Capacitive sensor

Abstract

This single device enables high-precision pressure measurement across a wide range of conditions. [Solution] The capacitive sensor comprises a pressure receiving unit 1 having a sensor element that outputs a sensor signal based on capacitance that fluctuates according to the pressure of the object to be measured, an analog processing circuit unit 20 that amplifies the sensor signal, and a pressure calculation unit 14a that calculates a pressure value based on the output signal of the analog processing circuit unit 20. The analog processing circuit unit 20 comprises a plurality of amplification circuits 5a, 5b with different amplification ratios. The pressure calculation unit 14a calculates a plurality of pressure values ​​based on the outputs of the plurality of amplification circuits 5a, 5b.

Description

[Technical Field]

[0001] This invention relates to a capacitive sensor. [Background technology]

[0002] A capacitive sensor, whose capacitance fluctuates according to a physical quantity (e.g., pressure), converts pressure and temperature signals from a pressure-receiving unit to analog and inputs them to a CPU. The CPU performs polynomial calculations, converts the resulting pressure value into an analog value, and outputs it (Patent Document 1). Figure 17 shows the circuit of a conventional capacitive sensor.

[0003] The capacitive sensor comprises a pressure receiving unit 1, a signal generator 2, charge amplification circuits 3 and 4, a differential amplification circuit 5, detection circuits 6 to 8, low-pass filters (LPFs) 9 to 11, a multiplexer 12, an AD converter 13, a pressure calculation unit 14, a communication circuit 15, and an output circuit 16.

[0004] Figure 18 is a cross-sectional view showing the structure of the sensor chip of the pressure receiving unit 1. A recess is formed in the center of the base 101 of the sensor chip 100. A diaphragm 102, which is configured to be deformable according to the pressure PV of the medium to be measured (e.g., process gas), is bonded to the surface of the base 101 where this recess is formed. Together with the diaphragm 102, the recess of the base 101 forms a reference vacuum chamber 103.

[0005] A fixed electrode 104 is formed on the base 101 on the side facing the reference vacuum chamber 103, and a movable electrode 105 is formed on the side of the diaphragm 102 facing the reference vacuum chamber 103 so as to face the fixed electrode 104. In this way, the fixed electrode 104 and the movable electrode 105 are arranged to face each other with a gap between them. When the diaphragm 102 flexes under the pressure PV of the medium being measured, the distance between the movable electrode 105 and the fixed electrode 104 changes, and the capacitance CX between the movable electrode 105 and the fixed electrode 104 changes. The pressure PV of the medium being measured, which the diaphragm 102 is subjected to, can be detected from this change in capacitance CX.

[0006] Furthermore, a fixed electrode 106 is formed on the surface of the base 101 on the outside of the fixed electrode 104 that faces the reference vacuum chamber 103. A movable electrode 107 is formed on the surface of the diaphragm 102 on the outside of the movable electrode 105 that faces the reference vacuum chamber 103, so as to face the fixed electrode 106. The fixed electrode 106 and the movable electrode 107 are formed on the edge of the diaphragm 102. Even if the diaphragm 102 bends due to the pressure PV of the medium being measured, the edge of the diaphragm 102 hardly deforms, so the capacitance CY between the movable electrode 107 and the fixed electrode 106 does not change easily. This capacitance CY is provided to eliminate measurement errors based on temperature changes inside and outside the sensor and humidity changes inside the reference vacuum chamber 103. The diaphragm 102 and the base 101 are made of an insulator such as sapphire.

[0007] Figure 19 is a cross-sectional view of the package structure of the pressure receiving unit 1. As shown in Figure 19, the sensor chip 100 is housed in a metal housing 108. A partition wall 109 is provided inside the housing 108. The partition wall 109 consists of a base plate 109a and a support plate 109b, and separates the internal space of the housing 108 into a first space 110a and a second space 110b. The outer circumference of the support plate 109b is fixed to the housing 108 and supports the base plate 109a in a floating state within the internal space of the housing 108. The sensor chip 100 is fixed to the second space 110b side of the base plate 109a. The base plate 109a also has a pressure introduction hole 109c formed therein to guide the pressure in the first space 110a to the diaphragm 102 of the sensor chip 100. The second space 110b is in communication with the reference vacuum chamber 103 of the sensor chip 100 and is in a vacuum state.

[0008] The pressure introduction pipe 111 is connected to the first space 110a side of the housing 108. A baffle 112 is provided between the pressure introduction pipe 111 and the housing 108. The medium to be measured introduced from the pressure introduction pipe 111 strikes the plate surface of the baffle 112 and flows into the first space 110a of the housing 108 through the gap around the baffle 112. The pressure-receiving section temperature detection circuit 113 shown in Figure 17 measures the temperature of the housing 108 as the temperature of the pressure-receiving section 1 and outputs a temperature signal VS. The substrate temperature detection circuit 114 measures the temperature of the substrate on which the charge amplifier circuits 3 and 4, the differential amplifier circuit 5, the detection circuits 6 to 8, the LPFs 9 to 11, and the multiplexer 12 are mounted, and outputs a temperature signal VC.

[0009] The signal generator 2 applies a sinusoidal sensor drive signal to the first electrode (e.g., fixed electrode 104) and the third electrode (e.g., fixed electrode 106) of the pressure receiving unit 1. The charge amplifier circuit 3, consisting of a capacitor CF and an operational amplifier A1, converts the current (sensor signal) output from the second electrode (e.g., movable electrode 105) of the pressure receiving unit 1 into a voltage. The charge amplifier circuit 4, consisting of a capacitor CF and an operational amplifier A2, converts the current (sensor signal) output from the fourth electrode (e.g., movable electrode 107) of the pressure receiving unit 1 into a voltage. The differential amplifier circuit 5 amplifies the difference between the output signal of the charge amplifier circuit 3 and the output signal of the charge amplifier circuit 4.

[0010] The detection circuit 6 half-wave or full-wave rectifies the output signal of the charge amplifier circuit 3. The LPF 9 smooths the output signal of the detection circuit 6. This yields a signal SCX with an amplitude proportional to capacitance CX. The detection circuit 7 half-wave or full-wave rectifies the output signal of the charge amplifier circuit 4. The LPF 10 smooths the output signal of the detection circuit 7. This yields a signal SCY with an amplitude proportional to capacitance CY. The detection circuit 8 half-wave or full-wave rectifies the output signal of the differential amplifier circuit 5. The LPF 11 smooths the output signal of the detection circuit 8. This yields a signal SXY with an amplitude proportional to capacitance CX-CY. The multiplexer 12 switches the input to the AD converter 13 in the order, for example, SCX→SCY→SXY→VS→VC→SCX→SCY→SXY→VS→VC→····. The AD converter 13 converts the output of the multiplexer 12 into a digital signal.

[0011] The operation of the pressure calculation unit 14, the communication circuit 15, and the output circuit 16 will be explained using Figure 20. When the AD conversion result of the signal SCX is input from the AD converter 13 (step S100), the pressure calculation unit 14 calculates the value of capacitance CX from this AD conversion result (step S101). When the AD conversion result of the signal SCY is input from the AD converter 13 (step S102), the pressure calculation unit 14 calculates the value of capacitance CY from this AD conversion result (step S103).

[0012] Next, when the AD conversion result of the signal SXY is input from the AD converter 13 (step S104), the pressure calculation unit 14 calculates the capacitance CX-CY value from this AD conversion result, and then divides the capacitance CX-CY by the capacitance CX calculated in step S101 to calculate VO = (CX-CR) / CX (step S105). When the AD conversion result of the temperature signal VS is input from the AD converter 13 (step S106), the pressure calculation unit 14 calculates the temperature ST of the pressure receiving unit 1 from this AD conversion result (step S107).

[0013] Next, the pressure calculation unit 14 calculates the pressure PV of the medium to be measured using the following formula (1) based on the calculation result VO from step S105 and the calculation result ST from step S107 (step S108).

