JP2019086343A - Pressure measuring device and method for diagnosing operating condition of pressure measuring device - Google Patents

Abstract

To provide a pressure measuring device comprising an operating condition diagnosing function with simple configuration.SOLUTION: The pressure measuring device is provided that comprises: a diaphragm unit that is displaced by an applied pressure; a plurality of piezoresistive elements provided in the diaphragm unit and constituting a bridge circuit; a calculation unit calculating a first calculation value using a first measured voltage value at the first output terminal of the bridge circuit and a predetermined constant; a comparison unit comparing the first calculation value with the value obtained from a second measured voltage value at a second output terminal that is different from the first output terminal in the bridge circuit; and a diagnosis unit diagnosing the operating condition of the pressure measuring device on the basis of the result of comparison performed by the comparison unit.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a pressure measurement device and a method of operating condition diagnosis of the pressure measurement device.

  Pressure measuring devices are widely used for control of equipment and the like. In the pressure measuring device, it is preferable to ensure the reliability of the measured value. There is known a technique of providing two sensors for the purpose of enhancing the reliability (see, for example, Non-Patent Document 1). This technique increases the reliability of the measurements by comparing the two sensor measurements.

There is also known a pressure measuring device having a function of diagnosing an operation state such as the presence or absence of a failure. For example, a technique has been proposed in which two bridge circuits are arranged on the diaphragm and the operating state is diagnosed by comparing two values measured by the two bridge circuits (see Patent Documents 1 and 2). . In addition, in a pressure measurement device in which one bridge circuit is configured by four piezoresistive elements, a technology is proposed that diagnoses the operating state by dividing each piezoresistive element and calculating and comparing the terminal output. (See Patent Documents 3 and 4).
[Prior art document]
[Non-patent literature]
[Non-Patent Document 1] IEC 61508 -7: 2010 Functional Safety of Electrical / Electronic / Programmable Electronic Safety-related Systems / Part 7: Overview of techniques and measures / A.12.1 Reference sensor
[Patent Document]
[Patent Document 1] Japanese Patent Application Publication No. 10-506718 [Patent Document 2] Japanese Patent Application Publication No. 2002-039891 [Patent Document 3] Japanese Patent Application Publication No. 2002-353991 [Patent Document 4] Japanese Patent Application Publication No. 2004-061164

  In order to suppress the increase in the size and cost of the pressure measurement device, a pressure measurement device capable of diagnosing an operating state with a simple circuit configuration is preferable. However, simply using two sensors for duplexing sensors has the disadvantage of increasing the size and cost of the pressure measuring device as compared to using one sensor.

  Further, in the method of using a plurality of bridge circuits on the diaphragm portion, the size of the sensor including the substrate is increased. In the method of dividing the piezoresistive element and providing a measurement terminal for operating state diagnosis, it is necessary to add a terminal for diagnosis in addition to the terminal for pressure detection. Thus, the size of the sensor is increased. Further, in the method of diagnosing the operating state by monitoring the change in resistance value of each piezoresistive element, the resistance value of each piezoresistive element changes due to pressure, so that the influence of pressure is distinguished from abnormality. Is difficult. Therefore, the method of monitoring the resistance value of each piezoresistive element can detect only a definite abnormality such as a break or a short circuit of the sensor. Therefore, an object of the present invention is to provide a pressure measurement device having an operation state diagnosis function with a simple configuration in order to suppress an increase in size and cost of the pressure measurement device.

  In a first aspect of the invention, a pressure measuring device is provided. The pressure measuring device may comprise a diaphragm part. The diaphragm portion may be displaced by the applied pressure. The pressure measuring device may comprise a plurality of piezoresistive elements. The plurality of piezoresistive elements may be provided on the diaphragm portion. The plurality of piezoresistive elements may form a bridge circuit. The pressure measuring device may comprise a calculating unit. The calculation unit may calculate the first calculated value using the first voltage measurement value at the first output terminal of the bridge circuit and a predetermined constant. The pressure measuring device may comprise a comparing unit. The comparing unit may compare the value obtained from the second voltage measurement value at the second output terminal with the first calculated value. The second output terminal may be a terminal different from the first output terminal in the bridge circuit. The pressure measuring device may comprise a diagnostic unit. The diagnosis unit may diagnose the operating state of the pressure measurement device based on the comparison result by the comparison unit.

  The plurality of piezoresistive elements may include a first piezoresistive element and a second piezoresistive element. One end of each of the first piezoresistive element and the second piezoresistive element may be electrically connected in common to one of the high potential terminal and the low potential terminal of the bridge circuit. The calculator uses a first voltage measurement value and a known voltage value to calculate a difference between an excitation voltage applied between the high potential terminal and the low potential terminal and a voltage between both ends of the first piezoresistive element. You may calculate as 1 calculation value. The comparing unit may compare the voltage across the second piezoresistive element with the first calculated value. The voltage across the second piezoresistive element may be obtained from a second voltage measurement.

  The calculation unit may further include a correction unit. The correction unit may correct the difference based on each resistance value of the plurality of piezoresistive elements in a state in which no pressure is applied to the diaphragm unit. The difference corrected by the correction unit may be calculated as a first calculated value.

  The plurality of piezoresistive elements may include a first piezoresistive element and a second piezoresistive element. One end of each of the first piezoresistive element and the second piezoresistive element may be electrically connected in common to one of the high potential terminal and the low potential terminal of the bridge circuit. The calculation unit may calculate the voltage ratio as a first calculated value using the first voltage measurement value and the known voltage value. The voltage ratio may be a voltage ratio obtained by dividing the difference between the excitation voltage applied between the high potential terminal and the low potential terminal and the voltage across the first piezoresistive element by the excitation voltage. The comparison unit may compare a first calculated value with a voltage ratio obtained by dividing the voltage across the second piezoresistive element by the excitation voltage.

  The pressure measuring device may comprise a fixed resistor. The fixed resistor may be electrically connected to one of the high potential terminal and the low potential terminal of the bridge circuit. The calculation unit may calculate the first calculated value using the first voltage measurement value, the voltage measurement value across the fixed resistor, and the known power supply voltage value. The voltage ratio obtained by dividing the voltage across the second piezoresistive element by the excitation voltage is obtained using the second voltage measurement, the voltage measurement across the fixed resistor, and the known supply voltage value. You may

  The calculation unit may further include a correction unit. The correction unit may correct a voltage ratio obtained by dividing the difference by the excitation voltage based on the respective resistance values of the plurality of piezoresistive elements in a state in which no pressure is applied to the diaphragm unit.

  The first piezoresistive element and the second piezoresistive element may be electrically connected to the low potential terminal.

  The pressure measuring device may comprise a fixed resistor. The fixed resistor may be electrically connected to one of the high potential terminal and the low potential terminal of the bridge circuit. The pressure measuring device may comprise a second comparing unit. The second comparator may compare the voltage measurement across the fixed resistor with the threshold. The diagnosis unit may further diagnose the operating state of the pressure measurement device based on the comparison result by the second comparison unit.

  The pressure measuring device may comprise an acquisition unit. The acquisition unit may acquire temperature information around the bridge circuit. The threshold may be changed based on the temperature information.

  In a second aspect of the present invention, a method of operating condition diagnosis of a pressure measurement device is provided. The pressure measuring device may comprise a diaphragm part. The diaphragm portion may be displaced by the applied pressure. The pressure measuring device may comprise a plurality of piezoresistive elements. The plurality of piezoresistive elements may be provided on the diaphragm portion. The plurality of piezoresistive elements may form a bridge circuit. The operating state diagnosis method of the pressure measuring device may include the step of calculating a first calculated value using a first voltage measurement value at a first output terminal of the bridge circuit and a predetermined constant. The method of operating condition diagnosis of a pressure measuring device may comprise the step of comparing the value obtained from the second voltage measurement value at the second output terminal different from the first output terminal in the bridge circuit with the first calculated value. The operating condition diagnosis method of the pressure measuring device may comprise diagnosing the operating condition of the pressure measuring device based on the comparison result.

  Note that the above summary of the invention does not enumerate all the necessary features of the present invention. In addition, a subcombination of these feature groups can also be an invention.

