Diaphragm vacuum gauge

Abstract

To reduce power consumption for heating to reduce the size of a sensor chip.SOLUTION: A diaphragm gauge comprises: a sensor chip in which the interval between first and second electrodes changes according to displacement of a diaphragm due to pressure of a medium to be measured; a signal generator 120 that selectively applies, to the second electrode, any one of a first sensor drive signal and a second sensor drive signal with a higher frequency than that of the first sensor drive signal; an amplifier 121 that converts current output from the first electrode into voltage; a capacity calculation unit 123 that calculates the value of the capacitance Cx between the first and second electrodes from an output signal from the amplifier 121; a pressure measuring unit that converts the capacitance into a measured pressure value; and a control unit that controls the signal generator 120 to apply the first sensor drive signal to the second electrode during pressure measurement and apply the second sensor drive signal to the second electrode during heating.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a diaphragm vacuum gauge. [Background technology]

[0002] Diaphragm vacuum gauges are used to measure the pressure in semiconductor process chambers. If the temperature of the semiconductor process gas is not appropriate, it will liquefy or solidify and adhere to the sensor chip of the diaphragm vacuum gauge, affecting the measurement. For this reason, the diaphragm vacuum gauge has a self-heating function to prevent adhesion of liquefied or solidified process gas (see Patent Document 1, Patent Document 2, and Patent Document 3).

[0003] However, since it is difficult to heat only the sensor chip, conventional diaphragm vacuum gauges having a self-heating function heat the entire pressure receiving section including the sensor chip. However, heating the entire pressure receiving section requires a large heater, which increases power consumption, and using a large heater also raises the temperature of nearby circuits, even if they are insulated, making it necessary to limit the ambient temperature at which the circuits can be used.

[0004] Although it is possible to install a heater inside the sensor chip, this requires making the electrodes for detecting pressure smaller, and also requires attaching a heater to the sensor chip and wiring to the heater, which results in a problem of making the sensor chip larger. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2010-117154 A [Patent Document 2] JP 2009-243887 A [Patent Document 3] JP 2019-7906 A Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention has been made to solve the above problems, and has an object to provide a diaphragm vacuum gauge that can reduce power consumption for heating by heating only the sensor chip, and can realize a miniaturized sensor chip. [Means for solving the problem]

[0007] A diaphragm vacuum gauge (first embodiment) of the present invention is characterized in that it comprises a sensor chip including a first electrode formed on a base and a second electrode formed on a diaphragm disposed across a gap from the base so as to face the first electrode, the distance between the first and second electrodes being changed in response to displacement of the diaphragm due to pressure of a medium to be measured, a signal generator configured to selectively apply to the second electrode either a first sensor drive signal or a second sensor drive signal having a higher frequency than the first sensor drive signal, an amplifier configured to convert a current output from the first electrode into a voltage and amplify the voltage, a capacitance calculation unit configured to calculate a capacitance value between the first and second electrodes from the output signal of the amplifier, a pressure measurement unit configured to convert the capacitance into a measured pressure value, and a control unit configured to control the signal generator so as to apply the first sensor drive signal to the second electrode during pressure measurement and to apply the second sensor drive signal to the second electrode during heating.

[0008] A diaphragm vacuum gauge (second embodiment) of the present invention includes a sensor chip including a first electrode formed on a base and a second electrode formed on a diaphragm disposed across a gap from the base so as to face the first electrode, the sensor chip being configured so that a distance between the first and second electrodes changes in response to a displacement of the diaphragm caused by a pressure of a medium to be measured; a first signal generator configured to output a first sensor drive signal; a second signal generator configured to output a second sensor drive signal having a higher frequency than the first sensor drive signal; an amplifier configured to convert a current output from the first electrode into a voltage and amplify the voltage; and a first switch provided between the first and second signal generators and the second electrode, the first switch configured to selectively connect either an output terminal of the first signal generator or an output terminal of the second signal generator to the second electrode; The pressure measuring device is characterized by comprising: a second switch provided between the first electrode and the amplifier and configured to selectively connect either the input terminal of the amplifier or ground to the first electrode; a capacitance calculation unit configured to calculate a capacitance value between the first and second electrodes from an output signal of the amplifier; a pressure measurement unit configured to convert the capacitance into a measured pressure value; and a control unit configured to control the first switch to connect the output terminal of the first signal generator to the second electrode and to control the second switch to connect the first electrode to the input terminal of the amplifier during pressure measurement, and to control the first switch to connect the output terminal of the second signal generator to the second electrode and to control the second switch to connect the first electrode to the ground during heating.

[0009] A diaphragm vacuum gauge (third embodiment) of the present invention includes a sensor chip including a first electrode formed on a base and a second electrode formed on a diaphragm disposed across a gap from the base so as to face the first electrode, the sensor chip being configured so that a distance between the first and second electrodes changes in response to a displacement of the diaphragm due to a pressure of a medium to be measured; a first signal generator configured to apply to the second electrode either a first sensor drive signal or a second sensor drive signal having a higher frequency than the first sensor drive signal; a second signal generator configured to output a signal out of phase with the first sensor drive signal; an amplifier configured to convert a current output from the first electrode into a voltage and amplify the voltage; and a signal synchronized with the first sensor drive signal, the second signal generator being configured to demodulate the output signal of the amplifier. a first synchronous detection unit configured to demodulate an output signal of the amplifier to a signal synchronized with the output signal of the second signal generator, a capacitance calculation unit configured to calculate a value of the capacitance between the first and second electrodes from the output signals of the first and second synchronous detection units, a temperature calculation unit configured to calculate a value of a series resistance of the first and second electrodes from the output signals of the first and second synchronous detection units and to obtain a temperature of the sensor chip from this series resistance value, a pressure measurement unit configured to convert the capacitance into a measured pressure value, and a control unit configured to control the first signal generator to apply the first sensor drive signal to the second electrode during pressure / temperature measurement and to apply the second sensor drive signal to the second electrode during heating.

[0010] A diaphragm vacuum gauge (fourth embodiment) of the present invention includes a sensor chip including a first electrode formed on a base and a second electrode formed on a diaphragm disposed across a gap from the base so as to face the first electrode, the sensor chip being configured such that a distance between the first and second electrodes changes in response to a displacement of the diaphragm caused by a pressure of a medium to be measured; a first signal generator configured to output a first sensor drive signal; a second signal generator configured to output a second sensor drive signal having a higher frequency than the first sensor drive signal; a third signal generator configured to output a signal out of phase with the first sensor drive signal; an amplifier configured to convert a current output from the first electrode into a voltage and amplify the voltage; a first switch provided between the first and second signal generators and the second electrode and configured to selectively connect either an output terminal of the first signal generator or an output terminal of the second signal generator to the second electrode; a second switch configured to selectively connect the first electrode to either the input terminal of the amplifier or ground; a first synchronous detection unit configured to demodulate a signal synchronized with the first sensor drive signal from the output signal of the amplifier; a second synchronous detection unit configured to demodulate a signal synchronized with the output signal of the third signal generator from the output signal of the amplifier; a capacitance calculation unit configured to calculate a value of capacitance between the first and second electrodes from the output signals of the first and second synchronous detection units; a temperature calculation unit configured to calculate a value of series resistance of the first and second electrodes from the output signals of the first and second synchronous detection units and to obtain a temperature of the sensor chip from the value of this series resistance;and a control unit configured to control the first switch to connect the output terminal of the second signal generator and the second electrode during heating and to control the second switch to connect the first electrode to ground.

[0011] Furthermore, in one configuration example (third and fourth embodiments) of the diaphragm vacuum gauge of the present invention, the control unit controls the amounts of heat generated by the first and second electrodes by controlling any one of the frequency of the second sensor drive signal, the amplitude of the second sensor drive signal, and the length of time for applying the second sensor drive signal based on the temperature of the sensor chip and a heating temperature set value.

[0012] In addition, the diaphragm vacuum gauge ( 4The present embodiment of the present invention relates to a sensor chip including 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, the sensor chip being configured such that a distance between the first and second electrodes changes in response to a displacement of the diaphragm due to a pressure of a medium to be measured, a first signal generator configured to apply a first sensor drive signal to the second electrode, and a second sensor drive signal having a frequency higher than that of the first sensor drive signal to the fourth sensor drive signal. a second signal generator configured to selectively apply a signal to the electrodes; a first amplifier configured to convert a current output from the first electrode into a voltage and amplify the voltage; a second amplifier configured to convert a current output from the third electrode into a voltage and amplify the voltage; a subtractor configured to subtract an output signal of the second amplifier from an output signal of the first amplifier; a first synchronous detection unit configured to demodulate a signal synchronized with the first sensor drive signal from the output signal of the first amplifier; a second synchronous detection unit configured to demodulate a signal synchronized with the first sensor drive signal from the output signal of the subtractor; Cx and a first capacitance calculation unit configured to calculate a value of from the output signal of the second synchronous detection unit. , a value Cx-Cr obtained by subtracting the second capacitance Cr between the third and fourth electrodes from the first capacitance Cx A second capacitance calculation unit configured to calculate From the calculation results of the first and second capacitance calculation units, The second capacitance Cr The first capacitance Cx Correction Calculate the value (Cx-Cr) / Cx a capacitance correction unit configured to correct the first capacitance (Cx-Cr) / Cx a pressure measuring unit configured to convert a pressure signal from the first sensor drive signal to the fourth electrode when measuring pressure, and a control unit configured to control the second signal generator to apply the first sensor drive signal to the fourth electrode when heating.

