Diaphragm vacuum gauge

Abstract

To measure a capacitance between electrodes of a sensor chip without influencing a parasitic capacitance or stray capacitance of a cable.SOLUTION: A diaphragm vacuum gauge comprises: a sensor chip 1 that comprises a first electrode formed on a pedestal, and a second electrode formed so as to face the first electrode on a diaphragm arranged across a gap from the pedestal, and in which an interval between the first and second electrodes changes according to the displacement of the diaphragm due to the pressure of a medium to be measured; an operational amplifier A1 that converts a 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 a virtual ground of the operational amplifier A1 through a core wire 22 of the coaxial cable 21.SELECTED DRAWING: Figure 3

Description

[Technical field]

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

[0002] A capacitance detection type diaphragm vacuum gauge measures pressure by detecting the displacement of a diaphragm through a change in capacitance. Because a diaphragm vacuum gauge must detect minute changes in capacitance, the measurement value is subject to the effects of parasitic capacitance and stray effects. In particular, it is subject to the effects of parasitic capacitance and stray effects in the wiring from the sensor section to the circuit section. For this reason, it is usually necessary to place the circuit section next to the sensor section in order to keep the wiring as short as possible.

[0003] Diaphragm vacuum gauges are often used in semiconductor manufacturing equipment. If the temperature of the semiconductor process gas is not appropriate, it will liquefy or solidify and adhere to the sensor of the diaphragm vacuum gauge, affecting the measurement. For this reason, the diaphragm vacuum gauge needs to be heated by a heating means provided inside or outside the diaphragm vacuum gauge to prevent adhesion of the liquefied or solidified process gas (see Patent Documents 1, 2, and 3). With such a diaphragm vacuum gauge, if a circuit with low heat resistance is installed near the sensor, the following problems arise:

[0004] (I) A thermal insulation structure is required to prevent heat from being transferred from the sensor section to the circuit section. (II) Heat dissipation from the circuit section is required. (III) If the temperature of the circuit section rises even after insulation and heat dissipation, it is necessary to lower the ambient temperature of the circuit section.

[0005] As described above, if the circuit section is placed close to the sensor section, problems arise with the heat resistance of the circuit section, so there is a demand for the circuit section to be placed separately from the sensor section. Also, since the area around the vacuum chamber where the sensor section is placed is complicated with piping, there is a demand for the circuit section, which requires space, to be placed separately. However, when the sensor unit and the circuit unit are separated, there is a problem that the sensor is subject to the effects of parasitic capacitance and stray effects as described above, causing errors in the pressure measurement results. [Prior art documents] [Patent documents]

[0006] [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]

[0007] The present invention has been made to solve the above-mentioned problems, and has an object to provide a diaphragm vacuum gauge that can measure the capacitance between the electrodes of a sensor chip without being affected by the parasitic capacitance or stray capacitance of the cable, even when the sensor chip and circuit unit are installed separately and connected via a cable. [Means for solving the problem]

[0011] The present invention also provides a diaphragm vacuum gauge comprising 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 operational amplifier configured to convert a current output from the first electrode into a voltage and amplify the voltage, and a second operational 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 operational amplifier from an output signal of the first operational amplifier; a capacitance calculation unit configured to calculate a value of a first capacitance between the first and second electrodes based on the output signal of the first operational amplifier; a capacitance difference calculation unit configured to calculate a value obtained by subtracting a second capacitance between the third and fourth electrodes from the first capacitance based on the output signal of the subtractor; a capacitance correction unit configured to correct the first capacitance by the second capacitance based on a calculation result of the capacitance calculation unit and a calculation result of the capacitance difference calculation unit; and a pressure measurement unit configured to convert the corrected first capacitance into a pressure measurement value. The first electrode Used only for output fromA first coaxial cable and the third electrode Used only for output from and a second coaxial cable, the first electrode being connected to a virtual ground of the first operational amplifier via a core of the first coaxial cable, and the third electrode being connected to a virtual ground of the second operational amplifier via a core of the second coaxial cable. a shield wire of the first coaxial cable and a shield wire of the second coaxial cable are connected to a ground of a circuit section including the first and second operational amplifiers; It is characterized by the above.

