HK1058231B - Pressure transmitter - Google Patents

Description

Pressure transmitter

Technical Field

The present invention relates to a pressure transmitter.

Background

The pressure measuring device generally consists of a pressure transmitter and a pressure sensor coupled to the pressure transmitter. A pressure to be measured is applied from the outside to the pressure measuring device via the pressure transmitter, and this pressure can then be measured by the pressure sensor. Pressure transmitters are often used as protective receptacles for extremely sensitive pressure sensors. The pressure transmitter has an isolating diaphragm in the direction of the working medium, which closes the pressure transmitter to the outside and which, together with the pressure transmitter base body, defines a chamber inside the pressure transmitter, in which chamber the pressure transmission medium is located. The substrate and barrier film materials comprising the chamber typically have a temperature coefficient of expansion that is significantly less than that of the pressure transmission medium. When the ambient temperature changes, the substrate, the isolation diaphragm and the pressure transmission medium expand differently due to such different temperature expansion coefficients.

The problem here is that the resulting, different volume changes of the chamber and of the pressure transmission medium, which are dependent on the temperature conditions, can sometimes lead to very large measurement errors.

In order to reduce such measurement errors due to temperature conditions, pressure transmitters have been proposed which have a relatively large-area separating membrane at the working end face. The volume of the pressure transfer medium in the chamber may alternatively or additionally be reduced. However, the volume of the pressure transmission medium cannot be reduced at will because of the measurement range to be achieved by the pressure sensor and its measurement tolerances. Furthermore, pressure transmitters generally require very small diaphragm diameters, so that the planar dimensions of the diaphragm are limited only by the spatial position.

In GM7603126 a pressure transmitter of this kind is described, in which a compensating element with a minimum coefficient of expansion is incorporated in the chamber of the base body of the pressure transmitter, which element is capable of compensating for the volume expansion of the pressure transmitting medium. However, such a pressure transmitter is very difficult to implement in terms of manufacturing technology. In addition, the calibration of such temperature-compensated pressure transmitters, i.e. the precise adjustment of the ratio of pressure transmission medium to compensating body, is extremely expensive. Finally, in particular for pressure measuring transducers which measure pressures in the mbar range, a pressure transmitter is required which transmits the pressure received from the outside reliably and uniformly to the downstream pressure sensor. However, this is not or only conditionally possible with the pressure transmitter described in GM7603126, in which the compensating member is arranged free-floating in the chamber.

Disclosure of Invention

It is therefore an object of the present invention to provide a temperature-compensated pressure transmitter which has a smallest possible barrier membrane area.

According to the invention, a pressure transmitter for a pressure measuring transducer is proposed, having a base body, having an isolation diaphragm which is arranged on a pressure-sensitive end face of the pressure transmitter and can be subjected to a pressure to be measured from the outside, having an associated space which accommodates a pressure transmission medium and is located inside the base body and which is closed off on the pressure-sensitive end face by the isolation diaphragm, characterized in that the temperature expansion coefficients of the isolation diaphragm and the base body and the temperature expansion coefficient of the pressure transmission medium are designed such that the isolation diaphragm contracts with decreasing temperature and elongates with increasing temperature, so that the volume change of the associated space caused by the temperature conditions is equal or at least equal to the volume change of the pressure transmission medium caused by the temperature conditions.

A pressure transmitter of the type mentioned above is therefore proposed, which is characterized in that the temperature expansion coefficients of the separating film and of the base body and of the pressure transmission medium are designed such that the volume change of the relevant space due to the temperature conditions is equal or at least approximately equal to the volume change of the pressure transmission medium due to the temperature conditions.

By means of these measures, an optimum temperature compensation of the pressure transmitter and thus of the pressure measuring transducer over a wide range can be achieved in a simple manner. A particular advantage of the pressure transmitter according to the invention is that no enlargement of the pressure transmitter head is necessary for the temperature compensation. Furthermore, no additional expensive process steps are required in the production process. If the pressure transmitter is designed such that the compensation volume of the separating film and the increase in volume of the pressure transmission medium cancel each other out by a suitable choice of the temperature expansion coefficient, no additional processing steps are necessary for processing the pressure transmitter.

