Capacitance sensor and pressure sensor

Abstract

To reduce the discontinuity of capacitance.SOLUTION: A capacitance sensor comprises: a sensor chip whose capacitance changes according to a physical quantity; a capacity detection unit 12 that converts output from the sensor chip into electric signals; a multiplexer 13 that performs switching so that two output signals from the capacity detection unit 12 are input to an AD converter 15 in a time-division manner; first and second capacity calculation units 160, 162 that calculate values of first and second capacitances on the basis of first and second output signals from the capacity detection unit 12 that are AD-converted by the AD converter 15; and a filter unit 161 that calculates the value of the first capacitance at the sampling timing of the AD converter 15 which is from when, of the first and second capacitances, the first capacitance having a longer sampling period in the AD converter 15 is calculated by the first capacity calculation unit 160, until when the first capacitance is calculated next.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a capacitance type sensor used in a diaphragm vacuum gauge or the like. [Background technology]

[0002] Pressure sensors such as vacuum gauges used in semiconductor manufacturing facilities, etc., use a variety of types of products that use various measurement principles depending on the required pressure range. For example, one of these is the capacitance-type diaphragm vacuum gauge, in which a movable diaphragm is subjected to pressure and the amount of deflection is detected as a capacitance value (see Patent Documents 1 to 4).

[0003] In such a diaphragm vacuum gauge, measurement errors occur due to temperature changes inside and outside the sensor, humidity changes in the reference vacuum chamber, etc. Therefore, Patent Documents 1 to 4 disclose methods for correcting the temperature characteristics of the sensor.

[0004] FIG. 12 is a cross-sectional view showing the configuration of a main part of a sensor chip of a conventional diaphragm vacuum gauge disclosed in Patent Documents 1 to 4, and FIG. 13 is a block diagram showing the configuration of a capacitance detection part of a conventional diaphragm vacuum gauge. A recess is formed in the center of base 101 of sensor chip 1. A diaphragm 102 configured to be deformable in response to pressure P of a medium to be measured (e.g., a process gas) is bonded to the surface of base 101 on which this recess is formed. The recess of base 101 forms a reference vacuum chamber 104 together with diaphragm 102.

[0005] In the sensor chip 1 of Fig. 12, a fixed electrode 105 is formed on the surface of the base 101 facing the reference vacuum chamber 104, and a movable electrode 106 is formed on the surface of the diaphragm 102 facing the reference vacuum chamber 104 so as to face the fixed electrode 105. In this way, the fixed electrode 105 and the movable electrode 106 are arranged to face each other across a gap. When the diaphragm 102 is deflected by receiving the pressure P of the medium to be measured, the distance between the movable electrode 106 and the fixed electrode 105 changes, and the electrostatic capacitance between the movable electrode 106 and the fixed electrode 105 changes. From this change in electrostatic capacitance, the pressure P of the medium to be measured received by the diaphragm 102 can be detected. The diaphragm 102 and the base 101 are made of an insulator such as sapphire.

[0006] Furthermore, a fixed electrode 107 is formed on the surface of the base 101 facing the reference vacuum chamber 104 outside the fixed electrode 105. A movable electrode 108 is formed on the surface of the diaphragm 102 facing the reference vacuum chamber 104 outside the movable electrode 106 so as to face the fixed electrode 107. The fixed electrode 107 and the movable electrode 108 are formed on the edge of the diaphragm 102. Even if the diaphragm 102 is deflected by the pressure P of the medium to be measured, the edge of the diaphragm 102 is hardly deformed, so that the capacitance between the movable electrode 108 and the fixed electrode 107 is unlikely to change. This capacitance is provided to eliminate measurement errors due to temperature changes inside and outside the sensor and humidity changes inside the reference vacuum chamber 104, etc.

[0007] 13, the capacitance detection unit includes a signal generator 200, amplifiers 201 and 202 each including a capacitance Cf and an operational amplifier A1, a subtractor 203, differential input type low-pass filters 204 and 205, a switch 206 provided between the amplifier 201 and the low-pass filter 204, and a switch 207 provided between the subtractor 203 and the low-pass filter 205. In FIG. 13, the capacitance (pressure-sensitive capacitance) between the movable electrode 106 and the fixed electrode 105 is represented by CX, and the capacitance (reference capacitance) between the movable electrode 108 and the fixed electrode 107 is represented by CR.

[0008] During pressure measurement, the signal generator 200 applies a sinusoidal sensor drive signal Esin(2πft) to the first electrode (e.g., fixed electrode 105) and third electrode (e.g., fixed electrode 107) of the sensor chip 1 and to the switches 206 and 207. E is the amplitude, f is the frequency, and t is the time.

[0009] Amplifier 201 converts the current output from a second electrode (e.g., movable electrode 106) of sensor chip 1 into a voltage, amplifies the voltage, and outputs a signal with an amplitude proportional to capacitance CX. Amplifier 202 converts the current output from a fourth electrode (e.g., movable electrode 108) of sensor chip 1 into a voltage, amplifies the voltage, and outputs a signal with an amplitude proportional to capacitance CR. Subtractor 203 subtracts the output signal of amplifier 202 from the output signal of amplifier 201. Note that it is also possible to configure the first electrode and the third electrode to be integrally formed, or to configure the second electrode and the fourth electrode to be integrally formed.

[0010] The switch 206 and the low-pass filter 204 constitute a synchronous detection unit 208. The cutoff frequency of the low-pass filter 204 is set so as to pass the sensor drive signal Esin(2πft). The synchronous detection unit 208 demodulates the output of the amplifier 201 into a signal synchronized with the sensor drive signal Esin(2πft).

