JP5387468B2 - Vacuum gauge - Google Patents

Description

  The present invention relates to a vacuum gauge using a vibrating body, and more particularly to a vacuum gauge capable of measuring a wide range of gas pressures.

  Conventionally, a vacuum sensor that measures the pressure of an atmosphere using a tuning fork type vibrating body is known (see Patent Document 1). The principle of measuring the atmospheric pressure using a tuning fork type vibrating body is to vibrate the vibrating body and specify the atmospheric pressure (that is, the degree of vacuum) from the vibration characteristics. The vibrating body is excited by using an electrostatic force between the vibrating body and the vibrating electrode, and detecting the change in capacitance corresponding to the change in the distance between the vibrating body and the detection electrode. Detect vibrations.

Japanese Patent Laid-Open No. 62-137533

When a voltage signal corresponding to the natural angular frequency ω _R (= 2πf _R , where f _R is the natural frequency) of the vibrating body is applied to the excitation electrode facing the vibrating body, the vibrating body enters a resonance state. The amplitude A of the vibrating body at this time can be expressed as the following formula (1).

Here, F ₀ is the electrostatic driving force applied to the vibrating body, Q is the Q value of the vibrating body (one of the vibration characteristics of the vibrating body), and is a dimensionless number representing the sharpness of the resonance peak, m is the mass of the vibrating body.
It is known that the Q value of the vibrating body is inversely proportional to the gas pressure P. For example, the Q value of the vibrating body is detected by detecting the amplitude A of the vibrating body under the condition that the electrostatic driving force F ₀ is kept constant. It is possible to indirectly measure the gas pressure P by converting the Q value into the gas pressure P value.

Next, as shown in the following formula (2), the electrostatic driving force F ₀ includes the voltage _{VA of the} AC signal applied as a drive signal to the excitation electrode, the potential of the vibrating body, and the potential of the excitation electrode. Is proportional to the absolute value of the product of the direct-current potential difference ΔV _O between

As the electrostatic driving force F ₀ is larger, the amplitude A becomes larger at the same pressure (ie, the same Q value), so that the measurement sensitivity of the vibration body amplitude is made higher, that is, higher pressure (lower) It is possible to measure pressure up to (Q value). In order to increase the electrostatic driving force F ₀ , the voltage _{VA of the} AC signal is increased from the equation (2), or the DC potential difference ΔV _O between the potential of the vibrating body and the potential of the excitation electrode is increased. It is to be.

However, when the voltage _VA of the AC signal that is the drive signal is increased, there is a problem that the AC signal interferes with the output signal (vibration detection signal) of the vibration detection circuit through a stray capacitance or the like.
In order to increase the direct-current potential difference ΔV _O between the potential of the vibrating body and the potential of the excitation electrode, the DC bias voltage V _B applied to the vibrating body may be increased. When the bias voltage V _B is increased, there is a problem that the vibrating body and the detection electrode that detects the vibration of the vibrating body are brought into contact by electrostatic attraction.

  The present invention solves the above-mentioned problems, reduces interference of the drive signal with the vibration detection signal and prevents contact between the vibrating body and the detection electrode due to electrostatic attraction. An object of the present invention is to provide a vacuum gauge capable of measuring pressure with sufficient accuracy.

  In order to achieve the above object, a vacuum gauge according to the present invention includes a vibrating body, an excitation electrode that faces the vibrating body and drives the vibrating body by electrostatic force, a detection electrode that faces the vibrating body, A vibration detection unit that detects a vibration of the vibrating body by detecting a capacitance between the body and the detection electrode, and a drive signal generation unit that generates a drive signal for exciting the vibrating body, In a vacuum gauge equipped with a pressure measurement unit that applies a signal to the excitation electrode to hold the vibrating body in a resonance state and measures the atmospheric pressure from the vibration characteristics of the vibrating body, the position where the vibrating body faces the excitation electrode And the position where the vibrating body is closer to the fixed portion of the vibrating body than the position where the vibrating body faces the detection electrode, and the drive signal generating section uses a signal obtained by adding a DC drive signal bias voltage to the AC signal as the drive signal. And the potential of the vibrating body and the potential of the excitation electrode Of the direct current potential difference, a configuration in which a larger than the DC potential difference between the potential of the detecting electrode of the vibrator (the invention of claim 1).

According to the first aspect of the present invention, a drive signal (V _O = V) obtained by adding a DC drive signal bias voltage (V _OB ) to an AC signal (hereinafter also referred to as “drive signal AC component”) (V _A ). _A + V _OB ) is applied to the excitation electrode. Therefore, by setting the drive signal bias voltage (V _OB ) to a high voltage level, the direct current potential difference (ΔVo = V _B − V _OB ) can be increased to increase the electrostatic driving force (Fo = | V _A * ΔVo |).

For this reason, in the present invention, when the required electrostatic driving force (Fo) is the same, the driving signal AC is increased by an amount corresponding to an increase in the DC potential difference (ΔVo) between the potential of the vibrating body and the potential of the excitation electrode. Since the voltage of the component (V _A ) can be suppressed to a lower voltage level, a detection signal (hereinafter also referred to as “vibration detection signal”) (V _CA ) of the vibration detection unit of the drive signal through the stray capacitance or the like The amount of interference with can be reduced to a lower level.

In the present invention, the DC potential difference (ΔVo = V _B −V _OB ) between the potential of the vibrating body and the potential of the excitation electrode can be increased by setting the drive signal bias voltage (V _OB ) to a high voltage level. Since the vibration body bias voltage (V _B ) can be suppressed to a lower voltage level, it is possible to prevent the vibration body and the detection electrode from coming into contact with each other due to electrostatic attraction.

