WO2005121737A1

WO2005121737A1 - Pressure transducer for abrasive media

Info

Publication number: WO2005121737A1
Application number: PCT/EP2005/005978
Authority: WO
Inventors: Bernd Futterer
Original assignee: EBM Brosa Messgeräte GmbH & Co. KG
Priority date: 2004-06-07
Filing date: 2005-06-03
Publication date: 2005-12-22
Also published as: DE202004009330U1

Abstract

The invention relates to a pressure transducer (10) for a static and/or dynamic pressure measurement. Said transducer comprises a pressure measuring cell (12) with a membrane (16) that extends over a base body (14), one measuring face (22) of the membrane (16) lying opposite the base body (14) being in contact with a medium, whose pressure is to be measured. The pressure that is to be measured causes the deflection of the membrane (16) and said deflection can be detected by means of an electromechanical transducer (26), in particular a resistance strain gauge that is attached to the membrane (16). The pressure transducer also comprises a stop element (32) to guard against excess pressure. The measuring face (22) is coupled to a pressure coupling element (28) in such a way that a cavity (30) is formed between the measuring face (22) and the pressure coupling element (28). The stop element (32) is positioned in said cavity in such a way that said element (32) has a degree of play (d) in the direction of a deflection of the membrane (16), caused by the measuring pressure, thus striking the membrane (16) in the vicinity of the base body (12) by means of the pressure coupling element (28) when an excess pressure is detected, in order to prevent the further deflection of the membrane (16).

Description

Pressure sensor for abrasive media

The present invention relates to a pressure sensor for static and / or dynamic pressure measurement, with a pressure measuring cell which has a membrane extending over a base body, a measurement side of the membrane, which lies opposite the base body, being coupled to a medium whose pressure is measured should, wherein a deflection of the membrane is caused by the pressure to be measured and wherein the deflection can be detected by means of an electromechanical transducer, in particular by means of a strain gauge (strain gauge) attached to the membrane, and with a stop element for protection against overload pressure.

Such a pressure sensor is known from document DE 102 21 219 AI. The pressure sensor of the present invention can be used with abrasive media, such as occur, for example, in concrete processing in concrete pumps or in tunnel boring machines, pile boring machines or slot milling machines. Abrasive (abrasive) media usually contain particles that are typically hard, with the abrasion energy increasing with increasing grain size. The faster the particles move, the greater the abrasion. Wear can lead to component failure.

Pressure sensors, pressure sensors and pressure sensors are generally known in the prior art. A pressure sensor either measures the pressure directly or pressure differences during a pressure measurement and converts this or these into electrical signals. In addition to pressure transducers with strain gauges (DMS) or capacitive, i.e. change the air gap between two capacitor plates, or work inductively, i.e. Transferring a membrane deflection to a plunger armature of a coil is also known for piezoelectric pressure sensors, which use the piezoelectric effect, and semiconductor pressure sensors based on the piezoresistive effect. In a semiconductor pressure sensor e.g. four p-doped piezowide stands in the form of a Wheatstone bridge diffused or implanted in an n-doped silicon membrane, which change their electrical resistance when deformed. As a result, the voltage measured at the bridge changes depending on the pressure acting on the membrane.

The present invention relates to a pressure sensor that belongs to the group of pressure measuring cells that work with strain gauges. One of the problems with such a sensor is overload capability.

Strain gauge pressure sensors usually have a cylindrical pressure measuring cell which consists of a base body and a membrane which is connected by a connecting material, e.g. a brazing solder is held at a defined distance from one another and are hermetically sealed together. Strain gauges can be attached to the inner surface of the membrane. The ohmic resistance value of the strain gauge resistors depends on the deflection of the membrane and thus represents a measure of the pressure applied to the membrane. In the case of such pressure sensors, the base body generally has a cup-shaped shape, so that the membrane rests on the medium whose pressure is to be measured is located on the side of the base body facing away. The bottom of the pot is formed by the membrane.

