3, has a central, deep cutout of smaller diameter.

The equalizing space 16, the sensor space 19, the free volume of the bore 13 and the interspace 18 form a common pressure space and are filled with a fluid pressure transmission medium, preferably silicone oil.

The measuring medium, which can be supplied via the process pressure connection 9, exerts a pressure on the separating diaphragm 14 which is transmitted with the aid of the pressure transmission medium, starting from the interspace 18, through the bore 13 into the sensor space 19 and further on to the pressure sensor 3. Any contact between the opt : ona) iy aggressive measuring medium and the pressure sensor 3 is thereby avoided. Any measuring medium can be applied in conjunction with a measuring mechanism which is retained unchanged by suitable selection of the materials of the separating diaphragm, and of its surface coating.

The overload diaphragm 2 is connected to the central body 1 in a pretensioned fashion.

The pretensioning is achieved by shaping the overload diaphragm 2 and/or the central body 1. The overload diaphragm 2 is preferably preformed concavely. Alternatively, the central body 1 can be preformed convexly. Finally, the overload diaphragm 2 can be preformed concavely and the central body 1 can be preformed convexly. As a consequence of the pretensioning, the overload diaphragm 2, which is firmly clamped on the outer edge by the weld 7, penetrates in a planar fashion into the equalizing space 16, which is thereby largely free of fluid in the measuring range of the pressuremeasuring device.

Upon the occurrence in the chamber 10 of a process pressure exceeding the measuring range of the pressure-measuring device, the separating diaphragm 14 bears against the first end face of the central body 1. As a result, the pressure transmission medium is displaced from the interspace 18 and pressed through the bore 13 into the sensor space 19. The pressure piling resulting therefrom in the sensor space 19 causes a lifting movement of the glass bushing 5 directed away from the central body 1, and thus a convex deformation of the overload diaphragm 2. The result is an enlargement of the volume of the equalizing space 16, which is filled by the pressure transmission medium displaced from the interspace 18.

The force exerted by pretensioning can be prescribed by the material properties of the overload diaphragm 2. The force is set such that the overload diaphragm 2 maintains its rest position at least over the entire measuring range. The force is preferably set such that the convex deformation of the overload diaphragm 2 starts at a process pressure of approximately 150% of the upper value of the measuring range.

The dosing of the filling quantity of the pressure transmission medium is advantageously not critical owing to the greater freedom of movement of the overload diaphragm 2 by comparison with the separating diaphragm 14. List of reference numerals 1 Central body 2 Overload diaphragm 3 Pressure sensor 4 Central tube 5 Glass bushing 6,7, 11 Weld 8 Connecting piece 9 Process pressure connection 10 Chamber 12 Connecting wire 13 Bore 14 Separating diaphragm 15 Cap 16 Equalizing space 17 Filling piece 18 Interspace 19 Sensor space

Claims

1. A pressure-measuring device having a pressure sensor and hydraulic force transmission, in which the pressure of a measuring medium is transmitted to the pressure sensor with the interposition of a separating diaphragm with the aid of a fluid pressure transmission medium, wherein the deflection of the separating diaphragm is mechanically limited to an amount prescribably exceeding a measuring range, and the pressure sensor is arranged such that it can move on a mechanically pretensioned overload diaphragm, which limits a volumetrically variable equalizing space for accepting excessive pressure transmission medium.

2. A pressure-measuring device according to claim 1, wherein the sensor in a piezoresistive pressure sensor.

3. A pressure-measuring device according to Claim 1 or 2, wherein the overload diaphragm is preformed concavely with reference to the equalizing space.

4. A pressure-measuring device according to Claim 1 or 2, wherein the boundary of the equalizing space opposite the overload diaphragm is convexly preformed with reference to the equalizing space.

5. A pressure-measuring device according to Claim 1 or 2, wherein the overload diaphragm is concavely preformed with reference to the equalizing space, and the boundary of the equalizing space opposite the overload diaphragm is convexly preformed with reference to the equalizing space.

6. A pressure-measuring device substantially as herein described with reference to the accompanying drawing.

7. A method of measuring pressure employing a device according to any preceding claim.