This reduces interference with the vibration detection signal (V _CA ) of the drive signal and prevents contact between the vibrating body and the detection electrode due to electrostatic attraction, and sufficiently increases the gas pressure (P) to a higher pressure. It becomes possible to measure with high accuracy.

  In a configuration in which the position where the vibrating body faces the excitation electrode is closer to the fixed portion of the vibrating body than the position where the vibrating body faces the detection electrode, the direct current between the potential of the vibrating body and the potential of the detection electrode The potential difference (ΔVr) needs to be smaller than the vibrating body / detection electrode potential difference condition value (| ΔVr | max) that prevents the vibrating body and the detection electrode from contacting each other due to electrostatic attraction. The vibrating body / excitation electrode potential difference condition value (| ΔVo | max) that does not contact the vibrating electrode due to electrostatic attraction is larger than the vibrating body / detection electrode potential difference condition value (| ΔVr | max).

Therefore, in correspondence with the relationship between the potential difference condition values as described above, the direct current potential difference (ΔVo) between the potential of the vibrating body and the potential of the excitation electrode is changed to the vibration body / excitation electrode potential difference condition value (| ΔVo | max), the electrostatic driving force (F _O ) can be further increased by setting the value larger than the DC potential difference (ΔVr) between the potential of the vibrating body and the potential of the vibration detection electrode. When the required electrostatic drive force (F _O ) is the same, the drive signal vibration detection signal (V _CA ) through the stray capacitance etc. while keeping the voltage of the drive signal AC component (V _A ) lower. The amount of interference with can be further reduced.

Further, in the vacuum gauge according to claim 1, the facing area between the vibrating body and the excitation electrode can be made smaller than the facing area between the vibrating body and the detection electrode (Invention of claim 2). ).
The vacuum gauge according to claim 1, further comprising: a drive signal bias voltage generation unit that generates a DC drive signal bias voltage; and a vibrator bias voltage generation unit that generates a DC vibrator bias voltage. The vibrator bias voltage is applied to the vibrator, and the drive signal bias voltage may be a DC voltage having a polarity opposite to that of the vibrator bias voltage (invention of claim 3).

According to the third aspect of the present invention, the drive signal bias voltage (V _OB ) is a DC voltage having a polarity opposite to that of the vibrator bias voltage (V _B ), so that the drive signal bias voltage (V _OB ) is the vibrator bias. as compared with the case that the voltage (V _B) and the polarity of the DC voltage, even the magnitude of the absolute value of the drive signal bias voltage (V _OB) are the same, the potential of the vibrating electrode of the vibrator Since the direct current potential difference (ΔVo = V _B −V _OB ) can be further increased, the electrostatic driving force (Fo = | V _A * ΔVo |) can be further increased. Therefore, when the required electrostatic driving force (Fo) is the same, the voltage of the drive signal AC component (V _A ) can be kept lower, so the vibration of the drive signal through stray capacitance etc. The amount of interference with the detection signal (V _CA ) can be reduced to a lower level.

According to the third aspect of the invention, the drive signal bias voltage (V _OB ) is a DC voltage having a polarity opposite to that of the vibrator bias voltage (V _B ), so that the drive signal bias voltage (V _OB ) is the vibrator bias. Even if the absolute value of the drive signal bias voltage (V _OB ) is smaller than when the DC voltage has the same polarity as the voltage V _B , the DC potential difference (ΔVo = V _B −V _OB ) and the electrostatic driving force Fo can be set to the same magnitude, so that the output voltage specification of the drive signal bias generator can be set to a lower voltage level.

  3. The vacuum gauge according to claim 1, further comprising: a drive signal bias voltage generating unit that generates a DC drive signal bias voltage; and a voltage dividing circuit that divides the drive signal bias voltage. The output voltage may be applied to the vibrating body as a DC vibrating body bias voltage (invention of claim 4).

According to the fourth aspect of the present invention, the voltage obtained by dividing the drive signal bias voltage (V _OB ) from the drive signal bias voltage generator by the voltage dividing circuit is obtained as the vibrator bias voltage (V _B = (1 / a)). * V _OB ) eliminates the need for a separate voltage generator (voltage source) for generating the vibrator bias voltage (V _B ), thereby further simplifying the configuration of the vacuum gauge.

  3. The vacuum gauge according to claim 1, further comprising: a vibrator bias voltage generator that generates a DC vibrator bias voltage; and a booster circuit that boosts the vibrator bias voltage; May be applied to the vibrating body, and the output voltage of the booster circuit may be a DC drive signal bias voltage (invention of claim 5).

According to the fifth aspect of the present invention, the voltage obtained by dividing the vibrator bias voltage (V _B ) from the vibrator bias voltage generator by the booster circuit is set as the drive signal bias voltage (V _OB = b * V _B ). By using this, a separate voltage generation unit (voltage source) for generating the drive signal bias voltage (V _OB ) is not required, and the configuration of the vacuum gauge can be further simplified.

  The vacuum gauge according to claim 1, further comprising: a detection bias voltage generation unit that generates a DC detection bias voltage; and a drive signal bias voltage generation unit that generates a DC drive signal bias voltage, The detection bias voltage is applied to a capacitance-voltage conversion circuit connected to the detection electrode in the vibration detection unit, and the potential of the detection electrode becomes the voltage level of the detection bias voltage, and the potential of the vibration body is set to the ground level. The absolute value of the signal bias voltage may be larger than the absolute value of the detection bias voltage (invention of claim 6).

  Further, in the vacuum gauge according to any one of claims 1 to 6, the AC signal in the drive signal generation unit is generated by changing the phase of the detection signal and amplifying it based on the detection signal of the vibration detection unit. (Invention of claim 7).

