EP3391001A1

EP3391001A1 - Pressure sensor and method for operating a pressure sensor

Info

Publication number: EP3391001A1
Application number: EP16795097.1A
Authority: EP
Inventors: Max JEHLE; Marc Andreas SCHLACHTER; Davide Parrotto
Original assignee: Endress and Hauser SE and Co KG
Current assignee: Endress and Hauser SE and Co KG
Priority date: 2015-12-15
Filing date: 2016-11-15
Publication date: 2018-10-24
Also published as: US20180372571A1; CN108474703A; CN108474703B; WO2017102210A1; DE102015121859A1

Abstract

The invention relates to a pressure sensor (1) for determining a pressure measurement variable, comprising at least one housing (2), a pressure sensor element (3) which is arranged in said housing (2), a lighting means (4) likewise arranged in said housing (2), and a control/analysis unit (8). The pressure sensor element (3) has a semiconductor material and a measuring membrane, and a first pressure (p₁) is applied to a first face of the measuring membrane (5) and a second pressure (p₂) is applied to a second face of the measuring membrane (5) such that said measuring membrane (5) undergoes a pressure-dependent deflection. The measuring membrane (5) comprises at least one integrated resistance element (6), and the control/analysis unit (8) detects an electric signal (10) with the aid of the integrated resistance element (6) in order to determine pressure measurement variables. The lighting means (4) optically excites the pressure sensor element (3), and the control/analysis unit (8), using a change in the electric signal (10) resulting from said optical excitation, determines a statistical pressure value inherent to the first and/or second pressure and implements correction or compensation of the pressure measurement variable with the aid of said statistical pressure value.

Description

Pressure sensor and method for operating a pressure sensor

The invention relates to a pressure sensor for determining a pressure measurement and a method for operating such a pressure sensor.

Pressure sensors are used to detect pressures and are often used in industrial metrology, for example for level measurement or flow measurement. Depending on the application, different types of pressure sensors are used. Thus, a pressure sensor, for example, as an absolute pressure sensor, as

Relative pressure sensor or be designed as a differential pressure sensor. In principle, however, all pressure sensors have the same structure and typically include a housing in which a pressure sensor element is arranged. In pressure measurement technology, semiconductor pressure sensor elements, for example silicon-based, are popular

Pressure sensor elements, used. The semiconductor pressure sensor elements in this case have a measuring diaphragm which typically has four in its edge region

Integrated resistor elements. The measuring diaphragm is pressurized on its first side with a first pressure and on its second side with a second pressure, so that the two pressures cause a deflection of the measuring diaphragm. The pressure-dependent deflection of the measuring diaphragm is via the integrated

Resistance elements detected and evaluated, so that a pressure measurement

can be issued. Depending on whether it is a

Relative pressure sensor, an absolute pressure sensor or a differential pressure sensor, the measuring membrane is applied to the corresponding two pressures. In the case where the pressure sensor is designed as an absolute pressure sensor, one of the two sides of the measuring diaphragm is exposed to a vacuum and the other side of the measuring diaphragm is supplied with a measured media pressure. The absolute pressure sensor thus measures the absolute pressure, ie the medium pressure to be measured in comparison to the vacuum as a reference pressure.

In the case that the pressure sensor is designed as a relative pressure sensor, one of the two sides of the measuring diaphragm is exposed to an atmospheric air pressure as the reference pressure and the other side of the measuring diaphragm becomes a measuring one

Media pressure supplied. The relative pressure sensor thus measures a relative pressure, ie the medium pressure to be measured in comparison to the atmospheric air pressure.

In the event that the pressure sensor is designed as a differential pressure sensor, one of the two sides of the measuring diaphragm is supplied with a first medium pressure to be measured and a second medium pressure to be measured is supplied to the other side of the measuring diaphragm. Of the Differential pressure sensor thus measures a differential pressure, ie the difference between the two media pressures.

Together, all pressure sensors have the fact that the measured pressure variable has measurement errors. These measurement errors are specified in the specification of the respective pressure sensor over a tolerance range in which the determined pressure measurement variable with a defined probability is correct. One cause of such measurement errors are changes in the static pressure inherent in the media pressure. It is therefore an object of the present invention to propose a way to reduce such measurement errors.

The object is achieved by a pressure sensor and a method for operating such a pressure sensor.

