Diaphragm vacuum gauge

Abstract

The present invention provides a diaphragm vacuum gauge that measures the electrostatic capacitance between electrodes of a sensor chip without being affected by parasitic capacitance and stray capacitance of a cable. The diaphragm vacuum gauge comprises: a sensor chip (1) having a first electrode formed on a base and a second electrode formed on a diaphragm arranged with a gap from the base so as to face the first electrode, wherein the gap between the first and second electrodes changes according to the displacement of the diaphragm caused by the pressure of the measured medium; an operational amplifier (A1) that converts the current output from the first electrode into a voltage and amplifies it; and a coaxial cable (21) that connects the first electrode and the operational amplifier (A1). The first electrode is connected to the virtual ground of the operational amplifier (A1) via a core wire (22) of the coaxial cable (21).

Description

Technical Field

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

[0002] Capacitive-sensing diaphragm vacuum gauges measure pressure by detecting diaphragm displacement through changes in capacitance. Because diaphragm vacuum gauges need to detect minute capacitance changes, the measured value is affected by parasitic capacitance, or stray capacitance (floating capacitance). This is particularly affected by parasitic capacitance and stray capacitance in the wiring from the sensor to the circuitry. Therefore, to minimize wiring, the circuitry is typically located close to the sensor.

[0003] Diaphragm vacuum gauges are often used in semiconductor manufacturing equipment. If the semiconductor process gas is kept at an inappropriate temperature, it can liquefy or solidify, adhering to the diaphragm vacuum gauge's sensor and affecting measurement. Therefore, to prevent the adhesion of liquefied or solidified process gas, diaphragm vacuum gauges require internal or external heating devices (see Patent Documents 1, 2, and 3). In such diaphragm vacuum gauges, installing circuits with low heat resistance near the sensor presents the following problems.

[0004] (I) In order to prevent heat from being transferred from the sensor unit to the circuit unit, a heat insulating structure is required.

[0005] (II) Heat dissipation of the circuit portion is required.

[0006] (III) If the temperature of the circuit portion rises despite heat insulation and heat dissipation, the ambient temperature of the circuit portion needs to be lowered.

[0007] As mentioned above, placing the circuitry near the sensor creates issues with its heat resistance, so it's necessary to separate the circuitry from the sensor. Furthermore, piping is required around the vacuum chamber where the sensor is located, requiring a separate circuitry that requires space.

[0008] However, if the sensor unit and the circuit unit are separated, there is a problem that the pressure measurement result may be affected by parasitic capacitance and stray capacitance as described above, resulting in errors.

[0009] Prior art literature

[0010] Patent Literature

[0011] Patent Document 1: Japanese Patent Application Laid-Open No. 2010-117154

[0012] Patent Document 2: Japanese Patent Application Laid-Open No. 2009-243887

[0013] Patent Document 3: Japanese Patent Application Laid-Open No. 2019-7906 Summary of the Invention

[0014] [Problems to be Solved by the Invention]

[0015] The present invention is proposed to solve the above-mentioned problems, and its purpose is to provide a diaphragm vacuum gauge that can measure the electrostatic capacitance between the electrodes of the sensor chip without being affected by the parasitic capacitance or stray capacitance (floating capacitance) of the cable even when the sensor chip and the circuit part are separated and connected by a cable.

[0016] [Methods of solving the problem]

[0017] The diaphragm vacuum gauge of the present invention is characterized in that it comprises: a sensor chip, which has a first electrode formed on a base, and a second electrode formed on a diaphragm arranged with a gap between the base and the first electrode in a manner opposite to the first electrode, and the interval between the first electrode and the second electrode changes according to the displacement of the diaphragm caused by the pressure of the medium to be measured; a first operational amplifier, which converts the current output from the first electrode into a voltage and amplifies it; and a coaxial cable, which connects the first electrode and the first operational amplifier, and the first electrode is connected to the virtual ground of the first operational amplifier via the core wire of the coaxial cable.

[0018] Furthermore, a configuration example of the diaphragm vacuum gauge of the present invention is characterized in that the shielded wire of the coaxial cable is connected to a ground of a circuit unit including the first operational amplifier.

[0019] In addition, a structural example of the diaphragm vacuum gauge of the present invention is characterized in that it further includes: a first coaxial connector, which is arranged on the side of the circuit part including the first operational amplifier, and the center contact is connected to the virtual ground of the first operational amplifier; and a second coaxial connector, one end of which is installed on the other end of the coaxial cable connected to the first electrode, and the center contact is connected to the other end of the core wire of the coaxial cable, and the first coaxial connector and the second coaxial connector are engaged, thereby connecting the first electrode to the virtual ground of the first operational amplifier.