  Further, in the vacuum gauge according to claim 7, the drive signal generation unit adjusts an amplification gain for a signal obtained by changing the phase of the detection signal of the vibration detection unit so that the voltage of the AC signal in the drive signal is constant. The pressure measuring unit can measure the pressure based on the magnitude of the detection signal of the vibration detecting unit (invention of claim 8).

  The vacuum gauge according to claim 7, wherein the drive signal generation unit is an amplification gain for a signal obtained by changing the phase of the detection signal of the vibration detection unit so that the magnitude of the detection signal of the vibration detection unit is constant. And the pressure measuring unit can measure the pressure based on the voltage of the AC signal in the drive signal (invention of claim 9).

  The vacuum gauge according to any one of claims 7 to 9, wherein the drive signal generation unit includes an initial excitation signal source that outputs an initial excitation signal having a frequency corresponding to the natural frequency of the vibrating body, When the body is initially driven, an initial drive signal obtained by adding a drive signal bias voltage to the initial excitation signal is applied to the excitation electrode as the drive signal instead of the drive signal based on the detection signal of the vibration detection unit. (Invention of claim 10).

  According to the present invention, since the drive signal obtained by adding the DC drive signal bias voltage to the drive signal AC component is applied to the excitation electrode, the potential of the vibrating body can be increased by setting the drive signal bias voltage to a high voltage level. The electrostatic driving force can be increased by increasing the direct current potential difference between the voltage and the potential of the excitation electrode.

  For this reason, when the required electrostatic driving force is the same, the voltage level of the drive signal AC component is lower by the amount corresponding to the increase in the DC potential difference between the potential of the vibrating body and the potential of the excitation electrode. As a result, the amount of interference of the drive signal with the vibration detection signal through the stray capacitance can be suppressed to a lower level.

  In addition, since the DC potential difference between the vibrator potential and the excitation electrode potential can be increased by setting the drive signal bias voltage to a high voltage level, the vibrator bias voltage is suppressed to a lower voltage level. Thus, the vibrating body and the detection electrode can be prevented from coming into contact with each other by electrostatic attraction.

  As a result, the interference of the drive signal with the vibration detection signal can be reduced and the contact between the vibrating body and the detection electrode due to electrostatic attraction can be prevented, and the gas pressure can be measured with sufficient accuracy up to a higher pressure. become able to.

  In a configuration in which the position where the vibrating body faces the excitation electrode is closer to the fixed portion of the vibrating body than the position where the vibrating body faces the detection electrode, the direct current between the potential of the vibrating body and the potential of the detection electrode The potential difference needs to be smaller than the vibrating body / detection electrode potential difference condition value so that the vibrating body and the detection electrode do not contact with each other due to electrostatic attraction, but the vibration body and the excitation electrode contact with each other due to electrostatic attraction. The vibration body / excitation electrode potential difference condition value is larger than the vibration body / detection electrode potential difference condition value. For this reason, in response to the relationship between the potential difference condition values as described above, the direct current potential difference between the potential of the vibrating body and the potential of the excitation electrode is set within a range that satisfies the vibration body / excitation electrode potential difference condition value. By making the value larger than the DC potential difference between the potential of the vibration detection electrode and the potential of the vibration detection electrode, the electrostatic driving force can be further increased and the required electrostatic driving force is the same. By reducing the voltage of the drive signal AC component to a lower level, it is possible to further reduce the amount of interference of the drive signal through the stray capacitance to the vibration detection signal.

It is a top view of the structure which comprises the mechanism part of the vacuum gauge which concerns on embodiment of this invention. FIG. 2 is a side view of the structure shown in FIG. It is a figure which shows an example of the design value of the vibrating body which concerns on embodiment of this invention. It is a figure which shows the relationship between Q value in the design value of the vibrating body shown in FIG. 3, and the pressure P of gas. It is a figure which illustrates the relationship between the amplitude A of the vibrating body and gas pressure P, and each part voltage condition in embodiment of this invention and a prior art. It is a block diagram which shows the circuit structure of the vacuum gauge which concerns on Example 1 of this invention. It is a block diagram which shows the circuit structure of the vacuum gauge which concerns on Example 2 of this invention. It is a figure which shows the example of the voltage dividing circuit applied to Example 2 of this invention. It is a block diagram which shows the circuit structure of the vacuum gauge which concerns on Example 3 of this invention. It is a figure which shows the example of the booster circuit applied to Example 3 of this invention. It is a block diagram which shows the circuit structure of the vacuum gauge which concerns on Example 4 of this invention.