Regardless of the type of measurement principle, there is the problem with the known pressure sensors that the membrane at overload pressure, i.e. Press over, can be mechanically damaged. Damage occurs particularly when impacts or pressures are not applied centrally to the membrane, e.g. through larger stones in a concrete mix. Furthermore, there may be a disadvantageous shift in the zero point of the sensor.

A known practical solution to this problem is to increase the thickness of the membrane accordingly. Since the bursting pressure, ie the pressure at which the membrane is mechanically destroyed, depends, inter alia, on the thickness of the membrane, the maximum bursting pressure can be increased by increasing the thickness of the membrane simple way can also be increased. The disadvantage here, however, is that with the increase in the thickness of the membrane, the deflection of the membrane at the nominal pressure, ie at the pressure of the medium to be measured by the pressure sensor, is simultaneously reduced. Thus, in the prior art the increase in the bursting pressure of the membrane is due to a reduction in the measurement accuracy, ie the maximum resolution of the pressure sensor.

DE 102 21 219 AI solves this problem by reducing the thickness of the membrane and at least one support element being arranged on the side of the membrane facing away from the medium, the support element being arranged at a distance from the membrane or being designed such that the Membrane at least partially abuts the support element or parts of the support element in the event of an overload. The deflection that normally occurs due to the reduced thickness of the membrane during overload and leads to the destruction of the membrane is prevented by the membrane being supported on the support element beforehand, as a result of which the maximum deflection of the membrane is limited to a value at which it is still the membrane is not destroyed. With such a pressure sensor, pressures up to 25 bar can be measured.

The invention has for its object to provide a pressure sensor of the type mentioned, which has both a high overload or burst strength, and also provides the largest possible measurement signal and thus enables the greatest possible resolution, with very high pressures should be measurable , This object is achieved with a pressure sensor of the type mentioned at the outset, the measuring side being coupled to a pressure coupling element in such a way that a cavity is formed between the measuring side and the pressure coupling element, in which the stop element is arranged such that the stop element in the direction of a deflection caused by the pressure measurement of the membrane has a play, so that the stop element strikes the membrane in an area of the base body via the pressure coupling element from an overload pressure in order to prevent further deflection of the membrane.

The provision of a pressure coupling element for transmitting the pressure to be measured enables better protection of the membrane. The membrane no longer comes into contact with the medium to be measured. The pressure coupling element is provided on the side of the membrane that came into contact with the medium in the prior art. The coupling element is designed such that a cavity is formed between the coupling element and the membrane, which can accommodate a stop element. The stop element limits the maximum deflection of the membrane. The wear caused by the medium no longer occurs on the membrane, but on the coupling element. In the event of damage or wear, the coupling element can be replaced without having to replace the pressure measuring cell.

It is preferred if the pressure coupling element is formed in one piece with the membrane.

A one-piece design of the pressure coupling element with the membrane ensures reliable pressure transmission. The Her Position is simplified since a unit formed in this way is easy to manufacture, for example it can be cast. Alternatively, it can also be machined.

It is further preferred if (also) the base body is formed in one piece with the membrane.

Here, too, there are the advantages mentioned above in the manufacture. The burst strength of the pressure measuring cell also increases.

It is particularly advantageous if the base body, the membrane, the stop element and the pressure coupling element are designed to be rotationally symmetrical, in particular cylindrical.

This measure also simplifies the manufacturing process, since such a unit e.g. is easy to manufacture on a lathe.

According to a preferred embodiment, the pressure coupling element 28 and the membrane 16 couple along the axis of rotation.

The axis of rotation represents the center of the membrane. A pressure or force transmission to the center of the membrane ensures a high response of the pressure sensor, since even the smallest forces lead to a deflection of the membrane. Even if the pressure-induced force does not act centrally on the pressure coupling element, the force is nevertheless transmitted centrally to the membrane. The pressure coupling element preferably has a T-shaped cross section along the axis of rotation.

It is also advantageous if the cavity is provided at least in the area of the base body.