[0020] A configuration example of the diaphragm vacuum gauge of the present invention is characterized by further comprising: a second operational amplifier for applying a sensor drive signal to the second electrode; and a cable for connecting an output terminal of the second operational amplifier and the second electrode.

[0021] In addition, a structural example of the diaphragm vacuum gauge of the present invention is characterized in that it further includes: a capacitance calculation unit, which calculates the value of the electrostatic capacitance between the first electrode and the second electrode based on the output signal of the first operational amplifier; and a pressure measurement unit, which converts the electrostatic capacitance into a pressure measurement value.

[0022] In addition, the diaphragm vacuum gauge of the present invention is characterized in that it comprises: a sensor chip having a first electrode formed on a base, a second electrode formed on a diaphragm arranged with a gap separated from the base in a manner opposite to 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 in a manner opposite to the third electrode, wherein the interval between the first electrode and the second electrode changes according to the displacement of the diaphragm caused by the pressure of the medium to be measured; a first operational amplifier that converts the current output from the first electrode into a voltage and amplifies the voltage; a second operational amplifier that converts the current output from the third electrode into a voltage and amplifies the voltage; a first coaxial cable that connects the first electrode and the first operational amplifier; and a second coaxial cable that connects the third electrode and the second operational amplifier, the first electrode is connected to the virtual ground of the first operational amplifier through the core wire of the first coaxial cable, and the third electrode is connected to the virtual ground of the second operational amplifier through the core wire of the second coaxial cable.

[0023] In one configuration example of the diaphragm vacuum gauge of the present invention, the shielded wire of the first coaxial cable and the shielded wire of the second coaxial cable are connected to a ground of a circuit unit including the first operational amplifier and the second operational amplifier.

[0024] In addition, a structural example of the diaphragm vacuum gauge of the present invention is characterized in that it further includes: a first coaxial connector, which is provided on the side of the circuit portion including the first operational amplifier and the second operational amplifier, and the center contact is connected to the virtual ground of the first operational amplifier; a second coaxial connector, one end of which is mounted on the other end of the first coaxial cable connected to the first electrode, and the center contact is connected to the other end of the core wire of the first coaxial cable; a third coaxial connector, which is provided on the side of the circuit portion including the first operational amplifier and the second operational amplifier, and the center contact is connected to the virtual ground of the second operational amplifier; and a fourth coaxial connector, one end of which is mounted on the other end of the second coaxial cable connected to the third electrode, and the center contact is connected to the other end of the core wire of the second coaxial cable, the first coaxial connector and the second coaxial connector being mated to connect the first electrode and the virtual ground of the first operational amplifier, and the third coaxial connector and the fourth coaxial connector being mated to connect the third electrode and the virtual ground of the second operational amplifier.

[0025] In addition, a structural example of the diaphragm vacuum gauge of the present invention is characterized in that it further includes: a third operational amplifier that applies a sensor drive signal to the second electrode and the fourth electrode; and a cable that connects the output terminal of the third operational amplifier and the second electrode and the fourth electrode.

[0026] In addition, a structural example of the diaphragm vacuum gauge of the present invention is characterized in that it further includes: a subtractor, which subtracts the output signal of the second operational amplifier from the output signal of the first operational amplifier; a capacitance calculation unit, which calculates the value of the first electrostatic capacitance between the first electrode and the second electrode based on the output signal of the first operational amplifier; a capacitance difference calculation unit, which calculates the value obtained by subtracting the second electrostatic capacitance between the third electrode and the fourth electrode from the first electrostatic capacitance based on the output signal of the subtractor; a capacitance correction unit, which corrects the first electrostatic capacitance using the second electrostatic capacitance based on the calculation result of the capacitance calculation unit and the calculation result of the capacitance difference calculation unit; and a pressure measurement unit, which converts the corrected first electrostatic capacitance into a pressure measurement value.

[0027] Furthermore, in one structural example of the diaphragm vacuum gauge of the present invention, the second electrode and the fourth electrode are electrically connected to form a single electrode.

[0028] [Effects of the Invention]

[0029] According to the present invention, even when the sensor chip and circuit unit are separately installed and connected by a cable, the tiny electrostatic capacitance between the electrodes of the sensor chip can be measured without being affected by the parasitic capacitance or stray capacitance of the cable, thereby reducing the pressure measurement error caused by parasitic capacitance and stray capacitance. In addition, in the past, in order to prevent the parasitic capacitance of the cable from changing, a structure was required to prevent the cable from moving. However, in the present invention, even if the cable moves, the effect on the electrostatic capacitance between the electrodes of the sensor chip is small, so flexible cables can be used. The pressure-receiving frame that houses the sensor chip and the other frame that houses the circuit unit can be placed in different locations. In addition, because the orientation of each frame can be arbitrarily determined, field instrument installation (on-site measurement) of the diaphragm vacuum gauge can be easily performed. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a block diagram showing the structure of a diaphragm vacuum gauge according to a first embodiment of the present invention.