[0014]

number

[0015] In equation (1), A ij is a correction coefficient determined for each product during the factory adjustment process, and i and j are the degrees of the polynomial. The communication circuit 15 transmits the digital value of pressure PV to the outside (step S109). The output circuit 16 converts the digital value of pressure PV into an analog signal (e.g., 0-10V output) and outputs it (step S110).

[0016] Furthermore, if the capacitance CX calculated in step S101 is below a predetermined capacitance threshold (Yes in step S111), the pressure calculation unit 14 determines that the capacitance CX detection unit (fixed electrode 104 and movable electrode 105) of the pressure receiving unit 1 is broken (step S112) and issues an alarm (step S113). Similarly, if the capacitance CY calculated in step S103 is below a predetermined capacitance threshold (Yes in step S114), the pressure calculation unit 14 determines that the capacitance CY detection unit (fixed electrode 106 and movable electrode 107) of the pressure receiving unit 1 is broken (step S115) and issues an alarm (step S116). Also, if the pressure PV calculated in step S108 is below a predetermined pressure threshold (Yes in step S117), the pressure calculation unit 14 lights up the LED (step S118).

[0017] The capacitive sensor repeatedly performs the process described in Figure 20. The reason for using VO=(CX-CR) / CX to calculate the pressure PV is to cancel out error components, as described in Patent Document 1. In the configuration of Figure 17, the capacitance CX-CY is calculated by subtracting the output signal of charge amplifier circuit 4 from the output signal of charge amplifier circuit 3, amplifying the signal, and then performing AD conversion. There is also a method of calculating SCX-SCY using a CPU, but the accuracy is not very good because the signals SCX and SCY are small. Therefore, in conventional capacitive sensors, the differential amplifier circuit 5 in the analog processing circuit amplifies the difference between the output signal of charge amplifier circuit 3 and the output signal of charge amplifier circuit 4, thereby obtaining a signal SXY with an amplitude proportional to the capacitance CX-CY.

[0018] Figures 21 and 22 are circuit diagrams showing an example configuration of differential amplifier circuit 5. The differential amplifier circuit 5 in Figure 21 consists of an operational amplifier A3 and resistors Ra, Rc, Re, and Rf. The output signal of the charge amplifier circuit 3 is connected to Vin + The output signal of the charge amplifier circuit 4 is Vin - Therefore, the output voltage of the differential amplifier circuit 5 in Figure 21 is (Vin + ―Vin - ) × Rf / Rc. Note that Ra = Rc and Re = Rf.

[0019] The differential amplifier circuit 5 in FIG. 22 is composed of operational amplifiers A4 to A6 and resistors R1 to R3, Ra, Rc, Re, and Rf. The output voltage of the differential amplifier circuit 5 in FIG. 22 is (Vin + −Vin - )×(1+2×R1 / R2)×Rf / Rc. In addition, Ra=Rc, Re=Rf, and R1=R3.

[0020] In the configurations shown in FIG. 17, FIG. 21, and FIG. 22, the output voltage of the differential amplifier circuit 5 increases as the pressure PV increases, but when PV exceeds a certain pressure value, it exceeds the outputtable range of the differential amplifier circuit 5, and the output voltage of the differential amplifier circuit 5 is clamped at its upper limit. Accordingly, the value of the pressure PV calculated using the output voltage of the differential amplifier circuit 5 is also clamped at its upper limit.

[0021] In conventional capacitive sensors, there is only one type of differential amplifier circuit 5. Although it is necessary to increase the amplification factor of the differential amplifier circuit 5 to measure the pressure PV with high accuracy, this limits the measurable range of pressure PV. On the other hand, reducing the amplification factor of the differential amplifier circuit 5 broadens the measurable range of pressure PV, but makes it impossible to measure pressure PV with high accuracy in a low pressure region. Therefore, in order to accurately measure a wide range of pressure PV, it is necessary to arrange a plurality of capacitive sensors side by side, which poses a problem that the installation space increases in proportion to the number of sensors.

Prior Art Literature

Patent Literature

[0022]

Patent Literature 1

Summary of the Invention

Problem to be Solved by the Invention

[0023] The present invention has been made to solve the above problem, and an object thereof is to provide a capacitive sensor that can achieve high-precision pressure measurement over a wide range with a single unit. [Means for solving the problem]

[0024] The capacitive sensor of the present invention comprises a pressure receiving unit having a sensor element configured to output a sensor signal based on capacitance that fluctuates according to the pressure of the object to be measured; an analog processing circuit unit configured to amplify the sensor signal; and a pressure calculation unit configured to calculate a pressure value based on the output signal of the analog processing circuit unit, wherein the analog processing circuit unit comprises a plurality of amplification circuits with different amplification ratios, and the pressure calculation unit calculates a plurality of pressure values ​​based on the outputs of each of the plurality of amplification circuits. Furthermore, in one example of the configuration of the capacitive sensor of the present invention, the sensor element comprises a first electrode formed on a base, a second electrode formed on a diaphragm separated from the base by a gap so as to face the first electrode, a third electrode formed on the base outside the first electrode, and a fourth electrode formed on the diaphragm outside the second electrode so as to face the third electrode, wherein the distance between the first and second electrodes changes according to the displacement of the diaphragm due to the pressure of the object to be measured, and the analog processing circuit unit comprises a plurality of amplification circuits that amplify the difference between a first sensor signal based on the capacitance CX between the first and second electrodes and a second sensor signal based on the capacitance CY between the third and fourth electrodes at different amplification factors. Furthermore, in one example configuration of the capacitive sensor of the present invention, the pressure calculation unit is characterized in that it calculates the value of the capacitance CX based on the first sensor signal, calculates a plurality of capacitance CX-CY values ​​based on the respective outputs of the plurality of amplification circuits, and calculates a plurality of pressure values ​​from the results of dividing each of the plurality of capacitance CX-CY values ​​by the value of the capacitance CX.

[0025] Furthermore, in one example configuration of the capacitive sensor of the present invention, the pressure receiving section is equipped with a plurality of sensor elements, and the analog processing circuit section is equipped with a plurality of differential amplifier circuits with different amplification factors for each sensor element. Furthermore, in one example configuration of the capacitive sensor of the present invention, the pressure calculation unit is characterized by calculating an integrated pressure value that combines the multiple pressure values ​​into one. Furthermore, in one configuration example of the capacitive sensor of the present invention, the pressure calculation unit is characterized in that, when there is one sensor element and two amplification circuits with different amplification factors are provided in the analog processing circuit unit, the first pressure value calculated based on the output of the amplification circuit with the smaller amplification factor among the first and second pressure values ​​calculated based on the outputs of the two amplification circuits is set as the monitoring pressure value, when the monitoring pressure value is within a predetermined overlapping range, the weighted average value of the first and second pressure values ​​is set as the integrated pressure value, when the monitoring pressure value is lower than the overlapping range, the second pressure value calculated based on the output of the amplification circuit with the larger amplification factor is set as the integrated pressure value, and when the monitoring pressure value is higher than the overlapping range, the first pressure value is set as the integrated pressure value.