[0011] Specifically, when sensor drive signal Esin(2πft) output from signal generator 200 is positive, switch 206 connects the output terminal of amplifier 201 to the non-inverting input terminal of low-pass filter 204. In addition, when sensor drive signal Esin(2πft) is negative, switch 206 connects the output terminal of amplifier 201 to the inverting input terminal of low-pass filter 204. This makes it possible to demodulate a signal (voltage E) synchronized with sensor drive signal Esin(2πft) from the output of amplifier 201.

[0012] Meanwhile, switch 207 and low-pass filter 205 constitute a synchronous detection unit 209. Low-pass filter 205 has a cutoff frequency set to pass sensor drive signal Esin(2πft). Synchronous detection unit 209 demodulates the output of subtractor 203 into a signal synchronized with sensor drive signal Esin(2πft).

[0013] Specifically, when sensor drive signal Esin(2πft) output from signal generator 200 is positive, switch 207 connects the output terminal of subtractor 203 to the non-inverting input terminal of low-pass filter 205. In addition, when sensor drive signal Esin(2πft) is negative, switch 207 connects the output terminal of subtractor 203 to the inverting input terminal of low-pass filter 205. This makes it possible to demodulate a signal (voltage F) synchronized with sensor drive signal Esin(2πft) from the output of subtractor 203.

[0014] Voltage E is proportional to CX. Voltage F is proportional to CX-CR. These voltages E and F are converted to AD by an AD converter, and the CPU divides the digital value of voltage F by the digital value of voltage E to obtain (CX-CR) / CX (called the physical quantity calculation formula, which in this case corresponds to the pressure calculation formula since the physical quantity is pressure). Then, the pressure P of the medium to be measured is calculated from (CX-CR) / CX.

[0015] In conventional diaphragm vacuum gauges, voltage E (hereafter referred to as the CX analog value) and voltage F (hereafter referred to as the CX-CR analog value) are switched by a multiplexer and converted into AD in a time-division manner by a single AD converter, but in order to emphasize fast response to pressure P, the CX-CR analog value is sampled with priority, and the sampling frequency of the CX analog value is reduced. For this reason, when the sampling result of the CX analog value is used to calculate (CX-CR) / CX, the value of (CX-CR) / CX may become discontinuous, and as a result, the value of pressure P becomes discontinuous, which may affect the pressure controllability of the pressure control device connected to the vacuum gauge.

[0016] Figures 14 and 15 are diagrams for explaining the problems with the conventional method. In Figure 14, 300 indicates a CX analog value, 301 indicates a time division value resulting from sampling the CX analog value, and 302 indicates a CX-CR analog value. In Figure 15, 303 indicates a value of (CX-CR) / CX calculated from the CX-CR analog value and the CX analog value, and 304 indicates a value of (CX-CR) / CX calculated from the CX-CR analog value and the CX time division value.

[0017] For ease of understanding, the examples in Figures 14 and 15 show a case where the sampling frequency of the CX analog value is 1 / 8 of the sampling frequency of the CX-CR analog value. Specifically, as shown in Figure 16, for example, AD conversion is performed in a time-division manner using one AD converter while switching the input to the AD converter in the following order: CX-CR → CX → CX-CR → Pressure sensor temperature → CX-CR → Circuit temperature → CX-CR → Power supply voltage → CX-CR → CX → CX-CR → Pressure sensor temperature → CX-CR → Circuit temperature → CX-CR → Power supply voltage →...

[0018] If the sampling frequency of the CX analog value is low as in this example, the calculated value of (CX-CR) / CX will be discontinuous when the CX analog value is sampled. Even if the pressure is increasing, the calculated value of (CX-CR) / CX may temporarily drop.

[0019] Filtering can be used to resolve the discontinuity in the calculated value of (CX-CR) / CX. For example, a first-order time constant filter as shown in formula (1) can be used. Y(n)=T / (T+τ)×(X(n)-Y(n-1))+Y(n-1) (1)

[0020] In equation (1), X(n) is the input, Y(n) is the output after filtering, Y(n-1) is the output after the previous filtering, T is the sampling period, and τ is the time constant.

[0021] 17 and 18 show an example in which filtering is applied when sampling the CX analog value in the example shown in FIG. 14 and FIG. 15. Specifically, as shown in FIG. 19, for example, while switching the input of the AD converter in the following order, CX-CR→CX→CX-CR→pressure sensor temperature→CX-CR→circuit temperature→CX-CR→power supply voltage→CX-CR→CX→CX-CR→pressure sensor temperature→CX-CR→circuit temperature→CX-CR→power supply voltage→···, AD conversion is performed in time division by one AD converter, and filtering is applied to the CX time division value. 305 in FIG. 17 shows the value obtained by filtering the CX time division value. 306 in FIG. 18 shows the value of (CX-CR) / CX calculated from the CX-CR analog value and the value obtained by filtering the CX time division value.

[0022] However, even if a filter process is applied to the CX time division value when the CX analog value is sampled as in FIG. 19, the discontinuity of (CX-CR) / CX cannot be reduced because the sampling frequency of the CX analog value is low.

[0023] 307 in Fig. 20 indicates a value obtained by filtering (CX-CR) / CX calculated from the CX-CR analog value and the CX time-division value in the example shown in Fig. 14 and Fig. 15. Specifically, for example, as shown in Fig. 21, while switching the input of the AD converter in the following order, CX-CR → CX → CX-CR → Pressure sensor temperature → CX-CR → Circuit temperature → CX-CR → Power supply voltage → CX-CR → CX → CX-CR → Pressure sensor temperature → CX-CR → Circuit temperature → CX-CR → Power supply voltage →..., AD conversion is performed in a time-division manner using one AD converter, (CX-CR) / CX is calculated at the timing of sampling of CX-CR and CX, and filtering is performed on (CX-CR) / CX.