Advantageously, the separating film is of undulating design at least in the radially outer region of the separating film. When the temperature increases, the waviness of the isolating membrane decreases, which increases the volume, the so-called compensation volume. In this way, given a volume increase under temperature conditions, the compensation can be adjusted in a targeted manner by means of the waviness.

Advantageously, the pressure transmitter head has a circular cross section of the separating membrane. Of course the isolating diaphragm may also have other shapes of the pressure transmitter head, such as oval, hexagonal, square, but circular is the most accurate for pressure measurements in millibar. A pressure transmitter, which can advantageously provide full compensation, is therefore one in which the isolating diaphragm diameter is less than 40 mm.

The substrate and the barrier film are typically at least partially made of a rust-resistant metal material. Preferably, high-grade steel is used. However, it is also conceivable for the separating film and/or the base body to be made of ceramic or ceramic-like material. As the pressure transmission medium, oil, for example hydraulic oil or silicone oil, is generally used. But other liquids and even gases may be used.

The substrate and the isolation diaphragm typically have a much smaller temperature coefficient of expansion than the pressure transmission medium. For a temperature range of 20 ℃ to 100 ℃, the temperature expansion coefficient is generally 10-10010^-6K^-6And is therefore 10 to 1000 times smaller than the pressure transmission medium.

Drawings

The invention is described in detail below with the aid of embodiments shown in the drawings. In the drawings:

fig. 1 a first embodiment of a pressure transmitter according to the invention;

fig. 2 shows a second embodiment of the pressure transmitter according to the invention.

Detailed Description

Fig. 1 shows a partial sectional view of a pressure transmitter according to the invention. The pressure transmitter of the pressure measuring transducer is denoted by 1. The pressure transmitter 1 has a metallic pressure transmitter base body 2, which is preferably made of a rust-proof, oxidation-resistant material. The base body 2 can however also be made at least partially of another material, for example a ceramic material. The base body 2 has a flange 4 on the sensor end face 3, which connects the pressure transmitter 1 to a pressure sensor, which is not shown in fig. 1.

The pressure transmitter 1 has a separating film 6 on the working end face 5, which is arranged in a recess 7 of the base body 2. The separating film 6 is arranged in the recess 7 in such a way that a chamber 8 is formed between the separating film 6 and the base body 2. The base body 2 of the pressure transmitter 1 furthermore has an opening 9 which is connected both to the chamber 8 and to the flange 4. A pressure transmission medium, for example oil filling, is introduced into the relevant space 8, 9, which is formed by the chamber 8 and the opening 9. The isolating diaphragm 6 isolates the medium (not shown in the figures) present on the working end face side from the pressure transmission medium inside the relevant space 8, 9. The pressure on the working end face side is transmitted via the isolating diaphragm 6 to the pressure transmission medium and thus to the downstream pressure sensor.

In this embodiment, both the pressure transmitter head and the isolating diaphragm 6 have a substantially circular cross-section. The separating film 6 is of undulating design at least in the radially outer region of the separating film 6.

The novel structure of the pressure transmitter 1 according to the invention and its mode of operation are described in detail below by way of example:

the base body 2 and the isolating diaphragm 6 of the pressure transmitter 1 are made of a material which generally has a temperature expansion coefficient which is much smaller than that of the pressure transmitting medium. When the temperature changes, the separator 6 contracts or elongates in the radial direction. If the temperature is increased from, for example, T20 c to, for example, T100 c, the separating film 6 elongates (see dashed line in fig. 1), which will increase the volume of the chamber 8. In contrast, when the temperature is lowered, the separator contracts again, which reduces the volume of the chamber 8. A compensation volume 10 is created by the difference in volume between the contraction and elongation of the separating membrane 6. At the same time, an increase in the volume or a decrease in the volume of the pressure transmission medium, i.e. the filling oil, as mentioned above, also occurs during the temperature increase and decrease.

