Electrostatic capacitance type sensor

Abstract

The present application realizes high-precision pressure measurement in a wide range with one device. An electrostatic capacitance type sensor includes a pressure receiving portion (1) having a sensor element that outputs a sensor signal based on an electrostatic capacitance that varies in correspondence with a pressure of a measurement object, an analog processing circuit portion (20) that amplifies the sensor signal, and a pressure calculating portion (14a) that calculates a pressure value based on an output signal of the analog processing circuit portion (20). The analog processing circuit portion (20) includes amplification circuits (5a, 5b) of different amplification rates. The pressure calculating portion (14a) calculates a plurality of pressure values based on outputs of the respective amplification circuits (5a, 5b).

Description

Technical Field

[0001] This invention relates to an electrostatic capacitive sensor. Background Technology

[0002] Electrostatic capacitive sensors, which detect changes in physical quantities (such as pressure), perform analog-to-digital (A / D) conversion on pressure or temperature signals from a pressurized part and input these signals to a central processing unit (CPU). The CPU performs polynomial calculations and converts the resulting pressure value into an analog value for output (Patent Document 1). A circuit diagram of a conventional electrostatic capacitive sensor is shown below. Figure 17 .

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

[0004] Figure 18 This is a cross-sectional view showing the structure of the sensor chip in the pressure-receiving section 1. A recess is formed in the center of the base 101 of the sensor chip 100. A diaphragm 102, which can be deformed to correspond to the pressure PV of the measured medium (e.g., process gas), is attached to the surface of the base 101 where this recess is formed. The recess of the base 101 and the diaphragm 102 together form a reference vacuum chamber 103.

[0005] A fixed electrode 104 is formed on the surface of the pedestal 101 facing the reference vacuum chamber 103, and a movable electrode 105 is formed on the surface of the diaphragm 102 facing the reference vacuum chamber 103, opposite to the fixed electrode 104. Thus, the fixed electrode 104 and the movable electrode 105 are arranged facing each other with a gap between them. When the diaphragm 102 is flexed by the pressure PV of the measured medium, the gap between the movable electrode 105 and the fixed electrode 104 changes, and the electrostatic capacitance CX between the movable electrode 105 and the fixed electrode 104 changes. Based on the change in the electrostatic capacitance CX, the pressure PV of the measured medium on the diaphragm 102 can be detected.

[0006] Furthermore, a fixed electrode 106 is formed on the surface of the base 101 on the side of the reference vacuum chamber 103, outside the fixed electrode 104. A movable electrode 107 is formed on the surface of the diaphragm 102 on the side of the reference vacuum chamber 103, outside the movable electrode 105, facing the fixed electrode 106. The fixed electrode 106 and the movable electrode 107 are formed at the edge of the diaphragm 102. Even if the diaphragm 102 is bent by the pressure PV of the measured medium, the edge of the diaphragm 102 hardly deforms, so the electrostatic capacitance CY between the movable electrode 107 and the fixed electrode 106 is difficult to change. This electrostatic capacitance CY is designed 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 contain, for example, an insulator such as sapphire.

[0007] Figure 19 This is a cross-sectional view of the encapsulation structure of the pressure-bearing part 1. (See diagram below.) Figure 19 As shown, the sensor chip 100 is housed within a metal housing 108. A partition 109 is provided inside the housing 108. The partition 109 includes a pedestal plate 109a and a support plate 109b, dividing the internal space of the housing 108 into a first space 110a and a second space 110b. The outer periphery of the support plate 109b is fixed to the housing 108, supporting the pedestal 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 pedestal plate 109a. Furthermore, a pressure inlet hole 109c is formed on the pedestal plate 109a to guide the pressure in the first space 110a to the diaphragm 102 of the sensor chip 100. The second space 110b communicates with the reference vacuum chamber 103 of the sensor chip 100 and is set to a vacuum state.

[0008] The pressure inlet pipe 111 is connected to the first space 110a side of the housing 108. A baffle 112 is provided between the pressure inlet pipe 111 and the housing 108. The measured medium introduced from the pressure inlet pipe 111 hits the surface of the baffle 112 and flows into the first space 110a of the housing 108 through the gaps around the baffle 112.

[0009] Figure 17 The pressure-bearing part temperature detection circuit 113 shown outputs a temperature signal VS as the temperature of the pressure-bearing part 1 by measuring the temperature of the housing 108. Furthermore, the substrate temperature detection circuit 114 measures the temperature of the substrate carrying circuits such as charge amplifier circuit 3, charge amplifier circuit 4, differential amplifier circuit 5, detector circuits 6 to 8, LPF 9 to LPF 11, and multiplexer 12, and outputs a temperature signal VC.

[0010] 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 part 1. Charge amplifier circuit 3, including capacitor CF and operational amplifier A1, converts the current (sensor signal) output from the second electrode (e.g., movable electrode 105) of the pressure-receiving part 1 into a voltage. Charge amplifier circuit 4, including capacitor CF and operational amplifier A2, converts the current (sensor signal) output from the fourth electrode (e.g., movable electrode 107) of the pressure-receiving part 1 into a voltage. Differential amplifier circuit 5 amplifies the difference between the output signal of charge amplifier circuit 3 and the output signal of charge amplifier circuit 4.

[0011] Detector circuit 6 performs half-wave or full-wave rectification on the output signal of charge amplifier circuit 3. LPF 9 smooths the output signal of detector circuit 6. This yields a signal SCX with an amplitude proportional to the electrostatic capacitance CX. Detector circuit 7 performs half-wave or full-wave rectification on the output signal of charge amplifier circuit 4. LPF 10 smooths the output signal of detector circuit 7. This yields a signal SCY with an amplitude proportional to the electrostatic capacitance CY. Detector circuit 8 performs half-wave or full-wave rectification on the output signal of differential amplifier circuit 5. LPF 11 smooths the output signal of detector circuit 8. This yields a signal SXY with an amplitude proportional to the electrostatic capacitance CX-CY. Multiplexer 12 switches the input to AD converter 13, for example, in the order SCX→SCY→SXY→VS→VC→SCX→SCY→SXY→VS→VC→… AD converter 13 converts the output of multiplexer 12 into a digital signal.

[0012] use Figure 20 The operation of the pressure calculation unit 14, the communication circuit 15, and the output circuit 16 will be explained. When the pressure calculation unit 14 receives the AD conversion result of the input signal SCX from the AD converter 13 (step S100), it calculates the value of the electrostatic capacitance CX based on this AD conversion result (step S101). When the pressure calculation unit 14 receives the AD conversion result of the input signal SCY from the AD converter 13 (step S102), it calculates the value of the electrostatic capacitance CY based on this AD conversion result (step S103).

[0013] Subsequently, when the pressure calculation unit 14 receives the AD conversion result of the input signal SXY from the AD converter 13 (step S104), it calculates the value of the electrostatic capacitance CX-CY based on this AD conversion result, and then divides the electrostatic capacitance CX-CY by the electrostatic capacitance CX calculated in step S101 to calculate VO = (CX-CY) / CX (step S105). When the pressure calculation unit 14 receives the AD conversion result of the input temperature signal VS from the AD converter 13 (step S106), it calculates the temperature ST of the pressure-bearing part 1 based on this AD conversion result (step S107).

[0014] Next, the pressure calculation unit 14 calculates the pressure PV of the measured medium based on the calculation result VO of step S105 and the calculation result ST of step S107 according to the following formula (1) (step S108).

[0015] [Number 1]

[0016]

[0017] In equation (1), A ij The correction factor is determined for each product during the adjustment process in the factory, where i and j are the degrees of the polynomial. Communication circuit 15 sends the digital value of pressure PV to the outside (step S109). Output circuit 16 converts the digital value of pressure PV into an analog signal (e.g., 0V-10V output) and outputs it (step S110).