[0024] However, even if filtering is performed after the calculation of (CX-CR) / CX as shown in Figure 21, the sampling frequency of the CX analog value is low, so the discontinuity of (CX-CR) / CX cannot be reduced, and the response speed must be sacrificed in order to reduce the discontinuity. [Prior art documents] [Patent documents]

[0025] [Patent Document 1] Patent No. 3969027 [Patent Document 2] Patent No. 4031215 Publication [Patent Document 3] Patent No. 4020318 Publication [Patent Document 4] JP 2022-176611 A Summary of the Invention [Problem to be solved by the invention]

[0026] The present invention has been made to solve the above-mentioned problems, and aims to provide a capacitance sensor and a pressure sensor that can improve the discontinuity of capacitance that changes in accordance with the physical quantity of the object to be measured. [Means for solving the problem]

[0027] The capacitance type sensor of the present invention includes a sensor chip configured to change capacitance in response to a physical quantity of a measurement target, a capacitance detection unit configured to convert an output of the sensor chip into an electrical signal, an AD converter configured to AD convert an output signal of the capacitance detection unit, a multiplexer configured to switch so that two different output signals of the capacitance detection unit are input to the AD converter in a time-division manner, a first capacitance calculation unit configured to calculate a value of a first capacitance based on a first output signal of the capacitance detection unit that has been AD converted by the AD converter, and a second capacitance calculation unit configured to calculate a value of a second capacitance based on a second output signal of the capacitance detection unit that has been AD converted by the AD converter. an interpolation unit configured to calculate a value of the first capacitance at a sampling timing of the AD converter between when the first capacitance calculation unit calculates the first capacitance, which has a longer sampling period of the AD converter out of the first and second capacitances, and when the first capacitance is next calculated; a physical quantity calculation unit that obtains a calculated value by substituting a calculation result of the interpolation unit and a calculation result of the second capacitance calculation unit into a physical quantity calculation formula for calculating the physical quantity; and a measurement unit configured to convert the calculated value into a corresponding physical quantity.

[0028] In addition, in one configuration example of the capacitance type sensor of the present invention, the interpolation unit performs filter processing on the value of the first capacitance, and is characterized in that it performs filter calculations on the value of the first capacitance not only at the sampling timing of the first output signal by the AD converter, but also at the sampling timing of other signals including the second output signal. Furthermore, in one configuration example of the capacitance type sensor of the present invention, the interpolation unit calculates a predicted value of the first capacitance to be calculated next by the first capacitance calculation unit from the latest value of the first capacitance calculated by the first capacitance calculation unit and the value of the first capacitance calculated one time before, and calculates, in an equal distribution, the value of the first capacitance at the sampling timing of the AD converter until the next first capacitance is calculated by the first capacitance calculation unit based on the latest value of the first capacitance and the predicted value.

[0029] The capacitance type sensor of the present invention includes a sensor chip configured to change capacitance according to a physical quantity of a measurement target, a capacitance detection unit configured to convert an output of the sensor chip into an electric signal, a first AD converter configured to perform AD conversion of a first output signal of the capacitance detection unit, a second AD converter configured to perform AD conversion of a second output signal of the capacitance detection unit, a multiplexer configured to perform switching so that a signal other than the second output signal and the first output signal are input to the first AD converter in a time division manner, and a multiplexer configured to calculate a value of a first capacitance based on the first output signal AD converted by the first AD converter. The capacitance calculation device is characterized in that it comprises a first capacitance calculation unit, a second capacitance calculation unit configured to calculate a value of a second capacitance based on the second output signal AD converted by the second AD converter, an interpolation unit configured to calculate a value of the first capacitance at a sampling timing of the first AD converter from when the first capacitance is calculated by the first capacitance calculation unit until when the first capacitance is next calculated, a physical quantity calculation unit that obtains a calculated value by substituting a calculation result of the interpolation unit and a calculation result of the second capacitance calculation unit into a physical quantity calculation formula for calculating the physical quantity, and a measurement unit configured to convert the calculated value into a corresponding physical quantity.

[0030] In addition, in one configuration example of the capacitance type sensor of the present invention, the interpolation unit performs filter processing on the value of the first capacitance, and is characterized in that it performs filter calculations on the value of the first capacitance not only at the sampling timing of the first output signal by the first AD converter but also at the sampling timing of another signal by the first AD converter. Furthermore, in one configuration example of the capacitance type sensor of the present invention, the interpolation unit calculates a predicted value of the first capacitance to be calculated next by the first capacitance calculation unit from the latest value of the first capacitance calculated by the first capacitance calculation unit and the value of the first capacitance calculated one time before, and calculates, in an equal distribution, the value of the first capacitance at the sampling timing of the first AD converter until the next first capacitance is calculated by the first capacitance calculation unit based on the latest value of the first capacitance and the predicted value.

[0031] In one configuration example of the capacitance type sensor of the present invention, the sensor chip includes a first electrode formed on a base, a second electrode formed on a diaphragm disposed across a gap from the base 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, and the distance between the first and second electrodes is changed by the displacement of the diaphragm according to the physical quantity, and the capacitance detection unit is configured to: The first output signal proportional to the capacitance between the first and second electrodes and the second output signal proportional to the capacitance between the third and fourth electrodes are output, the first capacitance calculation unit calculates the capacitance CX between the first and second electrodes as the first capacitance, the second capacitance calculation unit calculates a capacitance difference CX-CR between the capacitance CX between the first and second electrodes and the capacitance CR between the third and fourth electrodes as the second capacitance, and the physical quantity calculation unit calculates (CX-CR) / CX as the calculated value. Moreover, one configuration example of the capacitance type sensor of the present invention is characterized in that the first electrode and the third electrode are integrally formed. Moreover, one configuration example of the capacitance type sensor of the present invention is characterized in that the second electrode and the fourth electrode are integrally formed. Moreover, the pressure sensor of the present invention includes a capacitance type sensor, and the measurement section converts the calculated value into a pressure value, which is the physical quantity. Effect of the Invention

