DE3121799A1 - Measuring diaphragm for countering diffusion of pressure media - Google Patents

Abstract

A measuring diaphragm for pressure and differential pressure measuring arrangements for use with pressure media which can diffuse through metallic diaphragms consists of an accommodating member (2) for the measuring diaphragm which has a turned diaphragm bed (3) in a concentric, sinusoidal corrugation, and two metal diaphragms (4, 7) between which a filter diaphragm (6) is located. A pressure medium diffusing through the first metal diaphragm (7) can pass radially outwards through the filter diaphragm (6) into a ventilation groove (5) and from there to the external atmosphere via a ventilation bore (10). The pressure medium is prevented from pressing further forwards into the second metal diaphragm (4), which separates off the liquid (15) of the pressure medium. Consequent damage to the overall measuring arrangement cannot therefore occur. <IMAGE>

Description

Measuring membrane against pressure media diffusion

The invention relates to a measuring membrane for pressure and differential pressure measuring arrangements for use with pressure media that can diffuse through metallic membranes, especially for the hydrogen contained in the pressure media.

In the case of measuring diaphragms in differential pressure measuring arrangements, is located behind the membrane is filled with a liquid that allows the measurement at increased static pressure only allowed. This liquid filling must remain pure in its components, otherwise the hydrogen dissolved in it, for example, when the process technology is released System can lead to the destruction of the measuring arrangement.

The same problems exist with pressure gauges in which on The reason for the high temperatures in the process engineering systems is the diaphragm seal with liquid filling for pressure transmission attached to the actual measuring element will.

Usually one tries the diffusion rate through the membrane special selection of the membrane material to reduce the size.

According to the literature, the precious metals gold and Silver have lower diffusion rates.

For this reason, gold-coated stainless steel membranes are primarily used today used. Another common method is the spraying of special oils, which also increase the service life of the measuring devices.

Both previous solutions are a compromise.

With the gold-coated stainless steel membrane, the diffusion rate is relatively large for the sensitive measuring arrangement; the spray-on method is not generally applicable due to the limited temperature resistance of the oil.

The object of the invention is the previous partially satisfactory solutions to replace it with a universal one.

According to the innovation, this is done in the way that is common today simple membrane is replaced by two membranes, the space between them and the outside atmosphere is ventilated.

According to a further embodiment of the invention is located between the two membranes an insert, for example a sieve membrane, which is an intimate Touching the two membranes prevents the entire membrane surface from being vented ensures.

The diffusion of the z. B. hydrogen contained in the pressure medium can thus take place unhindered via the ventilation to the outside atmosphere and cause damage no longer the downstream measuring arrangement.

An embodiment of the invention is shown in the drawing and is described in more detail below.

The figures show: FIG. 1 a section of an exemplary embodiment of a measuring membrane according to the invention.

FIG. 2 shows an enlarged detail of a section of an exemplary embodiment a measuring membrane according to the invention.

Figure 1 shows a section of an embodiment of an inventive Measuring membrane. Not shown is the further measuring arrangement, such as pipe connection, capillary line, Transmitter etc.

In the front face 1 of the cylindrical measuring membrane receiving body 2 is the membrane bed 3 with concentric sinusoidal undulation. One cylindrical metal diaphragm 4 hugs the diaphragm bed 3 and is with its outer edge at the inner edge of a concentric vent groove 5 with the Measuring membrane receiving body 2 welded. A sieve membrane 6 and one of the same size Metal membrane 7 fit into the embossing of the metal membrane 4 and extend with it their flat edge zone 8 beyond the ventilation groove 5 to an extent 9, at the edge of which they are welded to the membrane receiving body 2. One The vent hole 10 leads radially from the lateral surface 11 of the membrane receiving body 2 on the ventilation groove 5. Likewise in the lateral surface 11 of the membrane receiving body 2 is a pressure medium filling hole 12, which in the outermost concentric Depression of the membrane bed 3 emerges.

A capillary line connection is located on the rear end face 13 14 with a capillary bore which emerges in the middle of the membrane bed 3.

The space between the metal membrane 4 and the membrane bed 3 is of the pressure transmitter fluid 15 is filled.

If pressure medium diffuses from the outside through the metal membrane 7, so the radially to the side through the membrane 6 into the ventilation groove 5 and get through the vent hole 10 into the outside atmosphere without further into the Metal menibrane 4, which penetrate the separating groove to the pressure transmitter fluid 16.

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Claims (2)

Claims 1. Measuring membrane, in particular for pressure and differential pressure measuring arrangements, for use with pressure media that can diffuse through metallic membranes, especially in the case of hydrogen, characterized in that the simple one commonly used today Membrane is replaced by two membranes (4, 7), the space between them and the outside atmosphere is ventilated. 2. Measuring membrane according to claim 1, characterized in that it is marked an insert, for example a sieve membrane, between the two membranes (47 7) (6) which prevents intimate contact of the two membranes (4, 7) and Ensures ventilation of the entire membrane surface.