[0031] Figure 2 It is a cross-sectional view showing the structure of the main part of the sensor chip of the diaphragm vacuum gauge according to the first embodiment of the present invention.

[0032] Figure 3It is a diagram showing the connection structure between the sensor chip and the circuit section, and the structure of the capacitance detection section of the diaphragm vacuum gauge according to the first embodiment of the present invention.

[0033] Figure 4 This is a flow chart illustrating the pressure measuring operation of the diaphragm vacuum gauge according to the first embodiment of the present invention.

[0034] Figure 5 This is a block diagram showing the structure of a diaphragm vacuum gauge according to a second embodiment of the present invention.

[0035] Figure 6 It is a cross-sectional view showing the structure of the main part of the sensor chip of the diaphragm vacuum gauge according to the second embodiment of the present invention.

[0036] Figure 7 It is a diagram showing a connection structure between a sensor chip and a circuit unit, and a structure of a capacitance detection unit of a diaphragm vacuum gauge according to a second embodiment of the present invention.

[0037] Figure 8 This is a flow chart illustrating the pressure measuring operation of the diaphragm vacuum gauge according to the second embodiment of the present invention.

[0038] Figure 9 This is a diagram showing another example of the connection structure between the sensor chip and the circuit portion of the diaphragm vacuum gauge according to the second embodiment of the present invention.

[0039] Figure 10 This is a diagram showing another example of the connection structure between the sensor chip and the circuit portion of the diaphragm vacuum gauge according to the second embodiment of the present invention.

[0040] Figure 11 This is a cross-sectional view showing another example of the sensor chip of the diaphragm vacuum gauge according to the second embodiment of the present invention.

[0041] Figure 12 This is a block diagram showing a configuration example of a computer that realizes the circuit section of the diaphragm vacuum gauges according to the first and second embodiments of the present invention. DETAILED DESCRIPTION

[0042] [First embodiment]

[0043] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. Figure 1 is a block diagram showing the structure of a diaphragm vacuum gauge according to a first embodiment of the present invention. Figure 2 This is a cross-sectional view showing the structure of the main parts of a sensor chip used in a diaphragm vacuum gauge.

[0044] The diaphragm vacuum gauge includes a pressure-receiving portion 10 and a circuit portion 11. The electrostatic capacitance of the pressure-receiving portion 10 changes according to the displacement of the diaphragm (diaphragm) caused by the pressure of the measured medium (such as process gas). The circuit portion 11 converts the change in the electrostatic capacitance of the pressure-receiving portion 10 into a pressure measurement value.

[0045] A recess is formed in the center of base 101 of sensor chip 1 in pressure-receiving portion 10. A diaphragm 102 is bonded to the surface of base 101 with this recess. This diaphragm 102 is configured to deform in response to the pressure P of the measured medium (e.g., process gas). The recess of base 101 and diaphragm 102 together form a reference vacuum chamber 104.

[0046] In the sensor chip 1, a fixed electrode 105 is formed on the surface of the base 101 facing the reference vacuum chamber 104. A movable electrode 106 is formed on the surface of the diaphragm 102 facing the reference vacuum chamber 104, facing the fixed electrode 105. Thus, the fixed electrode 105 and the movable electrode 106 are arranged to face each other with a gap therebetween. When the diaphragm 102 is subjected to the pressure P of the measured medium and deflects, the gap 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. This change in electrostatic capacitance allows the pressure P of the measured medium acting on the diaphragm 102 to be detected. The diaphragm 102 and the base 101 are made of an insulator such as sapphire.

[0047] Figure 1 The diaphragm vacuum gauge shown includes: a sensor chip 1 having the above structure; a housing 2 that accommodates the sensor chip 1; a pressure introduction pipe 3 that guides the pressure P of the medium being measured to the diaphragm 102 of the sensor chip 1; a sensor housing 4 that covers the housing 2; and a heater 5 that surrounds the outer circumference of the sensor housing 4. The sensor housing 4, on which the heater 5 is provided, is covered with a heat insulating material 6.

[0048] The heater 5 is not necessarily provided inside the housing 2, and may be provided outside the housing 2. The heat insulating material 6 is not necessarily provided.