[0032] According to the present invention, the interpolation unit calculates the value of the first capacitance not only at the sampling timing of the first output signal by the AD converter, but also at the sampling timing of the AD converter until the first capacitance is next calculated by the first capacitance calculation unit, so that discontinuity in capacitance can be reduced without sacrificing the response speed to changes in physical quantity. [Brief description of the drawings]

[0033] [Figure 1] FIG. 1 is a block diagram showing the configuration of a diaphragm vacuum gauge according to a first embodiment of the present invention. [Diagram 2] FIG. 2 is a block diagram showing the configuration of a circuit section of a diaphragm vacuum gauge according to a first embodiment of the present invention. [Diagram 3] FIG. 3 is a diagram for explaining the order in which signals are AD converted in a time-division manner, the timing of filter calculations, and the calculation timing of (CX-CR) / CX in the first embodiment of the present invention. [Figure 4] FIG. 4 is a diagram for explaining the effect of the first embodiment of the present invention. [Diagram 5] FIG. 5 is a diagram for explaining the effect of the first embodiment of the present invention. [Figure 6] FIG. 6 is a block diagram showing the configuration of a circuit section of a diaphragm vacuum gauge according to a second embodiment of the present invention. [Figure 7]FIG. 7 is a diagram for explaining the order in which signals are AD converted in a time-division manner, the timing of filter calculations, and the calculation timing of (CX-CR) / CX in the second embodiment of the present invention. [Figure 8] FIG. 8 is a block diagram showing the configuration of a circuit section of a diaphragm vacuum gauge according to a third embodiment of the present invention. [Figure 9] FIG. 9 is a diagram for explaining the order in which signals are AD converted in a time-division manner, the timing of the interpolation calculation, and the calculation timing of (CX-CR) / CX in the third embodiment of the present invention. [Figure 10] FIG. 10 is a diagram for explaining the operation of the interpolation unit according to the third embodiment of the present invention. [Figure 11] FIG. 11 is a diagram for explaining another example of the order in which signals are AD converted in a time-division manner, the timing of the interpolation calculation, and the calculation timing of (CX-CR) / CX in the third embodiment of the present invention. [Figure 12] FIG. 12 is a cross-sectional view showing the configuration of a main part of a sensor chip of a conventional diaphragm vacuum gauge. [Figure 13] FIG. 13 is a block diagram showing the configuration of a capacitance detection section of a conventional diaphragm vacuum gauge. [Figure 14] FIG. 14 is a diagram for explaining the problem in the conventional technology. [Figure 15] FIG. 15 is a diagram for explaining the problem in the conventional technology. [Figure 16] FIG. 16 is a diagram for explaining the order in which signals are AD converted in a time-division manner in a conventional diaphragm vacuum gauge. [Figure 17] FIG. 17 is a diagram for explaining the problem in the conventional technology. [Figure 18] FIG. 18 is a diagram for explaining the problem in the conventional technology. [Figure 19] FIG. 19 is a diagram for explaining the order in which signals are AD converted in a time-division manner and the timing of filter calculations in a conventional diaphragm vacuum gauge. [Figure 20] FIG. 20 is a diagram for explaining the problem in the conventional technology. [Figure 21]FIG. 21 is a diagram for explaining the order of time-division AD conversion of signals, the calculation timing of (CX-CR) / CX, and the timing of filter calculation in a conventional diaphragm vacuum gauge. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0034] [First Example] Fig. 1 is a block diagram showing the configuration of a diaphragm vacuum gauge according to a first embodiment of the present invention, and Fig. 2 is a block diagram showing the configuration of a circuit part of the diaphragm vacuum gauge. In this embodiment, an example in which a capacitance type sensor (pressure sensor) of the present invention is applied to a diaphragm vacuum gauge will be described.

[0035] The diaphragm vacuum gauge comprises a pressure receiving section 10 whose capacitance changes in response to the displacement of a diaphragm due to the pressure of a medium to be measured (e.g., a process gas), and a circuit section 11 that converts the change in capacitance of the pressure receiving section 10 into a pressure measurement value.

[0036] The pressure receiving section 10 comprises a sensor chip 1, a housing 2 that accommodates the sensor chip 1, a pressure introduction tube 3 that introduces the pressure P of the medium to be measured to the diaphragm 102 of the sensor chip 1, a sensor case 4 that covers the housing 2, and a heater 5 provided to surround the outer circumferential surface of the sensor case 4. The heater 5 is used for a self-heating function to prevent adhesion of liquefied or solidified process gas. The sensor case 4 with the heater 5 provided therein is covered with a heat insulating material 6. The configuration of the sensor chip 1 is as shown in FIG. 12.

[0037] A partition wall 7 is provided inside the housing 2. The partition wall 7 is composed of a base plate 7a and a support plate 7b, and divides the internal space of the housing 2 into a first space 2a and a second space 2b. The outer periphery of the support plate 7b is fixed to the housing 2, and supports the base plate 7a in a state where it is raised in the internal space of the housing 2. The sensor chip 1 is fixed to the second space 2b side of the base plate 7a. The base plate 7a is also formed with a pressure introduction hole 7c that introduces the pressure in the first space 2a to the diaphragm 102 of the sensor chip 1. The second space 2b is in communication with a reference vacuum chamber 104 of the sensor chip 1, and is in a vacuum state.

[0038] The pressure introduction pipe 3 is connected to the first space 2a side of the housing 2. A baffle 8 is provided between the pressure introduction pipe 3 and the housing 2. The medium to be measured introduced through the pressure introduction pipe 3 hits the plate surface of the baffle 8 and flows into the first space 2a of the housing 2 through the gap around the baffle 8. A temperature sensor 9 is provided on the outer wall surface of the housing 2. The temperature sensor 9 measures the temperature of the housing 2 as the temperature of the sensor chip 1.