With regard to the pressure sensor, the object is achieved by a pressure sensor for

Determining a Druckmessgröße solved, comprising at least one housing, a pressure sensor element arranged in the housing, also in the housing

arranged light source, as well as a control / evaluation unit, wherein the

Pressure sensor element comprises a semiconductor material and a measuring membrane, wherein on a first side of the measuring membrane, a first pressure and on a second side of the measuring membrane, a second pressure is applied, so that the measuring membrane a

experiences pressure-dependent deflection, wherein the measuring membrane has at least one integrated resistance element and the control / evaluation unit using the integrated resistive element determines an electrical signal for Druckmessgrößenbestimmung, wherein the illuminant is an optical excitation of the pressure sensor element and the control / evaluation unit based on a due optical excitation caused change in the electrical signal determines the first and / or second pressure inherent static pressure value and performs a correction or compensation of the pressure measured variable with the aid of the static pressure value.

According to the invention, the effect called photoconductivity is exploited to obtain information about a static pressure. The static pressure is inherent in at least one of the two sides of the measuring membrane applied media pressure.

Generally, photoconductive effect is an effect attributed to the internal photoelectric effect, in which the increase in the electrical conductivity of semiconductor materials occurs due to the formation of unbonded electron-hole pairs upon irradiation, Understood. Due to the irradiation of the pressure sensor element, which comprises at least one semiconductor material and a measuring diaphragm, an electrical signal, for example a bridge voltage signal, is changed. Based on this change, the static pressure value can thus be determined. With the help of this static pressure value, a pressure measured variable determined by the pressure sensor is corrected or compensated.

An advantageous embodiment of the pressure sensor according to the invention provides that the optical excitation comprises a plurality of individual optical pulses.

A further advantageous embodiment of the pressure sensor according to the invention provides that the measuring diaphragm has further integrated resistance elements and in each case one light-emitting means is provided for each further resistance element.

A further advantageous embodiment of the pressure sensor according to the invention provides that the lighting means is a light emitting diode.

A further advantageous embodiment of the pressure sensor according to the invention provides that the optical excitation occurs cyclically and wherein during two cycles, the control / evaluation unit the last determined static pressure value for correction or

Compensation used.

With regard to the method, the object is achieved by a method for operating a pressure sensor, which is designed in particular according to one of the preceding embodiments, wherein the pressure sensor comprises a pressure sensor element, which comprises a semiconductor material and a measuring diaphragm to the first side on a first pressure and a second side is applied a second pressure, the method comprising the following steps:

Optical excitation of the pressure sensor element;

Detecting a change in an electrical signal caused by the optical excitation;

Determining a static pressure value due to the change in the electrical signal; Correction or compensation of a pressure measured variable determined by the pressure sensor on the basis of the static pressure value.

An advantageous embodiment of the method according to the invention provides that a plurality of individual optical pulses are used for optical excitation and for

Detecting the change of the electrical signal several individual electrical signal values are detected. In particular, the embodiment provides that the change in the electrical signal is determined by averaging the detected individual electrical signal values. A further advantageous embodiment of the method according to the invention provides that the optical excitation is carried out cyclically during the measuring operation.

A last advantageous embodiment of the method according to the invention provides that the correction or compensation is performed via a look-up table and / or a mathematical equation.

The invention will be explained in more detail with reference to the following drawings. 1 shows a schematic representation of the pressure sensor according to the invention,

2 shows a schematic block diagram of the pressure sensor according to the invention, FIG. 3 shows a test setup which was used to investigate the effect,

FIG. 4 shows an experimentally determined first measurement curve or measurement curves, FIG.

FIG. 5 shows a second measurement curve or measurement curves determined experimentally on the basis of the experimental setup, FIG.

6 (a): an amplifier circuit of a photodiode,

Fig. 6 (b): an output signal of the amplifier circuit,

FIG. 7 shows a third measuring curve or measuring curves experimentally determined on the basis of the experimental setup, FIG.

8 shows an exemplary correction function which can be used for the correction or compensation of the pressure measurement variable of a pressure sensor, and

9 shows a schematic representation of the method steps of the method according to the invention. FIG. 1 shows a schematic representation of the pressure sensor 1 according to the invention.

This comprises a housing 2, a pressure sensor element 3 arranged in the housing 2 and a lighting means 4 likewise arranged in the housing. The introduced into the housing 2 pressure sensor element 3 comprises a semiconductor material, preferably silicon on. In the pressure sensor element 3 is a measuring diaphragm 5, for example. By an etching process, introduced. For determining a pressure measurement variable, for example when the pressure sensor 1 is designed as a relative pressure sensor, the measuring diaphragm 5 at a first side pi, eg. An atmospheric pressure, and at a second side a second pressure p ₂ , for example. A to be measured Media pressure, which is a static pressure inherent fed.