[0012] Also One configuration example of the diaphragm vacuum gauge of the present invention includes a first coaxial connector provided on the circuit section side including the first and second operational amplifiers, and having a center contact connected to a virtual ground of the first operational amplifier; a second coaxial connector attached to the other end of the first coaxial cable, one end of which is connected to the first electrode, and having a center contact connected to the other end of the core wire of the first coaxial cable; and a third coaxial connector provided on the circuit section side including the first and second operational amplifiers, and having a center contact connected to the virtual ground of the second operational amplifier. The semiconductor device further includes a fourth coaxial connector, one end of which is attached to the other end of the second coaxial cable connected to the third electrode, and a center contact of which is connected to the other end of the core wire of the second coaxial cable, wherein the first electrode is connected to the virtual ground of the first operational amplifier by mating the first coaxial connector with the second coaxial connector, and the third electrode is connected to the virtual ground of the second operational amplifier by mating the third coaxial connector with the fourth coaxial connector.

[0013] Moreover, one configuration example of the diaphragm vacuum gauge of the present invention is characterized by further comprising a third operational amplifier configured to apply a sensor drive signal to the second and fourth electrodes, and a cable configured to connect output terminals of the third operational amplifier to the second and fourth electrodes. Also In one configuration example 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. The present invention also provides a diaphragm vacuum gauge comprising: 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; and a thin metal plate bonded to the base, the distance between the first and second electrodes changing in response to displacement of the diaphragm due to the pressure of a medium to be measured; a first operational amplifier configured to convert a current output from the first electrode into a voltage and amplify the voltage; and a coaxial cable configured to connect the first electrode and the first operational amplifier, the first electrode being connected to a virtual ground of the first operational amplifier via a core wire of the coaxial cable, and a shield wire of the coaxial cable being connected to the ground of a circuit section including the first operational amplifier and to the thin metal plate of the sensor chip. The present invention also provides a diaphragm vacuum gauge comprising: 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; a fourth electrode formed on the diaphragm outside the second electrode so as to face the third electrode; and a metal thin plate bonded to the base, 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 operational amplifier configured to convert a current output from the first electrode into a voltage and amplify the voltage; and a second operational amplifier configured to convert a current output from the third electrode into a voltage and amplify the voltage. the first electrode is connected to a virtual ground of the first operational amplifier via a core wire of the first coaxial cable, the third electrode is connected to a virtual ground of the second operational amplifier via a core wire of the second coaxial cable, and a shield wire of the first coaxial cable and a shield wire of the second coaxial cable are connected to a ground of a circuit section including the first and second operational amplifiers and a thin metal plate of the sensor chip, respectively. Effect of the Invention

[0014] According to the present invention, even when the sensor chip and the circuit unit are installed separately and connected via a cable, it is possible to measure the minute capacitance between the electrodes of the sensor chip without being affected by the parasitic capacitance or stray capacitance of the cable, and it is possible to reduce pressure measurement errors due to the parasitic capacitance and stray capacitance. Furthermore, in the past, it was necessary to design the cable so that it would not move so that the parasitic capacitance of the cable would not change, but in the present invention, even if the cable moves, the effect on the capacitance between the electrodes of the sensor chip is small, so a flexible cable can be used, the pressure receiving unit housing that houses the sensor chip and the separate housing that houses the circuit unit can be installed in different locations, and the orientation of each housing can be determined arbitrarily, making it easy to perform on-site instrumentation of the diaphragm vacuum gauge. [Brief description of the drawings]

[0015] [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 diagram showing a connection structure between the sensor chip and the circuit section of the diaphragm vacuum gauge according to the first embodiment of the present invention, and a configuration of a capacitance detection section. [Figure 4] FIG. 4 is a flowchart illustrating the pressure measurement operation of the diaphragm vacuum gauge according to the first embodiment of the present invention. [Diagram 5] FIG. 5 is a block diagram showing the configuration of a diaphragm vacuum gauge according to a second embodiment of the present invention. [Figure 6] FIG. 6 is a cross-sectional view showing the configuration of a main part of a sensor chip of a diaphragm vacuum gauge according to a second embodiment of the present invention. [Figure 7] FIG. 7 is a diagram showing a connection structure between a sensor chip and a circuit section of a diaphragm vacuum gauge according to a second embodiment of the present invention, and a configuration of a capacitance detection section. [Figure 8] FIG. 8 is a flowchart illustrating the pressure measurement operation of the diaphragm vacuum gauge according to the second embodiment of the present invention. [Figure 9] FIG. 9 is a diagram showing another example of the connection structure between the sensor chip and the circuit section of the diaphragm vacuum gauge according to the second embodiment of the present invention. [Figure 10] FIG. 10 is a diagram showing another example of the connection structure between the sensor chip and the circuit section of the diaphragm vacuum gauge according to the second embodiment of the present invention. [Figure 11] FIG. 11 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. [Figure 12] FIG. 12 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 and second embodiments of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] [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.