[0039] As shown in FIG. 2, the circuit unit 11 includes a capacitance detection unit 12 that converts the output of the sensor chip 1 into an electrical signal, a multiplexer 13 that switches the signals, a temperature sensor 14 that measures the temperature of the circuit unit 11 (e.g., the temperature of the capacitance detection unit 12), an AD converter 15 that performs AD conversion of the output signal of the capacitance detection unit 12, a CPU 16, and a memory 17.

[0040] The CPU (Central Processing Unit) 16 executes processing according to a program stored in the memory 17, and functions as a first capacitance calculation unit 160, a filter unit 161 (interpolation unit), a second capacitance calculation unit 162, a physical quantity calculation unit 163, and a measurement unit 164.

[0041] The signal generator 200, the amplifiers 201 and 202, the subtractor 203, and the synchronous detection sections 208 and 209 constitute the capacitance detection section 12. The operation of the capacitance detection section 12 is as described in FIG.

[0042] FIG. 3 is a diagram for explaining the order in which signals are AD converted in a time-division manner, the timing of filter calculations, and the timing of calculation of (CX-CR) / CX in this embodiment. For example, as shown in Figure 3, multiplexer 13 switches the input of AD converter 15 in the following order: CX-CR → CX → CX-CR → Pressure sensor temperature → CX-CR → Circuit temperature → CX-CR → Power supply voltage → CX-CR → CX → CX-CR → Pressure sensor temperature → CX-CR → Circuit temperature → CX-CR → Power supply voltage →...

[0043] 3, "CX-CR" of the input to the AD converter 15 is a CX-CR analog value (voltage F which is the output of the capacitance detection unit 12), and "CX" of the same input is a CX analog value (voltage E which is the output of the capacitance detection unit 12). Furthermore, "pressure sensor temperature" is the temperature of the sensor chip 1 measured by the temperature sensor 9, and "circuit temperature" is the temperature of the circuit unit 11 measured by the temperature sensor 14. "Power supply voltage" is the power supply voltage of the circuit unit 11 measured by a voltmeter not shown.

[0044] The AD converter 15 converts the input signal from the multiplexer 13 into a digital signal every time the input is switched by the multiplexer 13. The first capacitance calculation section 160 calculates the value of the capacitance CX from the digital value after AD conversion of the CX analog value at the sampling timing of the CX analog value by the AD converter 15. The first capacitance calculation section 160 maintains the calculated value of the capacitance CX until the digital value obtained by AD converting the CX analog value is newly output from the AD converter 15 at the next sampling timing of the CX analog value.

[0045] The filter unit 161 performs a filter process on the value of the capacitance CX calculated by the first capacitance calculation unit 160. An example of the filter process is the first-order lag filter process (low-pass filter process) described in equation (1). Here, as shown in FIG. 3, the filter unit 161 of this embodiment performs a filter operation on the value of the capacitance CX calculated by the first capacitance calculation unit 160 not only at the sampling timing of the CX analog value by the AD converter 15 but also at each sampling timing of the CX-CR analog value, the pressure sensor temperature, the circuit temperature, and the power supply voltage.

[0046] On the other hand, the second capacitance calculation unit 162 calculates the value of the capacitance difference CX-CR from the digital value after AD conversion of the CX-CR analog value at the sampling timing of the CX-CR analog value by the AD converter 15. The second capacitance calculation unit 162 maintains the calculated value of the capacitance difference CX-CR until the digital value obtained by AD converting the CX-CR analog value is newly output from the AD converter 15 at the next sampling timing of the CX-CR analog value.

[0047] The physical quantity calculation section 163 reduces errors by calculating (CX-CR) / CX based on the calculation result of the filter section 161 and the calculation result of the second capacitance calculation section 162. As shown in Fig. 3, the physical quantity calculation section 163 calculates (CX-CR) / CX not only at the sampling timing of the CX analog value by the AD converter 15 but also at each sampling timing of the CX-CR analog value, the pressure sensor temperature, the circuit temperature, and the power supply voltage.

[0048] The measurement unit 164 corrects the capacitance (CX-CR) / CX calculated by the physical quantity calculation unit 163 using the temperature of the sensor chip 1 measured by the temperature sensor 9 and the temperature of the circuit unit 11 measured by the temperature sensor 14, converts it into a pressure value P, and outputs it. The method of correcting the capacitance (CX-CR) / CX using the temperature may be, for example, using the following formula (2).

[0049]

number

[0050] In the formula (2), Vo is (CX-CR) / CX calculated by the physical quantity calculation unit 163, Vs is the pressure sensor temperature, Vc is the circuit temperature, a ijk is a correction coefficient, and i, j, and k are the degrees of the polynomial. When the power supply voltage of the circuit unit 11 changes, the output voltage of the capacitance detection unit 12 may change in proportion to the change. Therefore, the power supply voltage of the circuit unit 11 may be measured and corrected. For example, the first capacitance calculation unit 160 performs a correction as shown in equation (3) on the digital value after AD conversion of the CX analog value. Ed' = Ed × a × Vd (3)

[0051] Moreover, the second capacitance calculation section 162 performs a correction as shown in equation (4) on the digital value after AD conversion of the CX-CR analog value. Fd' = Fd × b × Vd (4)

[0052] Ed is the digital value after AD conversion of the CX analog value, Ed' is the corrected value of Ed, Fd is the digital value after AD conversion of the CX-CR analog value, Fd' is the corrected value of Fd, Vd is the digital value after AD conversion of the power supply voltage, and a and b are correction coefficients.

[0053] Since the measurement unit 164 calculates (CX-CR) / CX at each sampling timing of the CX analog value, the CX-CR analog value, the pressure sensor temperature, the circuit temperature, and the power supply voltage, it calculates the pressure value P at each sampling timing. However, the pressure sensor temperature Vs is converted to a digital value in a time-division manner. Therefore, the measurement unit 164 calculates the pressure value P using the current pressure sensor temperature Vs until the digital value obtained by AD-converting the pressure sensor temperature Vs is newly output from the AD converter 15 at the next sampling timing of the pressure sensor temperature Vs. Similarly, the measurement unit 164 calculates the pressure value P using the current circuit temperature Vc until the digital value obtained by AD-converting the circuit temperature Vc is newly output from the AD converter 15 at the next sampling timing of the circuit temperature Vc.