According to the invention, the total volume of the pressure transmission medium and the temperature expansion coefficients of the materials used for the base body 2 and the separating membrane 6 are matched such that the volume change of the pressure transmission medium caused by the temperature conditions is equal or at least approximately equal to the change of the compensation volume 10 caused by the temperature conditions. According to the invention, a pressure transmitter 1 has been provided which is temperature compensated over a wide range, wherein a closed hydraulic or pneumatic system of the pressure transmitter 1 is temperature compensated if, when the temperature rises, the resulting increase in the volume of the pressure transmission medium (taking into account its characteristic temperature coefficient of expansion) is equal or approximately equal to the volume which is increased by the relevant space 8, 9 taking into account the temperature coefficient of expansion of the separating membrane 6 and the substrate 2.

The temperature dependency of the pressure transmitter 1 can be reduced to virtually zero by the following measures, which can also be used for very small measuring ranges of about 100 mbar:

on the one hand, the temperature dependence can be adjusted by suitable material combinations of the base body 2 and the separating film 6, for example by suitable selection of the temperature expansion coefficient thereof. Alternatively or additionally, the temperature dependence of the pressure transmitter 1 can be further reduced by a suitable membrane shape of the separating membrane 6.

It is also particularly advantageous if, for example, the separating film 6 is designed to be concave at low temperatures (for example T ═ 20 ℃) and to have an increasing convex shape as the temperature increases (for example T ═ 100 ℃). Furthermore, other advantageous measures for reducing the temperature dependence are of course also conceivable, such as reducing the volume of the pressure transmission medium, enlarging the area of the separating diaphragm 6 and making the distance of the pressure transmitter 1 as small as possible from the downstream pressure sensor. By these measures, therefore, an optimum temperature compensation of the pressure transmitter and thus of the pressure measuring transducer can be achieved over a wide range.

Fig. 2 shows a sectional view of a pressure transmitter 1 similar to fig. 1. Like reference numerals therefore refer to like parts. However, the separating film 6 is not designed in a wave-like manner in its outer region, but is now straight. Overall, the separating film 6 is designed in the form of a pot, the course of which is indicated by a solid line at T ═ 20 ℃ and by a dashed line at T ═ 100 ℃.

List of reference numerals:

1 pressure transmitter

2 (pressure transmitter) base body

3 end face of sensor

4 Flange

5 working end face

6 isolating film

7 gap

8 chamber

9 opening hole

10 compensation volume

Claims (10)

1. A pressure transmitter for a pressure measuring transducer,

comprising a base body (2),

having an isolating membrane (6) which is arranged on the pressure-sensitive end face (5) of the pressure transmitter (1) and to which a pressure to be measured can be applied from the outside,

having an associated space (8, 9) within the base body (2) for accommodating a pressure transmission medium, which is closed off at the pressure-sensitive end face (5) by the separating film (6),

characterized in that the temperature expansion coefficients of the separating film (6) and the base body (2) and of the pressure transmission medium are designed such that the separating film contracts with decreasing temperature and elongates with increasing temperature, so that the volume change of the relevant space (8, 9) caused by the temperature conditions is equal or at least equal to the volume change of the pressure transmission medium caused by the temperature conditions.

2. Pressure transmitter according to claim 1, characterized in that the isolating diaphragm (6) is at least partially designed in a wave-like manner, wherein the waviness of the isolating diaphragm (6) decreases with increasing temperature.

3. Pressure transmitter according to any of the previous claims, characterized in that the isolating diaphragm (6) is designed as a pot.

4. Pressure transmitter according to claim 1, characterized in that the isolating diaphragm (6) has a circular cross-section with a diameter (11) of less than 40 mm.

5. Pressure transmitter according to claim 1, characterized in that the base body (2) and/or the isolating diaphragm (6) are at least partly made of a rust-resistant metal material.

6. The pressure transmitter of claim 1, wherein the pressure transmission medium comprises an oil.

7. Pressure transmitter according to claim 1, characterized in that the matrix (2) and/or the isolating diaphragm (6) has a temperature expansion coefficient which is 10 to 1000 times smaller than that of the pressure transmitting medium.

8. Pressure transmitter according to claim 1, characterized in that the temperature expansion coefficient of the substrate (2) and/or the separating membrane (6) is in the range of 10-10010-6K-6 for a temperature range of 20-100 ℃.

9. The pressure transmitter of claim 5, wherein the rust-resistant metal material is high-grade steel.

10. Pressure transmitter according to claim 6, characterized in that the oil is a hydraulic oil or a silicone oil.