Hereinafter, embodiments of the present invention will be described based on examples shown in FIGS. About the same component, the same code | symbol is attached | subjected and the overlapping description is abbreviate | omitted. In addition, this invention is not limited to the following embodiment, In the range which does not change the summary, it can implement suitably.
Embodiment of the present invention
(B) Structure of the structure that forms the mechanism of the vacuum gauge:
First, as a technical matter common to each example described later, a structure constituting a mechanism part of a vacuum gauge according to an embodiment of the present invention will be described. FIG. 1 is a plan view schematically showing a structure constituting a mechanical part of a vacuum gauge according to an embodiment of the present invention, and FIG. 2 is a side view of the structure shown in FIG. In FIG. 1 and FIG. 2, the structure constituting the mechanism part of the vacuum gauge includes a vibrating body 4 including a weight 1, a beam 2 and a vibrating body fixing portion 3, and an excitation electrode 5 for exciting the vibrating body 4. And a vibration detection electrode 6 for detecting the vibration of the vibrating body. The vibrating electrode 5 is disposed to face the vibrating body 4, and the vibrating body 4 is driven by an electrostatic force by applying a drive signal to the vibrating electrode 5. The vibration detection electrode 6 is also arranged to face the vibration body 4, and the vibration of the vibration body 4 is detected by detecting the electrostatic capacitance between the vibration body 4 and the detection electrode 6. 1 and 2, the position where the vibrating body 4 faces the excitation electrode 5 is closer to the vibrating body fixing portion 3 than the position where the vibrating body 4 faces the vibration detection electrode 6. Further, the facing area So between the vibrating body 4 and the excitation electrode 5 is made smaller than the facing area Sr between the vibrating body 4 and the vibration detection electrode 6. Yes.
(C) Relationship between the shape of the vibrating body, the Q value of the vibrating body, the amplitude of the vibrating body, and the gas pressure:
Next, as technical matters common to the embodiments described later, the relationship between the shape of the vibrating body 4, the Q value of the vibrating body 4, the amplitude of the vibrating body 4, and the gas pressure P will be described. The vibrating body 4 receives a resistance force due to collision of gas molecules. In the molecular flow region, the resistance force by the gas molecules is directly proportional to the gas pressure P. As the pressure P of the gas decreases, the resistance force that the vibrating body 4 receives from the gas molecules decreases, so the Q value (resonance sharpness) of the vibrating body increases. However, the vibrating body 4 has a specific Q value Q _E and never exceeds the specific Q value Q _E. That is, the lower limit of the pressure P of the gas that can vibrator 4 is measured, meant to be limited by the specific Q value Q _E.

In relation to the gas pressure P, the Q value of the vibrating body 4 is f _R is the natural frequency of the vibrating body 4, m is the mass of the weight 1, S is the area that receives the gas resistance, R is the gas constant, T Is the temperature, and M is the mass per mol of gas molecule, it can be expressed as the following equation (3).

FIG. 3 is a diagram showing an example of the design value of the vibrating body according to the embodiment of the present invention. FIG. 4 shows the relationship between the Q value and the gas pressure P in the design value of the vibrating body shown in FIG. FIG.
3, the structure of the structure shown in FIGS. 1 and 2 is shown as a perspective view, and the vibration direction of the vibration body 4 (the same direction as the vibration direction shown by the arrow in FIG. 2) is shown by an arrow. .

  FIG. 4A shows the Q value-pressure characteristic when the vibrating body 4 shown in FIG. 3 is vibrated in the vibration direction indicated by the arrow (that is, the vibration direction perpendicular to the wide surface of the weight 1 of 1000 μm × 1000 μm). Is shown. Here, the excitation electrode 5 and the vibration detection electrode 6 shown in FIGS. 1 and 2 correspond to the pressure measurement in the vibration direction.

  As shown in FIG. 4A as Q value-pressure characteristics, the gas pressure that can be measured when the vibrating body 4 is vibrated in the vibration direction is about 0.1 Pa to about 100 Pa. Further, the natural frequency in the vibration direction of the vibrating body 4 shown in FIG. 3 is about 560 Hz when the material of the vibrating body is silicon, for example.

  For example, the relationship (Q value-pressure characteristics) between the Q value and the gas pressure P as shown in FIG. 4A is the thickness and the length of the beam as shown in FIG. It changes depending on the design value such as the area and the material of the vibrating body, and the pressure range of the gas that can be measured according to these specifications can be arbitrarily designed.

  FIG. 4B schematically illustrates only the portion in the pressure range from 0.1 Pa to 100 Pa in the Q value-pressure characteristics in the vibration direction (vibration direction indicated by the arrow in FIG. 2) in FIG. Are shown as linear characteristics.

FIG. 5 exemplifies the relationship between the amplitude A of the vibrating body and the pressure P of the gas (amplitude-pressure characteristics) and the voltage conditions of each part in the embodiment of the present invention and the prior art, and FIG. The amplitude-pressure characteristics corresponding to the Q value-pressure characteristics in the vibration direction (vibration direction indicated by the arrow in FIG. 2) shown in FIG. 4B are shown for each voltage condition shown in FIG. ing. Details of the voltage conditions described in FIG. 5B will be described later. In addition, the description of each scale value of “1E-10” to “1E-07” in the vertical axis “amplitude (m)” in FIG. 5A is “1 × 10 ⁻¹⁰ ” to “1 × 10”, respectively. ^-7 ".
(D) Potential difference condition where the vibrating body and the excitation electrode or vibration detection electrode are in contact:
Next, as a technical matter common to each embodiment described later, a potential difference condition in which the vibrating body 4 and the excitation electrode 5 or the vibration detection electrode 6 are in contact will be described. When the material of the vibrator 4 shown in FIG. 3 is, for example, silicon, the spring constant k in the vibration direction of the vibrator 4 (vibration direction perpendicular to the wide surface of the weight 1 shown in FIG. 2) is about 0.3 N / m. Then, typically, the voltage E _P of the vibrating body 4 and the vibrating electrode 5 or vibration detection electrodes 6 are in contact can be expressed by the following equation (4).

Here, d ₀ is a distance between the vibrating body 4 and the excitation electrode 5 or the vibration detection electrode 6, ε is a dielectric constant, and S is an area of the electrode.
In the vibrating body 4 having the design value illustrated in FIG. 3, the potential difference E _P at which the vibrating body 4 and the vibration detection electrode 6 are in contact is about 3.1V. On the other hand, vibration electrode 5 has a smaller area S as compared to the vibration detection electrode 6, also, because it is located near the vibrator fixing portion 3, by applying a 20 times the DC voltage E _P Is possible.
(E) Examples 1-4:
In the first to fourth embodiments described below, the interference of the drive signal to the vibration detection signal is reduced and the contact between the vibration body and the vibration detection electrode due to electrostatic attraction is prevented. An example of the configuration of a vacuum gauge suitable for enabling the pressure to be measured with sufficient accuracy is shown, and all are particularly characterized by the circuit configuration of the vacuum gauge and the voltage conditions of each part.