[0054] Fig. 4 and Fig. 5 are diagrams for explaining the effects of this embodiment. In Fig. 4, 400 indicates a CX analog value, 401 indicates a time division value resulting from sampling the CX analog value, 402 indicates a CX-CR analog value, and 403 indicates the result of filter calculation by the filter unit 161 of this embodiment. In Fig. 5, 404 indicates the value of (CX-CR) / CX calculated from the CX-CR analog value and the CX analog value, and 405 indicates the value of (CX-CR) / CX calculated from the CX-CR analog value and the result of filter calculation by the filter unit 161.

[0055] In this embodiment, by performing a filter operation on the capacitance CX value calculated by the first capacitance calculation unit 160 not only at the sampling timing of the CX analog value by the AD converter 15 but also at each sampling timing of the CX-CR analog value, the pressure sensor temperature, the circuit temperature, and the power supply voltage, it is possible to reduce the discontinuity of (CX-CR) / CX without sacrificing the response speed to capacitance changes (pressure changes in the medium to be measured).

[0056] [Second Example] 6 is a block diagram showing the configuration of a circuit section of a diaphragm vacuum gauge according to a second embodiment of the present invention. In this embodiment as well, an example in which a capacitance type sensor (pressure sensor) is applied to a diaphragm vacuum gauge will be described.

[0057] The overall configuration of the diaphragm vacuum gauge is similar to that of the first embodiment, and will be described using the symbols in Fig. 1. As shown in Fig. 6, the circuit section 11 of this embodiment includes a capacitance detection section 12, a multiplexer 13a, a temperature sensor 14, AD converters 15-1 and 15-2, a CPU 16a, and a memory 17.

[0058] The CPU 16a executes processes according to the programs stored in the memory 17, and functions as a first capacitance calculation section 160a, a filter section 161a (interpolation section), a second capacitance calculation section 162a, a physical quantity calculation section 163a, and a measurement section 164a.

[0059] In this embodiment, two AD converters are used in order to speed up the response to pressure changes in the medium to be measured. The sampling timing of the two AD converters 15-1 and 15-2 is the same. 7 is a diagram for explaining the order in which signals are AD converted in a time-division manner, the timing of filter calculations, and the calculation timing of (CX-CR) / CX in this embodiment. "AD converter input 1" in Fig. 7 indicates the input to AD converter 15-1, and "AD converter input 2" indicates the input to AD converter 15-2.

[0060] The AD converter 15-1 converts the CX-CR analog value (voltage F) output from the capacitance detection unit 12 into a digital signal. For example, as shown in FIG. 7, the multiplexer 13a switches the input of the AD converter 15-2 in the order of CX→pressure sensor temperature→circuit temperature→power supply voltage→CX→pressure sensor temperature→circuit temperature→power supply voltage→. . .

[0061] The AD converter 15-2 converts the input signal from the multiplexer 13a into a digital signal every time the input is switched by the multiplexer 13a. The first capacitance calculation unit 160a, like the first capacitance calculation unit 160 of the first embodiment, calculates the value of the capacitance CX from the digital value after AD conversion of the CX analog value at the sampling timing of the CX analog value by the AD converter 15-2. The first capacitance calculation unit 160a maintains the calculated value of the capacitance CX until the digital value obtained by AD converting the CX analog value is newly output from the AD converter 15-2 at the next sampling timing of the CX analog value.

[0062] The filter unit 161a performs a filter process on the value of the capacitance CX calculated by the first capacitance calculation unit 160a, similar to the filter unit 161 of the first embodiment. As shown in Fig. 7, the filter unit 161a performs a filter operation on the value of the capacitance CX calculated by the first capacitance calculation unit 160a not only at the sampling timing of the CX analog value by the AD converter 15-2 but also at each sampling timing of the pressure sensor temperature, the circuit temperature, and the power supply voltage.

[0063] The second capacitance calculation section 162a calculates the value of the capacitance difference CX-CR from the digital value after AD conversion of the CX-CR analog value at the sampling timing of the CX-CR analog value by the AD converter 15-1.

[0064] The physical quantity calculation section 163a reduces errors by calculating (CX-CR) / CX based on the calculation result of the filter section 161a and the calculation result of the second capacitance calculation section 162a. As shown in Fig. 7, the physical quantity calculation section 163a calculates (CX-CR) / CX not only at the sampling timing of the CX analog value by the AD converter 15-2 but also at each sampling timing of the pressure sensor temperature, the circuit temperature, and the power supply voltage.

[0065] The measuring unit 164a calculates the pressure value P by equation (2) in the same manner as the measuring unit 164 in the first embodiment. Since (CX-CR) / CX is calculated at each sampling timing of the CX analog value, the pressure sensor temperature, the circuit temperature, and the power supply voltage, the measuring unit 164a calculates the pressure value P at each sampling timing. Thus, in this embodiment, like the first embodiment, the discontinuity of (CX-CR) / CX can be reduced.

[0066] [Third Example] 8 is a block diagram showing the configuration of a circuit section of a diaphragm vacuum gauge according to a third embodiment of the present invention. In this embodiment as well, an example in which a capacitance type sensor (pressure sensor) is applied to a diaphragm vacuum gauge will be described.

[0067] The overall configuration of the diaphragm vacuum gauge is similar to that of the first embodiment, and will be described using the symbols in Fig. 1. As shown in Fig. 8, the circuit section 11 of this embodiment includes a capacitance detection section 12, a multiplexer 13, a temperature sensor 14, an AD converter 15, a CPU 16b, and a memory 17.

