Method for monitoring the function of a pressure gauge

Abstract

The invention relates to a method for monitoring the function of a pressure measuring device with a measuring element (1) made of a semiconductor substrate (2) and a measuring bridge consisting of at least one piezo-resistive resistive track, wherein the semiconductor substrate (2) has an n-conducting layer and a p-conducting layer and four first connection pads (10, 20, 30, 40) for electrical contacting the measuring bridge are connected to the p-conducting layer. According to the invention, at least one of the four electrical leads (3) provided for contacting the measuring bridge is connected to a switch unit (4) configured to switch between a pressure measurement mode and a diagnostic mode, and the semiconductor substrate (2) has a further connection pad (50) connected to the n-type layer. A microcontroller (5) is configured to detect a forward voltage between the n-type and the p-type layers by being connected at a point P to at least one of the four electrical leads (3) and, in diagnostic mode, measuring the voltage drop between this point P and the further connection pad (50).

Description

[0001] The invention relates to a method for monitoring the function of a pressure measuring device according to the preamble of claim 1.

[0002] Pressure gauges or pressure sensors are used to monitor and measure system pressure in hydraulic and pneumatic applications. One area of ​​application for such pressure gauges is the food industry, where the pressure of various media, especially different liquids, is monitored or measured. Depending on the application, there are numerous different designs, with the construction and configuration of the pressure gauges varying according to the expected maximum nominal pressure of the medium being monitored.

[0003] Typically, such pressure gauges consist of a metallic process connection for mechanically linking the gauge to the container holding the medium, and a housing mounted on the process connection, which essentially contains the evaluation electronics. Furthermore, a pressure sensor, usually metallic or ceramic, is provided to convert the pressure to be monitored into a proportional measurement signal using an electromechanical transducer. The pressure sensor has at least one deflectable measuring diaphragm, one side of which is in contact with the medium, and the electromechanical transducer is located on the other side, facing away from the medium.

[0004] One method for pressure measurement is the use of the so-called piezoresistive effect. For this, the measuring element for detecting the pressure consists of a semiconductor substrate, preferably silicon, and a measuring bridge with at least one piezoresistive resistive track. The semiconductor substrate has an n-type and a p-type layer. Typically, four connection pads are arranged on the p-type layer for electrical contacting the measuring bridge.

[0005] This often involves the use of highly sensitive electrical conductors, such as bond wires. To detect a break in these conductors, a redundant setup using a second measuring element is employed, or the response of the measuring element is verified by an additional LED.

[0006] Document DE 10 2021 104 607 A1 discloses a pressure sensor and an associated operating method for covering an extended measuring range with a single sensor element. This is achieved by switching the sensor between at least two operating modes, with a different measuring capacity for detecting a specific pressure range being formed in each mode by a different electrical connection of the electrodes.

[0007] The object of the invention is to enable a reliable verification of the uninterrupted contact of the measuring element intended for pressure measurement.

[0008] The problem is solved according to the invention by a method having the features of claim 1. Advantageous embodiments of the invention are specified in the dependent claims.

[0009] The invention is based on pressure sensing using the so-called piezoresistive effect. For this purpose, the measuring element for sensing the pressure consists of a semiconductor substrate, preferably a silicon chip, and a measuring bridge with at least one piezoresistive resistive track. The semiconductor substrate has an n-type and a p-type layer. Four first connection pads are arranged on the p-type layer for electrical contacting the measuring bridge.

[0010] According to the invention, at least one of the four electrical leads provided for contacting the measuring bridge is connected to a switching unit, preferably designed as a multiplexer, which is configured to switch between a pressure measurement mode and a diagnostic mode. Furthermore, the semiconductor substrate has an additional connection pad that is connected to the n-type layer. Between the p- and n-type dopants, the semiconductor substrate has a parasitic diode junction (body diode) that is not used during pressure measurement. The invention utilizes this diode junction to verify the uninterrupted contact of the measuring element intended for pressure measurement.For this purpose, a microcontroller detects a forward voltage between the n-type and p-type layers by being connected at a point P to at least one of the four electrical lines and measuring the voltage drop between this point P and the next connection pad in diagnostic mode.