It is a figure which shows the example of arrangement | positioning of the piezo-resistance element formed in the diaphragm part of the pressure measurement apparatus in 1st Embodiment of this invention. It is a figure which shows schematic structure of the pressure measurement apparatus in 1st Embodiment of this invention. It is a figure which shows schematic structure of the modification of the pressure measurement apparatus in 1st Embodiment. It is a figure which shows the example of an output at the time of the normal in 1st Embodiment. It is a figure which shows an example of the voltage difference at the time of normality in 1st Embodiment. It is a figure which shows the example of an output at the time of the abnormality in 1st Embodiment. It is a figure which shows an example of the voltage difference at the time of abnormality in 1st Embodiment. It is a flowchart which shows an example of the process by the pressure measurement apparatus in 1st Embodiment. It is a figure which shows schematic structure of the pressure measurement apparatus in 2nd Embodiment of this invention. It is a flowchart which shows an example of the process by the pressure measurement apparatus in 2nd Embodiment. It is a flow chart which shows an example of the 1st diagnostic processing in a 2nd embodiment. It is a flow chart which shows an example of the 2nd diagnostic processing in a 2nd embodiment. It is a figure which shows schematic structure of the pressure measurement apparatus in 3rd Embodiment of this invention. It is a flow chart which shows an example of the 1st diagnostic processing in a 3rd embodiment. It is a figure which shows schematic structure of the pressure measurement apparatus in 4th Embodiment of this invention. It is a flow chart which shows an example of the 1st diagnostic processing in a 4th embodiment. It is a figure which shows an example of the voltage ratio at the time of normal in 3rd Embodiment. It is a figure which shows an example of the difference of the voltage ratio at the time of normal in 3rd Embodiment. It is a figure which shows an example of the voltage ratio at the time of abnormality in 3rd Embodiment. It is a figure which shows an example of the difference of the voltage ratio at the time of abnormality in 3rd Embodiment. It is a figure which shows an example of the voltage of the both ends of the fixed resistor at the time of abnormality in 3rd Embodiment of this invention.

  Hereinafter, the present invention will be described through the embodiments of the invention, but the following embodiments do not limit the invention according to the claims. Moreover, not all combinations of features described in the embodiments are essential to the solution of the invention.

  FIG. 1 is a view showing an arrangement example of piezoresistive elements formed in a diaphragm portion of a pressure measurement device according to a first embodiment of the present invention. FIG. 1 shows a top view of the diaphragm portion 10 and a cross-sectional view taken along the line A-A '. The pressure measurement device according to the present embodiment may be collectively referred to as a diaphragm unit 10 and a plurality of piezoresistive elements 21-1, 21-2, 21-3, and 21-4 (hereinafter referred to as a plurality of piezoresistive elements 21). And. The diaphragm unit 10 is displaced by the applied pressure. The plurality of piezoresistive elements 21 are provided on the diaphragm unit 10. Specifically, four piezoresistive elements 21 may be formed on the front surface of the diaphragm unit 10. The plurality of piezoresistive elements 21 constitute a bridge circuit 20. The bridge circuit 20 will be described later. In FIG. 1, the plurality of piezoresistive elements 21 are denoted as R1, R2, R3 and R4.

  The diaphragm unit 10 is formed of, for example, a semiconductor substrate. The semiconductor substrate may be a silicon substrate or a compound semiconductor substrate such as silicon carbide (SiC). The piezoresistive element 21 may be a diffusion resistor formed on the surface layer in the semiconductor substrate. The piezoresistive element 21 may be formed by selectively doping a semiconductor substrate with a p-type or n-type dopant and further thermally diffusing it.

  A cavity 12 is provided on the back surface of the semiconductor substrate. In the top view of FIG. 1, the cavity 12 is shown by a dotted line. The hollow portion 12 which is a region surrounded by a dotted line has a thinner semiconductor substrate than the outside of the region surrounded by a dotted line. The area of the semiconductor substrate on the upper side of the cavity 12 is thinner than the area outside the area surrounded by the dotted line, so it is easily displaced by pressure. The semiconductor substrate on the upper side of the hollow portion 12 functions as the diaphragm portion 10.

  A plurality of piezoresistive elements 21 R 1, R 2, R 3 and R 4 may be provided in the region of the semiconductor substrate above the cavity 12. In this example, the area of the hollow portion 12 is rectangular in top view, and R1, R2, R3, and R4 are provided on four sides of the rectangular. When the diaphragm portion 10 receives pressure and is distorted, stress corresponding to the amount of distortion of the diaphragm portion 10 is generated in each of the piezoresistive elements 21. The resistance of the piezoresistive element 21 changes according to this stress.

  For example, when the stress direction generated in the piezoresistive element 21 when pressure is applied to the diaphragm portion 10 corresponds to the longitudinal direction in which current flows in the piezoresistive element 21, the rate of change in resistance of the piezoresistive element 21 is positive. It becomes. That is, as the pressure applied to the diaphragm portion 10 increases, the electrical resistance value of the piezoresistive element 21 increases. On the other hand, when the stress direction generated in the piezoresistive element 21 corresponds to the short direction orthogonal to the longitudinal direction in which current flows in the piezoresistive element 21, the rate of change in resistance of the piezoresistive element 21 is negative. That is, as the pressure applied to the diaphragm portion 10 increases, the electrical resistance value of the piezoresistive element 21 decreases.

  In this example, when pressure is applied from the lower side to the upper side of the diaphragm unit 10, the electrical resistance value of the piezoresistive element 21-1 (R1) and the piezoresistive element 21-4 (R4) increases. On the other hand, when pressure is applied from the lower side to the upper side of the diaphragm unit 10, the electrical resistance value of the piezoresistive element 21-2 (R2) and the piezoresistive element 21-3 (R3) decreases. However, the pressure measurement device of this example is not limited to such a layout.

  FIG. 2 is a view showing a schematic configuration of the pressure measurement device 1 in the first embodiment of the present invention. The four piezoresistive elements 21-1 to 21-4 are connected by wires 22, 23, 24, 25 to form a bridge circuit 20 as shown in the figure. The bridge circuit 20 is a detection circuit that detects a change in the electrical resistance of the piezoresistive elements 21-1 to 21-4. The bridge circuit 20 including the piezoresistive elements 21-1 to 21-4 is a pressure detection bridge circuit in which the bridge output changes according to the distortion of the diaphragm unit 10. The wirings 22, 23, 24 and 25 may be made of metal such as aluminum or copper formed on the front surface of the diaphragm 10 and formed on the surface layer in the semiconductor substrate. It may be a diffusion resistance.

  In this example, one end of the piezoresistive element 21-1 (R1) and one end of the piezoresistive element 21-2 (R2) are connected to the high potential terminal 26 through the wiring 22. One end of the piezoresistive element 21-3 (R 3) and one end of the piezoresistive element 21-4 (R 4) are connected to the low potential terminal 27 through the wiring 23. The piezoresistive element 21-3 (R 3) and the piezoresistive element 21-4 (R 4) of this example have one end commonly electrically connected to one of the high potential terminal and the low potential terminal. It is an example of a piezoresistive element and a 2nd piezoresistive element. In this example, the piezoresistive element 21-3 (R3) and the piezoresistive element 21-4 (R4) of this example are connected to the low potential terminal 27.

  The other end of the piezoresistive element 21-1 (R1) and the other end of the piezoresistive element 21-3 (R3) are electrically connected to the first output terminal 28 through the wiring 24. The other end of the piezoresistive element 21-2 (R2) and the other end of the piezoresistive element 21-4 (R4) are electrically connected to the second output terminal 29 different from the first output terminal 28 through the wiring 25. Be done.

  As described above, the electric resistance value of the piezoresistive element 21 is increased as the pressure applied to the diaphragm portion 10 is increased, and the end portion of the piezoresistive element (R1, R4) is applied to the diaphragm portion 10 The end portions of the piezoresistive elements (R2, R3) are connected, in which the electrical resistance value of the piezoresistive element 21 decreases as the pressure increases. In other words, elements having the same direction of change in resistance value according to pressure are located diagonally in the bridge circuit 20. The resistance value of the piezoresistive elements 21-1 to 21-4 and the rate of change in resistance with respect to pressure may be designed to be approximately the same.

  In the present example, the known power supply voltage Vcc is applied to the high potential terminal 26. The bridge circuit 20 may receive the supply of the power supply voltage Vcc from a power supply connected to the circuit board. The low potential terminal 27 may be connected to the ground potential (GND). Therefore, in this example, the excitation voltage Vex applied between the high potential terminal 26 and the low potential terminal 27 is the power supply voltage Vcc. However, the present invention is not limited to this case, and can be applied as long as the excitation voltage Vex is applied between the high potential terminal 26 and the low potential terminal 27.

  The pressure measurement device 1 of this example includes an AD conversion unit 30, a processing unit 40, and a storage unit 50. These components may be provided on a circuit board different from the diaphragm unit 10. The circuit board may be connected by a wire to a pressure sensor portion having the diaphragm portion 10 and the piezoresistive element 21. However, at least a part of each of the AD conversion unit 30, the processing unit 40, and the storage unit 50 may be formed on the semiconductor substrate constituting the diaphragm unit 10. The AD conversion unit 30 converts an analog signal output from the bridge circuit 20 into a digital signal. In this example, in the bridge circuit 20, the first voltage measurement value Vout1 at the first output terminal 28 which is the connection end of the resistor R1 and the resistor R2 is acquired and converted into a digital value. Similarly, a second voltage measurement value Vout2 at the second output terminal 29, which is a connection end of the resistor R2 and the resistor R4, is acquired and converted into a digital value. The storage unit 50 may store in advance the threshold value, the known power supply voltage Vcc value, and the correction coefficient value.