[0049] A partition wall 7 is provided within the housing 2. The partition wall 7, consisting of a base plate 7a and a support plate 7b, separates the interior 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, supporting the base plate 7a while it floats within the interior space of the housing 2. The sensor chip 1 is fixed to the second space 2b side of the base plate 7a. Furthermore, a pressure introduction hole 7c is formed in the base plate 7a to guide the pressure within the first space 2a to the diaphragm 102 of the sensor chip 1. The second space 2b is connected to the reference vacuum chamber 104 of the sensor chip 1, maintaining a vacuum state.

[0050] 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 from the pressure introduction pipe 3 hits the surface of the baffle 8, passes through the gap around the baffle 8, and flows into the first space 2a of the housing 2.

[0051] The circuit section 11 of the diaphragm vacuum gauge is composed of a capacitance detection section 12 , a pressure measurement section 13 , and a heater driving section 15 .

[0052] Figure 3 1 is a diagram showing the connection structure between the sensor chip 1 and the circuit unit 11 and the structure of the capacitance detection unit 12. Figure 4 This is a flowchart illustrating the pressure measurement operation of the diaphragm vacuum gauge of this embodiment.

[0053] The capacitance detection unit 12 is composed of a signal generator 120 that outputs a sensor drive signal, an operational amplifier 121 that transmits the sensor drive signal from the signal generator 120 to the sensor chip 1 via a cable 20, an amplifier 122 composed of a capacitor C1, a resistor R1, and an operational amplifier A1, a differential input type low-pass filter 123, a switch 124 provided between the amplifier 122 and the low-pass filter 123, and a capacitance calculation unit 125 that calculates the value of the electrostatic capacitance between the movable electrode 106 and the fixed electrode 105. Figure 3 In FIG. 1 , the electrostatic capacitance between the movable electrode 106 and the fixed electrode 105 of the sensor chip 1 is represented by Cx.

[0054] The signal generator 120 of the capacitance detection unit 12 outputs a sinusoidal sensor drive signal Esin(2πft) for pressure measurement to the operational amplifier 121 and the switch 124. E is amplitude, f is frequency, and t is time.

[0055] The inverting input terminal and output terminal of the operational amplifier 121 are connected, and the non-inverting input terminal is connected to the output terminal of the signal generator 120, forming a voltage follower (buffer). The output terminal of the operational amplifier 121 and the second electrode of the sensor chip 1 (for example, the movable electrode 106) are connected via the cable 20. The operational amplifier 121 applies the sensor drive signal Esin (2πft) to the second electrode ( Figure 4 Step S100).

[0056] The first electrode (for example, the fixed electrode 105 ) of the sensor chip 1 and the input terminal of the amplifier 122 of the capacitance detection unit 12 (the inverting input terminal of the operational amplifier A1 ) are connected via a coaxial cable 21 .

[0057] Amplifier 122 is composed of an operational amplifier A1, a capacitor C1 connected between the inverting input terminal and the output terminal of operational amplifier A1, and a resistor R1. Amplifier 122 converts the current output from the first electrode of sensor chip 1 into a voltage and amplifies it, outputting a signal with an amplitude proportional to capacitance Cx.

[0058] Switch 124 and low-pass filter 123 of capacitance detection unit 12 constitute synchronous detection unit 126. Low-pass filter 123 has a cutoff frequency set to allow sensor drive signal Esin(2πft) to pass through. Synchronous detection unit 126 demodulates a signal synchronized with sensor drive signal Esin(2πft) based on the output of amplifier 122.

[0059] Specifically, when the sensor drive signal Esin(2πft) is positive, switch 124 connects the output terminal of amplifier 122 to the non-inverting input terminal of low-pass filter 123. Furthermore, when the sensor drive signal Esin(2πft) is negative, switch 124 connects the output terminal of amplifier 122 to the inverting input terminal of low-pass filter 123. This allows demodulation of a signal synchronized with the sensor drive signal Esin(2πft) based on the output of amplifier 122.

[0060] The capacitance calculation unit 125 calculates the value of the electrostatic capacitance Cx based on the amplitude of the output signal of the synchronous detection unit 126 ( Figure 4 Step S101).

[0061] The pressure measuring unit 13 converts the change in the electrostatic capacitance Cx calculated by the capacitance detecting unit 12 into a pressure measurement value and outputs the result ( Figure 4 Step S102).

[0062] The heater driving unit 15 drives the heater 5 to heat the pressure receiving unit 10 , thereby preventing components in the gas to be measured from liquefying or solidifying and adhering to the sensor chip 1 .

[0063] The diaphragm vacuum gauge performs the processing of steps S100 to S102 in each measurement cycle until the pressure measurement operation is completed, for example, in response to a user instruction (at Figure 4 (“Yes” in step S103 ).