In order to detect a pressure-dependent deflection generated by application of the pressures p- ₁ and p ₂ , the measuring membrane again comprises four resistance elements 6, which are generated, for example, by doping the semiconductor material. The resistance elements 6 integrated in the measuring diaphragm 5 in this manner are typically arranged in the edge region of the measuring diaphragm 5 in order to detect the pressure-dependent deflection of the measuring diaphragm 5 in the form of a resistance change. Based on the

Resistance changes of the resistance elements 6, the pressure sensor 1 can determine or output a pressure measured variable.

Fig. 1 thus shows a relative pressure sensor. However, the invention is equally applicable to an absolute pressure or differential pressure sensor.

FIG. 2 shows a schematic block diagram of the pressure sensor 1 according to the invention, which additionally comprises a control / evaluation unit 8 in addition to the light source 4 with a corresponding light source drive unit 7, the resistance elements 6. The

Resistance elements 6 are connected to a Wheatstone bridge 9 and the control / evaluation unit 8 is typically used to detect an electrical signal 10 representing the resistance values, for example the bridge voltage signal U _B. On the basis of the detected electrical signal 10, in the case shown the

Bridge voltage U _B , the control / evaluation unit 8 determines a pressure measured variable. Fig. 3 shows a test setup which was used to study the effect. Of the

Experimental set-up comprises a first assembly 1 1 and a second assembly 12, which are connected to each other via a hydraulic chamber assembly 13. The first module 1 1 has a light emitting diode 4 (short: LED) on a transistor Outline carrier type 8 (short: TO-8) and the second module a pressure sensor element, which is also located on a TO-8 carrier. The hydraulic chamber assembly 13 has a filler neck 14 for filling the hydraulic chamber assembly 13 with a diaphragm seal fluid or a silicone oil. The pressure sensor element is electrically connected to a sensor electronics, which in particular comprises a control / evaluation unit. About the sensor electronics, the electrical signal, which due to the change in resistance of the

Resistance elements 6 of the Wheatstone bridge 9 results, converted into a pressure measurement.

FIG. 4 shows a multiplicity of first measurement curves determined experimentally on the basis of the experimental setup described above. For this purpose, both the LED and the pressure sensor element via the hydraulic chamber composite was simultaneously subjected to the static pressure. In addition, the pressure sensor element was optically excited by the LED. Specifically, a relative pressure sensor was operated at different static pressures (p = 0 - 40 bar) and different temperatures (T = -20 ° C - 70 ° C). The optical excitation was carried out by a variety of optical

Single pulses at the corresponding pressures and temperatures. The change or deviation of the electrical signal was detected by averaging the detected multiple individual signal values, wherein the variation or deviation represents the difference of the optical signal with optical excitation and the electrical signal without optical excitation. As can be seen from Fig. 4, the pressure sensor element showed both a

pressure-dependent as well as a temperature-dependent change of the electrical signal in the form of the bridge voltage, so that a determination of a static pressure value for the correction or compensation of the pressure measured by exploiting the

photoelectric effect appears possible in principle.

FIG. 5 shows a multiplicity of second measurement curves determined experimentally on the basis of the experimental setup described above. For this purpose, the pressure sensor element was replaced by a photodiode as a receiver in the experimental setup described and both the LED and the photodiode were exposed to the static pressure, wherein the hydraulic chamber assembly was not filled with the diaphragm seal fluid. The linearity deviations are due to the fact that the effect is superimposed on both the photodiode and the LED. For evaluation of the photodiode, the amplifier circuit shown in Fig. 6 (a) was used, which images a photon current of 0 to 15 μΑ to an output of 0 to 15V. By way of example, such an output signal is shown in FIG. 6 (b).

FIG. 7 shows a multiplicity of third measurement curves determined experimentally on the basis of the experimental setup. For this purpose, the pressure sensor element was again replaced by a photodiode as a receiver in the experimental setup described and both the LED as well as the photodiode were exposed to the static pressure, the hydraulic chamber assembly once filled with the diaphragm seal fluid and once was unfilled. From Fig. 7 it can be seen that a temperature-dependent

Absorption coefficient of the diaphragm seal results, which in the correction or

Compensation is also to be considered.

It can be seen from the first to third measurement curves that the photoelectric effect can also be used to estimate the static pressure in a pressure sensor, so that the measurement error of a pressure sensor can be reduced with the aid of a mathematical model. For this purpose, for example, a correction function, as shown by way of example in FIG. 8, can be used.