  In this example, the first voltage measurement value Vout1 at the first output terminal 28 with respect to the ground potential is the voltage V3 across the piezoresistive element 21-3 (R3). The second voltage measurement value Vout2 at the second output terminal 29 with respect to the ground potential is the voltage V4 across the piezoresistive element 21-4 (R4).

  The processing unit 40 executes various types of arithmetic processing using the first voltage measurement value and the second voltage measurement value that are digitally converted. The processing unit 40 may be a microprocessor or the like. In the present example, the processing unit 40 includes a calculation unit 42, a comparison unit 44, and a diagnosis unit 46.

  The calculator 42 calculates a first calculated value using the first voltage measurement value Vout1 at the first output terminal 28 of the bridge circuit 20 and a predetermined constant. In this example, the predetermined constant may be the known power supply voltage value Vcc. In this example, the first calculated value is the difference between the excitation voltage Vex applied between the high potential terminal 26 and the low potential terminal 27 and the voltage V3 across the piezoresistive element 21-3 (R3). Therefore, the calculation unit 42 of this example uses the first voltage measurement value Vout1 and the known voltage value Vcc to generate the excitation voltage Vex and the piezoresistive element 21-3 (R3), which is an example of the first piezoresistive element. The difference with the voltage between the two ends of may be calculated as a first calculated value. In the present example, the excitation voltage Vex is the power supply voltage Vcc. Therefore, the calculation unit 42 calculates Vcc-V3 as the first calculated value.

  The comparison unit 44 compares the value obtained from the second voltage measurement value Vout2 at the second output terminal 29 with the first calculated value. In this example, the comparison unit 44 compares the voltage V4 across the piezoresistive element 21-4 (R4), which is an example of the second piezoresistive element, with the first calculated value Vcc-V3. The voltage V4 across the piezoresistive element 21-4 (R4) is obtained from the second voltage measurement value Vout2. In this example, the voltage V4 across the piezoresistive element 21-4 (R4) is equal to the second voltage measurement value Vout2.

  The diagnosis unit 46 diagnoses the operation state of the pressure measurement device 1 based on the comparison result by the comparison unit 44. The diagnosis of the operating condition may include fault diagnosis. For example, diagnosis of the operating state includes detection of a failure. When the difference between the voltage V4 across the piezoresistive element 21-4 (R4) and the first calculated value Vcc-V3 exceeds a predetermined value, the diagnosis unit 46 Diagnose that an abnormality has occurred. The operation of the operation state diagnosis in the present embodiment will be described below.

Assuming that voltages across the respective resistors R1, R3 and R4 which are a plurality of piezoresistive elements 21 are V1, V3 and V4, each voltage can be expressed by the following equation. Here, R1 ₀ , R2 ₀ , R3 ₀ , and R4 ₀ are resistance values of the respective piezoresistive elements 21 in a state where no pressure is applied. ka and kb are rates of change in resistance with respect to pressure, and p is an applied pressure.

Here, each of the piezoresistive elements 21 is designed to have substantially the same resistance value. The term “substantially the same” may mean, for example, that the variation of each of the piezoresistive elements 21 is within 10%. Assuming that R1 ₀ = R2 ₀ = R3 ₀ = R4 ₀ , when the bridge circuit 20 and the like in the pressure measurement device 1 are normal, the symmetry of the bridge circuit 20 causes the equations (5) and (7) to be obtained. Become equal. That is, V1 and V4 have the same value.

  Here, it can be understood from the equation (3) that the voltage V1 can be obtained by calculating the difference between the known power supply voltage Vcc and the voltage V3 which is a measured value. Therefore, when the pressure measurement device 1 is normal, the voltage V4 across the piezoresistive element 21-4 (R4) and the first calculated value Vcc-V3 have the same value.

  Here, when an abnormality occurs in one piezoresistive element 21, the symmetry in the bridge circuit 20 is lost, and thus the first calculated value which is the difference between Vcc and V3 is separated from the value of the voltage V4. Therefore, the comparison unit 44 calculates the difference between the first calculated value Vcc-V3 and the voltage V4, and diagnoses when the difference between the first calculated value Vcc-V3 and the voltage V4 exceeds the threshold. The unit 46 determines that an abnormality has occurred in the pressure measuring device 1.

FIG. 3 is a view showing a schematic configuration of a modified example of the pressure measuring device 1. In the pressure measurement device 1 of the present modification, the calculation unit 42 includes a correction unit 43. The correction unit 43 is a difference based on the resistance values R1 ₀ , R2 ₀ , R3 ₀ , and R4 ₀ of the plurality of piezoresistive elements 21-1 to 21-4 in the state where no pressure is applied to the diaphragm unit 10. Correct (Vcc-V3). The pressure measurement device 1 of the present modification has the same structure as the pressure measurement device 1 shown in FIGS. 1 and 2 except that the correction unit 43 is provided. Therefore, repeated explanation is omitted.

The resistance of the piezoresistive elements 21-1 to 21-4 due to the difference in the arrangement position of the piezoresistive elements 21-1 to 21-4 with respect to the diaphragm portion 10 and the characteristic variation of the piezoresistive elements 21-1 to 21-4. The values of R1, R2, R3, R4 may be slightly different from one another. In this case, the correction unit 43 corrects the difference by multiplying the difference between Vcc and V3 by the correction coefficient α. Then, the calculation unit 42 calculates α (Vcc−V3), which is the difference corrected by the correction unit 43, as a first calculation value. The correction coefficient α is a coefficient for correcting the difference between the resistance values R1 ₀ , R2 ₀ , R3 ₀ , and R4 ₀ of the piezoresistive elements 21-1 to 21-4.

Specifically, the plurality of piezoresistive elements 21 are designed such that the rates of change in resistance ka and kb in the above formulas (2), (5) and (7) are substantially the same. Therefore, in the denominators of the equations (2), (5) and (7), the sum of resistances in the absence of pressure application, that is, R1 ₀ + R3 ₀ and R2 ₀ + R4 ₀ are dominant. Therefore, the correction unit 43 may calculate the correction coefficient α by the following equation (8). The calculation unit 42 multiplies the difference (Vcc−V3) by the correction coefficient to calculate a first calculated value V1 ′. The diagnosis unit 46 compares the first calculated value V1 ′ (α (Vcc−V3)) with the voltage V4 to diagnose whether or not an abnormality has occurred in the pressure measurement device 1.

The operation state of the pressure measurement device 1 is normal, and even if the correction by the correction unit 43 is performed, the first calculated value V1 'and the voltage V4 do not completely match due to measurement noise and the like. Therefore, the diagnosis unit 46 may diagnose the operation state by providing a reasonable tolerance value. Specifically, when the absolute value | V1′−V4 | of the difference between the first calculated value V1 ′ and the voltage V4 exceeds the threshold, the diagnosis unit 46 may determine that an abnormality has occurred. The threshold value may be set appropriately in consideration of the influence of measurement noise and the like. When the pressure measuring device 1 is normal, ideally, the difference between the voltage V1 (first calculated value Vcc-V3) and the voltage V4 becomes zero regardless of the pressure. Thus, the threshold may be constant regardless of pressure. However, the threshold may be changed according to the pressure. In the formula (5) and (7), the resistance change rate ka and kb for the pressure assuming approximately equal, R1 ₀ and R4 ₀ is not an ideal equal value, even running correction by the correction coefficient α If the values do not match completely due to the accuracy of the correction coefficient (the measurement accuracy of the resistance value at the time of correction coefficient calculation), the difference between the voltage V1 and the voltage V4 is proportional to the pressure. Therefore, when the abnormal mode is a change (deterioration) such as the rate of change in resistance ka, the amount of change V1-V4 decreases as the pressure decreases. Therefore, the processing unit 40 may reduce the threshold as the pressure decreases, and may increase the threshold as the pressure increases. By this configuration, when the pressure decreases, the detection accuracy of the abnormality is maintained, and when the pressure increases, the pressure measurement device 1 is erroneously detected as having an abnormality despite being normal. You may prevent that.

  As an example of the diagnosis of the operation state, examples of characteristics when the process by the pressure measurement device 1 of the first embodiment is applied are shown in FIGS. 4 to 7. FIG. 4 is a diagram showing an example of normal output in the first embodiment. In FIG. 4, V3 is a voltage at both ends of the piezoresistive element 21-3 (R3), and in this example, is a first voltage measurement value Vout1 at the first output terminal. V4 is a voltage across the piezoresistive element 21-4 (R4), and in this example, is a second voltage measurement value Vout2 at the second output terminal 29. V1 'is a first calculation value calculated from the first voltage measurement value Vout1 (V3) and the known power supply voltage value Vcc according to the equation (9). In this example, the first calculated value V1 'corrected by the correction unit 43 is used.