[0018] Furthermore, if the electrostatic capacitance CX calculated by the pressure calculation unit 14 in step S101 is below a predetermined capacitance threshold (Yes in step S111), it determines that the detection unit (fixed electrode 104 and movable electrode 105) of the electrostatic capacitance CX of the pressure-bearing part 1 has broken wire (step S112) and issues an alarm (step S113). Similarly, if the electrostatic capacitance CY calculated by the pressure calculation unit 14 in step S103 is below a predetermined capacitance threshold (Yes in step S114), it determines that the detection unit (fixed electrode 106 and movable electrode 107) of the electrostatic capacitance CY of the pressure-bearing part 1 has broken wire (step S115) and issues an alarm (step S116). Furthermore, if the pressure PV calculated by the pressure calculation unit 14 in step S108 is below a predetermined pressure threshold (Yes in step S117), it lights up the light-emitting diode (LED) (step S118).

[0019] Electrostatic capacitive sensor repeatedly executes Figure 20 The processing described herein. The reason for using VO=(CX-CY) / CX to calculate the pressure PV is, as stated in Patent Document 1, to eliminate error components. Figure 17 In the structure, the electrostatic capacitance CX-CY is calculated by performing an AD conversion on the signal amplified by subtracting the output signal of charge amplifier circuit 4 from the output signal of charge amplifier circuit 3. There is also a method using a CPU to calculate SCX-SCY, but the accuracy is not very good because the signals SCX and SCY are small. Therefore, in conventional electrostatic capacitive sensors, the difference between the output signals of charge amplifier circuit 3 and charge amplifier circuit 4 is amplified by a differential amplifier circuit 5 within the analog processing circuit, thereby obtaining a signal SXY with an amplitude proportional to the electrostatic capacitance CX-CY.

[0020] Figure 21 , Figure 22 This is a circuit diagram illustrating an example of the structure of differential amplifier circuit 5. Figure 21 The differential amplifier circuit 5 includes operational amplifier A3 and resistors Ra, Rc, Re, and Rf. If the output signal of charge amplifier circuit 3 is set to Vin... + Set the output signal of charge amplifier circuit 4 to Vin. - ,but Figure 21 The output voltage of the differential amplifier circuit 5 is (Vin) + -Vin - )×Rf / Rc. Additionally, Ra=Rc、Re=Rf.

[0021] Figure 22 The differential amplifier circuit 5 includes operational amplifiers A4 to A6 and resistors R1 to R3, resistor Ra, resistor Rc, resistor Re, and resistor Rf. Figure 22 The output voltage of the differential amplifier circuit 5 is (Vin) + -Vin - )×(1+2×R1 / R2)×Rf / Rc. Additionally, Ra=Rc, Re=Rf, R1=R3.

[0022] Figure 17 , Figure 21 , Figure 22 In the structure shown, the greater the pressure PV, the greater the output voltage of the differential amplifier circuit 5. However, if the pressure PV exceeds a certain level, it will exceed the output range of the differential amplifier circuit 5, causing the output voltage of the differential amplifier circuit 5 to stop at its upper limit. Consequently, the value of the pressure PV calculated using the output voltage of the differential amplifier circuit 5 will also stop at its upper limit.

[0023] In conventional capacitive sensors, the differential amplifier circuit 5 is of a single type. To measure pressure PV with high accuracy, the amplification of the differential amplifier circuit 5 needs to be increased, but this limits the range of measurable pressure PV. On the other hand, if the amplification of the differential amplifier circuit 5 is reduced, although the range of measurable pressure PV is wide, accurate measurement of pressure PV in the low-pressure region is not possible. Therefore, to measure a wide range of pressure PV with high accuracy, multiple capacitive sensors must be arranged, which increases the required installation space accordingly.

[0024] [Existing Technical Documents]

[0025] [Patent Literature]

[0026] Patent Document 1: Japanese Patent No. 4020318 Summary of the Invention

[0027] [The problem the invention aims to solve]

[0028] This invention was made to solve the aforementioned problems, and its purpose is to provide an electrostatic capacitive sensor capable of achieving high-precision pressure measurement over a wide range using a single unit.

[0029] [Technical means to solve the problem]

[0030] The electrostatic capacitive sensor of the present invention is characterized by comprising: a pressure receiving section having a sensor element configured to output a sensor signal based on the electrostatic capacitance varying according to the pressure of the object being measured; an analog processing circuit section configured to amplify the sensor signal; and a pressure calculation section configured to calculate a pressure value based on the output signal of the analog processing circuit section, wherein the analog processing circuit section includes a plurality of amplification circuits with different amplification rates, and the pressure calculation section calculates a plurality of pressure values ​​based on the outputs of the plurality of amplification circuits respectively.

[0031] Furthermore, in one structural example of the electrostatic capacitive sensor of the present invention, the sensor element is characterized in that it comprises a first electrode, a second electrode, a third electrode, and a fourth electrode. The first electrode is formed on a pedestal, the second electrode is formed on a diaphragm disposed with a gap between it and the pedestal, facing the first electrode. The third electrode is formed on the pedestal outside the first electrode, and the fourth electrode is formed on the diaphragm outside the second electrode, facing the third electrode. The spacing between the first and second electrodes varies according to the displacement of the diaphragm caused by the pressure of the measured object. The analog processing circuit includes a plurality of amplification circuits, which amplify the difference between a first sensor signal based on the electrostatic capacitance CX between the first and second electrodes and a second sensor signal based on the electrostatic capacitance CY between the third and fourth electrodes with different amplification rates.

[0032] Furthermore, in one structural example of the electrostatic capacitive sensor of the present invention, the pressure calculation unit calculates the value of the electrostatic capacitor CX based on the first sensor signal, calculates the values ​​of a plurality of electrostatic capacitors CX-CY based on the outputs of the plurality of amplifier circuits, and calculates a plurality of pressure values ​​based on the results obtained by dividing the values ​​of the plurality of electrostatic capacitors CX-CY by the value of the electrostatic capacitor CX.

[0033] Furthermore, in one structural example of the electrostatic capacitive sensor of the present invention, the pressure-bearing part includes a plurality of said sensor elements, and the analog processing circuit part includes a plurality of differential amplifier circuits with different amplification rates corresponding to each said sensor element.

[0034] Furthermore, in one structural example of the electrostatic capacitive sensor of the present invention, the pressure calculation unit calculates a combined pressure value that integrates the plurality of pressure values ​​into one.

[0035] Furthermore, in one structural example of the electrostatic capacitive sensor of the present invention, the pressure calculation unit, when the sensor element is one and the analog processing circuit unit is provided with two amplifier circuits with different amplification rates, sets the first pressure value calculated based on the output of the amplifier circuit with the smaller amplification rate from the first pressure value and the second pressure value calculated based on the output of the two amplifier circuits, as the monitoring pressure value; when the monitoring pressure value is within a predetermined overlapping region, the weighted average of the first pressure value and the second pressure value is set as the combined pressure value; when the monitoring pressure value is lower than the pressure of the overlapping region, the second pressure value calculated based on the output of the amplifier circuit with the larger amplification rate is set as the combined pressure value; and when the monitoring pressure value is higher than the pressure of the overlapping region, the first pressure value is set as the combined pressure value.

[0036] Furthermore, in one structural example of the electrostatic capacitive sensor of the present invention, the pressure calculation unit performs a saturation process to set the second pressure value as the over-range value when the second pressure value becomes above a predetermined over-range value, and then calculates the integrated pressure value.

[0037] Furthermore, in one structural example of the electrostatic capacitive sensor of the present invention, the pressure calculation unit, when the monitored pressure value is within the range of the overlapping region, does not calculate the weighted average of the first pressure value and the second pressure value if the difference between the second pressure value and the first pressure value is below a predetermined threshold, but instead sets the second pressure value as the integrated pressure value.