For correction or compensation, the control / evaluation unit 8 is designed to carry out the method according to the invention shown schematically in FIG. 9 and described below according to the following method steps:

Optical excitation of the pressure sensor element 100 by at least one

Light source, for example. In the form of a light emitting diode. The optical excitation can be effected by a single or selectively via a plurality of light sources, preferably in each case a light source for a resistance element. It has proved to be advantageous if the lighting means is pulsed, i. the respective optical excitation is carried out by a plurality of individual optical pulses, which follow one another directly. Furthermore, it has proven to be advantageous if the optical excitation is performed cyclically during the measuring operation.

Detecting a change in the electrical signal 101 caused by the optical excitation, in which case in each case a luminous means 4 for a resistive element 6 and thus a selective optical excitation of the

Resistive elements 6 is carried out, an electrical signal 10 is preferably detected by each of the resistive elements 6.

In the case that the optical excitation is generated by a plurality of individual pulses, it is advantageous to change the electrical signal by a

Determine averaging of the detected individual signal values. - Determine a static pressure value due to the change in the electrical

Signal (102).

Correction or compensation of a determined by the pressure sensor

Pressure measured by static pressure (103). LIST OF REFERENCE NUMBERS

1 pressure sensor

casing

3 pressure sensor element

Lamp

5 measuring membrane

6 resistance element

7 lamp drive unit

8 control / evaluation unit

9 Wheatstone Bridge

10 electrical signal

1 1 First assembly

12 Second module

13 Hydraulic chamber assembly

14 filler neck

15 TO-8 housing

16 sensor electronics

17 photodiode

Pi first print

P2 Second pressure

U _B bridge voltage

Claims

claims

1. Pressure sensor (1) for determining a pressure measurement variable, comprising at least one housing (2), a pressure sensor element (3) arranged in the housing (2), a light source (4) likewise arranged in the housing (2), and a control unit. ZAuswerteeinheit (8), wherein the pressure sensor element (3) comprises a semiconductor material and a measuring membrane, wherein on a first side of the measuring diaphragm (5) a first pressure (pi) and on a second side of the measuring diaphragm (5) a second pressure (p ₂ ), so that the measuring diaphragm (5) experiences a pressure-dependent deflection, wherein the measuring diaphragm (5) has at least one integrated resistance element (6) and the control / evaluation unit (8) with the aid of the integrated resistance element (6) generates an electrical signal ( 10) for Druckmessgrößenbestimmung determined, wherein by the lighting means (4) an optical excitation of the pressure sensor element (3) and the control / evaluation unit (8) based on a due to the optical excitation

caused change in the electrical signal (10) determines a static pressure value inherent to the first and / or second pressure and a correction or

Compensation of the pressure measured variable with the help of the static pressure value.

2. Pressure sensor according to claim 1, wherein the optical excitation comprises a plurality of individual optical pulses.

3. Pressure sensor according to one or more of the preceding claims, wherein the measuring diaphragm (5) further integrated resistance elements (6) and in each case a lighting means (4) for each further resistance element (6) is provided.

4. Pressure sensor according to one or more of the preceding claims, wherein the lighting means (4) is a light emitting diode.

5. Pressure sensor according to one or more of the preceding claims, wherein the optical excitation occurs cyclically and wherein during two cycles, the control ZAuswerteeinheit (8) uses the last determined static pressure value for correction or compensation.

6. A method for operating a pressure sensor (1), in particular according to one of the preceding claims, wherein the pressure sensor (1) comprises a pressure sensor element (3), which comprises a semiconductor material and a measuring diaphragm (5) to which at a first side a first pressure ( pi) and a second pressure (p ₂ ) is applied to a second side, the method comprising the following steps:

Optical excitation of the pressure sensor element (100);

Detecting a change of an electrical signal (101) caused by the optical excitation; Determining a static pressure value due to the change in the electrical signal (102);

Correction or compensation of a determined by the pressure sensor

Pressure measured by static pressure (103).

7. The method of claim 6, wherein for the optical excitation (100) a plurality of individual optical pulses are used and for detecting the change of the electrical signal, a plurality of individual electrical signal values are detected.

8. The method of claim 7, wherein the change of the electrical signal (10) is determined by averaging the detected plurality of individual electrical signal values.

9. The method according to at least one of claims 6 to 8, wherein the optical excitation (100) is performed cyclically during the measuring operation.

10. The method according to at least one of claims 6 to 9, wherein the correction or compensation via a look-up table and / or a mathematical equation is performed.