[0064] As described above, in this embodiment, the sensor chip 1 and the circuit unit 11 are provided separately and connected to the cable 20 via the coaxial cable 21. As is well known, the coaxial cable 21 is composed of a core wire 22, an insulator (not shown) covering the core wire 22, a shield wire 23 as an outer conductor covering the insulator, and a protective cover (not shown) covering the shield wire 23.

[0065] The first electrode of sensor chip 1 is connected to the inverting input terminal of operational amplifier A1, which constitutes capacitance detection unit 12 of circuit unit 11, or the virtual ground, via core wire 22 of coaxial cable 21. Shield wire 23 of coaxial cable 21 is connected to the ground of circuit unit 11, which has the same potential as the virtual ground of operational amplifier A1.

[0066] With the above-described connection structure between the sensor chip 1 and the circuit unit 11 , in this embodiment, the sensor chip 1 is less susceptible to the influence of parasitic capacitance and stray capacitance of the portion extending from the cable 20 and the coaxial cable 21 .

[0067] Specifically, a cable 20 that inputs a sensor drive signal to the second electrode on the input side of the sensor chip 1 is connected to the output terminal of the operational amplifier 121. Since the output impedance of the operational amplifier 121 is low on the input side of the sensor chip 1, it is less susceptible to the effects of the parasitic capacitance and stray capacitance of the cable 20.

[0068] On the other hand, the output side is susceptible to the parasitic and stray capacitance of cable 21 due to the high input impedance of operational amplifier A1. To reduce the effects of these parasitic and stray capacitances, in this embodiment, cable 21 is a coaxial cable. The core wire 22 of coaxial cable 21 connects the first electrode of sensor chip 1 to the virtual ground of operational amplifier A1, while the shield wire 23 of coaxial cable 21 is connected to the ground of circuit unit 11. By setting the core wire 22 and shield wire 23 to the same potential, the output is less susceptible to the effects of the parasitic and stray capacitance of coaxial cable 21.

[0069] [Second embodiment]

[0070] Next, a second embodiment of the present invention will be described. Figure 5 This is a block diagram showing the structure of a diaphragm vacuum gauge according to a second embodiment of the present invention. Figure 1 The same components are given the same reference numerals. The diaphragm vacuum gauge of this embodiment includes a pressure receiving portion 10a and a circuit portion 11a.

[0071] Figure 6 This is a cross-sectional view showing the main structure of the sensor chip 1a of this embodiment. In sensor chip 1a, fixed electrode 107 is formed on the surface of base 101 on the reference vacuum chamber 104 side, outside fixed electrode 105. Movable electrode 108 is formed on the surface of diaphragm 102 on the reference vacuum chamber 104 side, outside movable electrode 106, so as to face fixed electrode 107. The remaining structure of sensor chip 1a is the same as that of sensor chip 1.

[0072] Fixed electrode 107 and movable electrode 108 are formed at the edge of diaphragm 102. Even if diaphragm 102 is deflected by pressure P from the medium being measured, the edge of diaphragm 102 hardly deforms, so the capacitance between movable electrode 108 and fixed electrode 107 is unlikely to change. This capacitance is provided to eliminate measurement errors caused by temperature changes inside and outside the sensor and humidity changes within reference vacuum chamber 104.

[0073] The circuit section 11 a is composed of a capacitance detection section 12 a , a pressure measurement section 13 a , and a heater driving section 15 .

[0074] Figure 7 1 is a diagram showing the connection structure between the sensor chip 1a and the circuit unit 11a and the structure of the capacitance detection unit 12a. Figure 8 This is a flow chart illustrating the pressure measurement operation of the diaphragm vacuum gauge of this embodiment.

[0075] The capacitance detection unit 12a is composed of a signal generator 120, an operational amplifier 121, an amplifier 122, a low-pass filter 123, a switch 124, a capacitance calculation unit 125, an amplifier 127 composed of a capacitor C2, a resistor R2 and an operational amplifier A2, a subtractor 128, a differential input type low-pass filter 129, a switch 130 provided between the subtractor 128 and the low-pass filter 129, a capacitance difference calculation unit 131, and a capacitance correction unit 132. Figure 7 In FIG. 5 , the electrostatic capacitance between the movable electrode 108 and the fixed electrode 107 of the sensor chip 1 a is represented by Cr.

[0076] The signal generator 120 of the capacitance detection unit 12a outputs the sensor drive signal Esin (2πft) to the operational amplifier 121 and the switches 124 and 130. The operational amplifier 121 applies the sensor drive signal Esin (2πft) to the second electrode (e.g., movable electrode 106) and the fourth electrode (e.g., movable electrode 108) of the sensor chip 1a via the cable 20. Figure 8 Step S200).