[0026] Furthermore, in one example configuration of the capacitive sensor of the present invention, the pressure calculation unit is characterized in that, when the second pressure value exceeds a predetermined overrange value, it performs a saturation process to set the second pressure value to the overrange value and then calculates the integrated pressure value. Furthermore, in one configuration example of the capacitive sensor of the present invention, the pressure calculation unit is characterized in that, when the monitoring pressure value is within the range of the overlapping area and the difference between the second pressure value and the first pressure value is less than or equal to a predetermined threshold, it does not calculate a weighted average of the first and second pressure values, but instead uses the second pressure value as the integrated pressure value. Furthermore, in one configuration example of the capacitive sensor of the present invention, the pressure calculation unit is characterized in that, when there is one sensor element and three or more amplification circuits with different amplification factors are provided in the analog processing circuit unit, the pressure value calculated based on the output of the amplification circuit with the smallest amplification factor among the three or more latest pressure values ​​calculated based on the output of each of the three or more amplification circuits is set as the monitoring pressure value, when the monitoring pressure value is within a predetermined overlapping range, the weighted average of the first and second pressure values ​​adjacent to the immediately preceding integrated pressure value among the three or more pressure values ​​is set as the latest integrated pressure value, when the monitoring pressure value is lower than the overlapping range, the second pressure value calculated based on the output of the amplification circuit with the larger amplification factor among the first and second pressure values ​​is set as the latest integrated pressure value, and when the monitoring pressure value is higher than the overlapping range, the first pressure value calculated based on the output of the amplification circuit with the smaller amplification factor among the first and second pressure values ​​is set as the latest integrated pressure value.

[0027] Furthermore, in one configuration example of the capacitive sensor of the present invention, the pressure calculation unit is characterized in that, when there are multiple sensor elements and multiple differential amplifier circuits with different amplification factors are provided for each sensor element in the analog processing circuit unit, the pressure value calculated based on the output of the smallest amplification factor among the two or more amplifier circuits provided for the sensor element with the highest pressure range from among the four or more latest pressure values ​​calculated based on the output of each of the four or more amplifier circuits, is set as the monitoring pressure value, when the monitoring pressure value is within a predetermined overlapping range, the weighted average of the first and second pressure values ​​adjacent to the immediately preceding integrated pressure value from among the four or more pressure values ​​is set as the latest integrated pressure value, when the monitoring pressure value is lower than the overlapping range, the second pressure value with the lower pressure range among the first and second pressure values ​​is set as the latest integrated pressure value, and when the monitoring pressure value is higher than the overlapping range, the first pressure value with the higher pressure range among the first and second pressure values ​​is set as the latest integrated pressure value. [Effects of the Invention]

[0028] According to the present invention, by providing multiple amplification circuits with different amplification factors in the analog processing circuit section, and by having the pressure calculation section calculate multiple pressure values ​​based on the outputs of each of the multiple amplification circuits, high-precision pressure measurement over a wide range can be achieved with a single capacitive sensor. [Brief explanation of the drawing]

[0029] [Figure 1] Figure 1 is a circuit diagram of a capacitive sensor according to the first embodiment of the present invention. [Figure 2] Figure 2 is a flowchart illustrating the operation of the pressure calculation unit, communication circuit, and output circuit of a capacitive sensor according to the first embodiment of the present invention. [Figure 3] Figure 3 is a circuit diagram of a capacitive sensor according to a second embodiment of the present invention. [Figure 4] Figure 4 is a flowchart illustrating the operation of the pressure calculation unit, communication circuit, and output circuit of a capacitive sensor according to a second embodiment of the present invention. [Figure 5] Figure 5 is a circuit diagram of a capacitive sensor according to a third embodiment of the present invention. [Figure 6] Figure 6 is a flowchart illustrating the operation of the pressure calculation unit, communication circuit, and output circuit of a capacitive sensor according to a third embodiment of the present invention. [Figure 7] Figure 7 illustrates the problems that arise when two pressure values ​​are combined into a single output. [Figure 8] Figure 8 illustrates the problems that arise when two pressure values ​​are combined into a single output. [Figure 9] Figure 9 illustrates the weighted averaging process of pressure values ​​in the fourth embodiment of the present invention. [Figure 10] Figure 10 shows the results of the weighted averaging process of pressure values ​​in the fourth embodiment of the present invention. [Figure 11] Figure 11 shows the change in the weighted average ratio to the monitoring pressure value. [Figure 12]Figure 12 is a flowchart illustrating the sequence from factory adjustment to pressure measurement of a capacitive sensor according to a fourth embodiment of the present invention. [Figure 13] Figure 13 illustrates the problems of the fourth embodiment of the present invention. [Figure 14] Figure 14 is a diagram illustrating the effects of the fifth embodiment of the present invention. [Figure 15] Figure 15 is a cross-sectional view of the package structure of the pressure-receiving part according to the eighth embodiment of the present invention. [Figure 16] Figure 16 is a block diagram showing an example of the configuration of a computer that implements a capacitive sensor according to the first to seventh embodiments of the present invention. [Figure 17] Figure 17 is a circuit diagram of a conventional capacitive sensor. [Figure 18] Figure 18 is a cross-sectional view showing the structure of the sensor chip of the pressure-receiving part of a conventional capacitive sensor. [Figure 19] Figure 19 is a cross-sectional view of the package structure of the pressure-receiving part of a conventional capacitive sensor. [Figure 20] Figure 20 is a flowchart illustrating the operation of the pressure calculation unit, communication circuit, and output circuit of a conventional capacitive sensor. [Figure 21] Figure 21 is a circuit diagram showing one example configuration of a differential amplifier circuit for a conventional capacitive sensor. [Figure 22] Figure 22 is a circuit diagram showing another example configuration of a differential amplifier circuit for a conventional capacitive sensor. [Modes for carrying out the invention]

[0030] [First Embodiment] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Figure 1 is a circuit diagram of a capacitive sensor according to the first embodiment of the present invention, and the same components as in Figure 17 are denoted by the same reference numerals. The capacitive sensor of this embodiment includes a pressure receiving unit 1, a signal generator 2, charge amplification circuits 3, 4, differential amplification circuits 5a, 5b, detection circuits 6, 7, 8a, 8b, LPFs 9, 10, 11a, 11b, multiplexer 12a, AD converter 13, pressure calculation unit 14a, communication circuit 15, and output circuit 16. The charge amplification circuits 3, 4, differential amplification circuits 5a, 5b, detection circuits 6, 7, 8a, 8b, LPFs 9, 10, 11a, 11b, and multiplexer 12a constitute an analog processing circuit unit 20.

[0031] The configuration and operation of the pressure receiving unit 1, the signal generator 2, and the charge amplifier circuits 3 and 4 are the same as in the conventional design. The differential amplifier circuits 5a and 5b amplify the difference between the output signal of the charge amplifier circuit 3 and the output signal of the charge amplifier circuit 4, respectively. The difference from the conventional design is that two differential amplifier circuits 5a and 5b with different amplification factors are provided. In this embodiment, the amplification factor of differential amplifier circuit 5b is set to be greater than the amplification factor of differential amplifier circuit 5a. As explained in Figures 21 and 22, the amplification factors of differential amplifier circuits 5a and 5b can be set by the value of the resistors used in the circuit.

[0032] The operation of detection circuits 6 and 7 and LPFs 9 and 10 is the same as before. Detection circuits 8a and 8b rectify the output signals of differential amplifier circuits 5a and 5b in half-wave or full-wave, respectively. LPFs 11a and 11b smooth the output signals of detection circuits 8a and 8b, respectively. As a result, signals SXY1 and SXY2 with amplitudes proportional to the capacitance CX-CY are obtained. Due to the amplification settings of the differential amplifier circuits 5a and 5b described above, the amplitude of signal SXY2 is greater than the amplitude of signal SXY1.

[0033] The multiplexer 12a switches the inputs of the AD converter 13 in the following order, for example: SCX→SCY→SXY1→SXY2→VS→VC→SCX→SCY→SXY1→SXY2→VS→VC→... The AD converter 13 converts the output of the multiplexer 12a into a digital signal.

[0034] The operation of the pressure calculation unit 14a, communication circuit 15, and output circuit 16 in this embodiment will be explained using Figure 2. The processing in steps S100 to S103 in Figure 2 is the same as in the conventional method. When the AD conversion result of signal SXY1 is input from the AD converter 13 (step S104a), the pressure calculation unit 14a calculates the capacitance CX-CY value from this AD conversion result. The pressure calculation unit 14a divides the capacitance CX-CY calculated from the AD conversion result of signal SXY1 by the capacitance CX calculated in step S101 to calculate VO1 = (CX-CR) / CX (step S105a).