(A) Example 1 of the present invention is used, the number a drive signal bias voltage source 11 for generating a drive signal bias voltage V _OB DC, and a vibrator bias voltage source 13 for generating a vibrating body bias voltage V _B of the DC and, vibrator bias voltage V _B, together is applied to the vibrating body 4, drive signal bias voltage V _OB is obtained by the such that the vibrating body bias voltage V _B and opposite polarity of the DC voltage.

(B) Structure of the structure constituting the mechanical part of the vacuum gauge:
First, as the structure constituting the mechanical part of the vacuum gauge according to the first embodiment, the configuration described with reference to FIGS.

(C) Vacuum gauge circuit configuration:
Next, the circuit configuration of the vacuum gauge according to the first embodiment will be described. FIG. 6 is a block diagram showing the circuit configuration of the vacuum gauge according to the first embodiment of the present invention, and the same reference numerals as those in FIGS. As shown in FIG. 6, the circuit of the vacuum gauge according to the first embodiment includes a capacitance-voltage conversion circuit 21 that converts a change in capacitance between the vibrating body 4 and the vibration detection electrode 6 into a change in voltage, a capacitance A pressure conversion circuit 31 that converts the vibration detection signal V _CA from the voltage conversion circuit 21 into a pressure measurement signal V _P that is a voltage signal corresponding to the gas pressure P, and a phase shift circuit that shifts the phase of the vibration detection signal V _CA 9, the initial pressure mutabilis signal to generate an initial excitation signal V _AI for initial excitation voltage control circuit 10 for controlling the voltage of the output signal V _CAP of the phase shift circuit 9, a vibrating member 4 by adjusting the gain of the amplifier source 15, the switch circuit 16 to select the AC signal V _a to be applied to the excitation electrodes 5, the vibrating body bias voltage source 13 for generating a vibrating body bias voltage V _B of the DC, to generate a drive signal bias voltage V _OB DC Drive signal bias voltage source 11, switch circuit 1 6 is composed of a signal synthesis circuit 12 for adding the drive signal bias voltage _VOB to the AC signal _VA selected by 6.

Then, in Example 1, a drive signal bias voltage source 11 is configured to generate a DC voltage of opposite sign as the drive signal bias voltage V _OB is a vibrator bias voltage V _B.
The capacitance-voltage conversion circuit 21 is connected to the vibration detection electrode 6 as a vibration detection circuit in the vibration detection unit of the vacuum gauge, and electrostatic capacitance between the vibration body 4 and the vibration detection electrode 6 due to the vibration of the vibration body 4 is detected. A change in capacitance is converted into a change in voltage and output as a vibration detection signal _VCA . FIG. 6 shows a circuit configuration example as a charge amplifier. In FIG. 6, the capacitance / voltage conversion circuit 21 includes a differential amplifier 22, a resistor 23, and a capacitor 24. In the capacitor voltage conversion circuit 21, a parallel circuit of the resistor 23 and the capacitor 24 is connected between the inverting input terminal and the output terminal of the differential amplifier 22, and the non-inverting input terminal of the differential amplifier 22 is grounded. to the potential, the sense bias voltage V _R at the capacitance-voltage conversion circuit 21 is a 0V, thereby, the voltage V _D of the vibration detection electrodes 6 also has the same 0V as sense bias voltage V _R. Note that the capacitance-voltage conversion circuit in the present invention is not limited to the configuration shown in FIG.

(D) Excitation operation of the vibrator:
Next, the vibration operation of the vibrating body 4 by the drive signal from the drive signal generation unit in the first embodiment will be described. In FIG. 6, when the vibrating body 4 is initially excited, the switch circuit 16 is connected to A and B, and the initial excitation signal V _AI is selected as the AC signal V _A applied to the excitation electrode 5. It has become. In this initial vibration state, the frequency of the sine wave voltage signal corresponding to the natural frequency f _R of the vibrating member 4 from the voltage source 15 for initial excitation, or, from the pulse voltage signal repetition frequency corresponding to the natural frequency f _R initial excitation signal V _AI is outputted becomes the drive signal by a signal combining circuit 12 an initial excitation signal V _AI to the drive signal bias voltage V _OB is formed by adding _{V O (= V AI + V} OB) is vibration electrode 5 The vibrating body 4 is vibrated by being applied to. The initial excitation signal source 15 is used only for initial excitation. After the vibrating body 4 starts to vibrate, the switch circuit 16 is switched and A and C are connected.

In the state where A and C are connected by the switch circuit 16 and the AC signal _VAP from the voltage control circuit 10 is selected as the AC signal _VA to be applied to the excitation electrode 5, the capacitance voltage conversion in the vibration detection unit is performed. Based on the vibration detection signal V _CA from the circuit 21, the phase of the vibration detection signal V _CA is shifted by the phase shift circuit 9, and the voltage of the output signal V _CAP of the phase shift circuit 9 is amplified by the gain of the voltage control circuit 10. An AC signal V _AP is generated by controlling by adjustment, and a drive signal V _O (= V _AP + V _OB ) obtained by adding a DC drive signal bias voltage V _OB to the AC signal V _AP is added by the signal synthesis circuit 12. By applying the vibration electrode 5, the resonance state of the vibrating body 4 is maintained.