[0013] In addition, the diaphragm vacuum gauge ( 5 The present invention relates to an embodiment of a sensor chip including 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, the sensor chip being configured such that a distance between the first and second electrodes changes in response to a displacement of the diaphragm due to a pressure of a medium to be measured, a first signal generator configured to apply a first sensor drive signal to the second electrode, a second signal generator configured to selectively apply to the fourth electrode either the first sensor drive signal or a second sensor drive signal having a higher frequency than the first sensor drive signal, and a second signal generator configured to output a signal out of phase with the first sensor drive signal. a third signal generator configured to convert a current output from the first electrode into a voltage and amplify the voltage; a first amplifier configured to convert a current output from the third electrode into a voltage and amplify the voltage; a subtractor configured to subtract an output signal of the second amplifier from an output signal of the first amplifier; a first synchronous detection unit configured to demodulate a signal synchronized with the first sensor drive signal from the output signal of the first amplifier; a second synchronous detection unit configured to demodulate a signal synchronized with the first sensor drive signal from the output signal of the subtractor; a third synchronous detection unit configured to demodulate a signal synchronized with the output signal of the third signal generator from the output signal of the first amplifier; Cx and a first capacitance calculation unit configured to calculate a value of from the output signal of the second synchronous detection unit. , a value Cx-Cr obtained by subtracting the second capacitance Cr between the third and fourth electrodes from the first capacitance Cx a second capacitance calculation unit configured to calculate a capacitance of the first and second electrodes from the output signals of the first and third synchronous detection units, and a temperature calculation unit configured to calculate a series resistance value of the first and second electrodes from the output signals of the first and third synchronous detection units, and to obtain a temperature of the sensor chip from the series resistance value; From the calculation results of the first and second capacitance calculation units, The second capacitance Cr The first capacitance Cx Correction Calculate the value (Cx-Cr) / Cx a capacitance correction unit configured to correct the first capacitance (Cx-Cr) / Cx and a control unit configured to control the second signal generator so as to apply the first sensor drive signal to the fourth electrode during pressure / temperature measurement and to apply the second sensor drive signal to the fourth electrode during heating.

[0014] A diaphragm vacuum gauge (sixth embodiment) of the present invention includes a sensor chip including 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, the sensor chip being configured such that a distance between the first and second electrodes changes in response to a displacement of the diaphragm due to a pressure of a medium to be measured, a first signal generator configured to apply a first sensor drive signal to the second electrode, a second signal generator configured to selectively apply to the fourth electrode either the first sensor drive signal or a second sensor drive signal having a frequency higher than that of the first sensor drive signal, and a phase difference between the first sensor drive signal and the second sensor drive signal. a third signal generator configured to output a signal with a shift in phase between the first and second electrodes, a first amplifier configured to convert a current output from the first electrode into a voltage and amplify the voltage, a second amplifier configured to convert a current output from the third electrode into a voltage and amplify the voltage, a subtractor configured to subtract an output signal of the second amplifier from an output signal of the first amplifier, a first synchronous detection unit configured to demodulate a signal synchronized with the first sensor drive signal from the output signal of the first amplifier, a second synchronous detection unit configured to demodulate a signal synchronized with the first sensor drive signal from the output signal of the subtractor, a third synchronous detection unit configured to demodulate a signal synchronized with the output signal of the third signal generator from the output signal of the subtractor, and a first capacitance between the first and second electrodes from the output signal of the first synchronous detection unit. Cxand a first capacitance calculation unit configured to calculate a value of from the output signals of the second and third synchronous detection units. , a value Cx-Cr obtained by subtracting the second capacitance Cr between the third and fourth electrodes from the first capacitance Cx a second capacitance calculation unit configured to calculate a series resistance value of the third and fourth electrodes from the output signals of the second and third synchronous detection units, and a temperature calculation unit configured to calculate a temperature of the sensor chip from the series resistance value; From the calculation results of the first and second capacitance calculation units, The second capacitance Cr The first capacitance Cx Correction Calculate the value (Cx-Cr) / Cx a capacitance correction unit configured to correct the first capacitance (Cx-Cr) / Cx and a control unit configured to control the second signal generator so as to apply the first sensor drive signal to the fourth electrode during pressure / temperature measurement and to apply the second sensor drive signal to the fourth electrode during heating.

[0015] Furthermore, in one configuration example (fourth to sixth embodiments) of the diaphragm vacuum gauge of the present invention, the control unit controls the amounts of heat generated by the third and fourth electrodes by controlling any one of the frequency of the second sensor drive signal, the amplitude of the second sensor drive signal, or the length of time for applying the second sensor drive signal based on the temperature of the sensor chip and a heating temperature set value. In addition, in one configuration example (fourth to sixth embodiments) of the diaphragm vacuum gauge of the present invention, the second electrode and the fourth electrode are electrically connected to each other and formed as a single electrode. Effect of the Invention

[0016] According to the present invention, by applying a first sensor drive signal to the second electrode of the sensor chip during pressure measurement and applying a second sensor drive signal to the second electrode of the sensor chip during heating, it is possible to heat the sensor chip using the first and second electrodes for pressure measurement, so there is no need to heat the entire pressure receiving part including the sensor chip, and a large heater is not required, so power consumption for heating can be reduced compared to the conventional case. Also, since there is no need to attach a heater to the sensor chip and wire the heater, the sensor chip can be made smaller than when a heater is attached to the sensor chip.

[0017] In addition, in the present invention, by providing first and second switches, a first sensor drive signal can be applied to the second electrode of the sensor chip during pressure measurement, and a second sensor drive signal can be applied to the second electrode of the sensor chip during heating, and pressure measurement and heating can be performed in a time-division manner by utilizing the first and second electrodes for pressure measurement.

[0018] In addition, in the present invention, by providing first and second signal generators, first and second amplifiers, first and second synchronous detection units, and a temperature calculation unit, it is possible to measure the temperature of the sensor chip without using a temperature sensor, and pressure and temperature measurement and heating can be achieved with a single sensor chip.

[0019] In addition, in the present invention, by providing first to third signal generators, an amplifier, first and second synchronous detection units, a temperature calculation unit, and first and second switches, it is possible to measure the temperature of the sensor chip without using a temperature sensor, and pressure, temperature, and heating can be performed in a time-division manner with a single sensor chip.

[0020] In addition, in the present invention, a first and second signal generator, a first and second amplifier, a subtractor, a first and second synchronous detection unit, a first and second capacitance calculation unit, a capacitance correction unit, and a pressure measurement unit are provided, and a first sensor drive signal is applied to the second and fourth electrodes of the sensor chip during pressure measurement, and a second sensor drive signal is applied to the fourth electrode of the sensor chip during heating.This makes it possible to perform capacitance measurement for pressure measurement using the first and second electrodes of the sensor chip, and to perform capacitance measurement and heating for capacitance correction using the third and fourth electrodes of the sensor chip, and thus it is possible to realize pressure measurement, capacitance correction, and heating with a single sensor chip.

[0021] In addition, in the present invention, first to third signal generators, first and second amplifiers, a subtractor, first to third synchronous detection units, first and second capacitance calculation units, a temperature calculation unit, a capacitance correction unit, and a pressure measurement unit are provided, and a first sensor drive signal is applied to the second and fourth electrodes of the sensor chip during pressure / temperature measurement, and a second sensor drive signal is applied to the fourth electrode of the sensor chip during heating.This makes it possible to perform capacitance measurement and temperature measurement for pressure measurement using the first and second electrodes of the sensor chip, and to perform capacitance measurement and heating for capacitance correction using the third and fourth electrodes of the sensor chip, and thus pressure measurement, temperature measurement, capacitance correction, and heating can be achieved with a single sensor chip.

[0022] In addition, in the present invention, first to third signal generators, first and second amplifiers, a subtractor, first to third synchronous detection units, first and second capacitance calculation units, a temperature calculation unit, a capacitance correction unit, and a pressure measurement unit are provided, and a first sensor drive signal is applied to the second and fourth electrodes of the sensor chip during pressure / temperature measurement, and a second sensor drive signal is applied to the fourth electrode of the sensor chip during heating.This makes it possible to perform capacitance measurement for pressure measurement using the first and second electrodes of the sensor chip, and to perform capacitance measurement for capacitance correction, temperature measurement, and heating using the third and fourth electrodes of the sensor chip, and thus pressure measurement, temperature measurement, capacitance correction, and heating can be achieved with a single sensor chip. [Brief description of the drawings]