This measure supports protection against overload (pressure). A force that would be too great for the membrane and would lead to its destruction is transmitted from the coupling element to the stop element, which strikes the base body of the pressure measuring cell. This means that the membrane cannot be subjected to a maximum (permissible) deflection.

According to a further preferred embodiment, the stop element is of annular design, so that the pressure coupling element reaches through the stop element for coupling to the membrane.

Furthermore, it has proven to be advantageous if an area of the stop element opposite the membrane is smaller than an area opposite the pressure coupling element.

This measure further increases the overload protection. Regardless of the location of the force exerted on the pressure coupling element, the (overload) raft is directed in the direction of the base body.

According to a preferred embodiment, the electromechanical converter is a strain gauge. With a strain gauge, the smallest deformations can be converted into an electrical signal. This measure promotes the response behavior and the resolving power of the pressure sensor.

It is also preferred if the strain gauge is arranged on the side of the membrane opposite the measurement side.

This protects the strain gauge from being destroyed by the medium whose pressure is to be measured. If the pressure coupling element is destroyed or damaged so that the medium can penetrate in the direction of the membrane, the electromechanical transducer is still protected against destruction.

It is further preferred if the pressure sensor has a housing with a recess in which the pressure measuring cell and the pressure coupling element are arranged.

In this way, the pressure measuring cell is protected from damage and destruction by the medium.

According to a further preferred embodiment, the pressure coupling element closes off the recess areally with respect to the medium whose pressure is to be measured.

A flat covering of the recess by the pressure coupling element makes it possible for the pressure sensor to be attached, for example, to the side of a line which carries the medium to be measured. Due to the flat termination there is no resistance that can inhibit or disturb the flow in the line could. However, the functionality of the pressure sensor is retained.

It is further preferred if at least one seal is provided between the housing and the pressure coupling element in order to protect the pressure measuring cell against the medium whose pressure is to be measured.

Such a seal has two functions. On the one hand, it holds the pressure coupling element of the multi-part embodiment of the pressure sensor according to the invention, in which the pressure measuring cell and the pressure coupling element are not integrally formed with one another. On the other hand, the seal prevents the medium from penetrating in the direction of the pressure measuring cell.

The height and width of the cavity are preferably selected so that the pressure resolution is as large as possible without the membrane falling below a predetermined burst strength.

It is further preferred if the annular stop element has a slot.

The slot-shaped interruption of the ring enables the ring or the stop element to be easily installed in the cavity between the pressure coupling element and the membrane, in particular when assembling the pressure sensor according to the invention.

It goes without saying that the features mentioned above and those yet to be explained below not only in the respectively specified combination but also in other combinations or can be used alone without departing from the scope of the present invention.

Embodiments of the invention are shown in the drawing and are explained in more detail in the following description. Show it:

1 shows a sectional view through a pressure sensor according to the present invention along a longitudinal axis;

Fig. 2 is an enlarged view of a selected area of the pressure sensor of Fig. 1; and

Fig. 3 is a schematic perspective view of the stop element, as used in the pressure sensor of Fig. 1.

The pressure sensor according to the present invention is generally designated with reference number 10 below.

In Fig. 1, a pressure sensor 10 according to the present invention is shown schematically in the form of a sectional view along a longitudinal or rotational axis R. It goes without saying that the ro ation symmetry is optional.

The pressure sensor 10 has a pressure measuring cell 12. The pressure measuring cell 12 comprises a base body 14 and a membrane 16. The base body 14 and the membrane 16 can be formed in one piece or in two parts, as indicated by dotted lines, and form a pot-shaped pressure measuring cell 12. In the view in FIG. 1, the pot-shaped pressure measuring cell 12 after open at the top, the bottom of the pot being formed by the membrane 16.

The pressure measuring cell 12 can be inserted into a housing 18, which is why the housing 18 has a correspondingly shaped recess 19. The recess 19 can be provided in the form of a central bore along the axis R.