Note that, as described above, the switch circuit 16 operates so as to switch the connection according to the amplitude of the vibrating body 4, for example, according to the amplitude A of the vibrating body 4, that is, according to the displacement of the vibrating body 4. detected by the switch circuit control unit the size of the vibration detection signal V _CA is not shown that it has reached the preset value from the capacitance-voltage conversion circuit 21 to be outputted from the switching circuit control section at the detection timing By applying a switching signal from the B side to the C side to the switch circuit 16, a connection switching operation according to the amplitude of the vibrating body 4 can be performed.

(E) Pressure measurement operation:
Then, the pressure measurement by the first embodiment, the driving signal _{V 0 (= V AP + V} OB) AC signal at (drive signal AC component) V magnitude of _AP is constant is applied to, for example, excitation electrode 5 As described above, in the state where the control for adjusting the gain of amplification in the voltage control circuit 10 with respect to the signal V _{CAP obtained} by shifting the phase of the vibration detection signal V _CA from the capacitance voltage conversion circuit 21 by the phase shift circuit 9 is performed. The amplitude A of the vibrating body 4 that changes corresponding to the Q value of 4, that is, the magnitude of the vibration detection signal V _CA from the capacitance-voltage conversion circuit 21 is converted into a pressure measurement signal V corresponding to the pressure P value by the pressure conversion circuit 31. it can be a method of measuring the pressure P (hereinafter referred to as "driving voltage fixing method") by converting the _P.

As a method of converting the vibration body amplitude A (the magnitude of the vibration detection signal V _CA ) into the pressure P value (pressure measurement signal V _P ) in the above-described constant drive voltage method, the vibration body amplitude A (vibration detection) The magnitude of the signal V _CA may be converted into a Q value, and this Q value may be further converted into a pressure P value (pressure measurement signal V _P ), and the amplitude A of the vibrating body (vibration detection signal) The magnitude of V _CA may be directly converted into a pressure P value (pressure measurement signal V _P ) without using a Q value.

Here, as described in the section (c) above, for example, when the vibrating body 4 is the design value shown in FIG. 3 and the material is a vibrating body made of silicon, the vibration direction shown in FIG. In the vibration direction perpendicular to the wide surface), the relationship between the Q value and the pressure P value (Q value-pressure characteristics) is a high pressure region (about 0.1 Pa or more) as shown in FIG. Then, the amplitude is approximately inversely proportional to the pressure, and on the low pressure side, the amplitude is saturated toward its maximum limit value. Corresponding to such Q value-pressure characteristics, the relationship between the amplitude A (the magnitude of the vibration detection signal _VCA ) and the pressure P value (amplitude A-pressure characteristics) in the above-described constant drive voltage method. ) However, in the high pressure region (about 0.1 Pa or more), the amplitude A is almost inversely proportional to the pressure, and the amplitude A saturates toward its maximum limit as the pressure level decreases on the low pressure side. It becomes a characteristic that becomes a saturated region.

For this reason, in the case of the above-described constant drive voltage method, particularly when the pressure measurement range includes the low-pressure side saturation region as described above, the pressure conversion circuit 31 may, for example, detect the amplitude A (vibration detection signal V _{CA of the} vibrating body). The characteristic data of the relationship between the pressure and the pressure P value (amplitude A-pressure characteristic) is obtained, and the vibrating body at the time of actual measurement is obtained by the conversion means having a storage unit storing the data table of this characteristic data. It is preferable to convert the amplitude A (the magnitude of the vibration detection signal _VCA ) into a pressure P value, and a storage unit storing a relational expression approximately obtained from the curve of the characteristic data is provided. The conversion means may convert the amplitude A (the magnitude of the vibration detection signal _VCA ) of the vibrating body during actual measurement into a pressure P value.

(F) Relationship between the voltage conditions of each part and the amplitude of the vibrating body:
Next, the relationship between the voltage condition (voltage condition 3) of each part of the vibrator bias voltage V _B , the drive signal bias voltage V _OB and the AC signal V _A in Example 1 and the amplitude A of the vibrator 4 is shown in FIG. This will be described in comparison with (Voltage conditions 1 and 2).

In FIG. 5B, voltage condition 3 (first embodiment) and voltage condition 1 (prior art) set the drive signal bias voltage V _OB to +18 V (first embodiment) and 0 V (prior art), respectively. In this case, the voltage of the AC signal _VA is set to 0.1V. Since the voltage of the AC signal V _A is equal in the voltage condition 3 (Example 1) and the voltage condition 1 (Prior art), the AC signal V in the voltage condition 3 (Example 1) and the voltage condition 1 (Prior art). _The amount of interference of _{A with} the vibration detection signal V _CA is the same. On the other hand, the direct current potential difference ΔVo between the potential of the vibrating body 4 and the potential of the drive electrode 5 is ΔVo = 20V in the voltage condition 3 and ΔVo = 2V in the voltage condition 1, so that the voltage in the voltage condition 3 (Example 1). Compared with condition 1 (prior art), an amplitude A that is 10 times greater can be obtained. Thereby, in the voltage condition 3 (Example 1), the magnitude of the vibration detection signal V _CA is 10 times that of the voltage condition 1 (prior art). Therefore, assuming that the interference of the AC signal V _{A to} the vibration detection signal V _CA is the main cause of noise in the vacuum gauge, the voltage condition 3 (Example 1) is S compared with the voltage condition 1 (prior art). The / N ratio is 10 times, and noise can be greatly reduced.