[0023] [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 cross-sectional view showing the configuration of a main part of a sensor chip of a diaphragm vacuum gauge according to a first embodiment of the present invention. [Diagram 3] FIG. 3 is a flowchart illustrating the pressure measurement operation of the diaphragm vacuum gauge according to the first embodiment of the present invention. [Figure 4] FIG. 4 is a block diagram showing the configuration of a capacitance detection section of a diaphragm vacuum gauge according to a first embodiment of the present invention. [Diagram 5] FIG. 5 is a flowchart illustrating the heating operation of the diaphragm vacuum gauge according to the first embodiment of the present invention. [Figure 6] FIG. 6 is a block diagram showing the configuration of a diaphragm vacuum gauge according to a second embodiment of the present invention. [Figure 7] FIG. 7 is a block diagram showing the configuration of a capacitance detection section of a diaphragm vacuum gauge according to a second embodiment of the present invention. [Figure 8] FIG. 8 is a block diagram showing the configuration of a diaphragm vacuum gauge according to a third embodiment of the present invention. [Figure 9] FIG. 9 is a flowchart illustrating the pressure and temperature measurement operation of the diaphragm vacuum gauge according to the third embodiment of the present invention. [Figure 10] FIG. 10 is a block diagram showing the configuration of a capacitance / temperature detection section of a diaphragm vacuum gauge according to a third embodiment of the present invention. [Figure 11] FIG. 11 is a diagram showing a waveform of an amplifier output when the diaphragm vacuum gauge according to the third embodiment of the present invention measures pressure and temperature. [Figure 12] FIG. 12 is a diagram showing waveforms of the output of the synchronous detection unit when the diaphragm vacuum gauge according to the third embodiment of the present invention measures pressure and temperature. [Figure 13] FIG. 13 is a diagram showing waveforms of the output of the synchronous detection unit when the diaphragm vacuum gauge according to the third embodiment of the present invention measures pressure and temperature. [Figure 14] FIG. 14 is a block diagram showing the configuration of a diaphragm vacuum gauge according to a fourth embodiment of the present invention. [Figure 15]FIG. 15 is a cross-sectional view showing the configuration of a main part of a sensor chip of a diaphragm vacuum gauge according to a fourth embodiment of the present invention. [Figure 16] FIG. 16 is a flowchart illustrating the pressure measurement operation of the diaphragm vacuum gauge according to the fourth embodiment of the present invention. [Figure 17] FIG. 17 is a block diagram showing the configuration of a capacitance detection section of a diaphragm vacuum gauge according to a fourth embodiment of the present invention. [Figure 18] FIG. 18 is a block diagram showing the configuration of a diaphragm vacuum gauge according to a fifth embodiment of the present invention. [Figure 19] FIG. 19 is a flowchart illustrating the pressure and temperature measurement operation of the diaphragm vacuum gauge according to the fifth embodiment of the present invention. [Figure 20] FIG. 20 is a block diagram showing the configuration of a capacitance / temperature detection section of a diaphragm vacuum gauge according to a fifth embodiment of the present invention. [Figure 21] FIG. 21 is a block diagram showing the configuration of a diaphragm vacuum gauge according to a sixth embodiment of the present invention. [Figure 22] FIG. 22 is a block diagram showing the configuration of a capacitance / temperature detection section of a diaphragm vacuum gauge according to a sixth embodiment of the present invention. [Figure 23] FIG. 23 is a block diagram showing an example of the configuration of a computer that realizes the circuitry of the diaphragm vacuum gauge according to the first to sixth embodiments of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] [First Example] Hereinafter, embodiments of the present invention will be described with reference to the drawings. 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 cross-sectional view showing the configuration of a main part of a sensor chip used in the diaphragm vacuum gauge.

[0025] The diaphragm vacuum gauge comprises a pressure receiving section 10 whose capacitance changes in response to the displacement of a diaphragm (membrane) due to the pressure of the 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 measured pressure value.

[0026] A recess is formed in the center of the base 101 of the sensor chip 1 of the pressure receiving portion 10. A diaphragm 102 configured to be deformable in response to the pressure P of a medium to be measured (e.g., a process gas) is bonded to the surface of the base 101 on which the recess is formed. The recess of the base 101 forms a reference vacuum chamber 104 together with the diaphragm 102.

[0027] In the sensor chip 1, 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 a 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. The pressure P of the medium to be measured received by the diaphragm 102 can be detected from this change in electrostatic capacitance. The diaphragm component 100 and the base 101 are made of an insulator such as sapphire.

[0028] 1 comprises sensor chip 1 configured as above, a housing 2 that accommodates sensor chip 1, a pressure introducing pipe 3 that introduces pressure P of the medium to be measured to diaphragm 102 of sensor chip 1, and a sensor case 4 that covers the housing 2. Sensor case 4 is covered with a thermal insulating material 6.

[0029] 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.

[0030] 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.

[0031] The circuit section 11 of the diaphragm vacuum gauge comprises a capacitance detection section 12 that calculates the value of the capacitance between the movable electrode 106 and the fixed electrode 105, a pressure measurement section 13 that converts the capacitance into a measured pressure value, and a control section 14 that controls a sensor drive signal applied by a signal generator, which will be described later.

[0032] FIG. 3 is a flow chart for explaining the pressure measuring operation of the diaphragm vacuum gauge of this embodiment, and FIG. The capacitance detection unit 12 is composed of a signal generator 120, an amplifier 121 consisting of a capacitance Cf and an operational amplifier A1, a low-pass filter 122, and a capacitance calculation unit 123. In Fig. 4, the electrostatic capacitance between the movable electrode 106 and the fixed electrode 105 of the sensor chip 1 is represented by Cx. Also, the component of the series resistance between the movable electrode 106 and the fixed electrode 105 is represented by Rx.

[0033] During pressure measurement, the signal generator 120 applies a sine wave sensor drive signal for pressure measurement to the second electrode (eg, the movable electrode 106) of the sensor chip 1 (step S100 in FIG. 3). The amplifier 121 converts the current output from the first electrode (for example, the fixed electrode 105) of the sensor chip 1 into a voltage, amplifies it, and outputs a signal with an amplitude proportional to the capacitance Cx.

[0034] The low-pass filter 122 removes noise from the signal output from the amplifier 121. The capacitance calculation unit 123 calculates the value of the capacitance Cx from the amplitude of the signal that has passed through the low-pass filter 122 (Step S101 in FIG. 3). The pressure measuring unit 13 converts the change in the capacitance Cx calculated by the capacitance detecting unit 12 into a measured pressure value MP and outputs it (Step S102 in FIG. 3).

[0035] The capacitance detection unit 12 and the pressure measurement unit 13 perform the processes of steps S100 to S102 for each measurement period until the pressure measurement operation is ended, for example, in response to an instruction from the user (YES in step S103 in FIG. 3).

[0036] Fig. 5 is a flow chart explaining the heating operation of the diaphragm vacuum gauge of this embodiment. The movable electrode 106 and the fixed electrode 105 of the sensor chip 1 have a series resistor Rx as shown in Fig. 4. In this embodiment, this series resistor Rx is used as a heater.

[0037] In this embodiment, the sensor drive signal for pressure measurement is E1 sin(2πf1t), and the sensor drive signal for heating is E2 sin(2πf2t). E1 and E2 are amplitudes, f1 and f2 are frequencies, and t is time. In this embodiment, the frequency f2 of the sensor drive signal for heating is made higher than the frequency f1 of the sensor drive signal for pressure measurement (f2>f1), increasing the current flowing through the series resistor Rx and causing the movable electrode 106 and the fixed electrode 105 to generate heat.

[0038] The impedance Z of the equivalent circuit of the electric circuit of the sensor chip 1 is expressed by the following formula. Z = Rx + 1 / (2πfCx) (1)

[0039] If the voltage applied between the movable electrode 106 and the fixed electrode 105 is E, then the current I flowing between the movable electrode 106 and the fixed electrode 105 is given by equation (2), and the power consumption W of the resistor Rx is given by equation (3). I = E / Z (2) W=I 2 ×Rx ···(3)

[0040] Increasing the frequency f of the sensor drive signal reduces the impedance Z and increases the current I, allowing the power consumption W to be increased. Specific examples are shown in Table 1.

[0041] [Table 1]

[0042] As is apparent from Table 1, by increasing the frequency of the sensor drive signal for heating, it is possible to cause the movable electrode 106 and the fixed electrode 105 to generate heat.

[0043] The control unit 14 outputs a signal CTL to the signal generator 120 so that the signal generator 120 generates a sensor drive signal E2sin(2πf2t) for heating (FIG. 5, step S200).

[0044] During heating, the signal generator 120 applies a sinusoidal sensor drive signal E2sin(2πf2t) having a frequency f2 corresponding to the control signal CTL from the control unit 14 to the second electrode (e.g., the movable electrode 106) of the sensor chip 1 (FIG. 5, step S201). In this way, by controlling the signal generator 120 to generate the sensor drive signal E2sin(2πf2t), the amount of heat generation can be controlled.

[0045] The capacitance detection unit 12 and the control unit 14 perform the processes of steps S200 and S201 for each heating cycle until the heating operation is ended by, for example, an instruction from the user (YES in step S202 in FIG. 5).

[0046] In this embodiment, the pressure measurement and the heating may be performed at different times, or the pressure measurement and the heating may be performed simultaneously. Therefore, the sensor drive signal E1sin(2πf1t) for pressure measurement and the sensor drive signal E2sin(2πf2t) for heating may be output simultaneously from the signal generator 120, and the frequency components of the sensor drive signals E1sin(2πf1t) and E2sin(2πf2t) may be output simultaneously from the amplifier 121.

[0047] The cutoff frequency of low-pass filter 122 is set to pass sensor drive signal E1sin(2πf1t) and block sensor drive signal E2sin(2πf2t). Therefore, the frequency component of sensor drive signal E2sin(2πf2t) is removed by low-pass filter 122 and only the frequency of sensor drive signal E1sin(2πf1t) passes through low-pass filter 122, so that the frequency component of sensor drive signal E2sin(2πf2t) for heating does not affect the detection of capacitance Cx.