[0017] The diaphragm vacuum gauge comprises a pressure receiving section 10 whose capacitance changes in response to the displacement of a diaphragm due to the pressure of a medium to be measured (e.g., a process gas), and a circuit section 11 that converts the change in capacitance of the pressure receiving section 10 into a pressure measurement value.

[0018] 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.

[0019] 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.

[0020] 1 comprises the sensor chip 1 constructed as above, a housing 2 that accommodates the sensor chip 1, a pressure introduction tube 3 that introduces the pressure P of the medium to be measured to the diaphragm 102 of the sensor chip 1, a sensor case 4 that covers the housing 2, and a heater 5 provided so as to surround the outer circumferential surface of the sensor case 4. The sensor case 4 with the heater 5 provided therein is covered with a heat insulating material 6. It should be noted that the heater 5 does not necessarily have to be provided inside the housing 2, and may be provided outside the housing 2. Moreover, the heat insulating material 6 does not necessarily have to be provided.

[0021] 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.

[0022] 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.

[0023] 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 drive section 15. FIG. 3 is a diagram showing the connection structure between the sensor chip 1 and the circuit section 11, and the configuration of the capacitance detection section 12, and FIG. 4 is a flow chart for explaining the pressure measurement operation of the diaphragm vacuum gauge of this embodiment.

[0024] The capacitance detection unit 12 is composed of a signal generator 120 that outputs a sensor drive signal, an operational amplifier 121 that sends the sensor drive signal from the signal generator 120 to the sensor chip 1 via the cable 20, an amplifier 122 consisting of a capacitance 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 capacitance between the movable electrode 106 and the fixed electrode 105. In Fig. 3, the capacitance between the movable electrode 106 and the fixed electrode 105 of the sensor chip 1 is represented by Cx.

[0025] The signal generator 120 of the capacitance detection unit 12 outputs a sine wave sensor drive signal Esin(2πft) for pressure measurement to an operational amplifier 121 and a switch 124. E is the amplitude, f is the frequency, and t is the time.

[0026] The operational amplifier 121 has an inverting input terminal and an output terminal connected thereto, and a non-inverting input terminal connected to the output terminal of the signal generator 120, forming a voltage follower (buffer). The output terminal of the operational amplifier 121 is connected to a second electrode (e.g., the movable electrode 106) of the sensor chip 1 by a cable 20. The operational amplifier 121 applies a sensor drive signal Esin (2πft) to the second electrode of the sensor chip 1 via the cable 20 (step S100 in FIG. 4).

[0027] A coaxial cable 21 connects between a first electrode (for example, the fixed electrode 105) of the sensor chip 1 and an input terminal of the amplifier 122 of the capacitance detection unit 12 (the inverting input terminal of the operational amplifier A1). The amplifier 122 is composed of an operational amplifier A1, and a capacitance C1 and a resistance R1 connected between the inverting input terminal and the output terminal of the operational amplifier A1. The amplifier 122 converts the current output from the first electrode of the sensor chip 1 into a voltage, amplifies the voltage, and outputs a signal with an amplitude proportional to the capacitance Cx.

[0028] The switch 124 and low-pass filter 123 of the capacitance detection unit 12 constitute a synchronous detection unit 126. The cutoff frequency of the low-pass filter 123 is set so as to pass the sensor drive signal Esin(2πft). The synchronous detection unit 126 demodulates the output of the amplifier 122 into a signal synchronized with the sensor drive signal Esin(2πft).

[0029] Specifically, when the sensor drive signal Esin(2πft) is positive, the switch 124 connects the output terminal of the amplifier 122 to the non-inverting input terminal of the low-pass filter 123. In addition, when the sensor drive signal Esin(2πft) is negative, the switch 124 connects the output terminal of the amplifier 122 to the inverting input terminal of the low-pass filter 123. This makes it possible to demodulate a signal synchronized with the sensor drive signal Esin(2πft) from the output of the amplifier 122.