[0038] Furthermore, in one structural example of the electrostatic capacitive sensor of the present invention, 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 rates, sets the pressure value calculated based on the output of the amplification circuit with the lowest amplification rate among the latest three or more pressure values ​​calculated based on the outputs of the three or more amplification circuits. When the monitored pressure value is within a predetermined overlap region, the weighted average of the first pressure value and the second pressure value adjacent to the most recent combined pressure value among the three or more pressure values ​​is set as the latest combined pressure value. When the monitored pressure value is lower than the pressure of the overlap region, the second pressure value calculated based on the output of the amplification circuit with the higher amplification rate among the first and second pressure values ​​is set as the latest combined pressure value. When the monitored pressure value is higher than the pressure of the overlap region, the first pressure value calculated based on the output of the amplification circuit with the lower amplification rate among the first and second pressure values ​​is set as the latest combined pressure value.

[0039] Furthermore, in one structural example of the electrostatic capacitive sensor of the present invention, the pressure calculation unit, when there are multiple sensor elements and the analog processing circuit unit is provided with multiple differential amplifier circuits with different amplification rates corresponding to each sensor element, sets the pressure value calculated based on the output of the amplifier circuit with the smallest amplification rate among the latest four or more pressure values ​​calculated based on the output of each of the four or more amplifier circuits, which is used for the sensor element with the highest pressure range, as the monitoring pressure value. When the monitoring pressure value is within a predetermined overlapping region, the weighted average of the first pressure value and the second pressure value adjacent to the most recent combined pressure value among the four or more pressure values ​​is set as the latest combined pressure value. When the monitoring pressure value is lower than the pressure of the overlapping region, the second pressure value with the lower pressure range among the first and second pressure values ​​is set as the latest combined pressure value. When the monitoring pressure value is higher than the pressure of the overlapping region, the first pressure value with the higher pressure range among the first and second pressure values ​​is set as the latest combined pressure value.

[0040] [The effects of the invention]

[0041] According to the present invention, multiple amplification circuits with different amplification rates are provided in the analog processing circuit section, and the pressure calculation section calculates multiple pressure values ​​based on the outputs of the multiple amplification circuits, thereby enabling high-precision pressure measurement over a wide range using a single electrostatic capacitive sensor. Attached Figure Description

[0042] Figure 1 This is a circuit diagram of the electrostatic capacitive sensor according to the first embodiment of the present invention.

[0043] Figure 2 This is a flowchart illustrating the operation of the pressure calculation unit, communication circuit, and output circuit of the electrostatic capacitive sensor according to the first embodiment of the present invention.

[0044] Figure 3 This is a circuit diagram of an electrostatic capacitive sensor according to a second embodiment of the present invention.

[0045] Figure 4 This is a flowchart illustrating the operation of the pressure calculation unit, communication circuit, and output circuit of the electrostatic capacitive sensor according to the second embodiment of the present invention.

[0046] Figure 5 This is a circuit diagram of an electrostatic capacitive sensor according to the third embodiment of the present invention.

[0047] Figure 6 This is a flowchart illustrating the operation of the pressure calculation unit, communication circuit, and output circuit of the electrostatic capacitive sensor according to the third embodiment of the present invention.

[0048] Figure 7 This diagram illustrates the problem when two pressure values ​​are set to one and the output is the same.

[0049] Figure 8 This diagram illustrates the problem when two pressure values ​​are set to one and the output is the same.

[0050] Figure 9 This is a diagram illustrating the weighted average processing of pressure values ​​in the fourth embodiment of the present invention.

[0051] Figure 10 This is a graph showing the result of weighted average processing of pressure values ​​in the fourth embodiment of the present invention.

[0052] Figure 11 It is a graph showing the change in the weighted average of the monitored pressure values.

[0053] Figure 12 This is a flowchart illustrating the sequence of adjusting the electrostatic capacitive sensor of the fourth embodiment of the present invention to pressure measurement upon shipment.

[0054] Figure 13 (A) to Figure 13 (C) is a diagram illustrating a problem with the fourth embodiment of the present invention.

[0055] Figure 14 (A) to Figure 14 (C) is a diagram illustrating the effects of the fifth embodiment of the present invention.

[0056] Figure 15 This is a cross-sectional view of the encapsulation structure of the pressure-bearing part according to the eighth embodiment of the present invention.

[0057] Figure 16 This is a block diagram illustrating a structural example of a computer implementing the electrostatic capacitive sensor of the first to seventh embodiments of the present invention.

[0058] Figure 17 This is a circuit diagram of a traditional electrostatic capacitive sensor.

[0059] Figure 18 This is a cross-sectional view showing the structure of the sensor chip in the pressure-bearing part of a conventional electrostatic capacitive sensor.

[0060] Figure 19 This is a cross-sectional view of the packaging structure of the pressure-bearing part of a conventional electrostatic capacitive sensor.

[0061] Figure 20 This is a flowchart illustrating the operation of the pressure calculation unit, communication circuit, and output circuit of a conventional electrostatic capacitive sensor.

[0062] Figure 21 This is a circuit diagram illustrating a structural example of a differential amplifier circuit for a conventional electrostatic capacitive sensor.

[0063] Figure 22 This is a circuit diagram showing another structural example of a differential amplifier circuit for a conventional electrostatic capacitive sensor.

[0064] Explanation of icon numbers

[0065] 1, 1a, 1-1, 1-2: Pressure-bearing parts

[0066] 2: Signal Generator

[0067] 3, 3_1, 3_2, 4, 4_1, 4_2: Charge Amplification Circuit

[0068] 5a, 5a_1, 5a_2, 5b, 5b_1, 5b_2, 5c: Differential amplifier circuit

[0069] 6, 6_1, 6_2, 7, 7_1, 7_2, 8a, 8a_1, 8a_2, 8b, 8b_1, 8b_2, 8c: Detection circuit

[0070] 9, 9_1, 9_2, 10, 10_1, 10_2, 11a, 11a_1, 11a_2, 11b, 11b_1, 11b_2, 11c: Low-pass filters

[0071] 12a~12c: Multiplexer

[0072] 13: AD converter

[0073] 14a~14c: Pressure calculation section

[0074] 15: Communication circuits

[0075] 16: Output Circuit

[0076] 20, 20a, 20b: Analog Processing Circuit Section

[0077] 120: Sensor element Detailed Implementation

[0078] [First Embodiment]

[0079] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. Figure 1 This is a circuit diagram of the electrostatic capacitive sensor according to the first embodiment of the present invention. Figure 17 The same structure is labeled with the same symbols. The electrostatic capacitive sensor of this embodiment includes a pressure receiving unit 1, a signal generator 2, a charge amplification circuit 3, a charge amplification circuit 4, a differential amplification circuit 5a, a differential amplification circuit 5b, a detection circuit 6, a detection circuit 7, a detection circuit 8a, a detection circuit 8b, LPF 9, LPF 10, LPF 11a, LPF 11b, a multiplexer 12a, an AD converter 13, a pressure calculation unit 14a, a communication circuit 15, and an output circuit 16. The charge amplification circuit 3, charge amplification circuit 4, differential amplification circuit 5a, differential amplification circuit 5b, detection circuit 6, detection circuit 7, detection circuit 8a, detection circuit 8b, LPF 9, LPF 10, LPF 11a, LPF 11b, and multiplexer 12a constitute an analog processing circuit unit 20.

[0080] The structure and operation of the pressure-receiving part 1, signal generator 2, and charge amplifier circuits 3 and 4 are the same as in the past. Differential amplifier circuits 5a and 5b amplify the difference between the output signal of charge amplifier circuit 3 and the output signal of charge amplifier circuit 4, respectively. The difference from the past is that two differential amplifier circuits 5a and 5b with different amplification rates are provided. In this embodiment, the amplification rate of differential amplifier circuit 5b is assumed to be greater than that of differential amplifier circuit 5a. For example... Figure 21 , Figure 22 As explained in the document, the amplification of differential amplifier circuits 5a and 5b can be set by the value of the resistors used in the circuit.