The medium, the pressure of which is to be measured, is not shown in FIG. 1. However, an arrow 20 illustrates a direction of a force that is caused by the pressure of the medium. The arrow or the direction of force 20 is oriented parallel to the axis R in the example of FIG. 1. The membrane 16 is also deflected in the direction of the arrow 20, i.e. parallel to the axis R. The force 20 acts on a measuring side 22 of the membrane 16.

On the opposite side 24 of the membrane 16, a strain gauge 26 is attached as an electromechanical converter. The wiring and the detection and evaluation unit required for evaluating a generated measurement signal are not shown in FIG. 1. The DMS 26 could also be attached to the measuring side 22.

Furthermore, the pressure sensor 10 comprises a pressure coupling element 28. In the example of FIG. 1, the pressure coupling element 28 has a T-shaped cross section. 1, the “T” is turned upside down. The supporting bar of the “T” is oriented upwards along the axis R and is connected to the measuring side 22 of the membrane 16. The supporting beam or ram is also referred to below with the reference line 46 are referred to. The connection between the plunger 46 and the measuring side 22 of the membrane 16 can be established, for example, by means of an adhesive (not shown). A loose connection is also possible. The pressure coupling element 28 can also be formed in one piece with the membrane 16 and possibly also in one piece with the base body 14.

The shape of the pressure coupling element 28 is selected such that a cavity 30 is formed between the membrane 16 and the pressure coupling element 28. In the example in FIG. 1, the cavity 30 is further delimited by the housing 18. However, the limitation by the housing 18 is not absolutely necessary.

An annular stop element 32 is provided in the cavity 30, which will be described in detail below with reference to FIG. 3.

The ring-shaped stop element 32 in the example in FIG. 1 has an exemplary outer radius which corresponds to the outer radius of the pressure measuring cell 12 and the head-like part of the pressure coupling element 28. The inside diameter of the annular stop element 32 is chosen to be only slightly smaller here, so that the stop element 32 is mainly provided in the radial outer region relative to the axis R in the cavity 30.

Referring to FIG. 2, which is an enlarged view of the pressure sensor 10 of FIG. 1. It can clearly be seen that the stop element 32 has a height in the direction of the axis R which is smaller than the distance between the membrane 16 and the head-shaped part of the pressure coupling element 28 or is smaller than the height of the plunger 46. The difference between the height of the stop element 32 and the distance between the membrane 16 and the pressure coupling element 28 is identified in FIG. 2 as play d. The play d indicates the distance between a first stop surface 34 and the measuring side 22 when the stop element 32 abuts the pressure coupling element 28 with its second stop surface 36. The first stop surface 34 is arranged opposite the measuring side 22. The second stop surface 36 is arranged opposite the head-like part of the pressure coupling element 28.

The play d corresponds to the maximum possible deflection of the membrane 16 or the pressure coupling element in the direction of the axis R. Suppose the force 20 acts on the pressure coupling element 28, as shown in FIGS. 1 and 2, the force 20 being greater than a permissible (overload ) Power is. The permissible force corresponds to the force from which the pressure measuring sensor 10 operates in the overload range, in which there is a risk of damage or destruction and inaccurate measurements.

Furthermore, a first sealing ring 38 and / or a second sealing ring 40 can be provided circumferentially, which protect the pressure measuring cell 12 and in particular the membrane 16 from the medium. For this purpose, the pressure coupling element 28 and / or the housing 18 have corresponding recesses.

The stop element 32 is designed, for example, such that it has a play of a few 0.01 mm, depending on the measuring range and travel, so that when the overload is not permitted, the stop element 32 in the area of the base body 14, ie on a diaphragm neck, touches the measuring side 22 the membrane 16 goes. Furthermore, it can be seen in FIG. 2 that a measuring surface 42 of the stop element 28 is flush with an outer surface of the housing 18.

In Fig. 3, the stop element 32 is shown schematically in a perspective view.