[0011] For this purpose, the semiconductor substrate is set to its lowest potential, and a constant current or voltage is applied to one of the four first connection pads, which are connected to the p-doped layer. This allows the forward voltage of the diode junction to be measured. If the connection between one of the connection pads is broken, this voltage can no longer be measured. This allows the determination of which connection is broken and whether the fault lies with the chip itself or with its connection to the evaluation electronics.

[0012] Advantageous further developments of the invention provide that the switch unit is controlled by the microcontroller or that the microcontroller is connected to all four electrical lines.

[0013] The invention will now be explained in more detail using exemplary embodiments and with reference to the drawings.

[0014] They show schematically: Fig. 1. A top view of a measuring element; Fig. 2 Setup for carrying out the method according to the invention.

[0015] In the following description of preferred embodiments, identical reference numerals denote identical or comparable components.

[0016] In the very schematic representation in Fig. Figure 1 shows a measuring element 1 according to the invention in a top view, which is arranged on the membrane of a pressure measuring cell for detecting the pressure of a liquid, flowable, or gaseous medium. It essentially consists of a semiconductor substrate 2 with an n-type layer and a p-type layer. Four of the five connection pads 10, 20, 30, 40 shown are connected to the p-type layer. Piezoresistive resistance tracks 4 (not shown in the figure) are arranged between these four connection pads 10, 20, 30, 40, forming a measuring bridge 4. The connection pads 10, 20, 30, 40 serve for the electrical contact of the measuring bridge 3. An applied pressure causes a deflection of the membrane, which can be detected by a change in the resistance of the piezoresistive resistance tracks 4 and evaluated using the measuring bridge. This measuring principle is known.

[0017] The semiconductor substrate 2 now has an additional connection pad 50, which is connected to the n-type layer. A microcontroller 5 can be connected between this additional connection pad 50 and one of the first four connection pads 10, 20, 30, 40. This microcontroller is configured to detect a forward voltage between the n-type and p-type layers, thus enabling the verification of uninterrupted contact of the measuring element 1.

[0018] In Fig. Figure 2 shows an exemplary setup with which the method according to the invention can be carried out. The central elements for the pressure measurement are, firstly, the measuring element 1 and an evaluation unit 6 connected to the measuring element 1. In addition, the measuring element 1 is connected to the supply voltage Vcc and ground GND.

[0019] As already mentioned, the measuring element 1 essentially consists of a semiconductor substrate 2 designed as a chip with an n-type layer and a p-type layer. The semiconductor substrate 2 comprises a measuring bridge (not shown) consisting of four piezoresistive resistance tracks with terminals 10, 20, 30, 40, which are connected via the in Fig. The connection pads shown in point 1 are contactable. Contact is made via a sensitive bond wire, which is characterized by the semicircular shape of the conductor.

[0020] For reliable wiring verification, a microcontroller 5 and a switch unit 4 configured as a multiplexer are now provided. The diagram omits the corresponding connections for powering the microcontroller 5 and for tapping the measurement signals, e.g., for forwarding them to a higher-level control unit (PLC).

[0021] Firstly, the microcontroller 5 controls the switch unit 4, which is represented by the dashed connecting line, and can thus switch between a pressure measurement mode and a diagnostic mode. In pressure measurement mode, the pressure measurement takes place, and during diagnostic mode, the uninterrupted contact of the measuring element 1 is checked.

[0022] The diode junction between terminals 10, 20, 30, 40 and the additional terminal 50 is indicated by a corresponding symbol. The forward voltage drop across this diode junction is detected by the microcontroller 5, which is connected at a point P located within the oval to at least one of the four electrical lines 3 and measures the voltage drop between this point P and the additional terminal pad 50. Reference symbol list 1 measuring element 2 Semiconductor substrate 3 electrical lines 4 switch unit, multiplexer 5 microcontrollers 6 evaluation unit 10 Connection pad Vcc 20 Connection pad S+ 30 Connection pad S- 40 Connection pad GND 50 connection pad substrate

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