[0081] The operation of detector circuits 6 and 7, and LPFs 9 and 10, is the same as before. Detector circuits 8a and 8b perform half-wave rectification or full-wave rectification on the output signals of differential amplifier circuits 5a and 5b, respectively. LPFs 11a and 11b smooth the output signals of detector circuits 8a and 8b, respectively. This yields signals SXY1 and SXY2 with amplitudes proportional to the electrostatic capacitance CX-CY. By setting the amplification ratio of differential amplifier circuits 5a and 5b, the amplitude of signal SXY2 is greater than the amplitude of signal SXY1.

[0082] Multiplexer 12a switches the input of AD converter 13 in the order of SCX→SCY→SXY1→SXY2→VS→VC→SCX→SCY→SXY1→SXY2→VS→VC→… AD converter 13 converts the output of multiplexer 12a into a digital signal.

[0083] use Figure 2 The operation of the pressure calculation unit 14a, communication circuit 15, and output circuit 16 in this embodiment will be explained. Figure 2 The processing of steps S100 to S103 is the same as before. When the pressure calculation unit 14a receives the AD conversion result of the input signal SXY1 from the AD converter 13 (step S104a), it calculates the value of the electrostatic capacitance CX-CY based on this AD conversion result. The pressure calculation unit 14a divides the electrostatic capacitance CX-CY calculated based on the AD conversion result of the signal SXY1 by the electrostatic capacitance CX calculated in step S101, and calculates VO1 = (CX-CY) / CX (step S105a).

[0084] Furthermore, when the pressure calculation unit 14a receives the AD conversion result of the input signal SXY2 from the AD converter 13 (step S104b), it calculates the value of the electrostatic capacitance CX-CY based on this AD conversion result. The pressure calculation unit 14a divides the electrostatic capacitance CX-CY calculated based on the AD conversion result of the signal SXY2 by the electrostatic capacitance CX calculated in step S101, and calculates VO2 = (CX-CY) / CX (step S105b). Figure 2 The processing of steps S106 and S107 is the same as before.

[0085] Next, the pressure calculation unit 14a calculates the pressure value PV1 of the measured medium based on the calculation result VO1 of step S105a and the calculation result ST of step S107 according to the following formula (2) (step S108a).

[0086] [Number 2]

[0087]

[0088] Similarly, the pressure calculation unit 14a calculates the pressure value PV2 of the measured medium based on the calculation result VO2 of step S105b and the calculation result ST of step S107 according to the following formula (3) (step S108b).

[0089] [Number 3]

[0090]

[0091] In equations (2) and (3), A ij B ij The correction factors, i and j, are the degrees of the polynomials determined for each product in the adjustment process within the factory. Communication circuit 15 sends the digital values ​​of PV1 and PV2 to the outside (step S109a). Output circuit 16 converts the digital values ​​of PV1 and PV2 into analog signals (e.g., 0V-10V output) and outputs them (step S110a).

[0092] Figure 2 The processing of steps S111 to S116 is the same as before. If at least one of PV1 and PV2 calculated by the pressure calculation unit 14a in steps S108a and S108b is below a predetermined pressure threshold (yes in step S117a), the LED is turned on (step S118).

[0093] According to this embodiment, the user of the electrostatic capacitive sensor can use it in the following manner. In the low applied pressure range, PV2 can be measured with good accuracy (due to the high amplification of the differential amplifier circuit 5b), so the user uses PV2 for pressure monitoring and control. Furthermore, in the high pressure range, PV1 can be measured with good accuracy (due to the low amplification of the differential amplifier circuit 5a), so the user uses PV1 for pressure monitoring and control. Specifically, at a certain applied pressure, the value of PV2 reaches its upper limit, so PV1 is used thereafter, thus constructing a pressure monitoring system or a pressure control system. Therefore, pressure can be measured with good accuracy in both low and high pressure ranges. That is, a single electrostatic capacitive sensor can achieve high-precision pressure measurement over a wide range.

[0094] Here, according to this embodiment, the reason why pressure can be measured with good accuracy in both low and high pressure regions will be explained. PV1 is the pressure value calculated using the output of the differential amplifier circuit 5a with low amplification, so the error rate appears large. However, if the true pressure of the measured medium is set as PV, then the error rate of PV1 is (PV1-PV) / PV×100 [%reading]. Therefore, in the region of high pressure PV, since the denominator of the error rate formula is large, it can be said that the calculated value of the error rate of PV1 is small.

[0095] On the other hand, in regions with low pressure PV, the calculated error rate of PV1 will be larger because the denominator of the error rate of PV1 is small. Thus, for regions with low pressure PV, the pressure value PV2 is calculated using the output of the differential amplifier circuit 5b with high amplification, thereby enabling accurate pressure measurement in both low and high pressure regions.

[0096] [Second Embodiment]

[0097] In the first embodiment, two differential amplifier circuits with different amplification rates are provided, but three or more differential amplifier circuits with different amplification rates can also be provided. Figure 3 This is a circuit diagram of the electrostatic capacitive sensor according to the second embodiment of the present invention. Figure 17 , Figure 1 The same structure is labeled with the same symbols. The electrostatic capacitive sensor of this embodiment includes a pressure receiving unit 1, a signal generator 2, a charge amplification circuit 3, a charge amplification circuit 4, differential amplification circuits 5a to 5c, a detection circuit 6, a detection circuit 7, detection circuits 8a to 8c, LPF 9, LPF 10, LPF 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 amplification circuits 3, 4, 5a to 5c, 6, 7, 8a to 8c, LPF 9, LPF 10, 11a to 11c, and the multiplexer 12b constitute an analog processing circuit unit 20a.

[0098] 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 rate of differential amplifier circuit 5c is assumed to be greater than that of differential amplifier circuit 5b, and the amplification rate of differential amplifier circuit 5b is assumed to be greater than that of differential amplifier circuit 5a. Detector circuit 8c performs half-wave rectification or full-wave rectification on the output signal of differential amplifier circuit 5c. LPF 11c smooths the output signal of detector circuit 8c. Thus, a signal SXY3 with an amplitude proportional to the electrostatic capacitance CX-CY is obtained.

[0099] Multiplexer 12b switches the input of AD converter 13 in the following order, for example: SCX→SCY→SXY1→SXY2→SXY3→VS→VC→SCX→SCY→SXY1→SXY2→SXY3→VS→VC→… AD converter 13 converts the output of multiplexer 12b into a digital signal.

[0100] use Figure 4 The operation of the pressure calculation unit 14b, communication circuit 15, and output circuit 16 in this embodiment will be explained. Furthermore, the processing of steps S102, S103, and S114-S116 is the same as in the first embodiment, therefore, details in... Figure 4 The pressure calculation unit 14b calculates the value of the electrostatic capacitance CX-CY based on the AD conversion result of the input signal SXY3 from the AD converter 13 (step S104c). The pressure calculation unit 14b divides the electrostatic capacitance CX-CY calculated based on the AD conversion result of the signal SXY3 by the electrostatic capacitance CX calculated in step S101, and calculates VO3 = (CX-CY) / CX (step S105c).

[0101] The pressure calculation unit 14b calculates the pressure value PV3 of the measured medium based on the calculation result VO3 of step S105c and the calculation result ST of step S107 according to the following formula (4) (step S108c).

[0102] [Number 4]

[0103]

[0104] In equation (4), C ijThese are correction coefficients determined for each product during the adjustment process in the factory. Communication circuit 15 sends the digital values ​​of PV1, PV2, and PV3 to the outside (step S109b). Output circuit 16 converts the digital values ​​of PV1, PV2, and PV3 into analog signals (e.g., 0V-10V output) and outputs them (step S110b). 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 LED is illuminated (step S118). Other processing is the same as in the first embodiment. Of course, the same implementation as this embodiment is possible when four or more differential amplifier circuits with different amplification rates are provided.