The stop element 32 can also have a slot 44. The slot 44 enables the stop element 32 to be easily installed in the cavity 30, in that the stop ring 32 is guided past the plunger 46 of the pressure coupling element 28 in the region of the slot 44. This is particularly advantageous if the pressure coupling element 28 and the membrane 16 are formed in one piece.

The second stop surface 36 is preferably larger than the first stop surface 34, which increases the effect that the force 20 is only transmitted to the membrane neck.

Claims

claims

1. Pressure sensor (10) for static and / or dynamic pressure measurement, with a pressure measuring cell (12) which has a membrane (16) extending over a base body (14), a measuring side (22) of the membrane (16) which is opposite the base body (14), is coupled to a medium, the pressure of which is to be measured, a deflection of the membrane (16) being caused by the pressure to be measured and the deflection using an electromechanical transducer (26), in particular can be detected by means of a strain gauge attached to the membrane (16) and with a stop element (32) for protection against overload pressure, characterized in that the measuring side (22) is coupled to a pressure coupling element (28) such that between a cavity (30) is formed on the measuring side (22) and the pressure coupling element (28), in which the stop element (32) is arranged such that the stop element (32) in the direction of a deflection of the measurement caused by the measuring pressure membrane (16) has a play (d), so that the stop element (32) strikes the membrane (16) in a region of the base body (12) via the pressure coupling element (28) from an overload pressure in order to further deflect the membrane ( 16) to prevent.

2. Pressure sensor according to claim 1, characterized in that the pressure coupling element (28) is integrally formed with the membrane (16).

3. Pressure sensor according to claim 1 or 2, characterized in that the base body (14) is integrally formed with the membrane (16).

4. Pressure sensor according to one of claims 1 to 3, characterized in that the base body (14), the membrane (16), the stop element (32) and the pressure coupling element (28) are rotationally symmetrical.

5. Pressure sensor according to claim 4, characterized in that the pressure coupling element (28) and the membrane (16) couple along the axis of rotation (R).

6. Pressure sensor according to claim 4 or 5, characterized in that the pressure coupling element has a T-shaped cross section along the axis of rotation.

7. Pressure sensor according to claims 1 to 6, characterized in that the cavity (30) is provided at least in the region of the base body (14).

8. Pressure sensor according to one of claims 1 to 7, characterized in that the stop element (32) is annular, so that the pressure coupling element (28) for coupling to the membrane (16) passes through the stop element (32).

9. Pressure sensor according to one of claims 1 to 8, characterized in that sides (34, 36) of the Ansσhlagselements (32) are flattened, which are opposite the membrane (16) and the pressure coupling element (28).

10. Pressure sensor according to claim 9, characterized in that a side of the stop element (32) opposite the membrane is smaller than a side (36) opposite the pressure coupling element (26).

11. Pressure sensor according to one of claims 1 to 10, characterized in that the electro-mechanical converter is a strain gauge (26).

12. Pressure sensor according to claim 11, characterized in that the strain gauge (26) on the measuring side (22) opposite side (24) of the membrane (16) is arranged.

13. Pressure sensor according to one of claims 1 to 12, characterized in that the pressure sensor has a housing (18) with a recess (19) in which the pressure measuring cell (12) and the pressure coupling element (28) are arranged.

14. Pressure sensor according to claim 13, characterized in that the pressure coupling element (28) closes the recess (19) flat against the medium whose pressure is to be measured.

15. Pressure sensor according to claim 14, characterized in that between the housing (18) and the pressure coupling element (28) at least one seal (38, 40) is provided in order to protect the pressure measuring cell (12) against the medium whose pressure is measured should.

16. Pressure sensor according to one of claims 1 to 15, characterized in that the height and width of the cavity (30) are chosen so that the pressure resolution is as large as possible without the membrane (16) falling below a predetermined burst strength.

17. Pressure sensor according to claim 7, characterized in that the annular stop element (32) has a slot (44) in order to be able to insert the stop element (32) into the cavity (30).