[0048] In this embodiment, since the electrodes 105 and 106 for pressure measurement can be used to heat the sensor chip 1, there is no need to heat the entire pressure receiving section, and a large heater is not required, so the power consumption for heating can be reduced compared to the conventional case. Also, since it is not necessary to attach a heater to the sensor chip 1 and wire the heater, the sensor chip 1 can be made smaller than when a heater is attached to the sensor chip 1.

[0049] [Second Example] Next, a second embodiment of the present invention will be described. Fig. 6 is a block diagram showing the configuration of a diaphragm vacuum gauge according to the second embodiment of the present invention, and the same components as those in Fig. 1 are given the same reference numerals. In this embodiment, the configuration of the pressure receiving section 10 is the same as that described in the first embodiment. The circuit section 11a is made up of a capacitance detection section 12a, a pressure measurement section 13, and a control section 14a.

[0050] 7 is a block diagram showing the configuration of the capacitance detection unit 12a of this embodiment. The capacitance detection unit 12a is composed of signal generators 120-1 and 120-2, an amplifier 121, a low-pass filter 122, a capacitance calculation unit 123, a switch 124 provided between the signal generators 120-1 and 120-2 and a second electrode (e.g., movable electrode 106) of the sensor chip 1, and a switch 125 provided between a first electrode (e.g., fixed electrode 105) of the sensor chip 1 and the input of the amplifier 121.

[0051] The signal generator 120-1 outputs a sensor drive signal E1sin(2πf1t) for pressure measurement. The signal generator 120-2 outputs a sensor drive signal E2sin(2πf2t) for heating.

[0052] The control unit 14a of this embodiment controls the switching of the switches 124, 125 by the control signal SWCTL. The control unit 14a controls the switches 124, 125 to select the S side in FIG. 7 during pressure measurement. As a result, the switch 124 selects the output terminal of the signal generator 120-1, so that the output terminal of the signal generator 120-1 is connected to the second electrode (e.g., the movable electrode 106) of the sensor chip 1. Also, the switch 125 selects the input terminal of the amplifier 121, so that the first electrode (e.g., the fixed electrode 105) of the sensor chip 1 is connected to the input terminal of the amplifier 121. With such switch control, the pressure measurement operation becomes the same as the operation described in FIG. 3 of the first embodiment.

[0053] On the other hand, during heating, the control unit 14a controls the switches 124 and 125 to select the T side in Fig. 7. As a result, the switch 124 selects the output terminal of the signal generator 120-2, so that the output terminal of the signal generator 120-2 is connected to a second electrode (e.g., movable electrode 106) of the sensor chip 1. Also, the switch 125 selects the ground, so that the first electrode (e.g., fixed electrode 105) of the sensor chip 1 is connected to the ground. With such switch control, the heating operation becomes the same as the operation described in Fig. 5 of the first embodiment.

[0054] In this way, pressure measurement and heating can be performed in a time-division manner by switching the switches 124, 125 between pressure measurement and heating. In this embodiment, when it is difficult to change the sensor drive signal using one signal generator, the circuits connected to the electrodes 105, 106 can be changed between pressure measurement and heating.

[0055] As in the first embodiment, the control unit 14a may control the amount of heat generated by changing the frequency f2 of the sensor drive signal E2sin(2πf2t) during heating, or may control the amount of heat generated by changing the amplitude E2.

[0056] Furthermore, the control unit 14a may control the amount of heat generation by changing the length of time for which the sensor drive signal E2sin(2πf2t) is applied. In the first embodiment, the length of time for which the signal generator 120 outputs the sensor drive signal E2sin(2πf2t) is changed. In the present embodiment, the length of time for which the signal generator 120-2 outputs the sensor drive signal E2sin(2πf2t) may also be changed. In a configuration in which the signal generator 120-2 constantly outputs the sensor drive signal E2sin(2πf2t), the length of time for which the switches 124 and 125 select the T side may be changed.

[0057] [Third Example] Next, a third embodiment of the present invention will be described. Figure 8 is a block diagram showing the configuration of a diaphragm vacuum gauge according to the third embodiment of the present invention, and the same components as those in Figures 1 and 6 are given the same reference numerals. The diaphragm vacuum gauge of this embodiment comprises a pressure receiving portion 10b and a circuit portion 11b.

[0058] The difference between the pressure-receiving portion 10 of the first and second embodiments is that the temperature of the sensor chip 1 can be measured without providing a temperature sensor 9 on the pressure-receiving portion 10b. The circuit section 11b is made up of a capacitance / temperature detection section 12b, a pressure measurement section 13, and a control section 14b.

[0059] Fig. 9 is a flow chart for explaining the pressure and temperature measurement operation of the diaphragm vacuum gauge of this embodiment, and Fig. 10 is a block diagram showing the configuration of the capacitance and temperature detection unit 12b of this embodiment. The capacitance and temperature detection unit 12b is composed of a signal generator 120, an amplifier 121, differential input type low pass filters 122b-1 and 122b-2, a capacitance calculation unit 123b, a switch 126 provided between the amplifier 121 and the low pass filter 122b-1, a switch 127 provided between the amplifier 121 and the low pass filter 122b-2, a temperature calculation unit 128, and a signal generator 129 that outputs a signal E1sin(2πf1t+π / 2) that has the same frequency as the sensor drive signal E1sin(2πf1t) but is shifted in phase by 90 degrees.

[0060] As in the first embodiment, the signal generator 120 applies the sensor drive signal E1sin(2πf1t) to the second electrode (eg, the movable electrode 106) of the sensor chip 1 and the switch 126 during pressure and temperature measurement (FIG. 9, step S300). During pressure and temperature measurement, the signal generator 129 applies a signal E1sin(2πf1t+π / 2) that is out of phase with the sensor drive signal E1sin(2πf1t) by 90 degrees to the switch 127 (step S301 in FIG. 9).

[0061] The switch 126 and the low-pass filter 122b-1 constitute a synchronous detection unit 130. The low-pass filter 122b-1 has a cutoff frequency set to pass the sensor drive signal E1sin(2πf1t) and block the sensor drive signal E2sin(2πf2t). The synchronous detection unit 130 demodulates the output of the amplifier 121 into a signal synchronized with the sensor drive signal E1sin(2πf1t).

[0062] Specifically, when the sensor drive signal E1sin(2πf1t) output from the signal generator 120 during pressure and temperature measurement is positive, the switch 126 connects the output terminal of the amplifier 121 to the non-inverting input terminal of the low-pass filter 122b-1. In addition, when the sensor drive signal E1sin(2πf1t) is negative, the switch 126 connects the output terminal of the amplifier 121 to the inverting input terminal of the low-pass filter 122b-1. This makes it possible to demodulate a signal synchronized with the sensor drive signal E1sin(2πf1t) from the output of the amplifier 121.

[0063] Meanwhile, switch 127 and low-pass filter 122b-2 constitute a synchronous detection unit 131. Low-pass filter 122b-2 has a cutoff frequency set to pass sensor drive signal E1sin(2πf1t) and block sensor drive signal E2sin(2πf2t). Synchronous detection unit 131 demodulates the output of amplifier 121 into a signal synchronized with signal E1sin(2πf1t+π / 2) that is out of phase with sensor drive signal E1sin(2πf1t) by 90 degrees.

[0064] Specifically, when signal E1sin(2πf1t+π / 2) output from signal generator 129 during pressure and temperature measurement is positive, switch 127 connects the output terminal of amplifier 121 to the non-inverting input terminal of low-pass filter 122b-2. Also, when signal E1sin(2πf1t+π / 2) is negative, switch 127 connects the output terminal of amplifier 121 to the inverting input terminal of low-pass filter 122b-2. This makes it possible to demodulate, from the output of amplifier 121, a signal synchronized with signal E1sin(2πf1t+π / 2) that is 90 degrees out of phase with sensor drive signal E1sin(2πf1t).

[0065] 11 is a diagram showing the waveform of the output A of the amplifier 121 during pressure and temperature measurement. The output A of the amplifier 121 can be expressed by the following equation.

[0066]

number

[0067] 12 is a diagram showing the waveform of the output vc of the synchronous detection unit 130 when measuring pressure and temperature. The output vc of the synchronous detection unit 130 can be expressed by the following equation. This vc mainly depends on the capacitance Cx, but is also affected by the value of the series resistance Rx.

[0068]

number

[0069] 13 is a diagram showing the waveform of the output vt of the synchronous detection unit 131 during pressure and temperature measurement. The output vt of the synchronous detection unit 131 can be expressed by the following equation. This vt depends on the value of the series resistance Rx, but is also affected by the value of the electrostatic capacitance Cx.

[0070]

number

[0071] When the following equation is calculated from the output vc of the synchronous detection section 130 and the output vt of the synchronous detection section 131, a value proportional to only the capacitance Cx is obtained.

[0072]

number

[0073] Furthermore, when the following equation is calculated from the output vc of the synchronous detection section 130 and the output vt of the synchronous detection section 131, a value proportional to only the series resistance Rx is obtained.

[0074]

number

[0075] In equations (7) and (8), α and β are constants resulting from circuit constants Cf, f, and E1 that are independent of capacitance Cx and series resistance Rx. The capacitance calculation unit 123b calculates the value of the capacitance Cx from the output vc of the synchronous detection unit 130 and the output vt of the synchronous detection unit 131 by equation (7) (step S302 in FIG. 9). The operation of the pressure measurement unit 13 (step S303 in FIG. 9) is the same as that in the first embodiment.