[0035] Furthermore, when the AD conversion result of the signal SXY2 is input from the AD converter 13 (step S104b), the pressure calculation unit 14a calculates the capacitance CX-CY value from this AD conversion result. The pressure calculation unit 14a divides the capacitance CX-CY calculated from the AD conversion result of the signal SXY2 by the capacitance CX calculated in step S101 to calculate VO2 = (CX-CR) / CX (step S105b). The processing in steps S106 and S107 in Figure 2 is the same as in the conventional method.

[0036] Next, the pressure calculation unit 14a calculates the pressure value PV1 of the medium to be measured using the following formula (2) based on the calculation result VO1 from step S105a and the calculation result ST from step S107 (step S108a).

[0037]

number

[0038] Similarly, the pressure calculation unit 14a calculates the pressure value PV2 of the medium to be measured using the following formula (3) based on the calculation result VO2 in step S105b and the calculation result ST in step S107 (step S108b).

[0039]

number

[0040] In formulas (2) and (3), A ij , B ij are correction coefficients determined for each product in the factory adjustment process, and i and j are the degrees of the polynomial. The communication circuit 15 transmits the digital values of PV1 and PV2 to the outside (step S109a). The output circuit 16 converts the digital values of PV1 and PV2 into analog signals (e.g., 0-10V output) respectively and outputs the converted signals (step S110a).

[0041] The processing of steps S111 to S116 in FIG. 2 is the same as that in the conventional art. When at least one of PV1 and PV2 calculated in steps S108a and S108b is equal to or lower than a predetermined pressure threshold (Yes in step S117a), the pressure calculation unit 14a turns on an LED (step S118).

[0042] According to the present embodiment, a user of the capacitive sensor can use the sensor in the following manner. In a low applied pressure range, PV2 (with a higher amplification factor of the differential amplifier circuit 5b) can perform measurement with higher accuracy, so the user performs pressure monitoring and pressure control using PV2. Further, in a high pressure range, PV1 (with a lower amplification factor of the differential amplifier circuit 5a) can perform measurement with higher accuracy, so the user performs pressure monitoring and pressure control using PV1. Specifically, since the value of PV2 reaches the upper limit at a certain applied pressure, a pressure monitoring system or a pressure control system is constructed to use PV1 after that applied pressure. This enables accurate pressure measurement in both low pressure ranges and high pressure ranges. That is, high-precision pressure measurement over a wide range can be realized with a single capacitive sensor.

[0043] Here, we will explain why, according to this embodiment, pressure can be measured accurately in both low and high pressure ranges. PV1 appears to have a large error rate because it is a pressure value calculated using the output of the differential amplifier circuit 5a, which has a small amplification factor. However, if PV is the true pressure of the medium being measured, the error rate of PV1 is (PV1-PV) / PV × 100 [% reading]. Therefore, in the high pressure range PV, the denominator of the error rate formula becomes large, and thus the calculated error rate of PV1 is small.

[0044] On the other hand, in the low pressure PV region, the denominator of the error rate of PV1 becomes smaller, resulting in a larger calculated error rate for PV1. Thus, in the low pressure PV region, by using PV2, which is the pressure value calculated using the output of the differential amplifier circuit 5b with a large amplification factor, it is possible to measure the pressure accurately in both the low and high pressure regions.

[0045] [Second Example] In the first embodiment, two differential amplifier circuits with different amplification factors are provided, but three or more differential amplifier circuits with different amplification factors may be provided. Figure 3 is a circuit diagram of a capacitive sensor according to the second embodiment of the present invention, and the same components as in Figures 17 and 1 are denoted by the same reference numerals. The capacitive sensor of this embodiment includes a pressure receiving unit 1, a signal generator 2, charge amplifier circuits 3 and 4, differential amplifier circuits 5a to 5c, detection circuits 6, 7, 8a to 8c, LPFs 9, 10, 11a to 11c, a multiplexer 12b, an AD converter 13, a pressure calculation unit 14b, a communication circuit 15, and an output circuit 16. The charge amplifier circuits 3 and 4, the differential amplifier circuits 5a to 5c, the detection circuits 6, 7, 8a to 8c, the LPFs 9, 10, 11a to 11c, and the multiplexer 12b constitute an analog processing circuit section 20a.

[0046] Differential amplifier circuits 5a to 5c amplify the difference between the output signal of charge amplifier circuit 3 and the output signal of charge amplifier circuit 4, respectively. In this embodiment, the amplification factor of differential amplifier circuit 5c is greater than that of differential amplifier circuit 5b, and the amplification factor of differential amplifier circuit 5b is greater than that of differential amplifier circuit 5a. Detection circuit 8c half-wave rectifies or full-wave rectifies the output signal of differential amplifier circuit 5c. LPF 11c smooths the output signal of detection circuit 8c. As a result, a signal SXY3 with an amplitude proportional to the capacitance CX-CY is obtained.

[0047] The multiplexer 12b switches the inputs of the AD converter 13 in the following order, for example: SCX→SCY→SXY1→SXY2→SXY3→VS→VC→SCX→SCY→SXY1→SXY2→SXY3→VS→VC→... The AD converter 13 converts the output of the multiplexer 12b into a digital signal.

[0048] The operation of the pressure calculation unit 14b, communication circuit 15, and output circuit 16 in this embodiment will be explained using Figure 4. Note that the processing in steps S102, S103, S114 to S116 is the same as in the first embodiment, so it is omitted from Figure 4. When the AD conversion result of the signal SXY3 is input from the AD converter 13 (step S104c), the pressure calculation unit 14b calculates the capacitance CX-CY value from this AD conversion result. The pressure calculation unit 14b divides the capacitance CX-CY calculated from the AD conversion result of the signal SXY3 by the capacitance CX calculated in step S101 to calculate VO3 = (CX-CR) / CX (step S105c).

[0049] The pressure calculation unit 14b calculates the pressure value PV3 of the medium to be measured using the following formula (4) based on the calculation result VO3 from step S105c and the calculation result ST from step S107 (step S108c).

[0050]

number

[0051] In equation (4), C ijThis is a correction coefficient determined for each product during the factory adjustment process. The communication circuit 15 transmits the digital values ​​of PV1, PV2, and PV3 to the outside (step S109b). The output circuit 16 converts the digital values ​​of PV1, PV2, and PV3 into analog signals (e.g., 0-10V output) and outputs them (step S110b). The pressure calculation unit 14b lights up the LED (step S118) if at least one of PV1, PV2, and PV3 calculated in steps S108a, S108b, and S108c is below a predetermined pressure threshold (Yes in step S117b). The other processes are the same as in the first embodiment. It goes without saying that the same can be achieved in the case of providing four or more differential amplifier circuits with different amplification factors.

[0052] [Third embodiment] In the first embodiment, as shown in Figure 18, the sensor chip 100 of the pressure receiving unit 1 is provided with one sensor element 120 consisting of a diaphragm 102, a reference vacuum chamber 103, and electrodes 104-107. However, by forming two sensor elements with different pressure ranges on the sensor chip 100, it is possible to accurately measure pressure over an even wider pressure range.

[0053] Figure 5 is a circuit diagram of a capacitive sensor according to a third embodiment of the present invention, and the same components as in Figures 17, 1 and 3 are denoted by the same reference numerals. The capacitive sensor of this embodiment includes a pressure receiving unit 1a, a signal generator 2, charge amplification circuits 3_1, 3_2, 4_1, 4_2, differential amplification circuits 5a_1, 5a_2, 5b_1, 5b_2, detection circuits 6_1, 6_2, 7_1, 7_2, 8a_1, 8a_2, 8b_1, 8b_2, LPFs 9_1, 9_2, 10_1, 10_2, 11a_1, 11a_2, 11b_1, 11b_2, multiplexer 12c, AD converter 13, pressure calculation unit 14c, communication circuit 15, and output circuit 16. The charge amplifier circuits 3_1, 3_2, 4_1, 4_2, differential amplifier circuits 5a_1, 5a_2, 5b_1, 5b_2, detection circuits 6_1, 6_2, 7_1, 7_2, 8a_1, 8a_2, 8b_1, 8b_2, LPFs 9_1, 9_2, 10_1, 10_2, 11a_1, 11a_2, 11b_1, 11b_2, and multiplexer 12c constitute the analog processing circuit section 20b.