[0030] The capacitance calculation section 125 calculates the value of the capacitance Cx from the amplitude of the output signal of the synchronous detection section 126 (Step S101 in FIG. 4). The pressure measuring unit 13 converts the change in the capacitance Cx calculated by the capacitance detecting unit 12 into a pressure measurement value and outputs it (Step S102 in FIG. 4).

[0031] The heater driving section 15 drives the heater 4 to heat the pressure receiving section 10 , thereby preventing components in the gas to be measured from liquefying or solidifying and adhering to the sensor chip 1 .

[0032] The diaphragm vacuum gauge performs 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. 4).

[0033] As described above, in this embodiment, the sensor chip 1 and the circuit unit 11 are installed separately and connected via the cable 20 and the coaxial cable 21. As is well known, the coaxial cable 21 is composed of a core wire 22, an insulator (not shown) that covers the periphery of the core wire 22, a shield wire 23 that is an outer conductor that covers the periphery of the insulator, and a protective coating (not shown) that covers the periphery of the shield wire 23.

[0034] A first electrode of the sensor chip 1 is connected to the inverting input terminal of the operational amplifier A1 constituting the capacitance detection unit 12 of the circuit unit 11, i.e., to the virtual ground, via the core wire 22 of the coaxial cable 21. A shield wire 23 of the coaxial cable 21 is connected to the ground of the circuit unit 11, which has the same potential as the virtual ground of the operational amplifier A1.

[0035] In this embodiment, the connection structure between the sensor chip 1 and the circuit unit 11 as described above makes it difficult for the influence of the parasitic capacitance and stray capacitance of the cable 20 and the portion extended by the coaxial cable 21 to occur. Specifically, the cable 20 that inputs a sensor drive signal to a second electrode on the input side of the sensor chip 1 is connected to the output terminal of the operational amplifier 121. The input side of the sensor chip 1 is less susceptible to the effects of the parasitic capacitance and stray capacitance of the cable 20 because the output impedance of the operational amplifier 121 is low.

[0036] On the other hand, the output side is susceptible to the influence of the parasitic capacitance and stray capacitance of the cable 21 because the input impedance of the operational amplifier A1 is high. In order to reduce the influence of the parasitic capacitance and stray capacitance of the cable 21, in this embodiment, the cable 21 is a coaxial cable, the core wire 22 of the coaxial cable 21 connects the first electrode of the sensor chip 1 and the virtual ground of the operational amplifier A1, and the shield wire 23 of the coaxial cable 21 is connected to the ground of the circuit unit 11. By making the core wire 22 and the shield wire 23 the same potential, the output side is less susceptible to the influence of the parasitic capacitance and stray capacitance of the coaxial cable 21.

[0037] [Second Example] Next, a second embodiment of the present invention will be described. Fig. 5 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. The diaphragm vacuum gauge of this embodiment comprises a pressure receiving portion 10a and a circuit portion 11a.

[0038] 6 is a cross-sectional view showing the configuration of the main part of sensor chip 1a of this embodiment. In sensor chip 1a, fixed electrode 107 is formed on the surface of base 101 facing reference vacuum chamber 104, outside fixed electrode 105. 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 1a is the same as that of sensor chip 1.

[0039] The fixed electrode 107 and the movable electrode 108 are formed on the edge of the diaphragm 102. Even if the diaphragm 102 is deflected by 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.

[0040] The circuit section 11 a includes a capacitance detection section 12 a, a pressure measurement section 13 a, and a heater driving section 15 . FIG. 7 is a diagram showing the connection structure between the sensor chip 1a and the circuit section 11a, and the configuration of the capacitance detection section 12a, and FIG. 8 is a flow chart for explaining the pressure measurement operation of the diaphragm vacuum gauge of this embodiment.

[0041] The capacitance detection unit 12a includes 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 consisting of a capacitance 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. In Fig. 7, the electrostatic capacitance between the movable electrode 108 and the fixed electrode 107 of the sensor chip 1a is represented by Cr.

[0042] The signal generator 120 of the capacitance detection unit 12a outputs a 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., the movable electrode 106) and the fourth electrode (e.g., the movable electrode 108) of the sensor chip 1a via the cable 20 (step S200 in FIG. 8).