[0076] The temperature calculation unit 128 calculates the value of the series resistance Rx by equation (8) from the output vc of the synchronous detection unit 130 and the output vt of the synchronous detection unit 131 (step S304 in FIG. 9). Then, the temperature calculation unit 128 derives the temperature of the sensor chip 1 from the value of the series resistance Rx (step S305 in FIG. 9). The relationship between the series resistance Rx and the temperature is stored in advance in the temperature calculation unit 128. The temperature calculation unit 128 may calculate the temperature from the value of the series resistance Rx by a preset equation, or may obtain the temperature value corresponding to the value of the series resistance Rx from a preset table.

[0077] The capacitance / temperature detection unit 12b and the pressure measurement unit 13 perform the processes of steps S300 to S305 every measurement period until the pressure measurement operation is ended, for example, by a user instruction (YES in step S306 in FIG. 9).

[0078] The flow of the heating process in this embodiment is similar to that in the first embodiment, and will be described using the reference numerals in FIG. During heating, the control unit 14b of this embodiment outputs a control signal CTL to the signal generator 120 so that the signal generator 120 generates the frequency f2 of the sensor drive signal E2sin(2πf2t) for heating (FIG. 5, step S200).

[0079] As in the first embodiment, during heating, the signal generator 120 applies a sensor drive signal E2sin(2πf2t) of frequency f2 corresponding to the control signal CTL from the control unit 14b to the second electrode (e.g., the movable electrode 106) of the sensor chip 1 (FIG. 5 step S201).

[0080] The capacitance / temperature detection unit 12b and the control unit 14b perform the processes of steps S200 and S201 for each heating cycle until the heating operation is ended, for example, by a user instruction (YES in step S202 in FIG. 5).

[0081] In this manner, in this embodiment, the temperature of the sensor chip 1 can be measured without using a temperature sensor, and one sensor chip 1 can achieve three functions: pressure measurement, temperature measurement, and heating. As in the first embodiment, in this embodiment, the pressure / temperature measurement and the heating may be performed at different times, or the pressure / temperature measurement and the heating may be performed simultaneously.

[0082] The control unit 14b may control the amount of heat generation by changing the amplitude E2 so that the temperature measured by the capacitance-temperature detection unit 12b coincides with the heating temperature set value tsp. The control unit 14b may also control the amount of heat generation by changing the length of time for which the sensor drive signal E2sin(2πf2t) is applied so that the temperature measured by the capacitance-temperature detection unit 12b coincides with the heating temperature set value tsp.

[0083] The second embodiment may be applied to this embodiment. In this case, signal generators 120-1 and 120-2 are provided instead of the signal generator 120 of the capacitance / temperature detection unit 12b, a switch 124 is inserted between the signal generators 120-1 and 120-2 and the second electrode (e.g., the movable electrode 106) of the sensor chip 1, and a switch 125 is inserted between the first electrode (e.g., the fixed electrode 105) of the sensor chip 1 and the input of the amplifier 121. The control unit 14b controls the switches 124 and 125 in the same manner as the control unit 14a of the second embodiment.

[0084] [Fourth Example] Next, a fourth embodiment of the present invention will be described. Figure 14 is a block diagram showing the configuration of a diaphragm vacuum gauge according to the fourth embodiment of the present invention, and the same components as those in Figures 1, 6, and 8 are given the same reference numerals. The diaphragm vacuum gauge of this embodiment comprises a pressure receiving portion 10c and a circuit portion 11c.

[0085] 15 is a cross-sectional view showing the configuration of the main part of sensor chip 1c of this embodiment. In sensor chip 1c, a fixed electrode 107 is formed on the surface of base 101 facing reference vacuum chamber 104, outside fixed electrode 105. A movable electrode 108 is formed on the surface of diaphragm 102 facing reference vacuum chamber 104, outside movable electrode 106, so as to face fixed electrode 107. The other configuration of sensor chip 1c is the same as that of sensor chip 1.

[0086] The fixed electrode 107 and the movable electrode 108 are formed on the edge of the diaphragm 102. Even if the diaphragm 102 is bent by pressure P of the medium to be measured, the edge of the diaphragm 102 is hardly deformed, so 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, humidity changes inside the reference vacuum chamber 104, etc.

[0087] The circuit section 11c is composed of a capacitance detection section 12c, a pressure measurement section 13, and a control section 14c. FIG. 16 is a flow chart for explaining the pressure measuring operation of the diaphragm vacuum gauge of this embodiment, and FIG. 17 is a block diagram showing the configuration of the capacitance detection section 12c.

[0088] The capacitance detection unit 12c includes signal generators 132 and 133, amplifiers 134 and 135, a subtractor 136, differential input type low-pass filters 137 and 138, a switch 139 provided between the amplifier 134 and the low-pass filter 137, a switch 140 provided between the amplifier 135 and the low-pass filter 138, a capacitance calculation unit 141, a reference capacitance calculation unit 142, and a capacitance correction unit 143. In FIG. 17, the electrostatic capacitance between the movable electrode 108 and the fixed electrode 107 of the sensor chip 1c is represented by Cr. Also, the component of the series resistance between the movable electrode 108 and the fixed electrode 107 is represented by Rr.

[0089] During pressure measurement, the signal generator 132 applies a sine wave sensor drive signal E1sin(2πf1t) for pressure measurement to a second electrode (e.g., the movable electrode 106) of the sensor chip 1c and to the switch 139. During pressure measurement, the signal generator 133 applies the sensor drive signal E1sin(2πf1t) to a fourth electrode (e.g., the movable electrode 108) of the sensor chip 1c and to the switch 140 (step S400 in FIG. 16).

[0090] The amplifier 134 converts the current output from the first electrode (e.g., the fixed electrode 105) of the sensor chip 1c into a voltage, amplifies the voltage, and outputs a signal with an amplitude proportional to the capacitance Cx. The amplifier 135 converts the current output from the third electrode (e.g., the fixed electrode 107) of the sensor chip 1c into a voltage, amplifies the voltage, and outputs a signal with an amplitude proportional to the capacitance Cr. The subtractor 136 subtracts the output signal B of the amplifier 135 from the output signal A of the amplifier 134 .

[0091] Switch 139 and low-pass filter 137 constitute a synchronous detection unit 144. Low-pass filter 137 has a cutoff frequency set to pass sensor drive signal E1sin(2πf1t) and block sensor drive signal E2sin(2πf2t). Synchronous detection unit 144 demodulates the output of amplifier 134 into a signal synchronized with sensor drive signal E1sin(2πf1t).

[0092] Specifically, when the sensor drive signal E1sin(2πf1t) output from the signal generator 132 during pressure measurement is positive, the switch 139 connects the output terminal of the amplifier 134 to the non-inverting input terminal of the low-pass filter 137. In addition, when the sensor drive signal E1sin(2πf1t) is negative, the switch 139 connects the output terminal of the amplifier 134 to the inverting input terminal of the low-pass filter 137. This makes it possible to demodulate a signal synchronized with the sensor drive signal E1sin(2πf1t) from the output of the amplifier 134.

[0093] Meanwhile, switch 140 and low-pass filter 138 constitute a synchronous detection unit 145. A cutoff frequency of low-pass filter 138 is set so as to pass sensor drive signal E1sin(2πf1t) and cut off sensor drive signal E2sin(2πf2t). Synchronous detection unit 145 demodulates a signal synchronized with sensor drive signal E1sin(2πf1t) from the output of subtractor 136.

[0094] Specifically, when the sensor drive signal E1sin(2πf1t) output from the signal generator 133 during pressure measurement is positive, the switch 140 connects the output terminal of the subtractor 136 to the non-inverting input terminal of the low-pass filter 138. In addition, when the sensor drive signal E1sin(2πf1t) is negative, the switch 140 connects the output terminal of the subtractor 136 to the inverting input terminal of the low-pass filter 138. This makes it possible to demodulate a signal synchronized with the sensor drive signal E1sin(2πf1t) from the output of the subtractor 136.

[0095] The capacitance calculation unit 141 calculates the value of the capacitance Cx from the amplitude of the output vc of the synchronous detection unit 144 (Step S401 in FIG. 16). The reference capacitance calculation section 142 calculates the value of the capacitance (reference capacitance) Cr from the amplitude of the output vr of the synchronous detection section 145 (Step S402 in FIG. 16).

[0096] The capacitance corrector 143 calculates a value (Cx-Cr) / Cx obtained by correcting the capacitance Cx using the reference capacitance Cr (Step S403 in FIG. 16). The pressure measuring unit 13 converts the change in capacitance (Cx-Cr) / Cx calculated by the capacitance detecting unit 12c into a measured pressure value MP and outputs it (Step S404 in FIG. 16).

[0097] The capacitance detection unit 12c and the pressure measurement unit 13 perform the processes of steps S400 to S404 every measurement period until the pressure measurement operation is ended by, for example, an instruction from the user (YES in step S405 in FIG. 16).

[0098] The flow of the heating process in this embodiment is similar to that in the first embodiment, and will be described using the reference numerals in FIG. During heating, the control unit 14c of this embodiment outputs a control signal CTL to the signal generator 133 so that the signal generator 133 generates a sensor drive signal E2sin(2πf2t) for heating (FIG. 5, step S200).