[0077] The amplifier 122 converts the current output from the first electrode (eg, the fixed electrode 105 ) of the sensor chip 1 a into a voltage, amplifies the voltage, and outputs a signal having an amplitude proportional to the electrostatic capacitance Cx.

[0078] Amplifier 127 is composed of an operational amplifier A2, a capacitor C2 connected between the inverting input terminal and the output terminal of operational amplifier A2, and a resistor R2. Amplifier 127 converts the current output from the third electrode (e.g., fixed electrode 107) of the sensor chip 1a into a voltage and amplifies it, outputting a signal with an amplitude proportional to the electrostatic capacitance Cr.

[0079] The subtractor 128 subtracts the output signal of the amplifier 127 from the output signal of the amplifier 122 .

[0080] Similar to the first embodiment, the synchronous detection unit 126 demodulates a signal synchronized with the sensor drive signal Esin(2πft) based on the output of the amplifier 122 .

[0081] Meanwhile, switch 130 and low-pass filter 129 constitute synchronous detection unit 133. Low-pass filter 129 has a cutoff frequency set so as to pass sensor drive signal Esin(2πft). Synchronous detection unit 133 demodulates a signal synchronized with sensor drive signal Esin(2πft) based on the output of subtractor 128.

[0082] Specifically, when the sensor drive signal Esin(2πft) is positive, switch 130 connects the output terminal of subtractor 128 to the non-inverting input terminal of low-pass filter 129. Conversely, when the sensor drive signal Esin(2πft) is negative, switch 130 connects the output terminal of subtractor 128 to the inverting input terminal of low-pass filter 129. This allows demodulation of a signal synchronized with the sensor drive signal Esin(2πft) based on the output of subtractor 128.

[0083] The capacitance calculation unit 125 calculates the value of the electrostatic capacitance Cx based on the amplitude of the output signal of the synchronous detection unit 126 ( Figure 8 Step S201).

[0084] The capacitance difference calculation unit 131 calculates the value of the capacitance difference (Cx-Cr) based on the amplitude of the output signal of the synchronous detection unit 133 ( Figure 8 Step S202).

[0085] The capacitance correction unit 132 calculates the value (Cx-Cr) / Cx ( Figure 8 Step S203).

[0086] The pressure measuring unit 13a converts the electrostatic capacitance (Cx-Cr) / Cx calculated by the capacitance correction unit 132 into a pressure measurement value ( Figure 8 Step S204).

[0087] The heater driving unit 15 drives the heater 5 to heat the pressure receiving portion 10 a , thereby preventing components in the gas to be measured from liquefying or solidifying and adhering to the sensor chip 1 a .

[0088] The diaphragm vacuum gauge performs the processing of steps S200 to S204 in each measurement cycle until the pressure measurement operation is completed, for example, in response to a user instruction (at Figure 8 in step S205).

[0089] Similar to the first embodiment, in this embodiment, the sensor chip 1 a and the circuit portion 11 a are provided separately and connected via the cable 20 and the coaxial cables 21 and 24 .

[0090] The first electrode of the sensor chip 1a is connected to the virtual ground of the operational amplifier A1, which constitutes the capacitance detection unit 12a of the circuit unit 11a, via a core wire 22 of a coaxial cable 21. The shield wire 23 of the coaxial cable 21 is connected to the ground of the circuit unit 11a, which has the same potential as the virtual ground of the operational amplifier A1. The third electrode of the sensor chip 1a is connected to the virtual ground of the operational amplifier A2, which constitutes the capacitance detection unit 12a of the circuit unit 11a, via a core wire 25 of a coaxial cable 24. The shield wire 26 of the coaxial cable 24 is connected to the ground of the circuit unit 11a, which has the same potential as the virtual ground of the operational amplifier A2.

[0091] As described above, in this embodiment, similarly to the first embodiment, the present embodiment is less susceptible to the influence of the parasitic capacitance and stray capacitance of the cable 20 and the coaxial cables 21 and 24 .

[0092] In the first and second embodiments, the cable 20 is a single-wire cable, but may be a coaxial cable.

[0093] In the first and second embodiments, a coaxial connector may be used for at least one of the connection between the coaxial cable and the pressure receiving portion 10 or 10 a and the connection between the coaxial cable and the circuit portion 11 or 11 a . Figure 9 Indicates the structure when using a coaxial connector. Figure 9 In the example, the center contact of the socket 110 (female terminal of the coaxial connector) on the pressure-receiving part 10a side is connected to the second electrode and the fourth electrode of the sensor chip 1a, the center contact of the socket 111 is connected to the first electrode of the sensor chip 1a, and the center contact of the socket 112 is connected to the third electrode of the sensor chip 1a.