  The horizontal axis in FIG. 4 indicates the input pressure (%) to the diaphragm unit 10. In this example, as the pressure on the diaphragm portion 10 increases, the voltage V3 decreases and the voltage V4 and the first calculated value V1 'increase. As shown in FIG. 4, in the state where the pressure measurement device 1 is normal, the first calculated value V1 ′ and the voltage V4 almost coincide with each other.

  FIG. 5 is a view showing an example of a voltage difference at the normal time in the first embodiment. The horizontal axis in FIG. 5 indicates the input pressure (%) to the diaphragm unit 10. The vertical axis in FIG. 5 indicates the difference between the first calculated value V1 'and the voltage V4. When the pressure measuring device 1 is normal, the difference between the first calculated value V1 'and the voltage V4 remains near zero. Since the difference between the first calculated value V1 'and the voltage V4 remains in the range between the lower limit threshold and the upper limit threshold, the diagnosis unit 46 can diagnose that the pressure measurement device 1 is normal. FIG. 5 shows a case where both the upper threshold and the lower threshold are constant regardless of the pressure.

  FIG. 6 is a diagram showing an output example at the time of abnormality in the first embodiment. FIG. 7 is a view showing an example of a voltage difference at the time of abnormality in the first embodiment. In FIGS. 6 and 7, items indicated by V3, V4, V1 ′, the horizontal axis, and the vertical axis are the same as those in FIGS. 4 and 5. FIGS. 6 and 7 illustrate the case where an abnormality occurs in the piezoresistive element 21-4 (R 4) in the vicinity of 83% of the input pressure to the diaphragm unit 10. As shown in FIG. 6, when an abnormality occurs in the pressure measuring device 1, the first calculated value V1 'and the voltage V4 diverge. Therefore, as shown in FIG. 7, when an abnormality occurs in the pressure measuring device 1, the difference between the first calculated value V1 'and the voltage V4 is from the normal range given by the lower threshold and the upper threshold. Get out. In this example, the difference between the first calculated value V1 ′ and the voltage V4 is less than the lower limit threshold. Therefore, the diagnosis unit 46 can diagnose that the pressure measurement device 1 has an abnormality.

  FIG. 8 is a flowchart showing an example of processing by the pressure measurement device 1 in the first embodiment. FIG. 8 shows an example of a method of diagnosing the operation state of the pressure measurement device 1 provided with the diaphragm portion 10 and the plurality of piezoresistive elements 21.

  The calculation unit 42 acquires a first voltage measurement value Vout1 at the first output terminal 28 of the bridge circuit 20 (step S101). In the present example, the first voltage measurement value Vout1 corresponds to the voltage V3 across the piezoresistive element 21-3 (R3). The calculation unit 42 acquires a second voltage measurement value Vout2 at the second output terminal 29 of the bridge circuit 20 (step S102). In this example, the second voltage measurement value Vout2 corresponds to the voltage V4 across the piezoresistive element 21-4 (R4). The order of step S101 and step S102 is not limited to this case.

  The calculation unit 42 uses the first voltage measurement value Vout1 at the first output terminal 28 and the known power supply voltage Vcc to set the excitation voltage Vex and both ends of the piezoresistive element 21-3 (R3) as a first calculated value. The difference between the voltage V3 and the voltage V3 is calculated (step S103). The known power supply voltage Vcc may be stored in advance in the storage unit 50. In this example, since the power supply voltage Vcc itself is the excitation voltage Vex and the first voltage measurement value Vout1 is V3, the calculation unit 42 may calculate Vcc−Vout1.

The correction unit 43 is a difference based on the resistance values R1 ₀ , R2 ₀ , R3 ₀ , and R4 ₀ of the plurality of piezoresistive elements 21-1 to 21-4 in the state where no pressure is applied to the diaphragm unit 10. (Vcc-V3) is corrected (step S104). The correction unit 43 may calculate the first calculated value (V1 ′) by multiplying the difference (Vcc−V3) by the correction coefficient α. However, the process of step S104 may be omitted. The processes in steps S101 to S104 calculate a first calculated value using the first voltage measurement value Vout1 at the first output terminal 28 of the bridge circuit 20 and a predetermined constant (known power supply voltage Vcc). It corresponds to an example of the stage.

  The comparison unit 44 compares the first calculated value (V1 ′) with the second voltage measurement value Vout2 (step S105). In the present example, the second voltage measurement value Vout corresponds to the voltage V4 across the piezoresistive element 21-4 (R4). If the absolute value | V1′−V4 | of the difference between the first calculated value (V1 ′) and the voltage V4 exceeds the threshold (step S106: YES), the diagnostic unit 46 causes an abnormality in the pressure measurement device 1 It is diagnosed (step S107). When the absolute value | V1′−V4 | of the difference between the first calculated value (V1 ′) and the voltage V4 is equal to or less than the threshold (step S106: NO), the pressure measuring device 1 is normal. Therefore, the process returns to step S101. The process of step S105 corresponds to the step of comparing the value obtained from the second voltage measurement value Vout at the second output terminal 29 different from the first output terminal 28 in the bridge circuit 20 with the first calculated value. The processes of step S106 and step S107 correspond to the stage of diagnosing the operating state of the pressure measurement device 1 based on the comparison result.

  According to the pressure measurement device 1 in the first embodiment, since the duplexing of the sensors is not performed using two sensors, the increase in the size and cost of the pressure measurement device 1 can be suppressed. Further, since it is not necessary to form a plurality of bridge circuits in the diaphragm portion 10, the sensor including the substrate can be miniaturized. Furthermore, the first output terminal 28 and the second output terminal 29 of the bridge circuit 20 for pressure detection can be used as terminals for operating condition diagnosis. Therefore, since it is not necessary to separately provide a terminal for operation state diagnosis, the sensor can be miniaturized. The AD conversion unit 30 may also be used as a pressure detection AD conversion circuit.

  Therefore, according to the pressure measurement device 1 of the present embodiment, it is possible to provide the pressure measurement device 1 capable of diagnosing the operation state with a simple circuit configuration. In addition, when correcting by the correction unit 43, in consideration of the difference in the arrangement position of the piezoresistive elements 21-1 to 21-4 with respect to the diaphragm unit 10 and the characteristic variation of the piezoresistive elements 21-1 to 21-4, It is possible to diagnose the operating condition accurately.

  FIG. 9 is a view showing a schematic configuration of a pressure measurement device 1 according to a second embodiment of the present invention. In the first embodiment, the case where the abnormality of some of the piezoresistive elements 21 constituting the bridge circuit 20 is diagnosed has been described. However, the pressure measuring device 1 may affect the entire plurality of piezoresistive elements 21 and cause an abnormality of a type that does not lose symmetry in the bridge circuit 20, such as a change in resistance value due to aging. Therefore, the pressure measurement device 1 according to the second embodiment can diagnose both the case where some of the piezoresistive elements 21 become abnormal and the case where all of the plurality of piezoresistive elements 21 become abnormal. I assume.

  The pressure measurement device 1 of the present embodiment includes a fixed resistor 60. In FIG. 9, the fixed resistor 60 is indicated as a resistor R5. The fixed resistor 60 may be disposed on the circuit board on which the AD conversion unit 30 and the like are disposed. However, the diffusion resistor of the semiconductor substrate on which the piezoresistive element 21 is formed may be used as the fixed resistor 60. If the fixed resistor 60 is formed on the diaphragm, it may be affected by strain due to pressure changes. Therefore, fixed resistor 60 may be provided on the semiconductor substrate at a position that is less susceptible to distortion. For example, the fixed resistor 60 may be spaced apart from the cavity 12. Fixed resistor 60 is electrically connected to one of high potential terminal 26 and low potential terminal 27. In the present example, the fixed resistor 60 is electrically connected to the low potential terminal 27. One end of the fixed resistor 60 may be connected to the low potential terminal 27, and the other end of the fixed resistor 60 may be connected to the ground potential (GND). The resistance value of the fixed resistor 60 may be designed according to the resolution of the AD conversion unit 30 in the subsequent stage. However, preferably, the resistance value of the fixed resistor 60 (R5) is approximately the same as the resistance value of the piezoresistive element 21. In one example, the resistance value of the fixed resistor 60 (R5) may be 1/10 or more and 10 times or less of the resistance value of the piezoresistive element 21, and more preferably 1/0 of the resistance value of the piezoresistive element 21. It may be 10 or more and 1 or less. When the piezoresistance element 21 is several kΩ, the resistance value of the fixed resistor 60 may be about 1 kΩ. If the resistance value of the fixed resistor 60 becomes too large, the change in the calculated value due to the change of the piezoresistive element 21 (V5, equation (26) described later) becomes smaller, so the fixed resistance is smaller than that of the piezoresistive element. It is desirable not to be too big. On the other hand, when the resistance value of the fixed resistor 60 is too small, the calculated value is the ratio of the fixed resistor 60 resistance value to the piezoresistive element 21, so the calculated value itself becomes small. Therefore, it is not desirable that the resistance value of the fixed resistor 60 be too small.