[0054] In this embodiment, the pressure receiving section 1a has two diaphragms of different sizes formed on a single sensor chip 100, and a sensor element 120 with the structure shown in Figure 18 is formed on each diaphragm. The two sensor elements 120 are configured to receive the pressure of the medium to be measured by the structure described in Figure 19.

[0055] In Figure 5, the capacitance between the movable electrode 105 formed on the first sensor element 120_1 and the fixed electrode 104 formed on the base of the sensor chip so as to face the movable electrode 105 is defined as CX_1, and the capacitance between the movable electrode 107 formed on the first sensor element 120_1 and the fixed electrode 106 formed on the base so as to face the movable electrode 107 is defined as CY_1. Furthermore, the capacitance between the movable electrode 105 formed on the second sensor element 120_2 and the fixed electrode 104 formed on the base of the sensor chip so as to face the movable electrode 105 is defined as CX_2, and the capacitance between the movable electrode 107 formed on the second sensor element 120_2 and the fixed electrode 106 formed on the base so as to face the movable electrode 107 is defined as CY_2.

[0056] Charge amplifier circuits 3-1, 3-2, 4-1, and 4-2 convert the current (sensor signal) output from one end of capacitors CX_1, CX_2, CY_1, and CY_2, respectively, into a voltage. Differential amplifier circuits 5a_1 and 5b_1 amplify the difference between the output signal of charge amplifier circuit 3_1 and the output signal of charge amplifier circuit 4_1, respectively. Differential amplifier circuits 5a_2 and 5b_2 amplify the difference between the output signal of charge amplifier circuit 3_2 and the output signal of charge amplifier circuit 4_2, respectively. In this embodiment, the amplification factor of differential amplifier circuits 5b_1 and 5b_2 is assumed to be greater than the amplification factor of differential amplifier circuits 5a_1 and 5a_2.

[0057] Detection circuits 6_1, 6_2, 7_1, and 7_2 each perform half-wave or full-wave rectification of the output signals of charge amplifier circuits 3_1, 3_2, 4_1, and 4_2, respectively. Detection circuits 8a_1, 8a_2, 8b_1, and 8b_2 each perform half-wave or full-wave rectification of the output signals of differential amplifier circuits 5a_1, 5a_2, 5b_1, and 5b_2, respectively. LPFs 9_1, 9_2, 10_1, 10_2, 11a_1, 11a_2, 11b_1, and 11b_2 each smooth the output signals of detection circuits 6_1, 6_2, 7_1, 7_2, 8a_1, 8a_2, 8b_1, and 8b_2, respectively. Let the output signals of LPF9_1,9_2,10_1,10_2,11a_1,11a_2,11b_1,11b_2 be SCX_1,SCX_2,SCY_1,SCY_2,SXY1_1,SXY1_2,SXY2_1,SXY2_2, respectively.

[0058] The multiplexer 12c switches the inputs of the AD converter 13 in the following order: SCX_1→SCY_1→SXY1_1→SXY2_1→SCX_2→SCY_2→SXY1_2→SXY2_2→VS→VC→SCX_1→SCY_1→SXY1_1→SXY2_1→SCX_2→SCY_2→SXY1_2→SXY2_2→VS→VC→... The AD converter 13 converts the output of the multiplexer 12c into a digital signal.

[0059] The operation of the pressure calculation unit 14c, communication circuit 15, and output circuit 16 in this embodiment will be explained using Figure 6. Note that the processing in steps S102, S103, S106, S107, S114 to S116 is the same as in the first embodiment, so it is omitted from Figure 6. In this embodiment, similar to step S103, the pressure calculation unit 14c calculates the values ​​of capacitance CY_1 and CY_2 from the AD conversion results of signals SCY_1 and SCY_2, respectively. Similar to steps S114 to S116, if capacitance CY_1 or CY_2 is below a predetermined capacitance threshold, the pressure calculation unit 14c determines that the detection unit for capacitance CY_1 or CY_2 of the pressure receiving unit 1a is disconnected and issues an alarm.

[0060] The pressure calculation unit 14c calculates the values ​​of capacitance CX_1 and CX_2 from the AD conversion results of signals SCX_1 and SCX_2, respectively (steps S101a and S101b). The pressure calculation unit 14c divides the capacitance CX_1-CY_1 calculated from the AD conversion result of signal SXY1_1 by the capacitance CX_1 calculated in step S101a to calculate VO1_1 = (CX_1-CR_1) / CX_1 (step S105d). The pressure calculation unit 14c divides the capacitance CX_1-CY_1 calculated from the AD conversion result of signal SXY2_1 by the capacitance CX_1 calculated in step S101a to calculate VO2_1 = (CX_1-CR_1) / CX_1 (step S105e).

[0061] Furthermore, the pressure calculation unit 14c calculates VO1_2 = (CX_2 - CR_2) / CX_2 by dividing the capacitance CX_2 calculated from the AD conversion result of signal SXY1_2 by the capacitance CX_2 calculated in step S101b (step S105f). The pressure calculation unit 14c calculates VO2_2 = (CX_2 - CR_2) / CX_2 by dividing the capacitance CX_2 - CY_2 calculated from the AD conversion result of signal SXY2_2 by the capacitance CX_2 calculated in step S101b (step S105g).

[0062] Next, the pressure calculation unit 14c calculates the pressure value PV1_1 of the medium under measurement based on the calculation result VO1_1 from step S105d and the calculation result ST from step S107 (step S108d). Similarly, the pressure calculation unit 14c calculates the pressure value PV1_2 of the medium under measurement based on the calculation result VO1_2 from step S105f and the calculation result ST from step S107 (step S108f). The calculation formulas for PV1_1 and PV1_2 are equivalent to formula (2) with VO1 replaced by VO1_1 and VO1_2. However, the correction coefficient A ij The values ​​can be different for PV1_1 and PV1_2 (the first sensor element 120_1 and the second sensor element 120_2).

[0063] Furthermore, the pressure calculation unit 14c calculates the pressure value PV2_1 of the medium under measurement based on the calculation result VO2_1 from step S105e and the calculation result ST from step S107 (step S108e). Similarly, the pressure calculation unit 14c calculates the pressure value PV2_2 of the medium under measurement based on the calculation result VO2_2 from step S105g and the calculation result ST from step S107 (step S108g). The calculation formulas for PV2_1 and PV2_2 are equivalent to formula (3) with VO2 replaced by VO2_1 and VO2_2. However, the correction coefficient B ij The values ​​can be different for PV2_1 and PV2_2 (the first sensor element 120_1 and the second sensor element 120_2).

[0064] The communication circuit 15 transmits the digital values ​​of PV1_1, PV1_2, PV2_1, and PV2_2 to the outside (step S109c). The output circuit 16 converts the digital values ​​of PV1_1, PV1_2, PV2_1, and PV2_2 into analog signals (e.g., 0-10V output) and outputs them (step S110c).

[0065] Furthermore, if the capacitance CX_1 or CX_2 is below a predetermined capacitance threshold (Yes in step S111a), the pressure calculation unit 14c determines that the detection unit for capacitance CX_1 or CX_2 of the pressure receiving unit 1a is disconnected (step S112a) and issues an alarm (step S113). Also, if at least one of PV1_1, PV1_2, PV2_1, and PV2_2 is below a predetermined pressure threshold (Yes in step S117c), the pressure calculation unit 14c lights up an LED (step S118). Other processes are the same as in the first embodiment.