[0105] [Third Embodiment]

[0106] In the first embodiment, such as Figure 18 As shown, in the sensor chip 100 of the pressure-receiving part 1, there is a sensor element 120. The sensor element 120 includes a diaphragm 102, a reference vacuum chamber 103, and electrodes 104 to 107. However, by forming two sensor elements with different pressure ranges in the sensor chip 100, pressure measurement can be performed with good accuracy over a wider pressure range.

[0107] Figure 5 This is a circuit diagram of the electrostatic capacitive sensor according to the third embodiment of the present invention. Figure 17 , Figure 1 , Figure 3The same structure is labeled with the same symbols. The electrostatic capacitive sensor of this embodiment includes a pressure receiving part 1a, a signal generator 2, a charge amplification circuit 3_1, a charge amplification circuit 3_2, a charge amplification circuit 4_1, a charge amplification circuit 4_2, a differential amplification circuit 5a_1, a differential amplification circuit 5a_2, a differential amplification circuit 5b_1, a differential amplification circuit 5b_2, a detection circuit 6_1, a detection circuit 6_2, a detection circuit 7_1, a detection circuit 7_2, a detection circuit 8a_1, a detection circuit 8a_2, a detection circuit 8b_1, a detection circuit 8b_2, LPF 9_1, LPF 9_2, LPF 10_1, LPF 10_2, LPF 11a_1, LPF 11a_2, LPF 11b_1, LPF 11b_2, a multiplexer 12c, an AD converter 13, a pressure calculation part 14c, a communication circuit 15, and an output circuit 16. Charge amplifier circuits 3_1, 3_2, 4_1, 4_2, 5a_1, 5a_2, 5b_1, 5b_2, 6_1, 6_2, 7_1, 7_2, 8a_1, 8a_2, 8b_1, 8b_2, LPF 9_1, LPF 9_2, LPF 10_1, LPF 10_2, LPF 11a_1, LPF 11a_2, LPF 11b_1, LPF 11b_2 and multiplexer 12c constitute analog processing circuit section 20b.

[0108] In this embodiment, the pressure-bearing part 1a has two diaphragms of different sizes formed in a sensor chip 100, and each of the diaphragms has a... Figure 18 The sensor element 120 is shown in the diagram. The two sensor elements 120 are connected via... Figure 19 The structure described herein is designed to withstand the pressure of the measured medium.

[0109] Figure 5In this design, the electrostatic capacitance between the movable electrode 105 formed on the first sensor element 120_1 and the fixed electrode 104 formed on the sensor chip pedestal facing the movable electrode 105 is designated as CX_1, and the electrostatic capacitance between the movable electrode 107 formed on the first sensor element 120_1 and the fixed electrode 106 formed on the pedestal facing the movable electrode 107 is designated as CY_1. Furthermore, the electrostatic capacitance between the movable electrode 105 formed on the second sensor element 120_2 and the fixed electrode 104 formed on the sensor chip pedestal facing the movable electrode 105 is designated as CX_2, and the electrostatic capacitance between the movable electrode 107 formed on the second sensor element 120_2 and the fixed electrode 106 formed on the pedestal facing the movable electrode 107 is designated as CY_2.

[0110] 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 into voltage, respectively. 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 rate of differential amplifier circuits 5b_1 and 5b_2 is assumed to be greater than that of differential amplifier circuits 5a_1 and 5a_2.

[0111] Detector circuits 6_1, 6_2, 7_1, and 7_2 perform half-wave rectification or full-wave rectification on the output signals of charge amplifier circuits 3_1, 3_2, 4_1, and 4_2, respectively. Detector circuits 8a_1, 8a_2, 8b_1, and 8b_2 perform half-wave rectification or full-wave rectification on the output signals of differential amplifier circuits 5a_1, 5a_2, 5b_1, and 5b_2, respectively. LPF 9_1, LPF 9_2, LPF 10_1, LPF 10_2, LPF 11a_1, LPF 11a_2, LPF 11b_1, and LPF 11b_2 smooth the output signals of detector circuits 6_1, 6_2, 7_1, 7_2, 8a_1, 8a_2, 8b_1, and 8b_2, respectively. The output signals of LPF 9_1, LPF 9_2, LPF 10_1, LPF 10_2, LPF 11a_1, LPF 11a_2, LPF 11b_1, and LPF 11b_2 are then set to SCX_1, SCX_2, SCY_1, SCY_2, SXY1_1, SXY1_2, SXY2_1, and SXY2_2, respectively.

[0112] Multiplexer 12c switches the inputs of AD converter 13 in the following order, for example: 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→… AD converter 13 converts the output of multiplexer 12c into a digital signal.

[0113] use Figure 6 The operation of the pressure calculation unit 14c, communication circuit 15, and output circuit 16 in this embodiment will be explained. Furthermore, the processing of steps S102, S103, S106, S107, and S114-S116 is the same as in the first embodiment, therefore, details in... Figure 6 As described in the document. In this embodiment, similar to step S103, the pressure calculation unit 14c calculates the values ​​of electrostatic capacitance CY_1 and electrostatic capacitance CY_2 based on the AD conversion results of signals SCY_1 and SCY_2, respectively. Similar to steps S114 to S116, if the electrostatic capacitance CY_1 or electrostatic capacitance CY_2 is below a predetermined capacitance threshold, the pressure calculation unit 14c determines that the detection unit of electrostatic capacitance CY_1 or electrostatic capacitance CY_2 of the pressure-bearing part 1a has broken, and issues an alarm.

[0114] The pressure calculation unit 14c calculates the values ​​of electrostatic capacitance CX_1 and electrostatic capacitance CX_2 respectively based on the AD conversion results of signals SCX_1 and SCX_2 (steps S101a and S101b). The pressure calculation unit 14c divides the electrostatic capacitance CX_1-CY_1 calculated based on the AD conversion result of signal SXY1_1 by the electrostatic capacitance CX_1 calculated in step S101a to calculate VO1_1 = (CX_1-CY_1) / CX_1 (step S105d). The pressure calculation unit 14c divides the electrostatic capacitance CX_1-CY_1 calculated based on the AD conversion result of signal SXY2_1 by the electrostatic capacitance CX_1 calculated in step S101a to calculate VO2_1 = (CX_1-CY_1) / CX_1 (step S105e).

[0115] Furthermore, the pressure calculation unit 14c divides the electrostatic capacitance CX_2-CY_2 calculated based on the AD conversion result of signal SXY1_2 by the electrostatic capacitance CX_2 calculated in step S101b, and calculates VO1_2 = (CX_2-CY_2) / CX_2 (step S105f). The pressure calculation unit 14c divides the electrostatic capacitance CX_2-CY_2 calculated based on the AD conversion result of signal SXY2_2 by the electrostatic capacitance CX_2 calculated in step S101b, and calculates VO2_2 = (CX_2-CY_2) / CX_2 (step S105g).

[0116] Next, the pressure calculation unit 14c calculates the pressure value PV1_1 of the measured medium based on the calculation result VO1_1 of step S105d and the calculation result ST of step S107 (step S108d). Similarly, the pressure calculation unit 14c calculates the pressure value PV1_2 of the measured medium based on the calculation result VO1_2 of step S105f and the calculation result ST of step S107 (step S108f). The calculation formulas for PV1_1 and PV1_2 are equivalent to replacing VO1 in formula (2) with VO1_1 and VO1_2. Among them, the correction coefficient A ij The values ​​of PV1_1 and PV1_2 (the first sensor element 120_1 and the second sensor element 120_2) can be different.

[0117] Furthermore, the pressure calculation unit 14c calculates the pressure value PV2_1 of the measured medium 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 measured medium 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 replacing VO2 in formula (3) with VO2_1 and VO2_2. Among them, the correction coefficient B ij The values ​​can be different in PV2_1 and PV2_2 (first sensor element 120_1 and second sensor element 120_2).