  The first voltage measurement value Vout1 (voltage V13) at the first output terminal 28 and the second voltage measurement value Vout2 (voltage V24) at the second output terminal 29 are respectively acquired and converted into digital values by the AD conversion unit 30. Ru. The first voltage measurement value Vout1 may be the voltage of the first output terminal 28 with respect to the ground potential, and the second voltage measurement value Vout2 may be the voltage of the second output terminal 29 with respect to the ground potential.

  Furthermore, in this example, the voltage measurement value Vout3 at the connection end to which one end of the fixed resistor 60 is connected is obtained. In this example, the voltage measurement value Vout3 corresponds to the voltage V5 across the fixed resistor 60 (R5). The voltage measurement value Vout3 may also be converted into a digital value by the AD conversion unit 30. The processing unit 40 includes a second comparison unit 47. The second comparison unit 47 compares the voltage measurement value Vout3 (V5) across the fixed resistor 60 with the threshold value. The threshold may be stored in advance in the storage unit 50. The diagnosis unit 46 diagnoses the operation state of the pressure measurement device 1 based not only on the comparison result by the comparison unit 44 but also on the comparison result by the second comparison unit 47. Specifically, the diagnosis unit 46 diagnoses whether or not an abnormality has occurred in a part of the plurality of piezoresistance elements 21 based on the comparison result by the comparison unit 44, and based on the comparison result by the second comparison unit 47. Thus, it may be diagnosed whether an abnormality has occurred in the plurality of piezoresistive elements 21 as a whole.

  The calculation unit 42 of this example calculates the voltage ratio X1 (= (Vex−V3) / Vex) as a first calculated value using the first voltage measurement value Vout1 and the power supply voltage Vcc which is a known voltage value. Do. The voltage ratio X1 is the difference (Vex−V3) between the excitation voltage Vex applied between the high potential terminal 26 and the low potential terminal 27 and the voltage (V3) across the piezoresistive element 21-3 (R3). It means the value divided by the excitation voltage Vex. The piezoresistive element 21-3 (R3) is an example of a first piezoresistive element.

  The processing unit 40 also calculates a voltage ratio X4 (V4 / Vex) obtained by dividing the voltage V4 across the piezoresistive element 21-4 (R4) by the excitation voltage Vex. The piezoresistive element 21-4 (R4) is an example of a second piezoresistive element. The voltage ratio X4 (V4 / Vex) is an example of a value obtained from the second voltage measurement value Vout2 at the second output terminal 29. In this example, the comparison unit 44 compares the voltage ratio X4 (V4 / Vex) with the voltage ratio X1 which is the first calculated value. Except for the above point, the configuration of the pressure measurement device 1 of the present embodiment has the same structure as the pressure measurement device 1 of the first embodiment. Therefore, the repeated description is omitted.

  In the pressure measuring device 1 of the second embodiment, when some of the plurality of piezoresistive elements 21 become abnormal, the pressure measuring device 1 is 4 in the same manner as in the first embodiment. The operating condition is diagnosed using the symmetry of change of the individual piezoresistive elements. On the other hand, when the resistance value of the plurality of piezoresistive elements 21 as a whole becomes abnormal, in the pressure measuring device 1, the combined resistance of the bridge circuit 20 changes. Then, due to this, the voltage V5 across the fixed resistor 60 (R5) changes. The operating state is diagnosed by detecting a change in voltage V5. The operation of the operation state diagnosis in the present embodiment will be described below.

[First diagnostic process]
First, a process for determining that an abnormality has occurred in some of the plurality of piezoresistive elements 21 will be described. Assuming that voltages across the respective resistors R1, R3 and R4 which are a plurality of piezoresistive elements 21 are V1, V3 and V4, each voltage can be expressed by the following equation. Vex is an excitation voltage of the bridge circuit 20.

  Here, the voltage ratio of the voltages V3, V1 and V4 to the excitation voltage Vex can be expressed by the following equation from the equations (12) and (13).

Here, each of the piezoresistive elements 21 is designed to have substantially the same resistance value. That is, R1 ₀ = R2 ₀ = R3 ₀ = R4 ₀ . Therefore, when there is no abnormality in the bridge circuit 20 and the like in the pressure measurement device 1, the equations (16) and (19) become equal from the symmetry of the bridge circuit 20. That is, X1 and X4 have the same value.

  Here, when an abnormality occurs in one piezoresistive element 21, the symmetry in the bridge circuit 20 is lost, and the value of X1 and the value of X4 are separated. The diagnosis unit 46 determines that an abnormality has occurred when the difference between the value of X1 and the value of X4 exceeds a predetermined threshold.

  The process of calculating the voltage ratio X1 and the voltage ratio X4 from the first voltage measurement value Vout (V13) and the second voltage measurement value Vout (V24) will be described below. In the second embodiment shown in FIG. 9, the excitation voltages Vex, V3 and V4 can be expressed by the following equations. Here, V5 is a voltage measurement value Vout3 across the fixed resistor 60.

  Therefore, X1 is given by the following equation from equations (11), (14), (20), and (21).

  Further, X4 is given by the following equation from the equations (17), (20) and (22).

  According to the above equation (23), calculation unit 42 measures first voltage measurement value Vout1 (V13), voltage measurement value V5 across fixed resistor 60 (R5), and known power supply voltage value Vcc The voltage ratio X1 can be calculated as a first calculated value using Further, according to the equation (24), the voltage ratio X4 is a value obtained from the second voltage measurement value Vout2 (V24). The voltage ratio X4 is obtained based on the second voltage measurement value Vout2 (V24), the voltage measurement value V5 across the fixed resistor R5, and the known power supply voltage value Vcc.

  In addition, the correction part 43 may be provided also in the pressure measuring device 1 of 2nd Embodiment similarly to the modification demonstrated in FIG. In this case, the correction unit 43 performs correction by multiplying X1 by the correction coefficient α. The calculation unit 42 calculates the first calculated value X1 ′ by multiplying the voltage ratio X1 by the correction coefficient α. In this case, the operating state is accurately diagnosed in consideration of the difference in the arrangement position of the piezoresistive elements 21-1 to 21-4 with respect to the diaphragm portion 10 and the characteristic variation in the piezoresistive elements 21-1 to 21-4. Is possible.

[Second diagnostic process]
Next, a process for determining the operating state in the case where all of the plurality of piezoresistive elements 21 become abnormal without losing the symmetry of the bridge circuit 20 will be described. Assuming that the combined resistance of the bridge circuit 20 is R ', the voltage V5 across the fixed resistor 60 (R5) in the second embodiment can be expressed by the following equation.

  Here, when the plurality of piezoresistive elements 21 are normal, the combined resistance R ′ is substantially constant regardless of the applied pressure due to the symmetry of the bridge circuit 20. However, when the plurality of piezoresistive elements 21 as a whole become abnormal, the combined resistance R ′ changes. Therefore, the value of the voltage V5 changes in accordance with the change of the combined resistance R ′ according to the above equation (26). The second comparison unit 47 compares the voltage V5 across the fixed resistor 60 (R5) with a threshold. The diagnosis unit 46 diagnoses the operation state of the pressure measurement device 1 based on the comparison result of the second comparison unit 47. Specifically, when the voltage V5 across the fixed resistor 60 (R5) exceeds the threshold value, the diagnostic unit 46 determines that an abnormality has occurred in the pressure measurement device 1.

  FIG. 10 is a flowchart showing an example of processing by the pressure measurement device 1 in the second embodiment. FIG. 10 shows an example of a method of operating condition diagnosis of the pressure measuring device 1. As described above, the pressure measurement device 1 executes the first diagnosis process (step S10) and the second diagnosis process (step S20). The first diagnosis process is a process for diagnosing that an abnormality has occurred in some of the plurality of piezoresistive elements 21. The second diagnostic process is a process for diagnosing that the whole of the plurality of piezoresistive elements 21 has become abnormal. The order in which the first diagnosis process (step S10) and the second diagnosis process (step S20) are performed is not limited to the case shown in FIG. The first diagnosis process (step S10) and the second diagnosis process (step S20) may be performed in parallel.

  FIG. 11 is a flowchart illustrating an example of the first diagnosis process. FIG. 11 corresponds to the subroutine of step S10 of FIG. The calculation unit 42 acquires a first voltage measurement value Vout1 (V13) at the first output terminal 28 of the bridge circuit 20 (step S201). The calculation unit 42 acquires a second voltage measurement value Vout2 (V24) at the second output terminal 29 of the bridge circuit 20 (step S202). The calculating unit 42 acquires the voltage V5 across the fixed resistor 60 (step S203). The order of the processing from step S201 to step S203 is not limited to the case of FIG.

  The calculation unit 42 uses the first voltage measurement value Vout1 (V13) at the first output terminal 28, the voltage V5 across the fixed resistor 60, and the known power supply voltage Vcc to generate a voltage ratio X1 (= (Vex− V3) / Vex) is calculated as a first calculated value (step S204). The voltage ratio X1 corresponds to a value obtained by dividing the difference between the excitation voltage Vex and the voltage across the piezoresistive element 21-3 (R3) by the excitation voltage. The calculating unit 42 calculates the voltage ratio X1 by, for example, the above-described equation (23).