[0066] It goes without saying that the same method can be used when a single sensor chip is equipped with three or more sensor elements with different pressure ranges. Furthermore, it goes without saying that the same method can be used when three or more differential amplifier circuits with different amplification factors are provided for each of the multiple sensor elements.

[0067] Furthermore, although this embodiment describes a case where multiple sensor elements with different pressure ranges are provided on the same sensor chip, it is also possible to provide multiple sensor elements with the same pressure range. This allows for accurate pressure measurement over a wide pressure range with redundancy.

[0068] In addition, in the first to third embodiments, an AD converter may be provided for each signal SCX, SCX_1, SCX_2, SCY, SCY_1, SCY_2, SXY1, SXY1_1, SXY1_2, SXY2, SXY2_1, SXY2_2, SXY3, VS, and VC. This eliminates the need for a multiplexer and allows each signal to be AD converted simultaneously. As a result, the update cycle of the PV value can be shortened.

[0069] [Fourth embodiment] In the first embodiment, the calculated pressure values ​​PV1 and PV2 were output separately, but PV1 and PV2 may be output as a single integrated pressure value PVmix. In this embodiment as well, the configuration of the capacitive sensor is the same as in the first embodiment, so it will be explained using the reference numerals in Figure 1. In this embodiment, the pressure calculation unit 14a sets PVmix = PV2 if PV2 is within a predetermined pressure measurable range. Also, the pressure calculation unit 14a sets PVmix = PV1 if PV2 exceeds the pressure measurable range.

[0070] Therefore, when PV2 exceeds the measurable pressure range, the measured pressure result switches to PV1, but the switch from PV2 to PV1 may not be smooth. A specific example is explained using Figures 7 and 8. In Figures 7 and 8, the actual pressure of the medium being measured (applied pressure) is on the horizontal axis, and the pressure value calculated by the pressure calculation unit 14a is on the vertical axis.

[0071] If the calculated pressure values ​​PV1 and PV2 for the applied pressure have the characteristics shown in Figure 7, then calculating the pressure value PVmix using the method described above will result in a discontinuity (step-like) in the pressure value at the point of transition from PV2 to PV1, as shown in Figure 8. Such discontinuities can lead to control failures in systems that control the pressure of the measured medium based on the pressure value PVmix. In particular, the likelihood of control failures increases when controlling the pressure to slowly increase or decrease.

[0072] PV1 (with a small amplification factor of differential amplifier circuit 5a) can measure a wider pressure range than PV2 (with a large amplification factor of differential amplifier circuit 5b). Therefore, in this embodiment, PVmix is ​​calculated by weighting PV1 and PV2 in the overlapping region (relay zone) of PV1 and PV2, so that the switch from PV2 to PV1 is smooth. A specific example is shown below.

[0073] In the overlapping region OA in Figure 9 (the region from applied pressure P1' to P1), both PV1 and PV2 can measure pressure. Therefore, in the overlapping region OA, the pressure calculation unit 14a takes the weighted average of PV1 and PV2 and uses that as PVmix. This makes the switching from PV2 to PV1 continuous, as shown in Figure 10. The criterion for deciding whether to take a weighted average and for determining PV2:PV1 is the pressure value PV1 calculated using the output of a differential amplifier circuit with a small amplification factor. Hereafter, this criterion pressure value will be called the monitoring pressure value. In the overlapping region OA, the pressure calculation unit 14a calculates the pressure value PVmix using the following equation (5). PVmix=(1-α)PV2+αPV1 ···(5)

[0074] Figure 11 shows the change in the weighted average ratio α relative to the monitoring pressure value PV1. When PV1 = P1', α = 0.0, and when PV1 = P1, α = 1.0. Specifically, α is determined by equation (6). α={1 / (P1-P1')}PV1-{P1' / (P1-P1')} ···(6)

[0075] Furthermore, the overlapping region OA, i.e., the pressure values ​​of P1' and P1, vary from unit to unit due to the structure of the pressure receiving section 1, and cannot be uniformly determined. Therefore, it is necessary to determine P1' and P1 respectively at the time of product shipment. The sequence from shipment adjustment to pressure measurement will be explained using Figure 12.

[0076] First, the worker performing the factory adjustment of the capacitive sensor introduces the medium to be measured with a known pressure into the capacitive sensor (step S200) and records the signals SCX, SCY, SXY1, SXY2, VS at this time (step S201). The worker repeats steps S200 and S201 while changing the pressure of the medium to be measured.

[0077] Next, the worker calculates VO1 = (CX-CR) / CX from signals SCX and SXY1, and calculates the temperature ST from signal VS, for each pressure of the medium being measured applied in step S200. These calculation processes correspond to steps S101, S104a, S105a, and S107 in Figure 2. Then, based on the pressure of the medium being measured applied in step S200 and the VO1 and ST calculated for each pressure of the medium being measured, the worker applies a correction coefficient A using equation (2). ij Calculate (Step S202).

[0078] Furthermore, the operator calculates VO2 = (CX-CR) / CX from signals SCX and SXY2, and calculates the temperature ST from signal VS, for each pressure of the medium being measured applied in step S200. These calculation processes correspond to the processes in steps S101, S104b, S105b, and S107 in Figure 2. Then, based on the pressure of the medium being measured applied in step S200 and the VO2 and ST calculated for each pressure of the medium being measured, the operator applies a correction coefficient B using equation (3). ij Calculate (Step S203).

[0079] Next, the worker determines the starting pressure value P1' and ending pressure value P1 of the overlapping region OA (step S204). For example, P1 is the applied pressure value just before the signal SXY2 reaches a known upper limit (the upper limit of the output voltage of the differential amplifier circuit 5b), and P1' is 90% of the pressure value of P1. Then, the worker determines the correction coefficient A ij ,B ij The starting pressure value P1' and ending pressure value P1 of the overlapping region OA are written to the memory of the pressure calculation unit 14a (step S205).

[0080] Next, we will explain the operation of the capacitive sensor during pressure measurement after it has been shipped. The pressure calculation unit 14a calculates the pressure values ​​PV1 and PV by performing the processes in steps S100 to S103, S104a, S104b, S105a, S105b, S106, S107, S108a, and S108b in Figure 2 (step S206).

[0081] Next, the pressure calculation unit 14a calculates the pressure value PVmix from PV1 and PV2 (step S207). Specifically, the pressure calculation unit 14a sets PVmix = PV2 if the monitoring pressure value PV1 is 0 or greater and less than P1'. The pressure calculation unit 14a calculates the pressure value PVmix using equations (5) and (6) if the monitoring pressure value PV1 is P1' or greater and less than or equal to P1. Also, the pressure calculation unit 14a sets PVmix = PV1 if the monitoring pressure value PV1 exceeds P1.

[0082] The communication circuit 15 transmits the digital value of PVmix to the outside (step S208). The output circuit 16 converts the digital value of PVmix into an analog signal and outputs it (step S209). As described above, in this embodiment, PV1 and PV2 can be output as a single pressure value PVmix. This embodiment is also applicable to other embodiments.

[0083] [Fifth Example] In the fourth embodiment, the integrated pressure value PVmix calculated from PV1 and PV2 may not increase monotonically. If PVmix does not increase monotonically, the control of the system that controls the pressure of the measured medium based on PVmix may become disrupted. Therefore, in this embodiment, when the overlapping region is entered and PV2 is overranged, the overranged saturation value is used to perform a weighted average of the pressure values. In this embodiment as well, the configuration of the capacitive sensor is the same as in the first embodiment, so it will be explained using the reference numerals in Figure 1.