[0099] During heating, the signal generator 133 applies a sensor drive signal E2sin(2πf2t) having a frequency f2 in response to a control signal CTL from the control unit 14c to the fourth electrode (eg, the movable electrode 108) of the sensor chip 1c (FIG. 5, step S201).

[0100] The capacitance detection unit 12c and the control unit 14c perform the processes of steps S200 and S201 for each heating cycle until the heating operation is ended by, for example, a user instruction (YES in step S202 in FIG. 5).

[0101] Thus, in this embodiment, capacitance measurement for pressure measurement can be performed using the fixed electrode 105 and the movable electrode 106 of the sensor chip 1c, and reference capacitance measurement for capacitance correction and heating can be performed using the fixed electrode 107 and the movable electrode 108 of the sensor chip 1c, thereby enabling a single sensor chip 1c to achieve three functions: pressure measurement, capacitance correction, and heating. As in the first embodiment, in this embodiment, the pressure measurement and the heating may be performed at different times, or the pressure measurement and the heating may be performed simultaneously.

[0102] As in the first embodiment, the control unit 14c may control the amount of heat generation by changing the amplitude E2 of the sensor drive signal E2sin(2πf2t). Also, the control unit 14c may control the amount of heat generation by changing the length of time for which the sensor drive signal E2sin(2πf2t) is applied.

[0103] [Fifth Example] Next, a fifth embodiment of the present invention will be described. Figure 18 is a block diagram showing the configuration of a diaphragm vacuum gauge according to the fifth embodiment of the present invention, and the same components as those in Figures 1, 6, 8, and 14 are given the same reference numerals. The diaphragm vacuum gauge of this embodiment comprises a pressure receiving portion 10d and a circuit portion 11d.

[0104] The difference from the pressure-receiving portion 10c of the fourth embodiment is that the temperature of the sensor chip 1 can be measured without providing a temperature sensor in the pressure-receiving portion 10d. The circuit section 11d is made up of a capacitance / temperature detection section 12d, a pressure measurement section 13d, and a control section 14d.

[0105] Fig. 19 is a flow chart explaining the pressure / temperature measurement operation of the diaphragm vacuum gauge of this embodiment, and Fig. 20 is a block diagram showing the configuration of capacitance / temperature detection unit 12d of this embodiment. Capacitance / temperature detection unit 12d is made up of signal generators 132, 133, amplifiers 134, 135, subtractor 136, low-pass filters 137, 138, switches 139, 140, capacitance calculation unit 141d, reference capacitance calculation unit 142, capacitance correction unit 143, signal generator 146, differential input type low-pass filter 147, switch 148 provided between amplifier 134 and low-pass filter 147, and temperature calculation unit 149.

[0106] During pressure and temperature measurement, the signal generator 132 applies a sensor drive signal E1sin(2πf1t) to a second electrode (e.g., the movable electrode 106) of the sensor chip 1c and to a switch 139. During pressure and temperature measurement, the signal generator 133 applies a sensor drive signal E1sin(2πf1t) to a fourth electrode (e.g., the movable electrode 108) of the sensor chip 1c and to a switch 140 (step S500 in FIG. 19).

[0107] During pressure and temperature measurement, the signal generator 146 applies a signal E1sin(2πf1t+π / 2) that is out of phase with the sensor drive signal E1sin(2πf1t) by 90 degrees to the switch 148 (step S501 in FIG. 19).

[0108] As in the fourth embodiment, the synchronous detector 144 demodulates a signal synchronized with the sensor drive signal E1sin(2πf1t) from the output of the amplifier 134. The synchronous detector 145 demodulates a signal synchronized with the sensor drive signal E1sin(2πf1t) from the output of the subtractor 136.

[0109] Switch 148 and low-pass filter 147 constitute a synchronous detection unit 150. Low-pass filter 147 has a cutoff frequency set to pass sensor drive signal E1sin(2πf1t) and block sensor drive signal E2sin(2πf2t). Synchronous detection unit 150 demodulates the output of amplifier 134 into a signal synchronized with signal E1sin(2πf1t+π / 2) that is 90 degrees out of phase with sensor drive signal E1sin(2πf1t).

[0110] Specifically, when signal E1sin(2πf1t+π / 2) output from signal generator 146 during pressure and temperature measurement is positive, switch 148 connects the output terminal of amplifier 134 to the non-inverting input terminal of low-pass filter 147. Also, when signal E1sin(2πf1t+π / 2) is negative, switch 148 connects the output terminal of amplifier 134 to the inverting input terminal of low-pass filter 147. This makes it possible to demodulate, from the output of amplifier 134, a signal synchronized with signal E1sin(2πf1t+π / 2) that is 90 degrees out of phase with sensor drive signal E1sin(2πf1t).

[0111] The capacitance calculation unit 141d calculates the value of the capacitance Cx from the output vc of the synchronous detection unit 144 and the output vt of the synchronous detection unit 150 using equation (7) (Step S502 in FIG. 19). The reference capacitance calculation unit 142 calculates the value of the capacitance (reference capacitance) Cr from the amplitude of the output vr of the synchronous detection unit 145 (Step S503 in FIG. 19).

[0112] The capacitance corrector 143 calculates a value (Cx-Cr) / Cx obtained by correcting the capacitance Cx using the reference capacitance Cr (FIG. 19, step S504). As in the third embodiment, the temperature calculation unit 149 calculates the value of the series resistance Rx using equation (8) from the output vc of the synchronous detection unit 144 and the output vt of the synchronous detection unit 150 (step S505 in FIG. 19), and derives the temperature of the sensor chip 1c from the value of the series resistance Rx (step S506 in FIG. 19).

[0113] The pressure measuring unit 13d corrects the capacitance (Cx-Cr) / Cx calculated by the capacitance-temperature detecting unit 12d based on the temperature of the sensor chip 1c calculated by the capacitance-temperature detecting unit 12d, converts it into a measured pressure value MP, and outputs it (FIG. 19, step S507). The method of correcting the capacitance (Cx-Cr) / Cx based on the temperature of the sensor chip 1c may be performed using, for example, the following formula.

[0114]

number

[0115] In equation (9), Vo is the capacitance (Cx-Cr) / Cx calculated by the capacitance-temperature detection unit 12d, Vt is the temperature of the sensor chip 1c calculated by the capacitance-temperature detection unit 12d, a ij is the correction coefficient, and i,j are the orders of the polynomial.

[0116] The capacitance / temperature detection unit 12d and the pressure measurement unit 13d perform the processes of steps S500 to S507 every measurement period until the pressure measurement operation is ended by, for example, an instruction from the user (YES in step S508 in FIG. 19).

[0117] The flow of the heating process in this embodiment is similar to that in the fourth embodiment, and will be described using the reference numerals in FIG. In this embodiment, the control unit 14d outputs a control signal CTL to the signal generator 133 so that the signal generator 133 generates a sensor drive signal E2sin(2πf2t) for heating so that the temperature measured by the capacitance / temperature detection unit 12d matches a predetermined heating temperature set value tsp (Figure 5, step S200).

[0118] During heating, the signal generator 133 applies a sensor drive signal E2sin(2πf2t) having a frequency f2 in response to a control signal CTL from the control unit 14d to the fourth electrode (eg, the movable electrode 108) of the sensor chip 1c (FIG. 5, step S201).

[0119] The capacitance / temperature detection unit 12d and the control unit 14d perform the processes of steps S200 and S201 for each heating cycle until the heating operation is ended, for example, by a user instruction (YES in step S202 in FIG. 5).

[0120] Thus, in this embodiment, capacitance measurement and temperature measurement for pressure measurement can be performed using the fixed electrode 105 and movable electrode 106 of the sensor chip 1c, and reference capacitance measurement for capacitance correction and heating can be performed using the fixed electrode 107 and movable electrode 108 of the sensor chip 1c, making it possible to achieve four functions: pressure measurement, temperature measurement, capacitance correction, and heating with a single sensor chip 1c. As in the first embodiment, in this embodiment, the pressure / temperature measurement and the heating may be performed at different times, or the pressure / temperature measurement and the heating may be performed simultaneously.

[0121] As in the first embodiment, the control unit 14d may control the amount of heat generation by changing the amplitude E2 so that the temperature measured by the capacitance-temperature detection unit 12d coincides with the heating temperature set value tsp. The control unit 14d may also control the amount of heat generation by changing the length of time for which the sensor drive signal E2sin(2πf2t) is applied so that the temperature measured by the capacitance-temperature detection unit 12d coincides with the heating temperature set value tsp.

[0122] [Sixth Example] Next, a sixth embodiment of the present invention will be described. Fig. 21 is a block diagram showing the configuration of a diaphragm vacuum gauge according to the sixth embodiment of the present invention, where the same components as those in Figs. 1, 6, 8, 14, and 18 are given the same reference numerals. The diaphragm vacuum gauge of this embodiment comprises a pressure receiving section 10d and a circuit section 11e. The configuration of the pressure receiving section 10d is as explained in the fifth embodiment.

[0123] The circuit section 11e is made up of a capacitance / temperature detection section 12e, a pressure measurement section 13e, and a control section 14e. 22 is a block diagram showing the configuration of a capacitance / temperature detection unit 12e of this embodiment. The capacitance / temperature detection unit 12e includes signal generators 132 and 133, amplifiers 134 and 135, a subtractor 136, low-pass filters 137 and 138, switches 139 and 140, a capacitance calculation unit 141, a reference capacitance calculation unit 142e, a capacitance correction unit 143, a signal generator 146e, a temperature calculation unit 149e, a differential input type low-pass filter 151, and a switch 152 provided between the subtractor 136 and the low-pass filter 151.