Voltage condition 2 (prior art), and 0V to the drive signal bias voltage V _OB as with the voltage condition 1 (prior art), a voltage a voltage condition of the AC signal V _A 1 was 10 times 1V of (prior art) Is the case. Since the product of the DC potential difference ΔVo between the potential of the vibrating body 4 and the potential of the drive electrode 5 and the voltage of the AC signal _VA is the same in the voltage condition 3 (Example 1) and the voltage condition 2 (prior art), the voltage The amplitude A of the vibrating body 4 is equal between the condition 3 (Example 1) and the voltage condition 2 (prior art). On the other hand, in the voltage condition 2 (prior art), since the voltage of the AC signal V _A is 10 times that in the voltage condition 3 (Example 1), the amount of crosstalk of the AC signal V _{A to} the vibration detection signal V _CA is increased. Will also be 10 times. Therefore, assuming that the interference of the AC signal V _{A to} the vibration detection signal V _CA is the main cause of noise in the vacuum gauge, the voltage condition 3 (Example 1) is S as compared with the voltage condition 2 (prior art). The / N ratio is 10 times, and noise can be greatly reduced.

In addition, since the vibration body bias voltage V _B is V _B = −2 V in both the voltage condition 3 (Example 1) and the voltage conditions 1 to 2 (prior art), the potential of the vibration body 4 and the vibration detection electrode The DC potential difference ΔVr with respect to the potential 6 is ΔVr = 2V in both the voltage condition 3 (Example 1) and the voltage conditions 1 to 2 (prior art). In the above point, according to the present invention, the drive signal bias voltage V _{OB is set} to a high voltage level, whereby the DC potential difference ΔVo (= V _B −V _OB ) between the potential of the vibrating body 4 and the potential of the excitation electrode 5. Therefore, the vibrator bias voltage V _B can be suppressed to the same low voltage level as in the prior art, whereby the DC potential difference between the potential of the vibrator 4 and the potential of the vibration detection electrode 6 can be reduced. ΔVr can also be suppressed to the same size as in the prior art.

(G) As described above, in the first embodiment, since the drive signal V _O obtained by adding the drive signal bias voltage V _OB to the AC signal V _A is applied to the excitation electrode 5, for example, the voltage condition 1 in FIG. In the same manner as in the prior art, the AC signal _VA is suppressed to a low voltage level (for example, 0.1 V) and the vibrator bias voltage V _B is also suppressed to a low voltage level (for example, −2 V). _By setting _OB to a high voltage level (for example, +18 V), the direct current potential difference ΔVo between the potential of the vibrating body 4 and the potential of the excitation electrode 5 can be increased to increase the electrostatic driving force Fo. Therefore, in the first embodiment, since the drive signal AC component V _A can be suppressed to a low voltage level, the amount of interference of the drive signal with the vibration detection signal through the stray capacitance can be suppressed to a low level, and the vibrator bias voltage V _B In addition, since the voltage can be suppressed to a low voltage level, the vibrating body 4 and the vibration detecting electrode 6 can be prevented from contacting each other due to electrostatic attraction.

Also, like in Example 1, by which especially in a drive signal bias voltage V _OB and vibrator bias voltage V _B and the opposite polarity, for example, a voltage condition 4-5 in FIG. 5 (Examples 2-3 below) a drive signal bias voltage V _OB in comparison with the case that the vibrating body bias voltage V _B of the same polarity, even if the absolute value is smaller drive signal bias voltage V _OB, the potential of the potential and the vibrating electrode 5 of the vibrator 4 The direct current potential difference ΔVo and the electrostatic driving force Fo can be made the same. Therefore, in the first embodiment, the output voltage specification of the drive signal bias voltage source 11 can be set to a lower voltage level.

In the first embodiment, in particular, the drive signal bias voltage V _OB has a polarity opposite to that of the vibrator bias voltage V _B , so that the absolute value of the drive signal bias voltage V _OB is set to the voltage conditions 4 to 5 in FIG. When it is the same as (Examples 2 to 3 described later), the DC potential difference ΔVo between the potential of the vibrating body 4 and the potential of the excitation electrode 5 can be further increased. Therefore, in the first embodiment, even if the electrostatic drive force Fo is the same, the voltage of the drive signal AC component _VA can be kept lower. Therefore, the vibration detection signal of the drive signal through the floating capacitance or the like. The amount of interference with can be further reduced.

(H) In addition, as a circuit configuration of the vacuum gauge according to the first embodiment, in FIG. 6 described above, although the configuration in which the detection bias voltage V _R at the capacitance-voltage conversion circuit 21 has a 0V, the present invention is thus is not limited to Do configuration, a detection bias voltage source 25 as in FIG. 11 to be described later, the detection bias voltage V _R from the sense bias voltage source 25 is applied to the non-inverting input terminal of the differential amplifier 22 , the voltage V _D of the vibration detection electrode 6 also may be configured to the same voltage level as the detection bias voltage V _R, the DC potential difference ΔVr between the potential of the vibrator 4 and the potential of the vibration detection electrodes 6 (= V _B - If V _R ) is set to be smaller than the vibration body / detection electrode potential difference condition value | ΔVr | max (= E _P ) such that the vibration body 4 and the vibration detection electrode 6 do not contact with each other due to electrostatic attraction. Good. This also applies to Examples 2-3 described later.

(A) The second embodiment of the present invention differs from the first embodiment described above in that a drive signal bias voltage source 11 that generates a DC drive signal bias voltage V _OB and a voltage divider that divides the drive signal bias voltage V _OB. The voltage output from the voltage dividing circuit 17 is applied to the vibrating body 4 as a DC vibrating body bias voltage V _B (= (1 / a) * V _OB ).

(B) Structure of the structure constituting the mechanical part of the vacuum gauge:
First, as the structure constituting the mechanical part of the vacuum gauge according to the second embodiment, the configuration described with reference to FIGS.