[0118] Communication circuit 15 sends the digital values ​​of PV1_1, PV1_2, PV2_1, and PV2_2 to the outside (step S109c). Output circuit 16 converts the digital values ​​of PV1_1, PV1_2, PV2_1, and PV2_2 into analog signals (e.g., 0V-10V output) and outputs them (step S110c).

[0119] Furthermore, if the pressure calculation unit 14c determines that the detection unit of the electrostatic capacitor CX_1 or electrostatic capacitor CX_2 of the pressure-bearing part 1a has broken wire when the electrostatic capacitor CX_1 or electrostatic capacitor CX_2 is below a predetermined capacitance threshold (yes in step S111a), and issues an alarm (step S113). Moreover, if the pressure calculation unit 14c determines that at least one of PV1_1, PV1_2, PV2_1, and PV2_2 is below a predetermined pressure threshold (yes in step S117c), it illuminates the LED (step S118). Other processing is the same as in the first embodiment.

[0120] The same implementation can be achieved as in this embodiment, where three or more sensor elements with different pressure ranges are set in a single sensor chip. Furthermore, the same implementation can be achieved as in this embodiment, where three or more differential amplifier circuits with different amplification rates are set for each of the multiple sensor elements.

[0121] Furthermore, this embodiment describes the case where multiple sensor elements with different pressure ranges are set in the same sensor chip, but multiple sensor elements with the same pressure range can also be set. Therefore, pressure measurement over a wide pressure range can be performed with redundancy and good accuracy.

[0122] Alternatively, in the first to third embodiments, an AD converter can be provided for each of the signals 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 for simultaneous AD conversion of each signal. Consequently, the update cycle of the PV value can be shortened.

[0123] [Fourth Embodiment]

[0124] In the first embodiment, the calculated pressure values ​​PV1 and PV2 are output separately, but PV1 and PV2 can also be set as a unified pressure value PVmix and output. In this embodiment, the structure of the electrostatic capacitive sensor is the same as in the first embodiment, therefore it uses... Figure 1 The symbols are used to explain this. In this embodiment, the pressure calculation unit 14a sets PVmix = PV2 if PV2 is within the specified pressure measurable range. Furthermore, the pressure calculation unit 14a sets PVmix = PV1 if PV2 exceeds the pressure measurable range.

[0125] Therefore, when PV2 exceeds the measurable pressure range, the measured pressure result will switch to PV1, but sometimes the switch from PV2 to PV1 is not smooth. (Using...) Figure 7 , Figure 8 Let's illustrate with a specific example. Figure 7 , Figure 8 In this model, the actual pressure (applied pressure) of the measured medium is set as the horizontal axis, and the pressure value calculated by the pressure calculation unit 14a is set as the vertical axis.

[0126] The calculated results relative to the applied pressure values ​​PV1 and PV2 are as follows: Figure 7 Given such characteristics, if the pressure value PVmix is ​​calculated using the method described above, then... Figure 8 As shown, at the switching point from PV2 to PV1, the pressure value becomes discontinuous (step-like). When this discontinuity occurs, poor control may result in systems that control the pressure of the measured medium based on the pressure value PVmix. In particular, poor control may occur when the pressure is controlled to rise or fall slowly.

[0127] PV1 (with a smaller amplification rate of differential amplifier circuit 5a) can measure a wider pressure range than PV2 (with a larger amplification rate of differential amplifier circuit 5b). Therefore, in this embodiment, a weighted average of PV1 and PV2 is performed in the overlapping region (relay zone) of PV1 and PV2, thereby calculating PVmix in a way that smoothly switches from PV2 to PV1. A specific example will be given below.

[0128] exist Figure 9 In the overlapping region OA (the area where pressure is applied from P1' to P1), pressure can be measured for both PV1 and PV2. Therefore, the pressure calculation unit 14a sets the weighted average of PV1 and PV2 in the overlapping region OA as PVmix. Thus, as Figure 10 As shown, the switching from PV2 to PV1 becomes continuous. Furthermore, it is determined whether to perform a weighted average or to calculate PV2:PV1, based on the pressure value PV1 calculated using the output of a differential amplifier circuit with low amplification. Hereinafter, this pressure value will be referred to as the monitoring pressure value. The pressure calculation unit 14a calculates the pressure value PVmix in the overlapping region OA according to the following equation (5).

[0129] PVmix=(1-α)PV2+αPV1…(5)

[0130] The change in the weighted average relative to the monitored pressure value PV1 is shown in... Figure 11 When PV1 = P1', α = 0.0, and when PV1 = P1, α = 1.0. Specifically, α is determined by equation (6).

[0131] α={1 / (P1-P1')}PV1-{P1' / (P1-P1')}…(6)

[0132] Furthermore, the pressure values ​​of the overlapping areas OA, i.e., P1' and P1, vary individually due to structural differences in the pressure-bearing part 1, and cannot be generalized. Therefore, P1' and P1 must be determined separately at the time of product shipment. Figure 12 This explains the sequence for adjusting to pressure measurement during shipment.

[0133] First, during the shipment adjustment of the electrostatic capacitive sensor, the operator introduces a measured medium with a known pressure into the sensor (step S200) and records the signals SCX, SCY, SXY1, SXY2, and VS at this time (step S201). The operator repeatedly performs steps S200 and S201 while changing the pressure of the measured medium.

[0134] Next, the operator performs the following steps for each pressure applied to the measured medium in step S200: calculating VO1 = (CX - CY) / CX based on signals SCX and SXY1, and calculating the temperature ST based on signal VS. These calculations are equivalent to... Figure 2 The processing steps S101, S104a, S105a, and S107 are performed. Furthermore, based on the pressure of the measured medium applied in step S200 and the VO1 and ST calculated corresponding to each pressure of the measured medium, the operator calculates the correction coefficient A according to equation (2). ij (Step S202).

[0135] Furthermore, the operator performs the following steps for each pressure applied to the measured medium in step S200: calculating VO2 = (CX - CY) / CX based on signals SCX and SXY2, and calculating the temperature ST based on signal VS. These calculation processes are equivalent to... Figure 2 The processing steps S101, S104b, S105b, and S107 are performed. Furthermore, based on the pressure of the measured medium applied in step S200 and the VO2 and ST calculated corresponding to each pressure of the measured medium, the operator calculates the correction coefficient B according to equation (3). ij (Step S203).

[0136] Next, the operator determines the starting pressure value P1' and the ending pressure value P1 of the overlapping region OA (step S204). For example, the applied pressure value before signal SXY2 is about to reach the known upper limit (the upper limit of the output voltage of the differential amplifier circuit 5b) is set as P1, and 90% of the pressure value of P1 is set as P1'. Furthermore, the operator sets the correction factor A... ij Correction factor B ij The starting pressure value P1' and the ending pressure value P1 of the overlapping region OA are written into the memory of the pressure calculation unit 14a (step S205).

[0137] Next, the operation during pressure measurement after the electrostatic capacitive sensor is shipped will be explained. The pressure calculation unit 14a performs... Figure 2 The pressure values ​​PV1 and PV are calculated by processing steps S100 to S103, S104a, S104b, S105a, S105b, S106, S107, S108a, and S108b (step S206).

[0138] Next, the pressure calculation unit 14a calculates the pressure value PVmix based on PV1 and PV2 (step S207). Specifically, when the pressure value PV1 is 0 or higher and less than P1', the pressure calculation unit 14a sets PVmix = PV2. When the pressure value PV1 is P1' or higher and less than P1, the pressure calculation unit 14a calculates the pressure value PVmix according to equations (5) and (6). Furthermore, when the pressure value PV1 exceeds P1, the pressure calculation unit 14a sets PVmix = PV1.

[0139] Communication circuit 15 sends the digital value of PVmix to the outside (step S208). Output circuit 16 converts the digital value of PVmix into an analog signal and outputs it (step S209).