[0094] Meanwhile, the center contact of socket 140 on the circuit unit 11a side is connected to the output terminal of operational amplifier 121. The center contact of socket 141 is connected to the inverting input terminal of operational amplifier A1, and the center contact of socket 142 is connected to the inverting input terminal of operational amplifier A2. The main bodies of sockets 140 and 142 are connected to the ground of circuit unit 11a.

[0095] Coaxial cable 20 is composed of a core wire 27, an insulator (not shown) covering the core wire 27, a shield wire 28 covering the insulator, and a protective coating (not shown) covering the shield wire 28. One end of core wire 27 is connected to the center contact of plug 150 (the male terminal of the coaxial connector), and one end of shield wire 28 is connected to the main body of plug 150. The other end of core wire 27 is connected to the center contact of plug 151, and the other end of shield wire 28 is connected to the main body of plug 151.

[0096] One end of the core wire 22 of the coaxial cable 21 is connected to the center contact of the plug 152, and one end of the shield wire 23 is connected to the main body of the plug 152. The other end of the core wire 22 is connected to the center contact of the plug 153, and the other end of the shield wire 23 is connected to the main body of the plug 153. One end of the core wire 25 of the coaxial cable 24 is connected to the center contact of the plug 154, and one end of the shield wire 26 is connected to the main body of the plug 154. The other end of the core wire 25 is connected to the center contact of the plug 155, and the other end of the shield wire 26 is connected to the main body of the plug 155.

[0097] The pressure receiving portion 10a and the circuit portion 11a can be connected by fitting plugs 150 and 151 into receptacles 110 and 140, fitting plugs 152 and 153 into receptacles 111 and 141, and fitting plugs 154 and 155 into receptacles 112 and 142. A combination of a plug and a receptacle fitted therewith functions as a single coaxial connector.

[0098] As described above, a single-wire cable may be used as the cable 20 . In the case of using a single-wire cable, a connector for a single-wire cable may be used instead of a coaxial connector.

[0099] In the first and second embodiments, a multi-core coaxial cable may be used to combine the cables connecting the pressure-receiving portions 10, 10a and the circuit portions 11, 11a. A multi-core coaxial connector may be used to connect at least one of the multi-core coaxial cable to the pressure-receiving portions 10, 10a and the circuit portions 11, 11a. Figure 10 This shows the structure when using a multi-core coaxial connector.

[0100] exist Figure 10 In the example, the first center contact of the socket 113 on the pressure receiving portion 10a side is connected to the second electrode and the fourth electrode of the sensor chip 1a, the second center contact is connected to the first electrode of the sensor chip 1a, and the third center contact is connected to the third electrode of the sensor chip 1a.

[0101] Meanwhile, the first center contact of socket 143 on the circuit unit 11a side is connected to the output terminal of operational amplifier 121, the second center contact is connected to the inverting input terminal of operational amplifier A1, and the third center contact is connected to the inverting input terminal of operational amplifier A2. The main body of socket 143 is connected to the ground of circuit unit 11a.

[0102] One end of the first core wire 31 of the multi-core coaxial cable 30 is connected to the first center contact of the plug 156, one end of the second core wire 32 is connected to the second center contact of the plug 156, and one end of the third core wire 33 is connected to the third center contact of the plug 156. One end of the shield wire 34 of the multi-core coaxial cable 30 is connected to the main body of the plug 156. The other end of the first core wire 31 of the multi-core coaxial cable 30 is connected to the first center contact of the plug 157, the other end of the second core wire 32 is connected to the second center contact of the plug 157, and the other end of the third core wire 33 is connected to the third center contact of the plug 157. The other end of the shield wire 34 is connected to the main body of the plug 157.

[0103] By fitting the plugs 156 and 157 into the sockets 113 and 143 , the pressure receiving portion 10 a and the circuit portion 11 a can be connected.

[0104] exist Figure 9 、 Figure 10 In the example of FIG, a coaxial connector and a multi-core coaxial connector are used in the second embodiment, but a coaxial connector and a multi-core coaxial connector can also be used in the first embodiment.

[0105] In the first and second embodiments, the parasitic capacitance existing on the sensor chip 1 or 1a side may be shielded by the ground potential of the shield line of the coaxial cable. Figure 11 As shown, it is sufficient to bond a metal thin plate 109 to the sapphire base 101 of the sensor chip 1a and connect the metal thin plate 109 to the shielded wires 28, 23, 26, 34 of the coaxial cables 20, 21, 24, 30 (the main bodies of the sockets 110, 111, 112, 113). Figure 11 In the example shown, a shield is applied to the sensor chip 1a of the second embodiment. However, a shield can also be applied to the sensor chip 1 in the first embodiment.