[0043] The amplifier 122 converts the current output from the first electrode (eg, the fixed electrode 105) of the sensor chip 1a into a voltage, amplifies it, and outputs a signal with an amplitude proportional to the capacitance Cx. The amplifier 127 includes an operational amplifier A2, and a capacitance C2 and a resistance R2 connected between the inverting input terminal and the output terminal of the operational amplifier A2. The amplifier 127 converts the current output from the third electrode (e.g., the fixed electrode 107) of the sensor chip 1a into a voltage, amplifies the voltage, and outputs a signal with an amplitude proportional to the capacitance Cr. The subtractor 128 subtracts the output signal of the amplifier 127 from the output signal of the amplifier 122 .

[0044] As in the first embodiment, the synchronous detection section 126 demodulates the output of the amplifier 122 into a signal synchronized with the sensor drive signal Esin(2πft). Meanwhile, switch 130 and low-pass filter 129 constitute a synchronous detection unit 133. The cutoff frequency of low-pass filter 129 is set to pass sensor drive signal Esin(2πft). Synchronous detection unit 133 demodulates the output of subtractor 128 into a signal synchronized with sensor drive signal Esin(2πft).

[0045] Specifically, when the sensor drive signal Esin(2πft) is positive, the switch 130 connects the output terminal of the subtractor 128 to the non-inverting input terminal of the low-pass filter 129. In addition, when the sensor drive signal Esin(2πft) is negative, the switch 130 connects the output terminal of the subtractor 128 to the inverting input terminal of the low-pass filter 129. This makes it possible to demodulate a signal synchronized with the sensor drive signal Esin(2πft) from the output of the subtractor 128.

[0046] The capacitance calculation section 125 calculates the value of the capacitance Cx from the amplitude of the output signal of the synchronous detection section 126 (Step S201 in FIG. 8). The capacitance difference calculation unit 131 calculates the value of the capacitance difference (Cx-Cr) from the amplitude of the output signal of the synchronous detection unit 133 (Step S202 in FIG. 8).

[0047] The capacitance corrector 132 calculates a value (Cx-Cr) / Cx obtained by correcting the capacitance Cx with the reference capacitance Cr based on the calculation result of the capacitance calculator 125 and the calculation result of the capacitance difference calculator 131 (FIG. 8, step S203). The pressure measuring unit 13a converts the capacitance (Cx-Cr) / Cx calculated by the capacitance correcting unit 132 into a pressure measurement value (Step S204 in FIG. 8).

[0048] The heater driving section 15 drives the heater 4 to heat the pressure receiving section 10 , thereby preventing components in the gas to be measured from liquefying or solidifying and adhering to the sensor chip 1 . The diaphragm vacuum gauge performs the processes of steps S200 to S204 every measurement period until the pressure measurement operation is ended, for example, in response to an instruction from the user (YES in step S205 in FIG. 8).

[0049] As in the first embodiment, in this embodiment, the sensor chip 1a and the circuit section 11a are installed separately and connected via the cable 20 and the coaxial cables 21 and 24. A first electrode of the sensor chip 1a is connected to the virtual ground of the operational amplifier A1 constituting the capacitance detection unit 12a of the circuit unit 11a via a core wire 22 of a coaxial cable 21. A 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. A third electrode of the sensor chip 1a is connected to the virtual ground of the operational amplifier A2 constituting the capacitance detection unit 12a of the circuit unit 11a via a core wire 25 of a coaxial cable 24. A 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. In this manner, in this embodiment, similarly to the first embodiment, the influence of the parasitic capacitance and stray capacitance of the cable 20 and the coaxial cables 21 and 24 is reduced.

[0050] In the first and second embodiments, the cable 20 is a single-wire cable, but it may be a coaxial cable.

[0051] In the first and second embodiments, a coaxial connector may be used for at least one of the connections between the coaxial cable and the pressure receiving unit 10, 10a and between the coaxial cable and the circuit unit 11, 11a. A configuration in which a coaxial connector is used is shown in Fig. 9. In the example of Fig. 9, the center contact of the receptacle 110 (female terminal of the coaxial connector) on the pressure receiving unit 10a side is connected to the second electrode and the fourth electrode of the sensor chip 1a, the center contact of the receptacle 111 is connected to the first electrode of the sensor chip 1a, and the center contact of the receptacle 112 is connected to the third electrode of the sensor chip 1a.