[0140] As described above, in this embodiment, PV1 and PV2 can be set to a single pressure value PVmix for output. This embodiment can also be applied to other embodiments.

[0141] [Fifth Embodiment]

[0142] In the fourth embodiment, the combined pressure value PVmix calculated from PV1 and PV2 may not always increase monotonically. When PVmix does not increase monotonically, control may become disordered in a system that controls the pressure of the measured medium based on PVmix. Therefore, in this embodiment, when entering the overlap region, if PV2 has exceeded its range, the saturation value of the over-range value is used for the weighted average of the pressure values. In this embodiment, the structure of the electrostatic capacitive sensor is the same as in the first embodiment, therefore... Figure 1 The symbols are explained.

[0143] First, an example where PVmix does not increase monotonically will be explained. When a foreign object adheres to the diaphragm of a capacitive sensor, causing it to flex under the pressure of the measured medium, the measured pressure value may sometimes not be zero, even when the applied pressure is zero. This shift in the measured pressure value is called drift. When calculating PVmix using a weighted average of PV1 and PV2 as in the fourth embodiment, if only PV2 drifts in the positive direction, it will exhibit… Figure 13 (A) Figure 13 (C)-like behavior. Figure 13 (A) represents the case where the drift of PV2 is +0.05 Pa. Figure 13 (B) represents the case where the drift is +0.2 Pa. Figure 13 (C) represents the case where the drift is +0.3 Pa. It is known that... Figure 13 In example (B), a situation occurs in the overlapping region OA where PV1 increases but PVmix does not, and... Figure 13 In example (C), a situation occurs in the overlapping region OA where PV1 increases but PVmix still decreases.

[0144] Therefore, in this embodiment, an overrange value PV2' is set for PV2. For example, 1.1 times the value of PV2 calculated based on the value before SXY2 reaches its known upper limit is set as the overrange value PV2'. When PV2 becomes the overrange value PV2' or higher, 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 below. Figure 14 (A) Figure 14 (C) Figure 14 (A) represents the case where the drift of PV2 is +0.05 Pa. Figure 14 (B) represents the case where the drift is +0.2 Pa. Figure 14 (C) indicates the case where the drift is +0.3 Pa.

[0145] Figure 13 In example (B), a situation occurred in the overlapping region OA where PV1 increased but PVmix did not. In contrast, in this embodiment, as shown... Figure 14 As shown in (B), PVmix increases monotonically by saturating PV2 to PV2'. Furthermore, Figure 13 In example (C), a situation occurred in the overlapping region OA where PV1 increased but PVmix still decreased. In contrast, in this embodiment, as... Figure 14 As shown in (C), PVmix increases monotonically by saturating PV2 to PV2'.

[0146] [Sixth Embodiment]

[0147] 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, when the difference between PV2 and PV1 within the overlapping region OA, PV2-PV1, is below a predetermined threshold, the pressure calculation unit 14a does not calculate the weighted average of PV1 and PV2, but instead sets PVmix = PV2. This saves the time required for the weighted average process.

[0148] [Seventh Embodiment]

[0149] In the case of setting up three or more differential amplifier circuits with different amplification rates as in the second embodiment, or in the case of setting up multiple sensor elements in a sensor chip and setting up multiple differential amplifier circuits with different amplification rates for each sensor element as in the third embodiment, three or more (PV1, PV2, PV3, ...) measured pressure values ​​will be calculated.

[0150] In the case where the fourth embodiment applies to a structure where the sensor chip has a single sensor element and three or more differential amplifier circuits with different amplification rates, as in the second embodiment, the pressure calculation unit 14b sets the measured pressure value calculated based on the output of the differential amplifier circuit with the lowest amplification rate among the three or more measured pressure values ​​as the monitoring pressure value. Furthermore, two overlapping regions are provided, designated as P1'_1, P1_1, P1'_2, and P1_2.

[0151] In the structure of the fourth embodiment applied to the second embodiment, the pressure calculation unit 14b calculates the latest integrated pressure value PVmix based on two of the three or more measured pressure values ​​that are adjacent to the most recent integrated pressure value PVmix. For example, when the measured pressure values ​​are PV1, PV2, and PV3, let's assume the monitored pressure value is PV1 and the most recent pressure value PVmix is ​​between PV1 and PV2. In this case, the method for calculating PVmix is ​​as described in step S207.

[0152] In the structure of the fourth embodiment applied to the second embodiment, when the most recent pressure value PVmix is ​​between PV2 and PV3, the pressure calculation unit 14b sets PVmix = PV3 based on PV3 calculated from the output of the differential amplifier circuit with a high amplification factor when the monitored pressure value PV1 is 0 or higher and less than P1'_2. When the monitored pressure value PV1 is P1'_2 or higher and less than P1_2, the pressure calculation unit 14b calculates the pressure value PVmix according to equations (7) and (8). Furthermore, when the monitored pressure value PV1 exceeds P1_2, the pressure calculation unit 14b sets PVmix = PV2 based on PV2 calculated from the output of the amplifier circuit with a low amplification factor.

[0153] PVmix=(1-α)PV3+αPV2…(7)

[0154] α={1 / (P1_2-P1'_2)}PV1-{P1'_2 / (P1_2-P1'_2)}…(8)

[0155] On the other hand, when the fourth embodiment is applied to a structure where multiple sensor elements are provided in a single sensor chip, as in the third embodiment, and multiple differential amplifier circuits with different amplification rates are provided corresponding to each sensor element, the pressure calculation unit 14c sets the measured pressure value calculated based on the output of the differential amplifier circuit with the lowest amplification rate among the multiple differential amplifier circuits provided for the sensor element with the highest pressure range from the four or more measured pressure values ​​as the monitoring pressure value. Furthermore, three overlapping regions are provided, designated as P1'_1, P1_1, P1'_2, P1_2, P1'_3, and P1_3.

[0156] In the structure of the fourth embodiment applied to the third embodiment, the pressure calculation unit 14c calculates the latest integrated pressure value PVmix based on two of the four or more measured pressure values ​​that are adjacent to the most recent integrated pressure value PVmix. For example, when the measured pressure values ​​are PV1, PV2, PV3, and PV4, let's assume the monitored pressure value is PV1 and the most recent pressure value PVmix is ​​between PV1 and PV2.

[0157] When the pressure value PV1 is 0 or higher and less than P1'_1, the pressure calculation unit 14c sets PVmix = PV2, which is the pressure value with the lower pressure range between PV1 and PV2. When the pressure value PV1 is P1'_1 or higher and less than P1_1, the pressure calculation unit 14c calculates the pressure value PVmix according to equation (5). Furthermore, when the pressure value PV1 is higher than P1_1, the pressure calculation unit 14b sets PVmix = PV1, which is the pressure value with the higher pressure range, PV1.

[0158] In the structure of the fourth embodiment applied to the third embodiment, when the most recent pressure value PVmix is ​​between PV2 and PV3, the pressure calculation unit 14c, when monitoring a pressure value PV1 that is 0 or higher and less than P1'_2, sets PVmix = PV3 using the pressure value PV3, which has a lower pressure range between PV2 and PV3. When the pressure calculation unit 14c monitors a pressure value PV1 that is above P1'_2 and below P1_2, it calculates the pressure value PVmix according to equation (7). Furthermore, when the pressure calculation unit 14b monitors a pressure value PV1 that exceeds P1_2, it sets PVmix = PV2 using the pressure value PV2, which has a higher pressure range.

[0159] In the structure of the fourth embodiment applied to the third embodiment, when the previous pressure value PVmix is ​​between PV3 and PV4, the pressure calculation unit 14c, when monitoring a pressure value PV1 that is 0 or higher and less than P1'_3, sets PVmix = PV4 using the pressure value PV4, which has a lower pressure range between PV3 and PV4. When the pressure calculation unit 14c monitors a pressure value PV1 that is between P1'_3 and P1_3, it calculates the pressure value PVmix according to equations (9) and (10). Furthermore, when the pressure calculation unit 14b monitors a pressure value PV1 that exceeds P1_3, it sets PVmix = PV3 using the pressure value PV3, which has a higher pressure range.