[0106] The circuit units 11 and 11 a described in the first and second embodiments can be implemented by a computer including a CPU (Central Processing Unit), a storage device, and an interface, and a program for controlling these hardware resources. Figure 12 A configuration example of the computer is shown.

[0107] The computer includes a CPU 200, a storage device 201, and an interface device (I / F) 202. The hardware components of the capacitance detection units 12 and 12a and the hardware components of the heater driver 15 are connected to the I / F 202. In such a computer, a program for implementing the method of the present invention is stored in the storage device 201. The CPU 200 executes the processes described in the first and second embodiments according to the program stored in the storage device 201.

[0108] [Industrial Applicability]

[0109] The present invention can be applied to a diaphragm vacuum gauge.

[0110] [Explanation of symbols]

[0111] 1…Sensor chip, 10, 10a…Pressure receiving portion, 11, 11a…Circuit circuit portion, 12, 12a…Capacitance detection portion, 13, 13a…Pressure measurement portion, 15…Heater drive portion, 20, 21, 24, 30…Cable, 22, 25, 27, 31-33…Core wire, 23, 26, 28, 34…Shield wire, 102…Diaphragm, 105, 107…Fixed electrodes, 106, 108…movable electrode, 110-113, 140-143…socket, 120…signal generator, 122, 127…amplifier, 123, 129…low-pass filter, 124, 130…switch, 125…capacitance calculation unit, 126, 133…synchronous detection unit, 128…subtractor, 131…capacitance difference calculation unit, 132…capacitance correction unit, 150-157…plug.

Claims

1. A diaphragm vacuum gauge, characterized in that: have: A sensor chip comprising a first electrode formed on a base, a second electrode formed on a diaphragm disposed with a gap from the base so as to oppose 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 oppose the third electrode, wherein the gap between the first and second electrodes changes in response to displacement of the diaphragm caused by pressure of a medium to be measured; a first operational amplifier, which converts the current output from the first electrode into a voltage and amplifies the voltage; a second operational amplifier, which converts the current output from the third electrode into a voltage and amplifies the voltage; a third operational amplifier, configured to apply a sensor driving signal to the second electrode and the fourth electrode; a subtractor that subtracts the output signal of the second operational amplifier from the output signal of the first operational amplifier; a capacitance calculation unit configured to calculate a value of a first electrostatic capacitance between the first electrode and the second electrode based on an output signal of the first operational amplifier; a capacitance difference calculation unit for calculating a value obtained by subtracting a second electrostatic capacitance between the third electrode and the fourth electrode from the first electrostatic capacitance based on an output signal of the subtractor; a capacitance correction unit that corrects the first electrostatic capacitance using the second electrostatic capacitance based on a calculation result of the capacitance calculation unit and a calculation result of the capacitance difference calculation unit; a pressure measuring unit that converts the corrected first electrostatic capacitance into a pressure measurement value; a cable connecting the output terminal of the third operational amplifier and the second electrode and the fourth electrode; a first coaxial cable connecting the first electrode and the first operational amplifier; as well as a second coaxial cable connecting the third electrode and the second operational amplifier, The first electrode is connected to the virtual ground of the first operational amplifier through the core wire of the first coaxial cable, and the third electrode is connected to the virtual ground of the second operational amplifier through the core wire of the second coaxial cable. The shielded wire of the first coaxial cable and the shielded wire of the second coaxial cable are connected to a ground of a circuit portion including the first operational amplifier and the second operational amplifier.

2. The diaphragm vacuum gauge according to claim 1, characterized in that Also features: a first coaxial connector provided on a circuit portion including the first operational amplifier and the second operational amplifier, wherein a center contact is connected to a virtual ground of the first operational amplifier; a second coaxial connector, one end of which is mounted on the other end of the first coaxial cable connected to the first electrode, and a center contact connected to the other end of the core wire of the first coaxial cable; a third coaxial connector provided on the side of the circuit portion including the first operational amplifier and the second operational amplifier, wherein the center contact is connected to the virtual ground of the second operational amplifier; as well as a fourth coaxial connector, one end of which is mounted on the other end of the second coaxial cable connected to the third electrode, and a center contact connected to the other end of the core wire of the second coaxial cable; The first coaxial connector and the second coaxial connector are mated to connect the first electrode and the virtual ground of the first operational amplifier. The third coaxial connector and the fourth coaxial connector are mated to connect the third electrode and the virtual ground of the second operational amplifier.

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