[0124] The process flow of the pressure / temperature measurement operation of the diaphragm vacuum gauge of this embodiment is similar to that of the fifth embodiment, and will be described using the reference numerals in FIG. During pressure and temperature measurement, the signal generator 132 applies a sensor drive signal E1sin(2πf1t) to a second electrode (e.g., the movable electrode 106) of the sensor chip 1c and to a switch 139. During pressure and temperature measurement, the signal generator 133 applies a sensor drive signal E1sin(2πf1t) to a fourth electrode (e.g., the movable electrode 108) of the sensor chip 1c and to a switch 140 (step S500 in FIG. 19).

[0125] During pressure and temperature measurement, the signal generator 146e applies a signal E1sin(2πf1t+π / 2) that is out of phase with the sensor drive signal E1sin(2πf1t) by 90 degrees to the switch 152 (FIG. 19, step S501).

[0126] As in the fourth embodiment, the synchronous detector 144 demodulates a signal synchronized with the sensor drive signal E1sin(2πf1t) from the output of the amplifier 134. The synchronous detector 145 demodulates a signal synchronized with the sensor drive signal E1sin(2πf1t) from the output of the subtractor 136.

[0127] Switch 152 and low-pass filter 151 constitute synchronous detection unit 153. Low-pass filter 151 has a cutoff frequency set to pass sensor drive signal E1sin(2πf1t) and block sensor drive signal E2sin(2πf2t). Synchronous detection unit 153 demodulates the output of subtractor 136 into a signal synchronized with signal E1sin(2πf1t+π / 2) that is 90 degrees out of phase with sensor drive signal E1sin(2πf1t).

[0128] Specifically, when the signal E1sin(2πf1t+π / 2) output from the signal generator 146e during pressure and temperature measurement is positive, the switch 152 connects the output terminal of the subtractor 136 to the non-inverting input terminal of the low-pass filter 151. In addition, when the signal E1sin(2πf1t+π / 2) is negative, the switch 152 connects the output terminal of the subtractor 136 to the inverting input terminal of the low-pass filter 151. This makes it possible to demodulate, from the output of the subtractor 136, a signal synchronized with the signal E1sin(2πf1t+π / 2) that is 90 degrees out of phase with the sensor drive signal E1sin(2πf1t).

[0129] The capacitance calculation unit 141 calculates the value of the capacitance Cx from the amplitude of the output vc of the synchronous detection unit 144 (Step S502 in FIG. 19). The reference capacitance calculation unit 142e calculates the value of the capacitance (reference capacitance) Cr from the output vr of the synchronous detection unit 145 and the output vt of the synchronous detection unit 153 (FIG. 19, step S503). This reference capacitance Cr can be calculated by replacing Cx with Cr and vc with vr in equation (7).

[0130] The capacitance corrector 143 calculates a value (Cx-Cr) / Cx obtained by correcting the capacitance Cx using the reference capacitance Cr (FIG. 19, step S504). The temperature calculation unit 149e calculates the value of the series resistance Rr from the output vr of the synchronous detection unit 145 and the output vt of the synchronous detection unit 153 (FIG. 19, step S505), and derives the temperature of the sensor chip 1c from the value of the series resistance Rr (FIG. 19, step S506).

[0131] The series resistance Rr can be calculated by replacing Rx with Rr and vc with vr in equation (8). The relationship between the series resistance Rr and the temperature is stored in advance in the temperature calculation unit 149e. The temperature calculation unit 149e may calculate the temperature from the value of the series resistance Rr using a preset equation, or may obtain the temperature value corresponding to the value of the series resistance Rr from a preset table.

[0132] The pressure measuring unit 13e corrects the electrostatic capacitance (Cx-Cr) / Cx calculated by the capacitance-temperature detecting unit 12e based on the temperature of the sensor chip 1c calculated by the capacitance-temperature detecting unit 12e, converts it into a measured pressure value MP, and outputs it (FIG. 19, step S507).

[0133] The capacitance / temperature detection unit 12e and the pressure measurement unit 13e perform the processes of steps S500 to S507 every measurement period until the pressure measurement operation is ended by, for example, an instruction from the user (YES in step S508 in FIG. 19). The heating operation of this embodiment is similar to that of the fifth embodiment, and therefore a description thereof will be omitted.

[0134] Thus, in this embodiment, capacitance measurement for pressure measurement is performed using the fixed electrode 105 and the movable electrode 106 of the sensor chip 1c, and reference capacitance measurement for capacitance correction, temperature measurement, and heating are performed using the fixed electrode 107 and the movable electrode 108 of the sensor chip 1c, so that four functions of pressure measurement, temperature measurement, capacitance correction, and heating can be achieved with a single sensor chip 1c. As in the first embodiment, in this embodiment, the pressure / temperature measurement and the heating may be performed at different times, or the pressure / temperature measurement and the heating may be performed simultaneously. The two movable electrodes (second electrode 106 and fourth electrode 108) provided on the diaphragm 102 of the sensor chip 1 described in the fourth to sixth embodiments may be electrically connected to each other to form a single movable electrode.

[0135] The circuit units 11, 11a, 11b, 11c, 11d, and 11e described in the first to sixth embodiments can be realized by a computer having a CPU (Central Processing Unit), a storage device, and an interface, and a program that controls these hardware resources. An example of the configuration of this computer is shown in FIG.

[0136] The computer includes a CPU 200, a storage device 201, and an interface device (I / F) 202. The I / F 202 is connected to the hardware of the capacitance detection units 12, 12a, and 12c and the hardware of the capacitance / temperature detection units 12b, 12d, and 12e. In such a computer, a program for realizing the method of the present invention is stored in the storage device 201. The CPU 200 executes the processes described in the first to sixth embodiments according to the program stored in the storage device 201. [Industrial Applicability]

[0137] The present invention is applicable to diaphragm vacuum gauges. [Explanation of symbols]

[0138] 1, 1c... sensor chip, 10, 10b, 10c, 10d... pressure receiving section, 11, 11a, 11b, 11c, 11d, 11e... circuit section, 12, 12a, 12c... capacitance detection section, 12b, 12d, 12e... capacitance / temperature detection section, 13, 13d, 13e... pressure measurement section, 14, 14a, 14b, 14c, 14d, 14e... control section, 102... diaphragm, 105, 107... fixed electrode, 106, 108... movable electrode, 120, 120-1, 120-2, 129, 132, 133, 146 , 146e...signal generator, 121, 134, 135...amplifier, 122, 122b-1, 122b-2, 137, 138, 147, 151...low-pass filter, 123, 123b, 141, 141d...capacity calculation unit, 124 to 127, 139, 140, 148, 152...switch, 128, 149, 149e...temperature calculation unit, 130, 131, 144, 145, 150, 153...synchronous detection unit, 136...subtractor, 142, 142e...reference capacitance calculation unit, 143...capacity correction unit.

Claims

1. a sensor chip including a first electrode formed on a base and a second electrode formed on a diaphragm disposed across a gap from the base so as to face the first electrode, the distance between the first and second electrodes changing in response to displacement of the diaphragm due to pressure of a medium to be measured; a signal generator configured to selectively apply to the second electrode one of a first sensor drive signal and a second sensor drive signal having a higher frequency than the first sensor drive signal; an amplifier configured to convert the current output from the first electrode into a voltage and amplify the voltage; a capacitance calculation unit configured to calculate a value of a capacitance between the first and second electrodes from an output signal of the amplifier; a pressure measuring unit configured to convert the capacitance into a measured pressure value; and a control unit configured to control the signal generator so as to apply the first sensor drive signal to the second electrode during pressure measurement, and to apply the second sensor drive signal to the second electrode during heating.

2. a sensor chip including a first electrode formed on a base and a second electrode formed on a diaphragm disposed across a gap from the base so as to face the first electrode, the distance between the first and second electrodes changing in response to displacement of the diaphragm due to pressure of a medium to be measured; a first signal generator configured to output a first sensor drive signal; a second signal generator configured to output a second sensor drive signal having a higher frequency than the first sensor drive signal; an amplifier configured to convert the current output from the first electrode into a voltage and amplify the voltage; a first switch provided between the first and second signal generators and the second electrode, and configured to selectively connect one of an output terminal of the first signal generator and an output terminal of the second signal generator to the second electrode; a second switch provided between the first electrode and the amplifier and configured to selectively connect one of an input terminal of the amplifier and a ground to the first electrode; a capacitance calculation unit configured to calculate a value of a capacitance between the first and second electrodes from an output signal of the amplifier; a pressure measuring unit configured to convert the capacitance into a measured pressure value; a control unit configured to control the first switch to connect an output terminal of the first signal generator and the second electrode and to control the second switch to connect the first electrode and an input terminal of the amplifier during pressure measurement, and to control the first switch to connect the output terminal of the second signal generator and the second electrode and to connect the first electrode and ground during heating.