[0160] PVmix=(1-α)PV4+αPV3…(9)

[0161] α={1 / (P1_3-P1'_3)}PV1-{P1'_3 / (P1_3-P1'_3)}…(10)

[0162] According to the definition of the monitored pressure value, any value other than PV1 can also be set as the monitored pressure value. When the monitored pressure value is other than PV1, for example, when the monitored pressure value is PV2, the α used for weighted averaging can be calculated simply by replacing PV1 with PV2 in equation (6). In this embodiment, the pressure calculation in the pressure calculation unit is reduced to two times, thus shortening the calculation time.

[0163] [Eighth Embodiment]

[0164] In the third embodiment, an example in which two sensor elements with different pressure ranges are formed in a sensor chip 100 of the pressure receiving section 1a has been described, but multiple pressure receiving sections with different pressure ranges may also be provided. An example with two pressure receiving sections is shown below. Figure 15 The structures of the pressure-bearing parts 1-1 and 1-2 are respectively... Figure 19 Similarly, the diaphragm of the sensor chip 100 formed in the pressure-receiving part 1-1 has a different size than the diaphragm of the sensor chip 100 formed in the pressure-receiving part 1-2. For example, the sensor element of the sensor chip 100 formed in the pressure-receiving part 1-1 corresponds to the first sensor element 120-1 of the third embodiment (with electrostatic capacitance set as CX_1, CY_1), and the sensor element of the sensor chip 100 formed in the pressure-receiving part 1-2 corresponds to the second sensor element 120-2 of the third embodiment (with electrostatic capacitance set as CX_2, CY_2). Thus, the third embodiment can be applied to a structure with two pressure-receiving parts.

[0165] The pressure calculation units 14a to 14c of the first to eighth embodiments can be implemented by a computer including a central processing unit (CPU), memory, and interface, and a program that controls these hardware resources. The structure of this computer is illustrated below. Figure 16 .

[0166] The computer includes a CPU 200, a memory 201, and an interface (I / F) 202. An AD converter 13 or communication circuit 15, an output circuit 16, etc., are connected to the I / F 202. In this computer, a program for implementing the pressure measurement method of the present invention is stored in the memory 201. The CPU 200 executes the processing described in the first to eighth embodiments according to the program stored in the memory 201.

Claims

1. An electrostatic capacitive sensor, characterized in that... include: The pressure-bearing part has a sensor element configured to output a sensor signal based on the electrostatic capacitance that varies according to the pressure of the object being measured. The analog processing circuit is configured to amplify the sensor signal; as well as The pressure calculation unit is configured to calculate the pressure value based on the output signal of the analog processing circuit unit. The analog processing circuit section includes multiple amplifier circuits with different amplification rates. The pressure calculation unit calculates multiple pressure values ​​based on the outputs of the multiple amplifier circuits.

2. The electrostatic capacitive sensor according to claim 1, characterized in that, The sensor element comprises a first electrode, a second electrode, a third electrode, and a fourth electrode. The first electrode is formed on a base. The second electrode is formed on a diaphragm spaced apart from the base, facing the first electrode. The third electrode is formed on the base outside the first electrode. The fourth electrode is formed on the diaphragm outside the second electrode, facing the third electrode. The spacing between the first and second electrodes varies according to the displacement of the diaphragm caused by the pressure of the measured object. The analog processing circuit includes a plurality of amplification circuits, which amplify the difference between the first sensor signal based on the electrostatic capacitance CX between the first and second electrodes and the second sensor signal based on the electrostatic capacitance CY between the third and fourth electrodes with different amplification rates.

3. The electrostatic capacitive sensor according to claim 2, characterized in that, The pressure calculation unit calculates the value of the electrostatic capacitor CX based on the first sensor signal, calculates the values ​​of multiple electrostatic capacitors CX-CY based on the outputs of the multiple amplifier circuits, and calculates multiple pressure values ​​based on the results obtained by dividing the values ​​of the multiple electrostatic capacitors CX-CY by the value of the electrostatic capacitor CX.

4. The electrostatic capacitive sensor according to claim 1, characterized in that, The pressure-bearing part includes a plurality of the sensor elements. The analog processing circuitry includes multiple differential amplifier circuits with different amplification rates for each of the sensor elements.

5. The electrostatic capacitive sensor according to claim 1, characterized in that, The pressure calculation unit calculates a combined pressure value that integrates the multiple pressure values ​​into one.

6. The electrostatic capacitive sensor according to claim 5, characterized in that, When the sensor element is one and the analog processing circuit has two amplifier circuits with different amplification ratios, the pressure calculation unit sets the first pressure value calculated based on the output of the amplifier circuit with the smaller amplification ratio, which is one of the first pressure value and the second pressure value calculated based on the output of the two amplifier circuits, as the monitoring pressure value. When the monitoring pressure value is within a predetermined overlapping area, the weighted average of the first pressure value and the second pressure value is set as the combined pressure value. When the monitoring pressure value is lower than the pressure of the overlapping area, the second pressure value calculated based on the output of the amplifier circuit with the larger amplification ratio is set as the combined pressure value. When the monitoring pressure value is higher than the pressure of the overlapping area, the first pressure value is set as the combined pressure value.

7. The electrostatic capacitive sensor according to claim 6, characterized in that, When the second pressure value becomes above a predetermined overrange value, the pressure calculation unit performs a saturation process that sets the second pressure value to the overrange value and then calculates the integrated pressure value.

8. The electrostatic capacitive sensor according to claim 6, characterized in that, When the monitored pressure value is within the overlapping region, if the difference between the second pressure value and the first pressure value is below a predetermined threshold, the pressure calculation unit does not calculate the weighted average of the first pressure value and the second pressure value, but instead sets the second pressure value as the integrated pressure value.

9. The electrostatic capacitive sensor according to claim 5, characterized in that, When the sensor element is one and the analog processing circuit section has three or more amplifier circuits with different amplification rates, the pressure calculation unit sets the pressure value calculated based on the output of the amplifier circuit with the lowest amplification rate among the latest three or more pressure values ​​calculated based on the outputs of the three or more amplifier circuits. When the monitored pressure value is within a predetermined overlap region, the weighted average of the first pressure value and the second pressure value adjacent to the most recent combined pressure value among the three or more pressure values ​​is set as the latest combined pressure value. When the monitored pressure value is lower than the pressure of the overlap region, the second pressure value calculated based on the output of the amplifier circuit with the higher amplification rate among the first and second pressure values ​​is set as the latest combined pressure value. When the monitored pressure value is higher than the pressure of the overlap region, the first pressure value calculated based on the output of the amplifier circuit with the lower amplification rate among the first and second pressure values ​​is set as the latest combined pressure value.

10. The electrostatic capacitive sensor according to claim 5, characterized in that, When there are multiple sensor elements and the analog processing circuit section provides multiple differential amplifier circuits with different amplification rates for each sensor element, the pressure calculation unit sets the pressure value calculated based on the output of the amplifier circuit with the smallest amplification rate among the latest four or more pressure values ​​calculated based on the output of each of the four or more amplifier circuits. When the monitored pressure value is within a predetermined overlap region, the weighted average of the first pressure value and the second pressure value adjacent to the most recent combined pressure value among the four or more pressure values ​​is set as the latest combined pressure value. When the monitored pressure value is lower than the pressure of the overlap region, the second pressure value with the lower pressure range among the first and second pressure values ​​is set as the latest combined pressure value. When the monitored pressure value is higher than the pressure of the overlap region, the first pressure value with the higher pressure range among the first and second pressure values ​​is set as the latest combined pressure value.

Images