[0052] On the other hand, the center contact of receptacle 140 on the circuit unit 11a side is connected to the output terminal of operational amplifier 121, the center contact of receptacle 141 is connected to the inverting input terminal of operational amplifier A1, and the center contact of receptacle 142 is connected to the inverting input terminal of operational amplifier A2. The bodies of receptacles 140 to 142 are connected to the ground of circuit unit 11a.

[0053] Coaxial cable 20 is composed of a core wire 27, an insulator (not shown) that covers the periphery of core wire 27, a shield wire 28 that covers the periphery of the insulator, and a protective coating (not shown) that covers the periphery of shield wire 28. One end of core wire 27 is connected to a center contact of plug 150 (male terminal of a coaxial connector), and one end of shield wire 28 is connected to a body of plug 150. The other end of core wire 27 is connected to a center contact of plug 151, and the other end of shield wire 28 is connected to the body of plug 151.

[0054] 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 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 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 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 body of the plug 155.

[0055] Pressure-receiving unit 10a and circuit unit 11a can be connected by fitting plugs 150, 151 into receptacles 110, 140, fitting plugs 152, 153 into receptacles 111, 141, and fitting plugs 154, 155 into receptacles 112, 142. A set of one plug and one receptacle that fits with that plug functions as one coaxial connector. As described above, a single-wire cable may be used as cable 20. When a single-wire cable is used, a connector for a single-wire cable may be used instead of a coaxial connector.

[0056] In the first and second embodiments, a multi-core coaxial cable may be used that combines the cables connecting the pressure-receiving units 10, 10a and the circuit units 11, 11a. A multi-core coaxial connector may be used for at least one of the connections between the multi-core coaxial cable and the pressure-receiving units 10, 10a and between the multi-core coaxial cable and the circuit units 11, 11a. The configuration when a multi-core coaxial connector is used is shown in Figure 10.

[0057] In the example of Figure 10, the first center contact of the receptacle 113 on the pressure receiving section 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.

[0058] On the other hand, a first center contact of receptacle 143 on the circuit unit 11a side is connected to the output terminal of operational amplifier 121, a second center contact is connected to the inverting input terminal of operational amplifier A1, and a third center contact is connected to the inverting input terminal of operational amplifier A2. The body of receptacle 143 is connected to the ground of circuit unit 11a.

[0059] 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 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 body of the plug 157.

[0060] By fitting the plugs 156, 157 into the receptacles 113, 143, the pressure-receiving portions 10, 10a and the circuit portion 11a can be connected to each other.

[0061] In the examples of Figures 9 and 10, a coaxial connector and a multi-core coaxial connector are used in the second embodiment, but it goes without saying that a coaxial connector and a multi-core coaxial connector may also be used in the first embodiment.

[0062] In the first and second embodiments, the parasitic capacitance present on the sensor chip 1, 1a side may be shielded by the ground potential of the shield wire of the coaxial cable. Specifically, for example, as shown in Fig. 11, a metal sheet 109 may be joined to a sapphire base 101 of the sensor chip 1a, and the metal sheet 109 may be connected to the shield wires 28, 23, 26, 34 (bodies of receptacles 110, 111, 112, 113) of the coaxial cables 20, 21, 24, 30. In the example of Fig. 11, a shield is applied to the sensor chip 1a of the second embodiment, but it goes without saying that a shield may be applied to the sensor chip 1 in the first embodiment.

[0063] The circuit units 11 and 11a described in the first and second embodiments can be realized by a computer equipped with 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.

[0064] 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 parts of the capacitance detection units 12 and 12a and the hardware part of the heater driving unit 15. 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 and second embodiments in accordance with the program stored in the storage device 201. [Industrial Applicability]

[0065] The present invention is applicable to diaphragm vacuum gauges. [Explanation of symbols]

[0066] 1...sensor chip, 10, 10a...pressure receiving section, 11, 11a...circuit section, 12, 12a...capacitance detection section, 13, 13a...pressure measurement section, 15...heater driving section, 20, 21, 24, 30...cable, 22, 25, 27, 31 to 33...core wire, 23, 26, 28, 34...shield wire, 102...diaphragm, 105, 107...fixed electrode, 106, 108... movable electrode, 110-113, 140-143... receptacles, 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... plugs.

