Pressure measuring cell.

The invention relates to a pressure measuring cell according to the preamble of claim 1.

In recent times pressure sensors, such as piezo-electric or piezo-resistive pressure sensors have been developed which can be used for measuring pressures bar up to 400th Such pressure sensors are extremely small, with dimensions of one or a few millimeters. They are also sensitive to chemical influences and shocks, as can occur for example when measuring pressures in pipelines for aggressive chemical substances or more or less solid particles having bulk materials. Another problem is that no adequate piston area is provided which allows a uniform pressure measurement. Other concerns relate to the fitting of such pressure sensors, for example, in meter high tanks or other large dimension devices.

The invention has for its object to provide a pressure measuring cell for measuring very high pressures, which is resistant to chemical influences and mechanical shocks, has a corresponding piston surface for receiving a representative pressure and easily and stably at any place of pressurized equipment can be attached.

This object is achieved by a pressure measuring cell with the features of the characterizing part of claim 1.

The metal housing allows an easy and stable installation of the pressure measuring cell, while the elastomeric material protects the pressure sensor from external influences and on its outer side provides a sufficiently large piston area to the pressure receiving. The mounting of the terminal board within the housing from damage the extremely thin connections for the pressure sensor.

Preferred embodiments of the pressure measuring cell according to the invention are characterized in the dependent claims.

Further features and advantages of the pressure measuring cell of the invention will become apparent from the following description of embodiments with reference to the drawing. Show it:<ul><li>Figure 1 is a sectional view of a first embodiment of a pressure measuring cell according to the invention with fully embedded pressure sensor and</li><li>Figures 2-4 are sectional views of other embodiments of the invention the pressure measuring cell with built-in contact with the elastomeric material pressure sensor.</li></ul>

Figure 1 shows a first embodiment of a pressure-measuring cell 10 according to the invention with a stable, rigid housing 42, preferably made of metal or ceramics which is inserted by means of suitable seals 14 having its upper surface flush with the inner surface of a container, conduit or the like. 12th Here, the housing 42 via suitable fasteners, such as screws, are attached from the outside on the wall of the container or the like. 12th

The housing is cup-shaped with a recess 46, 44 has multiple diameters in comparison with the dimensions of a recess disposed in the pressure sensor. Preferably, the diameter of the recess 46 more than ten times as large as the diameter of the pressure sensor 44th

The depression 46 is virtually completely filled with an elastomeric material 43, which may be, for example, silicone rubber. In the embodiment of figure 1 the pressure sensor 44 is completely surrounded by the elastomeric material 43, and its lead wires 18 are guided through bores 20 in the bottom of the housing 42 of the elastomeric material 43 to a connector board 52 in a lower-side recess 49 housing 42 is attached. In the case of a metal casing 42 the bores 20 are isolated for example by ceramic tubes, which are held by, for example, an insulating plate 22 on the underside of the bottom of the housing 42nd

Via a cable 24 can now be lead out strong and unbreakable, the corresponding leads.

A cover plate 51 seals the recess 49 towards the environment from.

In operation, presses a pressure P on the formed by a top surface 45 of the elastomeric material 43 piston surface, wherein the pressure of the elastomeric material 43 is uniformly distributed to the pressure sensor 44th

Although the depression 46 completely 43 may be filled with elastomeric material Ma, in the embodiment, a piston is still in use 41, 46 a small gap 16 forms with the sidewall of the hole, which is filled with elastomeric material 43rd The piston 41 may either be embedded in a certain distance from the surface 45 in the elastomeric material 43 or else be placed over the elastomeric material 43 with its upper surface flush to the inner wall of the container 12th

The piston has thereby protecting the elastomeric material to chemical agents. It also ensures that the elastomeric material is 43 hergestelt bubbles, as described for example in DE-OS 34 44 996th For this purpose the underside of the piston 41 is provided with an elevation, such as a cone 26th

Because of the plan with the wall of the container 12 top 45 of the elastomeric material 43 or the plan top of the piston 41 of the pressure sensor 44 is completely protected from mechanical damage, for example in the promotion of fluidized solids.

It should be noted that the piston 41 is guided virtually without friction in the recess 46 due to the filled with elastomeric material 43 gap 16, so that the pressure P is transmitted completely through the piston 41 on the running example of a pressure sensor chip pressure sensor 44th The hermetic integration of the pressure sensor in the bubbles introduced elastomeric material avoids the otherwise critical support of the pressure sensor pad on the pressure housing so that high pressures can be measured by the pressure measuring cell according to the invention. Due to the excellent resistance of the silicone rubber and with appropriate selection of materials of the piston 41 and the housing, preferably made of ceramic or stainless steel, pressures in practically all media can be measured.

Figures 2 to 4 show further embodiments of a pressure measuring cell according to the invention, in which the pressure sensor is not completely embedded but only with its surface with the elastomeric material 43 in contact. Such an arrangement works for example, preferably with a ceramic pressure sensor, which is responsive to mechanical bending stresses.

Because different embodiments of FIGS. 2 to 4 only in the arrangement of the piston 41, the description of the embodiment of FIG. 2 should be enough to give even this refers to the variations of FIG. 1.

Deviating from the embodiment of FIG. 1, the recess 86 is provided at its bottom with a central opening 82, whose diameter is preferably slightly smaller than the diameter of the ceramic pressure sensor 84 which is embedded in the bottom of the housing 62. The pressure sensor 84 is in this case fixed, for example by means of a ring 88 in the bottom of the housing 62nd

Here, too, in turn provides the same advantages as they have already been described in connection with the first embodiment. Notwithstanding the first embodiment, the housing is to be mounted on flanges provided with holes 64 at the desired position.

As already mentioned in connection with the first embodiment, the piston 81 can be either in the elastomeric material 83 embedded (FIG. 2), the elastomeric material up to complete (Fig. 3) or not present (Fig. 4).

Of particular importance for the pressure measuring cell according to the invention that the elastomeric material 43 or 83 is free of bubbles.

To prepare the pressure-measuring cell according to the invention therefore a method is employed, as is known from DE-OS 34 44 996 and as it is used for example on load cells, as described in the international patent application PCT / EP 8500691 (WO 86/03584) described is , The content of these documents is made entirely on the content of the present patent application.

It should be noted that for the pressure measuring cell according to the invention a wide variety of pressure sensors can be used, such as thick-film ceramic membranes, GaAs Hall generators, piezoelectric and piezo-resistive membranes etc.

The pressure measuring cell according to the invention is particularly suitable for relatively exact determination of the pressure in liquids and gases in a pressure range from 2 to 400 bar.