3. a sensor chip including a first electrode formed on a base and a second electrode formed on a diaphragm disposed across a gap from the base so as to face the first electrode, the distance between the first and second electrodes changing in response to displacement of the diaphragm due to pressure of a medium to be measured; a first signal generator configured to apply to the second electrode one of a first sensor drive signal and a second sensor drive signal having a higher frequency than the first sensor drive signal; a second signal generator configured to output a signal out of phase with the first sensor drive signal; an amplifier configured to convert the current output from the first electrode into a voltage and amplify the voltage; a first synchronous detection unit configured to demodulate a signal synchronized with the first sensor drive signal from the output signal of the amplifier; a second synchronous detection unit configured to demodulate a signal synchronized with the output signal of the second signal generator from the output signal of the amplifier; a capacitance calculation unit configured to calculate a value of a capacitance between the first and second electrodes from output signals of the first and second synchronous detection units; a temperature calculation unit configured to calculate a series resistance value of the first and second electrodes from output signals of the first and second synchronous detection units and to obtain a temperature of the sensor chip from the series resistance value; a pressure measuring unit configured to convert the capacitance into a measured pressure value; and a control unit configured to control the first signal generator so as to apply the first sensor drive signal to the second electrode during pressure and temperature measurement, and to apply the second sensor drive signal to the second electrode during heating.

4. a sensor chip including a first electrode formed on a base and a second electrode formed on a diaphragm disposed across a gap from the base so as to face the first electrode, the distance between the first and second electrodes changing in response to displacement of the diaphragm due to pressure of a medium to be measured; a first signal generator configured to output a first sensor drive signal; a second signal generator configured to output a second sensor drive signal having a higher frequency than the first sensor drive signal; a third signal generator configured to output a signal out of phase with the first sensor drive signal; an amplifier configured to convert the current output from the first electrode into a voltage and amplify the voltage; a first switch provided between the first and second signal generators and the second electrode, and configured to selectively connect one of an output terminal of the first signal generator and an output terminal of the second signal generator to the second electrode; a second switch provided between the first electrode and the amplifier and configured to selectively connect the first electrode to one of an input terminal of the amplifier and ground; a first synchronous detection unit configured to demodulate a signal synchronized with the first sensor drive signal from the output signal of the amplifier; a second synchronous detection unit configured to demodulate a signal synchronized with the output signal of the third signal generator from the output signal of the amplifier; a capacitance calculation unit configured to calculate a value of a capacitance between the first and second electrodes from output signals of the first and second synchronous detection units; a temperature calculation unit configured to calculate a series resistance value of the first and second electrodes from output signals of the first and second synchronous detection units and to obtain a temperature of the sensor chip from the series resistance value; a pressure measuring unit configured to convert the capacitance into a measured pressure value; a control unit configured to control the first switch to connect an output terminal of the first signal generator and the second electrode and to control the second switch to connect the first electrode and an input terminal of the amplifier during pressure and temperature measurement, and to control the first switch to connect the output terminal of the second signal generator and the second electrode and to connect the first electrode to a ground during heating.

5. 5. The diaphragm vacuum gauge according to claim 3, the control unit controls any one of a frequency of the second sensor drive signal, an amplitude of the second sensor drive signal, or a length of time for applying the second sensor drive signal based on a temperature of the sensor chip and a heating temperature set value, thereby controlling the amounts of heat generated by the first and second electrodes.

6. a sensor chip including 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, wherein the distance between the first and second electrodes changes in response to displacement of the diaphragm due to pressure of a medium to be measured; a first signal generator configured to apply a first sensor drive signal to the second electrode; a second signal generator configured to selectively apply to the fourth electrode one of the first sensor drive signal and a second sensor drive signal having a higher frequency than the first sensor drive signal; a first amplifier configured to convert a current output from the first electrode into a voltage and amplify the voltage; a second amplifier configured to convert the current output from the third electrode into a voltage and amplify the voltage; a subtractor configured to subtract the output signal of the second amplifier from the output signal of the first amplifier; a first synchronous detection unit configured to demodulate a signal synchronized with the first sensor drive signal from the output signal of the first amplifier; a second synchronous detection unit configured to demodulate a signal synchronized with the first sensor drive signal from the output signal of the subtractor; a first capacitance calculation unit configured to calculate a value of a first capacitance Cx between the first and second electrodes from an output signal of the first synchronous detection unit; a second capacitance calculation unit configured to calculate a value Cx-Cr obtained by subtracting a second capacitance Cr between the third and fourth electrodes from the first capacitance Cx, based on an output signal of the second synchronous detection unit; a capacitance correction unit configured to calculate a value (Cx-Cr) / Cx obtained by correcting the first capacitance Cx by the second capacitance Cr from the calculation results of the first and second capacitance calculation units; a pressure measuring unit configured to convert the corrected first capacitance (Cx-Cr) / Cx into a measured pressure value; and a control unit configured to control the second signal generator so as to apply the first sensor drive signal to the fourth electrode during pressure measurement, and to apply the second sensor drive signal to the fourth electrode during heating.

7. a sensor chip including 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, wherein the distance between the first and second electrodes changes in response to displacement of the diaphragm due to pressure of a medium to be measured; a first signal generator configured to apply a first sensor drive signal to the second electrode; a second signal generator configured to selectively apply to the fourth electrode one of a first sensor drive signal and a second sensor drive signal having a higher frequency than the first sensor drive signal; a third signal generator configured to output a signal out of phase with the first sensor drive signal; a first amplifier configured to convert a current output from the first electrode into a voltage and amplify the voltage; a second amplifier configured to convert the current output from the third electrode into a voltage and amplify the voltage; a subtractor configured to subtract the output signal of the second amplifier from the output signal of the first amplifier; a first synchronous detection unit configured to demodulate a signal synchronized with the first sensor drive signal from the output signal of the first amplifier; a second synchronous detection unit configured to demodulate a signal synchronized with the first sensor drive signal from the output signal of the subtractor; a third synchronous detection unit configured to demodulate a signal synchronized with the output signal of the third signal generator from the output signal of the first amplifier; a first capacitance calculation unit configured to calculate a value of a first capacitance Cx between the first and second electrodes from output signals of the first and third synchronous detection units; a second capacitance calculation unit configured to calculate a value Cx-Cr obtained by subtracting a second capacitance Cr between the third and fourth electrodes from the first capacitance Cx, based on an output signal of the second synchronous detection unit; a temperature calculation unit configured to calculate a series resistance value of the first and second electrodes from output signals of the first and third synchronous detection units, and to obtain a temperature of the sensor chip from the series resistance value; a capacitance correction unit configured to calculate a value (Cx-Cr) / Cx obtained by correcting the first capacitance Cx by the second capacitance Cr from the calculation results of the first and second capacitance calculation units; a pressure measuring unit configured to convert the corrected first capacitance (Cx-Cr) / Cx into a measured pressure value by correcting the first capacitance (Cx-Cr) / Cx based on a temperature of the sensor chip; and a control unit configured to control the second signal generator so as to apply the first sensor drive signal to the fourth electrode during pressure / temperature measurement, and to apply the second sensor drive signal to the fourth electrode during heating.

8. a sensor chip including 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, wherein the distance between the first and second electrodes changes in response to displacement of the diaphragm due to pressure of a medium to be measured; a first signal generator configured to apply a first sensor drive signal to the second electrode; a second signal generator configured to selectively apply to the fourth electrode one of a first sensor drive signal and a second sensor drive signal having a higher frequency than the first sensor drive signal; a third signal generator configured to output a signal out of phase with the first sensor drive signal; a first amplifier configured to convert a current output from the first electrode into a voltage and amplify the voltage; a second amplifier configured to convert the current output from the third electrode into a voltage and amplify the voltage; a subtractor configured to subtract the output signal of the second amplifier from the output signal of the first amplifier; a first synchronous detection unit configured to demodulate a signal synchronized with the first sensor drive signal from the output signal of the first amplifier; a second synchronous detection unit configured to demodulate a signal synchronized with the first sensor drive signal from the output signal of the subtractor; a third synchronous detection unit configured to demodulate a signal synchronized with the output signal of the third signal generator from the output signal of the subtractor; a first capacitance calculation unit configured to calculate a value of a first capacitance Cx between the first and second electrodes from an output signal of the first synchronous detection unit; a second capacitance calculation unit configured to calculate a value Cx-Cr obtained by subtracting a second capacitance Cr between the third and fourth electrodes from the first capacitance Cx, based on output signals from the second and third synchronous detection units; a temperature calculation unit configured to calculate a series resistance value of the third and fourth electrodes from the output signals of the second and third synchronous detection units, and to obtain a temperature of the sensor chip from the series resistance value; a capacitance correction unit configured to calculate a value (Cx-Cr) / Cx obtained by correcting the first capacitance Cx by the second capacitance Cr from the calculation results of the first and second capacitance calculation units; a pressure measuring unit configured to convert the corrected first capacitance (Cx-Cr) / Cx into a measured pressure value by correcting the first capacitance (Cx-Cr) / Cx based on a temperature of the sensor chip; and a control unit configured to control the second signal generator so as to apply the first sensor drive signal to the fourth electrode during pressure / temperature measurement, and to apply the second sensor drive signal to the fourth electrode during heating.

9. 9. The diaphragm vacuum gauge according to claim 7, the control unit controls any one of a frequency of the second sensor drive signal, an amplitude of the second sensor drive signal, or a length of time for applying the second sensor drive signal based on a temperature of the sensor chip and a heating temperature set value, thereby controlling the amounts of heat generated by the third and fourth electrodes.

10. 10. The diaphragm vacuum gauge according to claim 6, The second electrode and the fourth electrode are electrically connected to each other to form a single electrode.

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