  The processing unit 40 uses the second voltage measurement value Vout2 (V24) at the second output terminal 29, the voltage V5 across the fixed resistor 60, and the known power supply voltage Vcc to obtain a voltage ratio X4 (V4 / Vex). Is calculated (step S205). The voltage ratio X4 corresponds to a value obtained by dividing the voltage V4 across the piezoresistive element 21-4 (R4) by the excitation voltage Vex. The calculating unit 42 calculates, for example, the voltage ratio X4 by the above-described equation (24).

The correction unit 43 sets the voltage ratio X1 (= (Vex = (Vex) based on the respective resistance values R1 ₀ , R2 ₀ , R3 ₀ , and R4 ₀ of the plurality of piezoresistive elements 21 in a state where pressure is not applied to the diaphragm unit 10. Correct -V3) / Vex) (step S206). The correction unit 43 may calculate the first calculated value (X1 ′) by multiplying the voltage ratio X1 by the correction coefficient α. However, the process of step S206 may be omitted. The processes of step S201 to step S204 and step S206 are first calculated using the first voltage measurement value Vout1 at the first output terminal 28 of the bridge circuit 20 and a predetermined constant (known power supply voltage Vcc). This corresponds to an example of calculating the value.

  The comparison unit 44 compares the first calculated value (X1 ′) with the voltage ratio X4 (step S207). When the absolute value | X1′−X4 | of the difference between the first calculated value (X1 ′) and the voltage ratio X4 exceeds the threshold (step S208: YES), the diagnosis unit 46 determines that the pressure measurement device 1 has an abnormality. A diagnosis is made (step S209). If the absolute value | X1'-X4 | of the difference between the first calculated value (X1 ') and the voltage ratio X4 is less than or equal to the threshold (step S208: NO), the pressure measuring device 1 is normal. Therefore, the process returns to the main routine. The process of step S207 corresponds to the step of comparing the value obtained from the second voltage measurement value Vout at the second output terminal 29 different from the first output terminal 28 in the bridge circuit 20 with the first calculated value. The processes of step S208 and step S209 correspond to the stage of diagnosing the operating state of the pressure measurement device 1 based on the comparison result.

  FIG. 12 is a flowchart illustrating an example of the second diagnosis process. FIG. 12 corresponds to the subroutine of step S20 of FIG. The second comparing section 47 may compare the voltage measurement value (V5) at both ends of the fixed resistor 60 (R5) with the first threshold P1 and the second threshold P2 (step S301). The first threshold P1 is a lower threshold, and the second threshold P2 is an upper threshold. If the voltage measurement value (V5) is less than the first threshold P1 or exceeds the second threshold P2 (step S302: NO), the pressure measuring device 1 is diagnosed as having an abnormality (step S303). When the voltage measurement value (V5) at both ends of the fixed resistor 60 (R5) is equal to or greater than the first threshold P1 and equal to or less than the second threshold P2 (step S302: YES), the pressure measurement device 1 is normal. Therefore, the process returns to the main routine.

  According to the pressure measurement device 1 of the second embodiment, in addition to the same effects as the pressure measurement device 1 of the first embodiment, the entire piezoresistive elements 21 are affected as a whole as the change of the resistance value due to the aged deterioration. It is also possible to diagnose a type of abnormality that does not lose symmetry in the bridge circuit 20.

  In the pressure measurement device 1 according to the second embodiment, one that executes both the first diagnosis process and the second diagnosis process has been described. However, the pressure measuring device 1 may include the fixed resistor 60 for the purpose other than the diagnosis of the operating state, and may execute only the first diagnostic process. In one example, a fixed resistor 60 may be provided to adjust the voltage of the first voltage measurement value Vout1 and the second voltage measurement value Vout2 of the bridge circuit 20 to an appropriate range. Also in this case, the first diagnostic process is performed as shown in FIG.

  FIG. 13 is a view showing an example of a circuit configuration of a pressure measurement device 1 according to a third embodiment of the present invention. The pressure measurement device 1 of the present embodiment includes a fixed resistor 60 and a fixed resistor 62. In FIG. 13, the fixed resistor 60 is indicated as a resistor R6. Fixed resistor 62 is labeled as resistor R7. The fixed resistor 60 and the fixed resistor 62 may be disposed on the circuit board on which the AD conversion unit 30 and the like are disposed. However, the diffusion resistors of the semiconductor substrate on which the piezoresistive elements 21 are formed may be used as the fixed resistor 60 and the fixed resistor 62. In this case, the fixed resistor 60 and the fixed resistor 62 may be provided on the semiconductor substrate at a position less susceptible to distortion. In this example, fixed resistors are connected to both the high potential terminal 26 and the low potential terminal 27 of the bridge circuit 20, respectively. In the present example, the fixed resistor 60 is electrically connected to the low potential terminal 27. One end of the fixed resistor 60 may be connected to the low potential terminal 27, and the other end of the fixed resistor 60 may be connected to the ground potential (GND). On the other hand, fixed resistor 62 is electrically connected to high potential terminal 26. One end of the fixed resistor 62 may be connected to the high potential terminal 26, and the other end of the fixed resistor 62 may be connected to the power supply voltage (Vcc).

  The pressure measurement device 1 of the present embodiment is common to the pressure measurement device 1 of the second embodiment except that the fixed resistor 62 is provided. Therefore, the repeated description is omitted. The fixed resistor 62 (R7) adjusts the voltage range of the first voltage measurement value Vout1 and the second voltage measurement value Vout2 of the bridge circuit 20 to be within the input available range to the AD conversion unit 30 in the subsequent stage. Therefore, the resistance value of the fixed resistor 62 (R7) may be set according to the specification of the AD conversion unit 30 in the subsequent stage. The resistance value of the fixed resistor 60 may be designed according to the resolution of the AD conversion unit 30 in the subsequent stage. Preferably, the resistance value of the fixed resistor 60 (R5) is approximately the same as the resistance value of the piezoresistive element 21. In one example, the resistance value of the fixed resistor 60 (R5) may be 1/10 or more and 10 times or less of the resistance value of the piezoresistive element 21, and more preferably 1/0 of the resistance value of the piezoresistive element 21. It may be 10 or more and 1 or less.

  In the third embodiment shown in FIG. 13, the excitation voltages Vex, V3 and V4 can be expressed by the following equations. Here, V5 is a voltage measurement value Vout3 across the fixed resistor 60. V7 is a voltage measurement across the fixed resistor 62.

  Therefore, X1 is given by the following equation from equations (11), (14), (27), (28).

  Further, X4 is given by the following equation from the equations (17), (27) and (29).

  According to the above equation (30), the calculation unit 42 measures the first voltage measurement value Vout1 (V13), the voltage measurement value V6 across the fixed resistor 60 (R6), and the fixed resistor 60 (R6). The voltage ratio X1 can be calculated as a first calculated value using the ratio of the resistance values of the fixed resistor 62 (R7) and the known power supply voltage Vcc. Further, according to Expression (31), the voltage ratio X4 is an example of a value obtained from the second voltage measurement value Vout2 (V24). The voltage ratio X4 is the second voltage measurement value Vout2 (V24), the voltage measurement value V6 across the fixed resistor 60 (R6), and the resistances of the fixed resistor 60 (R6) and the fixed resistor 62 (R7) It is calculated using the ratio of values and the known power supply voltage Vcc.

  That is, according to the equations (30) and (31), the power supply voltage Vcc which is a known value, the voltage measurement value across the fixed resistor 60 (R6), and the fixed resistor 60 (R6) and the fixed resistor Using the first voltage measurement value Vout1 (V13) and the second voltage measurement value Vout2 (V24), which are measurement values for detecting pressure, in addition to the ratio of the resistance value to 62 (R7), the voltage ratio X1 And the voltage ratio X4 can be calculated.

  Furthermore, the correction unit 43 may calculate the first calculated value X1 ′ by multiplying X1 by the correction coefficient α using Expression (25). The comparison unit 44 may compare the first calculated value (X1 ′) with the voltage ratio X4. When the absolute value | X1′−X4 | of the difference between the first calculated value (X1 ′) and the voltage ratio X4 exceeds the threshold, the diagnosis unit 46 may diagnose that an abnormality has occurred in the pressure measurement device 1 .

  In the third embodiment, the voltage V6 across the fixed resistor 60 (R6) can be expressed by the following equation.