[0084] First, let's explain an example where PVmix does not increase monotonically. In a capacitive sensor, if foreign matter adheres to the diaphragm, which flexes under the pressure of the medium being measured, the measured pressure value may not be zero even when the applied pressure is zero. This shift in the measured pressure value is called drift. When PVmix is ​​calculated as a weighted average of PV1 and PV2, as in the fourth embodiment, if only PV2 drifts to the positive side, it exhibits the behavior shown in Figures 13(A) to 13(C). Figure 13(A) shows the case where the drift amount of PV2 is +0.05 Pa, Figure 13(B) shows the case where the drift amount is +0.2 Pa, and Figure 13(C) shows the case where the drift amount is +0.3 Pa. In the example of Figure 13(B), it can be seen that in the overlapping region OA, even if PV1 increases, PVmix does not increase, and in the example of Figure 13(C), even if PV1 increases in the overlapping region OA, PVmix decreases.

[0085] Therefore, in this embodiment, an overrange value PV2' is set for PV2. For example, the overrange value PV2' is set to 1.1 times the value of PV2 calculated from the value of SXY2 just before it reaches a known upper limit. When PV2 becomes greater than or equal to the overrange value PV2', the pressure calculation unit 14a sets PV2 = PV2' and calculates the pressure value PVmix. The method for calculating PVmix is ​​as described in step S207. The PVmix calculated by this embodiment is shown in Figures 14(A) to 14(C). Figure 14(A) shows the case when the drift amount of PV2 is +0.05 Pa, Figure 14(B) shows the case when the drift amount is +0.2 Pa, and Figure 14(C) shows the case when the drift amount is +0.3 Pa.

[0086] In the example in Figure 13(B), a situation occurred where PVmix did not increase even when PV1 increased in the overlapping domain OA. In contrast, in this embodiment, as shown in Figure 14(B), PVmix increases monotonically by saturating PV2 with PV2'. Also, in the example in Figure 13(C), a situation occurred where PVmix decreased even when PV1 increased in the overlapping domain OA. In contrast, in this embodiment, as shown in Figure 14(C), PVmix increases monotonically by saturating PV2 with PV2'.

[0087] [Sixth Embodiment] In the fourth and fifth embodiments, a weighted average of PV1 and PV2 is always performed within the overlapping region OA, but this weighted average process is time-consuming. Therefore, the pressure calculation unit 14a sets PVmix = PV2 without calculating the weighted average of PV1 and PV2 if the difference between PV2 and PV1 (PV2-PV1) within the overlapping region OA is less than or equal to a predetermined threshold. This eliminates the time required for the weighted average process.

[0088] [Seventh Embodiment] In the case where three or more differential amplifier circuits with different amplification factors are provided, as in the second embodiment, or in the case where multiple sensor elements are provided on a single sensor chip and multiple differential amplifier circuits with different amplification factors are provided for each sensor element, as in the third embodiment, three or more measured pressure values ​​(PV1, PV2, PV3, ...) will be calculated.

[0089] When applying the fourth embodiment to a configuration where there is one sensor element on the sensor chip and three or more differential amplifier circuits with different amplification factors, as in the second embodiment, the pressure calculation unit 14b uses the measured pressure value calculated based on the output of the differential amplifier circuit with the smallest amplification factor among the three or more measured pressure values ​​as the monitoring pressure value. In addition, two overlapping regions are provided, which are designated as P1'_1, P1_1, P1'_2, and P1_2.

[0090] In the configuration in which the fourth embodiment is applied to the second embodiment, the pressure calculation unit 14b calculates the latest integrated pressure value PVmix based on two measured pressure values ​​adjacent to the immediately preceding integrated pressure value PVmix from among three or more measured pressure values. For example, suppose there are three measured pressure values ​​PV1, PV2, and PV3, the monitoring pressure value is PV1, and the immediately preceding pressure value PVmix was between PV1 and PV2. The method for calculating PVmix in this case is as described in step S207.

[0091] In a configuration in which the fourth embodiment is applied to the second embodiment, if the immediately preceding pressure value PVmix is ​​between PV2 and PV3, the pressure calculation unit 14b adopts PV3 calculated based on the output of the differential amplifier circuit with the larger amplification factor if the monitoring pressure value PV1 is 0 or greater and less than P1'_2, and sets PVmix = PV3. If the monitoring pressure value PV1 is P1'_2 or greater and less than or equal to P1_2, the pressure calculation unit 14b calculates the pressure value PVmix using equations (7) and (8). Furthermore, if the monitoring pressure value PV1 exceeds P1_2, the pressure calculation unit 14b adopts PV2 calculated based on the output of the amplifier circuit with the smaller amplification factor, and sets PVmix = PV2. PVmix=(1-α)PV3+αPV2 ···(7) α = {1 / (P1_2 - P1'_2)}PV1 -{P1'_2 / (P1_2-P1'_2)} ···(8)

[0092] On the other hand, when applying the fourth embodiment to a configuration in which multiple sensor elements are provided on a single sensor chip, as in the third embodiment, and multiple differential amplifier circuits with different amplification factors are provided for each sensor element, the pressure calculation unit 14c uses the measured pressure value calculated based on the output of the differential amplifier circuit with the smallest amplification factor among the multiple differential amplifier circuits provided for the sensor element with the highest pressure range, out of four or more measured pressure values, as the monitoring pressure value. In addition, three overlapping regions are provided, which are designated as P1'_1, P1_1, P1'_2, P1_2, P1'_3, and P1_3.

[0093] In a configuration in which the fourth embodiment is applied to the third embodiment, the pressure calculation unit 14c calculates the latest integrated pressure value PVmix based on two measured pressure values ​​adjacent to the immediately preceding integrated pressure value PVmix from among four or more measured pressure values. For example, suppose there are four measured pressure values ​​PV1, PV2, PV3, and PV4, the monitoring pressure value is PV1, and the immediately preceding pressure value PVmix was between PV1 and PV2.

[0094] The pressure calculation unit 14c adopts the lower pressure value PV2 from PV1 and PV2 if the monitoring pressure value PV1 is 0 or greater and less than P1'_1, and sets PVmix = PV2. The pressure calculation unit 14c calculates the pressure value PVmix using equation (5) if the monitoring pressure value PV1 is 0 or greater and less than or equal to P1'_1. The pressure calculation unit 14b adopts the higher pressure value PV1 if the monitoring pressure value PV1 exceeds P1_1, and sets PVmix = PV1.

[0095] In a configuration in which the fourth embodiment is applied to the third embodiment, if the immediately preceding pressure value PVmix is ​​between PV2 and PV3, the pressure calculation unit 14c adopts the pressure value PV3, which has a lower pressure range, from PV2 and PV3, if the monitoring pressure value PV1 is 0 or greater and less than P1'_2, and sets PVmix = PV3. The pressure calculation unit 14c calculates the pressure value PVmix using equation (7) if the monitoring pressure value PV1 is P1'_2 or greater and less than or equal to P1_2. Also, if the monitoring pressure value PV1 exceeds P1_2, the pressure calculation unit 14b adopts the pressure value PV2, which has a higher pressure range, and sets PVmix = PV2.

[0096] In a configuration in which the fourth embodiment is applied to the third embodiment, if the immediately preceding pressure value PVmix is ​​between PV3 and PV4, the pressure calculation unit 14c adopts the pressure value PV4, which has a lower pressure range, from PV3 and PV4, and sets PVmix = PV4, if the monitoring pressure value PV1 is 0 or greater and less than P1'_3. The pressure calculation unit 14c calculates the pressure value PVmix using equations (9) and (10) if the monitoring pressure value PV1 is P1'_3 or greater and less than or equal to P1_3. Furthermore, if the monitoring pressure value PV1 exceeds P1_3, the pressure calculation unit 14b adopts the pressure value PV3, which has a higher pressure range, and sets PVmix = PV3. PVmix=(1-α)PV4+αPV3 ···(9) α = {1 / (P1_3 - P1'_3)}PV1 -{P1'_3 / (P1_3-P1'_3)} ···(10)

[0097] Based on the above definition of the monitoring pressure value, a value other than PV1 may be used as the monitoring pressure value. If the monitoring pressure value is other than PV1, for example, if the monitoring pressure value is PV2, then PV1 in equation (6) should be replaced with PV2 and α, which is used for the weighted average, should be calculated. In this embodiment, the pressure calculation in the pressure calculation unit is limited to two steps, thus shortening the calculation time.