[0068] The CPU 16b executes processes according to the programs stored in the memory 17, and functions as a first capacitance calculation unit 160, an interpolation unit 165, a second capacitance calculation unit 162, a physical quantity calculation unit 163b, and a measurement unit 164.

[0069] 9 is a diagram for explaining the order of AD conversion of signals in a time-division manner, the timing of the interpolation calculation, and the calculation timing of (CX-CR) / CX in this embodiment. The operations of the multiplexer 13, the AD converter 15, and the first capacitance calculation unit 160 are the same as those in the first embodiment.

[0070] As in the first embodiment, the multiplexer 13 switches the input of the AD converter 15 in the following order: CX-CR → CX → CX-CR → pressure sensor temperature → CX-CR → circuit temperature → CX-CR → power supply voltage → CX-CR → CX → CX-CR → pressure sensor temperature → CX-CR → circuit temperature → CX-CR → power supply voltage →..., as shown in Fig. 9. The first capacitance calculation unit 160 calculates the value of the capacitance CX from the digital value after AD conversion of the CX analog value at the sampling timing of the CX analog value by the AD converter 15.

[0071] The interpolation section 165 performs an interpolation operation to calculate the value of the capacitance CX at the sampling timing of the AD converter 15 during the period from when the capacitance CX is calculated by the first capacitance calculation section 160 until the next calculation of the capacitance CX.

[0072] Fig. 10 is a diagram for explaining the operation of the interpolation unit 165. The interpolation unit 165 calculates a predicted value (CX(t+4) in Fig. 10) of the capacitance CX to be calculated next by the first capacitance calculation unit 160 from two values, namely, the latest value of the capacitance CX calculated by the first capacitance calculation unit 160 (CX(t) in Fig. 10) and the value of the capacitance CX calculated one time before (CX(t-4) in Fig. 10), and calculates the values ​​of the capacitance CX at the sampling timing of the AD converter 15 until the next calculation of the capacitance CX by the first capacitance calculation unit 160 (CX(t+1), CX(t+2), CX(t+3) in Fig. 10) in the same distribution.

[0073] If the latest value of the capacitance CX calculated by the first capacitance calculation unit 160 is X(n), the value of the capacitance CX calculated one time before by the first capacitance calculation unit 160 is X(n-1), and the predicted value of the capacitance CX to be calculated next by the first capacitance calculation unit 160 is X(n+1), the interpolation unit 165 calculates the predicted value X(n+1) as shown in equation (5) when the latest capacitance CX=X(n) is calculated by the first capacitance calculation unit 160. X(n+1)=X(n)+(X(n)-X(n-1)) ···(5)

[0074] Furthermore, the interpolation section 165 calculates the value Z of the capacitance CX at the sampling timing of the AD converter 15 until the first capacitance calculation section 160 next calculates the capacitance CX, as shown in Equation (6). Z=X(n)+(X(n+1)-X(n))×k / (m+1) ···(6)

[0075] In equation (6), m is the number of sampling timings at which the AD converter 15 converts another analog value into a digital value between the sampling timing of the CX analog value by the AD converter 15 and the sampling timing of the next CX analog value (m=7 in the example of Figure 9).

[0076] In formula (6), k is the number of times that the interpolation calculation (formula (6)) has been performed between the sampling timing of the CX analog value by the AD converter 15 and the sampling timing of the next CX analog value. For example, in the example of FIG. 10, when CX(t+3) is calculated, the calculations of CX(t+1) and CX(t+2) have already been performed, so k=2. When CX(t+2) is calculated, the calculation of CX(t+1) has already been performed, so k=1. On the other hand, when CX(t+1) is calculated, the interpolation calculation has not yet been performed, so k=0.

[0077] The interpolation unit 165 outputs the calculated value of the capacitance CX as is at the sampling timing when the capacitance CX is calculated by the first capacitance calculation unit 160. In this way, the interpolation unit 165 can perform linear interpolation calculation of the capacitance CX.

[0078] The operations of the second capacitance calculation unit 162 and the measurement unit 164 are the same as those in the first embodiment. The physical quantity calculation unit 163b reduces errors by calculating (CX-CR) / CX based on the output of the interpolation unit 165 and the calculation result of the second capacitance calculation unit 162. As shown in Fig. 9, the physical quantity calculation unit 163b calculates (CX-CR) / CX not only at the sampling timing of the CX analog value by the AD converter 15 but also at each sampling timing of the CX-CR analog value, the pressure sensor temperature, the circuit temperature, and the power supply voltage.

[0079] Thus, in this embodiment, like the first embodiment, the discontinuity of (CX-CR) / CX can be reduced.

[0080] In the configuration shown in Fig. 8, this embodiment is applied to the first embodiment, but it may also be applied to the second embodiment. In this case, the order in which the signals are AD converted in a time-division manner, the timing of the interpolation calculation, and the calculation timing of (CX-CR) / CX are shown in Fig. 11.

[0081] When applied to the second embodiment, the interpolation unit 165 performs an interpolation calculation to calculate the value of the capacitance CX at the sampling timing of the AD converter 15-2 between the time when the capacitance CX is calculated from the capacitance CX by the first capacitance calculation unit 160a of the second embodiment and the time when the capacitance CX is next calculated.

[0082] When applied to the second embodiment, the physical quantity calculation unit 163b reduces errors by calculating (CX-CR) / CX based on the output of the interpolation unit 165 and the calculation result of the second capacitance calculation unit 162a. As shown in Fig. 7, the physical quantity calculation unit 163b calculates (CX-CR) / CX not only at the sampling timing of the CX analog value by the AD converter 15-2 but also at each sampling timing of the pressure sensor temperature, the circuit temperature, and the power supply voltage.