  Here, when the plurality of piezoresistive elements 21 are normal, the combined resistance R ′ is substantially constant regardless of the applied pressure due to the symmetry of the bridge circuit 20. However, when the plurality of piezoresistive elements 21 as a whole become abnormal, the combined resistance R ′ changes. According to the equation (32), the value of the voltage V6 changes in accordance with the change of the combined resistance R ′. The second comparison unit 47 compares the voltage V6 across the fixed resistor 60 (R6) with a threshold. The diagnosis unit 46 diagnoses the operation state of the pressure measurement device 1 based on the comparison result of the second comparison unit 47. Specifically, when the voltage V6 across the fixed resistor 60 (R6) exceeds the threshold, the diagnosis unit 46 determines that an abnormality has occurred in the pressure measurement device 1.

  FIG. 14 is a flowchart showing an example of the first diagnostic process in the third embodiment. The processing content in the third embodiment is the same as the processing content in the second embodiment shown in FIG. In particular, the second diagnostic process in the third embodiment is similar to the second diagnostic process in the second embodiment shown in FIG. Therefore, the repeated description is omitted.

  FIG. 14 corresponds to the subroutine of step S10 of FIG. Steps S401 to S403 are the same as the processing shown in FIG. 11 in the second embodiment. The calculation unit 42 includes a first voltage measurement value Vout1 (V13) at the first output terminal 28, a voltage V6 across the fixed resistor 60 (R6), a fixed resistor 60 (R6), and a fixed resistor 62 (R7). The voltage ratio X1 (= (Vex−V3) / Vex) is calculated as a first calculated value using the ratio of (R7 / R6) and the known power supply voltage Vcc (step S404). The calculating unit 42 calculates, for example, the voltage ratio X1 by the above-described equation (30).

  The processing unit 40 includes a second voltage measurement value Vout2 (V24) at the second output terminal 29, a voltage V6 across the fixed resistor 60 (R6), a fixed resistor 60 (R6), and a fixed resistor 62 (R7). The voltage ratio X4 (V4 / Vex) is calculated using the ratio (R7 / R6) and the known power supply voltage Vcc (step S405). The voltage ratio X4 corresponds to a value obtained by dividing the voltage V4 across the piezoresistive element 21-4 (R4) by the excitation voltage Vex. The calculating unit 42 calculates the voltage ratio X4 by, for example, the above-described equation (31).

  The processes of steps S406 to S409 are the same as the processes of steps S206 to S209 in FIG. 11 of the second embodiment. Therefore, the repeated description is omitted.

  According to the pressure measurement device 1 of the third embodiment, as in the pressure measurement device 1 of the second embodiment, the bridge circuit 20 affects the entire plurality of piezoresistive elements 21 like a change in resistance value due to aging. It is also possible to diagnose types of abnormalities that do not lose symmetry in. In addition, it is possible to adjust the voltage range of the first voltage measurement value Vout1 and the second voltage measurement value Vout2 of the bridge circuit 20 to the input possible range of the circuit of the latter stage by the fixed resistor 62 (R7), and the operating state Can be diagnosed.

  FIG. 15 is a view showing a schematic configuration of a pressure measurement device 1 according to a fourth embodiment of the present invention. The pressure measurement device 1 of the fourth embodiment includes a temperature acquisition unit 70. The temperature acquisition unit 70 acquires temperature information on the periphery of the bridge circuit 20. The temperature acquisition unit 70 may be a temperature sensor or the like, or may acquire temperature information from a separate temperature sensor or the like. The temperature information may be converted into a digital value by the AD conversion unit 30. The processing unit 40 changes thresholds such as the first threshold P1 and the second threshold P2 to be compared with the voltage measurement value (V6) or the like at both ends of the fixed resistor 60 (R6) based on the temperature information. The other configuration of the present embodiment is the same as the configuration of the third embodiment shown in FIGS. 13 and 14. Therefore, the repeated description is omitted.

  FIG. 16 is a flowchart showing an example of the second diagnosis process in the fourth embodiment. FIG. 16 corresponds to the subroutine of step S20 of FIG. The processing content in the fourth embodiment is the same as the processing content in the third embodiment. In particular, the first diagnostic process is common to the process in the third embodiment shown in FIG. Therefore, the repeated description is omitted.

  The temperature acquisition unit 70 acquires temperature information on the periphery of the bridge circuit 20 (step S501). Then, the processing unit 40 changes the first threshold P1 and the second threshold P2 according to the acquired temperature information (step S502). The first threshold P1 and the second threshold P2 are thresholds to be compared with the voltage measurement value (V6) across the fixed resistor 60 (R6). The processes of steps S503 to S505 are the same as the processes of steps S301 to S303 of FIG. Therefore, the detailed description is omitted.

  The resistance value of the piezoresistive element 21 has a temperature characteristic. That is, the resistance value of the piezoresistive element 21 changes according to the temperature. Therefore, when using a constant value regardless of the temperature as the first threshold P1 and the second threshold P2, the first threshold P1 and the second threshold P2 do not erroneously detect that an abnormality has occurred although the pressure measuring device 1 is normal. It is necessary to provide one threshold P1 and a second threshold P2. As a result, since the threshold value is not exceeded unless the voltage measurement value (V6) at both ends of the fixed resistor 60 (R6) changes significantly, the diagnostic unit 46 determines that the resistance value of the piezoresistive element changes significantly. It is difficult to diagnose any other abnormalities. On the other hand, as in the present embodiment, by changing the first threshold value P1 and the second threshold value P2 according to the temperature, it is possible to diagnose also an abnormality in which the resistance value of the piezoresistive element changes small. .

  In the above description, as the fourth embodiment, in the case where the fixed resistor 60 and the fixed resistor 62 are provided, the case where the first threshold P1 and the second threshold P2 are changed according to the temperature has been described. The four embodiments are not limited to this case. In one example, when the pressure measurement device 1 has only the fixed resistor 60 as in the second embodiment, the first threshold P1 and the second threshold P2 may be changed according to the temperature.

  As an example of the diagnosis of the operation state, an example of characteristics when the process by the pressure measurement device 1 of the third embodiment and the fourth embodiment is applied is shown in FIG. 17 to FIG. FIG. 17 is a diagram showing an example of a voltage ratio at normal time in the third embodiment. In FIG. 17, X1 'is the first voltage measurement value Vout1 (V13), and the voltage measurement value V6 across the fixed resistor 60 (R6) fixed, as shown in equations (30) and (25). It is a voltage ratio calculated as a first calculated value using the ratio of the resistance values of the resistor 60 (R6) and the fixed resistor 62 (R7) and the known power supply voltage Vcc. X4 is a second voltage measurement value Vout2 (V24), a voltage measurement value V6 across the fixed resistor 60 (R6), and resistances of the fixed resistor 60 (R6) and the fixed resistor 62 (R7). It is calculated using the ratio and the known power supply voltage Vcc. Note that X3 is a voltage ratio obtained by dividing the voltage V3 at both ends of the piezoresistive element 21-3 (R3) by the excitation voltage Vex. X3 is obtained by the following equation.

  The horizontal axis in FIG. 17 indicates the input pressure (%) to the diaphragm unit 10. In this example, as the pressure on the diaphragm 10 increases, the voltage ratio X3 decreases and the voltage ratio X4 and the first calculated value X1 'increase. As shown in FIG. 4, in the state where no abnormality occurs in the pressure measurement device 1, the first calculated value X1 ′ and the voltage ratio X4 almost coincide with each other.

  FIG. 18 is a diagram showing an example of a difference in voltage ratio in a normal state in the third embodiment. The horizontal axis in FIG. 18 indicates the input pressure (%) to the diaphragm unit 10. The vertical axis in FIG. 18 indicates the difference between the first calculated value X1 'and the voltage ratio X4. In the state where no abnormality occurs in the pressure measuring device 1, the difference between the first calculated value X1 'and the voltage ratio X4 remains near zero. Since the difference between the first calculated value X1 'and the voltage ratio X4 remains in the range between the lower limit threshold and the upper limit threshold, the diagnosis unit 46 may diagnose that the pressure measuring device 1 does not have an abnormality. it can.

  FIG. 19 is a view showing an example of a voltage ratio at the time of abnormality in the third embodiment. FIG. 20 is a view showing an example of a difference in voltage ratio at the time of abnormality in the third embodiment. In FIGS. 19 and 20, items indicated by X3, X4, X1 ′, the horizontal axis, and the vertical axis are the same as those in FIGS. 17 and 18. FIGS. 19 and 20 illustrate the case where an abnormality occurs in the piezoresistive element 21-4 (R 4) in the vicinity of 83% of the input pressure to the diaphragm unit 10. As shown in FIG. 19, when an abnormality occurs in some of the plurality of piezoresistive elements 21 in the pressure measurement device 1, the first calculated value X1 ′ and the voltage X4 diverge. Therefore, as shown in FIG. 20, when abnormality occurs in some of the plurality of piezoresistive elements 21, the difference between the first calculated value X1 'and the voltage ratio X4 is equal to or higher than the lower threshold and lower than the upper threshold. It deviates from the normal range given. In this example, the difference between the first calculated value X1 'and the voltage X4 is less than the lower limit threshold. Therefore, the diagnosis unit 46 can diagnose that an abnormality has occurred in a part of the plurality of piezoresistive elements 21 in the pressure measurement device 1.