[0098] [Eighth embodiment] In the third embodiment, an example was described in which two sensor elements with different pressure ranges are formed on one sensor chip 100 of the pressure receiving unit 1a. However, multiple pressure receiving units with different pressure ranges may be provided. An example with two pressure receiving units is shown in Figure 15. The configurations of pressure receiving units 1-1 and 1-2 are the same as in Figure 19. The diaphragms formed on the sensor chip 100 of pressure receiving unit 1-1 and the diaphragms formed on the sensor chip 100 of pressure receiving unit 1-2 are of different sizes. For example, the sensor element formed on the sensor chip 100 of pressure receiving unit 1-1 corresponds to the first sensor element 120-1 (capacitances CX_1, CY_1) in the third embodiment, and the sensor element formed on the sensor chip 100 of pressure receiving unit 1-2 corresponds to the second sensor element 120-2 (capacitances CX_2, CY_2) in the third embodiment. In this way, the third embodiment can be applied to a configuration with two pressure receiving units.

[0099] The pressure calculation units 14a to 14c in the first to eighth embodiments can be implemented by a computer equipped with a CPU (Central Processing Unit), memory, and interfaces, and a program that controls these hardware resources. An example of the configuration of this computer is shown in Figure 16.

[0100] The computer comprises a CPU 200, a memory 201, and an interface device (I / F) 202. An AD converter 13, a communication circuit 15, an output circuit 16, etc., are connected to the I / F 202. In such a computer, the program for realizing the pressure measurement method of the present invention is stored in the memory 201. The CPU 200 executes the processes described in the first to eighth embodiments according to the program stored in the memory 201. [Explanation of symbols]

[0101] 1,1a,1-1,1-2…Pressure receiving section, 2…Signal generator, 3,3_1,3_2,4,4_1,4_2…Charge amplification circuit, 5a,5a_1,5a_2,5b,5b_1,5b_2,5c…Differential amplification circuit, 6,6_1,6_2,7,7_1,7_2,8a,8a_1,8a_2,8b,8b_1,8b_2,8c…Detection circuit, 9,9_1,9 _2,10,10_1,10_2,11a,11a_1,11a_2,11b,11b_1,11b_2,11c...Low-pass filter, 12a~12c...Multiplexer, 13...AD converter, 14a~14c...Pressure calculation unit, 15...Communication circuit, 16...Output circuit, 20,20a,20b...Analog processing circuit unit, 120...Sensor element.

Claims

1. A pressure receiving unit having a sensor element configured to output a sensor signal based on capacitance that fluctuates according to the pressure of the object being measured, An analog processing circuit section configured to amplify the aforementioned sensor signal, The system includes a pressure calculation unit configured to calculate a pressure value based on the output signal of the analog processing circuit unit, The analog processing circuit section includes multiple amplification circuits with different amplification ratios. The capacitive sensor is characterized in that the pressure calculation unit calculates a plurality of pressure values ​​based on the output of each of the plurality of amplification circuits.

2. In the capacitive sensor according to claim 1, The sensor element comprises a first electrode formed on a base, a second electrode formed on a diaphragm separated from the base by a gap and facing the first electrode, a third electrode formed on the base outside the first electrode, and a fourth electrode formed on the diaphragm outside the second electrode and facing the third electrode, and is configured such that the distance between the first and second electrodes changes in accordance with the displacement of the diaphragm due to the pressure of the object to be measured. The capacitive sensor is characterized in that the analog processing circuit section comprises a plurality of amplification circuits that amplify the difference between a first sensor signal based on the capacitance CX between the first and second electrodes and a second sensor signal based on the capacitance CY between the third and fourth electrodes at different amplification rates.

3. In the capacitive sensor according to claim 2, Capacitive sensor characterized in that the pressure calculation unit calculates the value of the capacitance CX based on the first sensor signal, calculates multiple values ​​of the capacitance CX-CY based on the output of each of the multiple amplification circuits, and calculates multiple pressure values ​​from the results of dividing each of the multiple values ​​of capacitance CX-CY by the value of capacitance CX.

4. In the capacitive sensor according to claim 1, The pressure receiving unit comprises a plurality of the sensor elements, The aforementioned analog processing circuit section is characterized by comprising a plurality of differential amplifier circuits with different amplification factors for each sensor element, thereby providing a capacitive sensor.

5. In the capacitive sensor according to claim 1, The capacitive sensor is characterized in that the pressure calculation unit calculates an integrated pressure value by combining the multiple pressure values ​​into one.

6. In the capacitive sensor according to claim 5, The pressure calculation unit is characterized in that, when the sensor element is one and the analog processing circuit unit is provided with two amplification circuits with different amplification factors, the first pressure value calculated based on the output of the amplification circuit with the smaller amplification factor among the first and second pressure values ​​calculated based on the outputs of the two amplification circuits is set as the monitoring pressure value, when the monitoring pressure value is within a predetermined overlapping range, the weighted average value of the first and second pressure values ​​is set as the integrated pressure value, when the monitoring pressure value is lower than the overlapping range, the second pressure value calculated based on the output of the amplification circuit with the larger amplification factor is set as the integrated pressure value, and when the monitoring pressure value is higher than the overlapping range, the first pressure value is set as the integrated pressure value.

7. In the capacitive sensor according to claim 6, The capacitive sensor is characterized in that, when the pressure calculation unit becomes equal to or greater than a predetermined overrange value, it performs a saturation process to set the second pressure value to the overrange value and then calculates the integrated pressure value.

8. In the capacitive sensor according to claim 6, Capacitive sensor characterized in that, when the monitoring pressure value is within the range of the overlapping area and the difference between the second pressure value and the first pressure value is less than or equal to a predetermined threshold, the second pressure value is used as the integrated pressure value without calculating a weighted average of the first and second pressure values.

9. In the capacitive sensor according to claim 5, The pressure calculation unit, when the sensor element is one and the analog processing circuit unit is provided with three or more amplification circuits with different amplification ratios, is characterized in that it sets the pressure value calculated based on the output of the amplification circuit with the smallest amplification ratio from among the three or more latest pressure values ​​calculated based on the output of each of the three or more amplification circuits as the monitoring pressure value, when the monitoring pressure value is within a predetermined overlapping range, it sets the weighted average of the first and second pressure values ​​adjacent to the immediately preceding integrated pressure value from among the three or more pressure values ​​as the latest integrated pressure value, when the monitoring pressure value is lower than the overlapping range, it sets the second pressure value calculated based on the output of the amplification circuit with the larger amplification ratio from among the first and second pressure values ​​as the latest integrated pressure value, and when the monitoring pressure value is higher than the overlapping range, it sets the first pressure value calculated based on the output of the amplification circuit with the smaller amplification ratio from among the first and second pressure values ​​as the latest integrated pressure value.

10. In the capacitive sensor according to claim 5, The pressure calculation unit, when there are multiple sensor elements and multiple differential amplifier circuits with different amplification factors are provided for each sensor element in the analog processing circuit, calculates the latest pressure value from among the four or more pressure values ​​calculated based on the output of each of the four or more amplifier circuits, and uses the pressure value calculated based on the output of the amplifier circuit with the smallest amplification factor among the two or more amplifier circuits provided for the sensor element with the highest pressure range as the monitoring pressure value; when the monitoring pressure value is within a predetermined overlapping range, uses the weighted average of the first and second pressure values ​​adjacent to the immediately preceding integrated pressure value as the latest integrated pressure value; when the monitoring pressure value is lower than the overlapping range, uses the second pressure value with the lower pressure range as the latest integrated pressure value; and when the monitoring pressure value is higher than the overlapping range, uses the first pressure value with the higher pressure range as the latest integrated pressure value.

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