[0083] 12 is used as the configuration of the sensor chip 1 in the first to third embodiments, but the present invention is not limited thereto, and a sensor chip having a configuration in which the first electrode and the third electrode are integrally formed may be used. Alternatively, a sensor chip having a configuration in which the second electrode and the fourth electrode are integrally formed may be used. [Industrial Applicability]

[0084] The present invention is applicable to diaphragm vacuum gauges. [Explanation of symbols]

[0085] 1...sensor chip, 9, 14...temperature sensor, 10...pressure receiving section, 11...circuit section, 12...capacitance detection section, 13, 13a...multiplexer, 15, 15-1, 15-2...AD converter, 16, 16a, 16b...CPU, 17...memory, 160, 160a...first capacitance calculation section, 161, 161a...filter section, 162, 162a...second capacitance calculation section, 163, 163a, 163b...physical quantity calculation section, 164, 164a...measurement section, 165...interpolation section.

Claims

1. A sensor chip configured such that its capacitance changes in response to a physical quantity to be measured; a capacitance detection unit configured to convert an output of the sensor chip into an electrical signal; an AD converter configured to perform AD conversion of an output signal of the capacitance detection unit; a multiplexer configured to perform switching so that two different output signals of the capacitance detection unit are input to the AD converter in a time division manner; a first capacitance calculation unit configured to calculate a value of a first capacitance based on a first output signal of the capacitance detection unit that has been AD converted by the AD converter; a second capacitance calculation unit configured to calculate a value of a second capacitance based on a second output signal of the capacitance detection unit that has been AD converted by the AD converter; an interpolation unit configured to calculate a value of the first capacitance at a sampling timing of the AD converter from when the first capacitance calculation unit calculates the first capacitance, which has a longer sampling period of the AD converter, to when the first capacitance is next calculated; and a physical quantity calculation unit that obtains a calculated value by substituting the calculation result of the interpolation unit and the calculation result of the second capacitance calculation unit into a physical quantity calculation formula for calculating the physical quantity; and a measuring unit configured to convert the calculated value into a corresponding physical quantity.

2. 2. The capacitance type sensor according to claim 1, The capacitance type sensor is characterized in that the interpolation unit performs filter processing on the value of the first capacitance, and performs filter calculations on the value of the first capacitance not only at the sampling timing of the first output signal by the AD converter, but also at the sampling timing of other signals including the second output signal.

3. 2. The capacitance type sensor according to claim 1, a capacitance-type sensor characterized in that the interpolation unit calculates a predicted value of the first capacitance to be calculated next by the first capacitance calculation unit from the latest value of the first capacitance calculated by the first capacitance calculation unit and the value of the first capacitance calculated one time before, and calculates, in an equal distribution, the value of the first capacitance at the sampling timing of the AD converter until the next first capacitance is calculated by the first capacitance calculation unit based on the latest value of the first capacitance and the predicted value.

4. A sensor chip configured such that its capacitance changes in response to a physical quantity to be measured; a capacitance detection unit configured to convert an output of the sensor chip into an electrical signal; A first AD converter configured to perform AD conversion of a first output signal of the capacitance detection unit; a second AD converter configured to AD convert a second output signal of the capacitance detection unit; a multiplexer configured to perform switching so that a signal other than the second output signal and the first output signal are input to the first AD converter in a time division manner; a first capacitance calculation unit configured to calculate a value of a first capacitance based on the first output signal that has been AD converted by the first AD converter; a second capacitance calculation unit configured to calculate a value of a second capacitance based on the second output signal that has been AD converted by the second AD converter; an interpolation unit configured to calculate a value of the first capacitance at a sampling timing of the first AD converter from when the first capacitance is calculated by the first capacitance calculation unit until when the first capacitance is next calculated; a physical quantity calculation unit that obtains a calculated value by substituting the calculation result of the interpolation unit and the calculation result of the second capacitance calculation unit into a physical quantity calculation formula for calculating the physical quantity; and a measuring unit configured to convert the calculated value into a corresponding physical quantity.

5. 5. The capacitance type sensor according to claim 4, The capacitance type sensor is characterized in that the interpolation unit performs filter processing on the value of the first capacitance, and performs filter calculations on the value of the first capacitance not only at the sampling timing of the first output signal by the first AD converter, but also at the sampling timing of another signal by the first AD converter.

6. 5. The capacitance type sensor according to claim 4, a first capacitance calculation unit that calculates a predicted value of the first capacitance to be calculated next by the first capacitance calculation unit from the latest value of the first capacitance calculated by the first capacitance calculation unit and the value of the first capacitance calculated one time before, and calculates, in an equal distribution, the value of the first capacitance at the sampling timing of the first AD converter until the next first capacitance is calculated by the first capacitance calculation unit based on the latest value of the first capacitance and the predicted value.

7. 7. The capacitance type sensor according to claim 1, the sensor chip includes a first electrode formed on a base, a second electrode formed on a diaphragm disposed across a gap from the base 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, and is configured such that a distance between the first and second electrodes changes due to a displacement of the diaphragm in response to the physical quantity; the capacitance detection unit outputs the first output signal proportional to a capacitance between the first and second electrodes and the second output signal proportional to a capacitance between the third and fourth electrodes; the first capacitance calculation unit calculates a capacitance Cx between the first and second electrodes as the first capacitance; the second capacitance calculation unit calculates a capacitance difference CX-CR between a capacitance CX between the first and second electrodes and a capacitance CR between the third and fourth electrodes as the second capacitance; The capacitance type sensor is characterized in that the physical quantity calculation unit calculates (CX-CR) / CX as the calculated value.

8. 8. The capacitance type sensor according to claim 7, A capacitance type sensor, wherein the first electrode and the third electrode are integrally formed.

9. 8. The capacitance type sensor according to claim 7, A capacitance type sensor, wherein the second electrode and the fourth electrode are integrally formed.

10. The capacitive sensor according to any one of claims 7 to 9, The pressure sensor is characterized in that the measurement unit converts the calculated value into a pressure value which is the physical quantity.

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