Claims

1. 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 operational amplifier configured to convert a current output from the first electrode into a voltage and amplify the voltage; a second operational 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 operational amplifier from the output signal of the first operational amplifier; a capacitance calculation unit configured to calculate a value of a first capacitance between the first and second electrodes based on an output signal of the first operational amplifier; a capacitance difference calculation unit configured to calculate a value obtained by subtracting a second capacitance between the third and fourth electrodes from the first capacitance based on an output signal of the subtractor; a capacitance correction unit configured to correct the first capacitance by the second capacitance based on a calculation result of the capacitance calculation unit and a calculation result of the capacitance difference calculation unit; a pressure measurement unit configured to convert the corrected first capacitance into a pressure measurement value; a first coaxial cable used only for output from the first electrode; a second coaxial cable used only for output from the third electrode; the first electrode is connected to a virtual ground of the first operational amplifier via a core wire of the first coaxial cable, and the third electrode is connected to a virtual ground of the second operational amplifier via a core wire of the second coaxial cable; a shield wire of the first coaxial cable and a shield wire of the second coaxial cable are connected to a ground of a circuit portion including the first and second operational amplifiers.

2. 2. The diaphragm vacuum gauge according to claim 1, a first coaxial connector provided on a circuit portion side including the first and second operational amplifiers, the first coaxial connector having a center contact connected to a virtual ground of the first operational amplifier; a second coaxial connector, one end of which is attached to the other end of the first coaxial cable connected to the first electrode, and a center contact of which is connected to the other end of the core wire of the first coaxial cable; a third coaxial connector provided on a circuit portion side including the first and second operational amplifiers, the third coaxial connector having a center contact connected to a virtual ground of the second operational amplifier; a fourth coaxial connector, one end of which is attached to the other end of the second coaxial cable connected to the third electrode, and a center contact of which is connected to the other end of the core wire of the second coaxial cable; a diaphragm vacuum gauge wherein the first electrode is connected to a virtual ground of the first operational amplifier by mating the first coaxial connector with the second coaxial connector, and the third electrode is connected to a virtual ground of the second operational amplifier by mating the third coaxial connector with the fourth coaxial connector.

3. 3. The diaphragm vacuum gauge according to claim 1, a third operational amplifier configured to apply a sensor drive signal to the second and fourth electrodes; and a cable configured to connect an output terminal of the third operational amplifier to the second and fourth electrodes.

4. 4. The diaphragm vacuum gauge according to claim 1, The second electrode and the fourth electrode are electrically connected to each other to form a single electrode.

5. A sensor chip comprising 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, and a thin metal plate joined to the base, wherein the sensor chip is configured such that the distance between the first and second electrodes changes in response to displacement of the diaphragm due to the pressure of a medium to be measured; a first operational amplifier configured to convert a current output from the first electrode into a voltage and amplify the voltage; a coaxial cable configured to connect the first electrode and the first operational amplifier; the first electrode is connected to a virtual ground of the first operational amplifier via a core wire of the coaxial cable; a shield wire of said coaxial cable being connected to a ground of a circuit section including said first operational amplifier and to a thin metal plate of said sensor chip.

6. A sensor chip comprising: a first electrode formed on a base; a second electrode formed on a diaphragm arranged across a gap from the base so as to face the first electrode; a third electrode formed on the base outside the first electrode; a fourth electrode formed on the diaphragm outside the second electrode so as to face the third electrode; and a thin metal plate joined to the base, wherein the sensor chip is configured so that the distance between the first and second electrodes changes in response to displacement of the diaphragm due to the pressure of a medium to be measured; a first operational amplifier configured to convert a current output from the first electrode into a voltage and amplify the voltage; a second operational amplifier configured to convert the current output from the third electrode into a voltage and amplify the voltage; a first coaxial cable configured to connect the first electrode and the first operational amplifier; a second coaxial cable configured to connect the third electrode and the second operational amplifier; the first electrode is connected to a virtual ground of the first operational amplifier via a core wire of the first coaxial cable, and the third electrode is connected to a virtual ground of the second operational amplifier via a core wire of the second coaxial cable; a shield wire of the first coaxial cable and a shield wire of the second coaxial cable are connected to a ground of a circuit portion including the first and second operational amplifiers and to a thin metal plate of the sensor chip, respectively.

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