  FIG. 21 is a diagram showing an example of voltages at both ends of the fixed resistor at the time of abnormality in the third embodiment of the present invention. FIG. 21 shows a change in voltage measurement value V6 between both ends of fixed resistor 60 (R6) before and after occurrence of abnormality. In FIG. 21, the solid line is the voltage measurement value V6 in the normal state, and the dotted line is the voltage measurement value V6 after the occurrence of an abnormality.

  The horizontal axis in FIG. 21 indicates the temperature around the bridge circuit 20. The vertical axis in FIG. 21 indicates a voltage measurement value V6 across the fixed resistor 60 (R6). In this example, as the temperature rises, the voltage measurement value V6 across the fixed resistor 60 (R6) decreases. In FIG. 21, the case where the first threshold value P1 and the second threshold value P2 are fixed regardless of the temperature is indicated by alternate long and short dash lines 2 and 3. On the other hand, the case where the first threshold value P1 and the second threshold value P2 are changed according to the temperature is indicated by two-dot chain lines 4 and 5.

  When fixing the first threshold P1 and the second threshold P2 regardless of the temperature, the first threshold P1 is set so that a change in the voltage measurement value V6 due to temperature characteristics of the piezoresistive element 21 or the like is not erroneously detected as a change due to abnormality. And a second threshold P2 is set. Therefore, when the voltage measurement value V6 largely changes and the voltage measurement value V6 falls below the first threshold P1 indicated by the alternate long and short dash line 2 or exceeds the second threshold P2 indicated by the alternate long and short dash line 3, abnormality occurs. It is diagnosed. Therefore, when the voltage measurement value V6 changes small, it is difficult to determine that it is abnormal.

  When the first threshold P1 and the second threshold P2 are changed according to the temperature as indicated by the two-dot chain lines 4 and 5, the first threshold P1 and the second threshold P2 are changed based on the temperature characteristics at the normal time. You may A value obtained by subtracting a predetermined constant d from the temperature characteristic V6 (t) at the normal time may be set as a first threshold P1, and a value obtained by adding the constant d may be set as a second threshold P2. In this case, it is possible to set a first threshold P1 and a second threshold P2 indicating characteristics obtained by translating the characteristics of the temperature change of V6 in parallel. By changing the first threshold value P1 and the second threshold value P2 in accordance with the temperature, it is possible to diagnose also an abnormality in which the resistance value of the piezoresistive element 21 changes small.

  Although the third embodiment and the fourth embodiment have been described with reference to FIGS. 17 to 21, the second embodiment also has the same characteristics as those of the first calculated values X1 ′ and X4 except that they have different calculation formulas. Show.

  In the above description, as the first piezoresistive element and the second piezoresistive element, the piezoresistive element 21-3 (R3) and the piezoresistive element commonly connected at one end to the low potential terminal 27 of the bridge circuit 20 The case where 21-4 (R4) is used has been described. However, as the first piezoresistive element and the second piezoresistive element, piezoresistive element 21-1 (R1) and piezoresistive element 21-2 (R2) commonly connected at one end to high potential terminal 26 of bridge circuit 20. ) May be used.

  As described above, according to each embodiment of the present invention, it operates only with the output voltage value of the bridge circuit 20 or the output voltage value of the bridge circuit 20 and the voltage value of the fixed resistor 60 connected to the bridge circuit. Since the state can be diagnosed, it is possible to provide the pressure measurement device 1 having the operation state diagnosis function with a simple configuration while suppressing increase in size and cost of the sensor.

  As mentioned above, although this invention was demonstrated using embodiment, the technical scope of this invention is not limited to the range as described in the said embodiment. It is apparent to those skilled in the art that various changes or modifications can be added to the above embodiment. It is also apparent from the scope of the claims that the embodiments added with such alterations or improvements can be included in the technical scope of the present invention.

  The execution order of each process such as operations, procedures, steps, and steps in the apparatuses, systems, programs, and methods shown in the claims, the specification, and the drawings is particularly “before”, “preceding” It is to be noted that “it is not explicitly stated as“ etc. ”and can be realized in any order as long as the output of the previous process is not used in the later process. With regard to the flow of operations in the claims, the specification and the drawings, even if it is described using “first,” “next,” etc. for convenience, it means that it is essential to carry out in this order. It is not a thing.

1 · · Pressure measuring device, 2 · · · 1 dotted line, 3 · · 1 dotted line, 4 · · 2 dotted line, 5 · · 2 dotted line, 10 · · · diaphragm portion, 12 · · · hollow portion, 20 · · bridge circuit , 21... Piezoresistive elements 22. 29 second output terminal 30 AD conversion unit 40 processing unit 42 calculation unit 43 correction unit 44 comparison unit 46 diagnosis unit 47 second Comparison unit, 50 · · · Storage unit, 60 · · · Fixed resistor, 62 · · · Fixed resistor, 70 · · · Temperature acquisition unit

Claims (10)

A pressure measuring device,
A diaphragm portion displaced by an applied pressure;
A plurality of piezoresistive elements provided in the diaphragm portion and constituting a bridge circuit;
A calculation unit that calculates a first calculation value using a first voltage measurement value at a first output terminal of the bridge circuit and a predetermined constant;
A comparator for comparing the first calculated value with a value obtained from a second voltage measurement value at a second output terminal different from the first output terminal in the bridge circuit;
And a diagnostic unit configured to diagnose an operation state of the pressure measurement device based on a comparison result by the comparison unit. The plurality of piezoresistive elements includes a first piezoresistive element and a second piezoresistive element commonly connected at one end to one of the high potential terminal and the low potential terminal of the bridge circuit. Yes,
The calculation unit uses the first voltage measurement value and a known voltage value to generate an excitation voltage applied between the high potential terminal and the low potential terminal and a voltage between both ends of the first piezoresistive element. Calculating the difference between the
The pressure measurement device according to claim 1, wherein the comparison unit compares a voltage between both ends of the second piezoresistive element obtained from the second voltage measurement value with the first calculated value. The calculation unit further includes a correction unit that corrects the difference based on resistance values of the plurality of piezoresistive elements in a state in which no pressure is applied to the diaphragm unit,
The pressure measurement device according to claim 2, wherein the difference corrected by the correction unit is calculated as the first calculated value. The plurality of piezoresistive elements includes a first piezoresistive element and a second piezoresistive element commonly connected at one end to one of the high potential terminal and the low potential terminal of the bridge circuit. Yes,
The calculation unit uses the first voltage measurement value and a known voltage value to generate an excitation voltage applied between the high potential terminal and the low potential terminal and a voltage between both ends of the first piezoresistive element. Calculating a voltage ratio obtained by dividing the difference between the voltage and the excitation voltage by the excitation voltage as the first calculation value,
The pressure measurement device according to claim 1, wherein the comparison unit compares the voltage ratio obtained by dividing the voltage between both ends of the second piezoresistive element by the excitation voltage, and the first calculated value. A fixed resistor electrically connected to one of the high potential terminal and the low potential terminal of the bridge circuit;
The calculation unit calculates the first calculated value using the first voltage measurement value, a voltage measurement value across the fixed resistor, and a known power supply voltage value.
The voltage ratio obtained by dividing the voltage across the second piezoresistive element by the excitation voltage is the second voltage measurement value, the voltage measurement across the fixed resistor, and the known power supply voltage value. The pressure measuring device according to claim 4 obtained by using. The calculation unit further corrects a voltage ratio obtained by dividing the difference by the excitation voltage based on resistance values of the plurality of piezoresistive elements in a state where no pressure is applied to the diaphragm unit. Including
The pressure measurement device according to claim 4, wherein the voltage ratio corrected by the correction unit is calculated as the first calculated value. The pressure measurement device according to any one of claims 2 to 6, wherein the first piezoresistive element and the second piezoresistive element are electrically connected to the low potential terminal. A fixed resistor electrically connected to one of the high potential terminal and the low potential terminal of the bridge circuit;
And a second comparison unit that compares a voltage measurement value across the fixed resistor with a threshold value,
The pressure measurement device according to any one of claims 2 to 7, wherein the diagnosis unit further diagnoses an operation state of the pressure measurement device based on a comparison result by the second comparison unit. An acquisition unit for acquiring temperature information around the bridge circuit;
The pressure measurement device according to claim 8, wherein the threshold is changed based on the temperature information. A method of diagnosing an operation state of a pressure measurement device, comprising: a diaphragm portion displaced by an applied pressure; and a plurality of piezoresistive elements provided on the diaphragm portion and forming a bridge circuit, the first output of the bridge circuit Calculating a first calculated value using a first voltage measurement value at the terminal and a predetermined constant;
Comparing the first calculated value with a value obtained from a second voltage measurement at a second output terminal different from the first output terminal in the bridge circuit;
Diagnosing the operating state of the pressure measuring device based on the comparison result;
A method of operating condition diagnosis of a pressure measuring device comprising: