DE3447397A1 - Electrical pressure sensor - Google Patents

Abstract

A pressure sensor (10) is proposed for producing electrical signals, having a membrane (13) which supports at least one sensor element (12a), can be deformed as a function of pressure and closes a reference-pressure chamber (19) towards a medium which is under pressure. Provided for leakage monitoring of the reference-pressure chamber (19) is a second membrane (25) which closes the reference-pressure chamber (19) towards a test pressure and which supports at least one test-sensor element (26a) which, in the event of a leakage in the reference-pressure chamber (19), emits a signal to a closed evaluation circuit, in order to indicate a defect. In this case, the pressure sensor can be constructed such that a large pressure difference acts on the second membrane when the reference-pressure chamber is pressure-tight, or the pressure difference on the membrane (25) occurs after a leakage in the reference-pressure chamber (19) (Figure 1). <IMAGE>

Description

R. I »/ Ö U

December 20, 19-81 »Ws / Hm

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ROBERT BOSCH GMBH, 7000 STUTTGART

Electric pressure transmitter
State of the art

The invention is based on a pressure transmitter for generating electrical signals according to the preamble of the main claim. In such a known semiconductor pressure transducer with an integrated piezoresistive resistor bridge, the sensor elements are attached in the edge area of a membrane made of a silicon semiconductor. Spark erosion, is obtained by etching or other processes and which closes a reference pressure chamber from the pressurized medium (US-PS k 079 508). To measure absolute pressures, the reference pressure chamber is closed under vacuum. With such and similar pressure transducers, which have a reference pressure chamber filled with gas or air at a predetermined pressure or under vacuum for pressure measurement, the signals emitted by the pressure sensor or a pressure switch are falsified as soon as the reference pressure chamber becomes leaky. With these pressure transducers, a leak in the reference pressure chamber can only be detected by a subsequent measurement during maintenance of the pressure transducer.

The aim of the present solution is to ensure the tightness of the reference pressure chamber while the pressure transducer is in use to be monitored when the evaluation circuit is connected.

Advantages of the invention

The pressure transmitter according to the invention with the characteristic Features of the main claim has the advantage that the reference pressure chamber with the connected evaluation circuit at any time can be checked for an increase or decrease in pressure. Since in the event of a leak in the reference pressure chamber is the reference pressure compared to the Test pressure -changed, which the second membrane separates from the reference pressure, is a corresponding one from the test sensor A leak signal is emitted, which is detected and displayed by the evaluation circuit. Another advantage is that the proposed solution not only for so-called semiconductor pressure sensors but for all pressure transducer systems can be used that work with a reference pressure chamber. Due to constant monitoring of the reference pressure chamber, such a pressure transducer can be advantageous This also applies to safety-relevant parts, such as tire pressure monitoring from Use motor vehicles.

The measures listed in the subclaims are advantageous developments and improvements of the Features specified in the main claim possible. It is particularly advantageous if the second membrane is the reference pressure chamber closes against a chamber containing the test pressure, the test pressure chamber in an expedient manner is arranged within the reference pressure chamber. Such training of the pressure transducer is particularly advantageous when the test sensor with the second membrane is from a semiconductor chip

is formed on which the sensor elements are integrated in the edge area <ier membrane as an integrated piezoresistive resistor bridge. Another advantageous development of the features specified in the main claim is that for leak monitoring of several pressure transducers, the reference pressure chamber of each pressure transducer is closed with its second membrane to a common test pressure, the test pressure preferably being atmospheric air pressure. Such a pressure transmitter is preferably also designed as a capacitive pressure transmitter with a high-frequency measurement signal, the first membrane of the reference pressure chamber carrying an electrode of a capacitive pressure sensor and the second membrane carrying a second electrode for a capacitive test sensor. Both electrodes cooperate with a common center electrode arranged in the reference pressure chamber between the two electrodes.

drawing

Three exemplary embodiments of the invention are shown in the drawing and explained in more detail in the description below. 1 shows a pressure transducer according to the invention with a capsule for the reference pressure chamber in cross section, FIG. 2 shows a semiconductor pressure transducer with a membrane each for a pressure space and a space with atmospheric pressure, and FIG. 3 shows a capacitive pressure transducer with a measuring sensor and a test sensor in the reference pressure chamber, Figure h shows the equivalent circuit diagram of the pressure transducer according to Figure 3.

Description of the exemplary embodiments

In Figure 1, a designated 10 pressure transducer is shown in an enlarged scale in cross section, the for measuring the absolute pressure of a liquid

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or a gas is to be used. The pressure transmitter 10 essentially contains a measuring sensor 12, which consists of a first

1-be.i + ek.f semiconductor chip 11, for example made of silicon ', on the surface of which four piezoresistive sensor elements 12a are arranged in the form of a resistance bridge circuit. The sensor elements 12a, only two of which can be seen in FIG. 1, are located on the edge of a membrane 13 which can be deformed by external forces and which is produced by removing the semiconductor material in a round or elliptical area on the back of the semiconductor chip 11. The semiconductor chip 11 is firmly seated on a substrate plate 1h by being soldered, glued or bonded to an annular conductor track 15 in a pressure-tight manner there. The elliptical area under the membrane 13 forms a space 16 which is connected to a pressurized medium, for example air, a gas or a liquid, via a bore 17 in the plate 1U. For the supply of the pressurized medium, a pipe socket 18 is placed on the bore 17 on the rear side of the plate 1U, through which the pressurized medium penetrates to the membrane 13 in the direction of the arrow. Above the semiconductor chip 11 there is a reference pressure chamber 19 which is closed off from the outside by a metal capsule 20. The reference pressure chamber 19 is closed off from the pressurized medium or to the outside by the membrane 13 and by the plate 1h.

To with the pressure transmitter 10 the absolute pressure of the medium To be able to measure, the reference pressure chamber 19 is under vacuum. To generate the vacuum, for example the capsule 20 is soldered pressure-tight in a vacuum to a further ring-shaped conductor track 21 on the plate 1U. These Conductor track 21, like conductor track 15, can be placed on a reference potential when the pressure transducer 10 is used, preferably also a connection of the bridge circuit

of the measuring sensor 12 is connected to the reference potential via one of these conductor tracks. Another connection of the measuring sensor 12 is connected via a connecting wire 22 to a contact pin 23 which is fastened in a pressure-tight manner in a glass feed-through 2k in the plate 1h.

To monitor the vacuum in the reference pressure chamber, the pressure transducer 10 is provided with a second membrane 25, which closes the reference pressure chamber 19 to a test pressure. The second membrane 25 is formed by a test sensor 26. It carries four piezoresistive test sensor elements 26a combined in a bridge circuit and it closes off the reference pressure chamber 19 from a test pressure chamber. The test sensor 2β with the second membrane 25 is formed by a second semiconductor chip 28 which is arranged within the reference pressure chamber 19 on the plate 1 k. The test pressure chamber 27 is formed by a recess formed out of the back of the semiconductor chip in the region of the second membrane 25. It is closed in a pressure-tight manner towards the bottom by the TtOlQ plate 1 k in that the second semiconductor chip 28 is also ring-shaped, which also carries a reference potential. Conductor 29 of the circuit board ~ \ k is bonded, glued or soldered. Since the two semiconductor chips 11 and 28, like the capsule, are soldered to the plate 1 ^ under vacuum, the test pressure chamber 27 is also under vacuum.The test sensor elements 26a are on the one hand connected to reference potential and on the other hand via a connecting wire 30 with a further contact pin 31 connected, which is also inserted pressure-tight in a glass duct 32 in the plate lh.

When using the pressure transducer 10, the connections are the Sensor elements 12a and 26a connected to an at-value circuit, the measuring sensor 12 the absolute pressure in the measuring

space 16 and the test sensor 26 the pressure in the reference pressure chamber 19 senses. When the pressure transducer 10 is intact, both the reference pressure chamber 19 and the test pressure chamber are in place under vacuum, so that the second membrane 25 does not experience any deflection. The output from the test sensor elements 26a Signals, e.g. O signal, are used in the connected evaluation circuit recorded and stored as a setpoint. The first membrane 13, however, is through the pressurized Medium bulged in space 16 and sensor elements 12a emit a dependent electrical signal, which is evaluated via the connected evaluation circuit.

As soon as air is now in the reference pressure chamber 19 through a leak or gas flows in, the measurement signal emitted by the sensor elements 12a is falsified. Since, however, the test pressure chamber 27 of the test sensor 26 is separated from the reference pressure chamber 19 by the second membrane 25, is at such a leak now the second membrane 25 pushed through by the pressure difference on both sides and the Test sensor elements 26a now emit a signal that deviates from the normal state (zero). This signal change will detected by the evaluation circuit and the defect in the pressure transmitter 10 is displayed. The verification of the pressure transducer 10 can be carried out either continuously during operation or when the pressure transmitter 10 is switched on will.

In a further exemplary embodiment, FIG. 2 shows a pressure transducer ^ O with a reference pressure chamber 1 * 1, which is closed at the top by a first membrane k2 of a measuring sensor h'J and at the bottom by a second membrane 1 * 3 of a test sensor U8. The membranes 1 * 2 and 1 + 3 are each formed from a semiconductor chip kh and 1 * 5 by removing the semiconductor material on their rear side. The two

Semiconductor chips are attached pressure-tight under vacuum on opposite sides of a support plate 1 + 6, the in the area of the reference pressure chamber 1 + 1 under vacuum has a corresponding recess. The upper membrane 1 + 2 closes the reference pressure chamber 1 + 1 against the under pressure standing medium and the lower membrane 1 + 3 closes the Reference pressure chamber H 1 against a test pressure. That under Pressurized medium as well as the test pressure are next to the reference pressure chamber 1 + 1 through the support plate 1 + 6 from each other separated. On the upper membrane 1 + 2 there are sensor elements 1 + 7a of the measuring sensor 1 + 7 for measuring the pressure of the medium and on the lower membrane 1 + 3 are test sensor elements 1 + 8a of the test sensor 1 + 8 for leak monitoring of the reference pressure chamber 1 + 1.

The pressure transducer 1 + 0 can be used, for example, to monitor the tire pressure on the vehicle tire by being inserted with the support plate 1 + 6 into a housing which, like a filling valve, can be screwed into a threaded hole in a wheel rim. Consequently, four pressure transducers ko are required for the four vehicle tires. For leak monitoring of the four pressure transducers, the reference pressure chamber 1 + 1 of each pressure transducer 1 + 0 is closed with its second membrane 1 + 3 from the pressure of the outside atmosphere, which forms a test pressure common to all four reference pressure chambers. When the pressure transducers 1 + 0 are connected to their evaluation circuit, the sensor elements 1 + 7a each emit electrical signals which are dependent on the air pressure prevailing in the tire. On the other hand, the test sensor elements 1 + 8a emit the same electrical signals from all four pressure transducers 1 + 0, since the atmospheric pressure is the same for all four pressure transducers 1 + 0. If a leak now occurs on one of the pressure transducers 1 + 0 in the reference pressure chamber 1 + 1, air can enter the

Flow in reference pressure chamber Ui. With that change too the electrical signals produced by the sensor elements ^ Ta and the test sensor elements U8a of the pressure transmitter * + 0 the evaluation circuit can be issued. The evaluation circuit now recognizes that the electrical signals from the test sensor elements U8a of the defective pressure transmitter Uo differs from those of the other, intact pressure transducers and triggers a corresponding error display.

In Figure 3, a capacitive pressure transducer 50 is enlarged Scale shown in cross section, the reference pressure chamber 51 also up through a first Diaphragm 52 and down through a second diaphragm 53 is completed. The first membrane 52 applies here the inside of the reference pressure chamber 51 has a large area Electrode 5 ^ - and the second membrane 53 carries likewise on the inside of the reference pressure chamber 51 a large-area electrode 55 · Both electrodes 5 ^ and 55 act with a common central electrode 56 together, which in the reference pressure chamber 51 between the two electrodes 5 ^ and 55 is arranged. The center electrode 56 is thereby electrically Formed conductive layer, which is applied to a support plate 57 made of insulating material. The support plate 57 has a hole 53 with a via in the middle the electrically conductive layer located on both sides of the support plate 57. Through the support plate 57 the reference pressure chamber 51 is divided in the middle, a space closed off by the first membrane 52 59 above and a space 60 closed off by the second membrane 53 below the support plate 57 will. Both spaces 59 and bO are connected to one another via hole 58. The first membrane 52 closes the reference pressure chamber 51 to the outside to one pressurized medium from and the second membrane closes the reference pressure chamber 51 to a test pressure down.

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This pressure transducer 50 can also be used for leak monitoring of several pressure transducers in such a way that the reference pressure chamber 51 of each pressure transducer 5'0 is closed with its second membrane 53 to a common test pressure, preferably to atmospheric pressure Pa. In figure h thereby the circuit diagram of such a capacitive pressure transducer 50 is shown. The electrode 5 ^ forms a measuring sensor acting as a capacitor 61 with the center electrode 56 and the second electrode 55 forms a test sensor acting as a capacitor 62 with the center electrode 56. If the center electrode 56 is connected to reference potential and a high-frequency measuring voltage is applied to the electrodes 5 ^ + and 55 of the sensors 61 and 62, the capacitance of the capacitors 61 and 62 can be determined via a measuring circuit of the connected evaluation circuit.

When the pressure on the upper membrane 52 changes, the distance between the upper electrode 5h and the center electrode 56 is changed and consequently the capacitance of the measuring sensor 61 as well Electrode 5 * + on the center electrode 56 and thus the capacitance of the test sensor 62 must be the same for all pressure transducers 50 to be monitored. If, on the other hand, a leak occurs in one of the reference pressure chambers 51 under vacuum, the capacitance of the test sensor 62 on the defective pressure transducer 50 changes. This is recognized and displayed by the evaluation circuit connected to the pressure transducers 50.

In the exemplary embodiment according to FIG. 3, the membranes 52 and 53 are formed from shell-shaped bodies 63 and Gh made of insulating material and are fastened in a pressure-tight manner on opposite sides of the support plate 57.

A f

However, the invention is not limited to the illustrated embodiments, since instead of the vacuum the reference pressure chamber can also be filled with a pressurized gas or with compressed air. To generate a clear signal in the event of a leak in the reference pressure chamber, however, it is advisable to that between the pressure in the reference pressure chamber on one side of the membrane of the test sensor and the test pressure on the other side of the membrane there is a sufficient pressure difference. This pressure difference occurs either according to Figure 1 only in the event of a leak in the reference pressure chamber or it must according to Figures 2 and 3 be present with intact pressure transducers and disappear in the event of a leak. The signal from the test sensor with the same pressure on both sides of a membrane, it must be clearly different from the signal in each case differentiate that with a strong pressure difference on both Sides of the diaphragm occurs.

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Claims (1)

December 20, 1989 U Ws / Hm ROBERT BOSCH GMBH, TOOO STUTTGART 1 Expectations 1. Pressure transmitter for generating electrical signals with a pressure-dependent deformable membrane carrying at least one sensor element, which closes a reference pressure chamber to a pressurized medium, characterized in that a second membrane (25, U3, 53) the reference pressure chamber (19, kl, 51) for leak monitoring to a test pressure and that the second membrane (25, Jj-3, 53 _{) carries at least one test sensor element (26a, ^ Ta 5} 55), which in the event of a leak in the reference pressure chamber (19 j lH , 51) emits a corresponding signal. 2. Pressure transmitter according to claim 1, characterized in that a test sensor (26) with the second membrane (25) the Reference pressure chamber (19) against a test pressure chamber (27) concludes. 3. Pressure transmitter according to claim 2, characterized in that the test sensor (26) with the test pressure chamber (27) is arranged in the reference pressure chamber (19). H. Pressure transducer according to Claim 3, characterized in that the test sensor (26) with the second membrane (25) and with the at least one test sensor element (26a) consists of a semiconductor chip (28). 19 7 P 6 5. Pressure transducer according to claim h, characterized in that the semiconductor chip (28) carrying the at least one test sensor element (26) has a recess in the region of the membrane (25) and is attached to a support plate (1 ^) in such a way that the recess for Formation of the test pressure chamber (27) by the support plate (lU) is sealed pressure-tight. 6. Pressure transmitter according to claim 5, characterized in that in addition to the semiconductor chip (28) of the test sensor ^ (26), another semiconductor chip (11) of a measuring sensor (12) is arranged on the support plate (lh) , which in the region of its membrane (13 ) also has a pressure-tight recess (16) from the support plate (1 ^), which, however, is to be connected to the pressurized medium through a bore (17) in the support plate (1 * 0) and that both semiconductor chips (11, 28) are arranged within a pressure-tight sealed capsule by the support plate (1 k ) to form the reference pressure chamber (19). 7. Pressure transmitter according to claim 1, characterized in that for leak monitoring of several pressure transmitters (kO, 50) the reference pressure chamber (M, 51) of each pressure transmitter (I + O, 50) with its second membrane (^ 3, 53) to a common one Test pressure, preferably closed to atmospheric pressure. 8. Pressure transmitter according to claim 7, characterized in that the first membrane (52) of the reference pressure chamber (51) an electrode (5M for a capacitive measuring sensor (61) and the second membrane (53) a second Electrode (55) for a capacitive test sensor (62) and that both interact with a common perforated central electrode (56) which is arranged in the reference pressure chamber (51) between the two electrodes (5 ^ ₅ 55). 9. Pressure transmitter according to claim 8, characterized in that the center electrode (56) is supported by a support plate (57) is formed, which has a hole (58) and carries an electrically conductive layer on both sides. 10. Pressure transmitter according to claim 9, characterized in that the reference pressure chamber (51) by a space (59) closed off by the first membrane (52) and a space (60) closed off by the second membrane (53) below the support plate (57) ), which are connected to one another via the hole (58) ..// ',