(C) Vacuum gauge circuit configuration:
Next, a circuit configuration of the vacuum gauge according to the second embodiment of the present invention will be described. FIG. 7 is a block diagram showing a circuit configuration of a vacuum gauge according to the second embodiment of the present invention, and the same reference numerals as those in FIG. 6 denote the parts having the same names as those in FIG. A voltage dividing circuit 17 divides the drive signal bias voltage V _OB from the drive signal bias voltage source 11 and then outputs the output voltage as a vibrator bias voltage V _B (= (1 / a) * V _OB ). Apply to vibrating body 4.

As the voltage dividing circuit 17 in the second embodiment, for example, a voltage dividing circuit composed of a series connection circuit of resistors can be applied. However, the voltage dividing circuit 17 is not limited to such a configuration. Any configuration that can _divide the voltage level of the drive signal bias voltage V _OB may be used. An example of a voltage dividing circuit composed of a series connection circuit of two resistors R1 and R2 is shown in FIG. In the circuit of FIG. 8, the output voltage is divided with respect to the input voltage _{V in V out = (R2 /} (R1 + R2)) × V in is obtained.

(D) Excitation operation of the vibrator:
The vibrating operation of the vibrator in the second embodiment is performed in the same manner as in the first embodiment.
(E) Pressure measurement operation:
The pressure measurement operation in the second embodiment is performed in the same manner as in the first embodiment.

(F) Relationship between the voltage conditions of each part and the amplitude of the vibrating body:
Next, the relationship between the voltage conditions (voltage condition 4) of the vibrator bias voltage V _B , the drive signal bias voltage V _OB and the AC signal V _A in Example 2 and the amplitude A of the vibrator 4 will be described with reference to FIG. .

In the voltage condition 4 of the second embodiment, the voltage of the AC signal V _A is set to 0.1 V as in the voltage condition 1 (conventional technology), the drive signal bias voltage V _OB is set to −22 V, and further divided. This is a case where the vibrator bias voltage V _B output from the voltage dividing circuit 17 is set to −2 V by setting the voltage dividing ratio of the circuit 17 to 1/11. Since the voltage of the AC signal V _A is equal in the voltage condition 4 (Example 2) and the voltage condition 1 (Prior art), the AC signal V in the voltage condition 4 (Example 2) and the voltage condition 1 (Prior art). _The amount of interference of _{A with} the vibration detection signal V _CA is the same. On the other hand, the direct-current potential difference ΔVo between the potential of the vibrating body 4 and the potential of the drive electrode 5 is ΔVo = 20V in the voltage condition 4 and ΔVo = 2V in the voltage condition 1, so that the voltage in the voltage condition 4 (Example 2). Similar to Condition 3 (Example 1), it is possible to obtain an amplitude A 10 times that of Voltage Condition 1 (Prior Art). Thereby, in the voltage condition 4 (Example 2), the magnitude of the vibration detection signal _VCA is 10 times that of the voltage condition 1 (conventional technology). Therefore, assuming that the interference of the AC signal V _{A to} the vibration detection signal V _CA is the main cause of noise in the vacuum gauge, the voltage condition 4 (Example 2) is S compared with the voltage condition 1 (prior art). The / N ratio is 10 times, and noise can be greatly reduced.

(G) In the first embodiment, two voltage sources of the vibrator bias voltage source 13 and the drive signal bias voltage source 11 are necessary. In the second embodiment, the drive signal bias for generating the drive signal bias voltage _{VOB is} used. to generate the vibration body bias voltage V _B by dividing the output voltage of the voltage source 11 in the voltage divider circuit 17, it is possible to configure the circuit with a single voltage source.

(A) Example 3 of the present invention differs from the first embodiment described above, the vibrating body bias voltage generator 13 for generating a vibrating body bias voltage V _B of the direct current, step-up for boosting the oscillating body bias voltage V _B And the oscillator bias voltage V _B is applied to the oscillator 4, and the output voltage of the booster circuit 18 is set to a DC drive signal bias voltage V _OB (= b * V _B ). It is a thing.

(B) Structure of the structure constituting the mechanical part of the vacuum gauge:
First, as the structure constituting the mechanical part of the vacuum gauge according to the third embodiment of the present invention, the structure described with reference to FIGS. it can.

(C) Vacuum gauge circuit configuration:
Next, a circuit configuration of the vacuum gauge according to the third embodiment of the present invention will be described. FIG. 9 is a circuit block diagram according to the third embodiment of the present invention, in which the same reference numerals as those in FIG. 6 denote parts having the same names as those in FIG. A booster circuit 18 boosts the vibrator bias voltage V _B from the vibrator bias voltage source 13 and then supplies the output voltage to the signal synthesizer 12 as the vibrator bias voltage V _OB (= b * V _B ). To do.

As the booster circuit 18 in the third embodiment, for example, an amplifier circuit such as a non-inverting amplifier circuit using an operational amplifier, a boost chopper circuit, or the like can be applied. However, the present invention is not limited to such a configuration. the voltage level of the vibrator bias voltage V _B from the bias voltage source 13 may be any configuration capable of boosting. An example of a step-up chopper circuit including a transistor Tr, a diode D, a coil L, a capacitor C, and a resistor R is shown in FIG. In the circuit of FIG. 10, when the transistor Tr on-time and off-time, respectively, and T _ON and T _OFF, the output voltage input voltage V _in is boosted _{V out = ((T ON +} T OFF) / T OFF) × V _in is obtained.

(D) Excitation operation of the vibrator:
The vibration operation of the vibrator in the third embodiment is performed in the same manner as in the first embodiment.
(E) Pressure measurement operation:
The pressure measurement operation in the third embodiment is performed in the same manner as in the first embodiment.

(F) Relationship between the voltage conditions of each part and the amplitude of the vibrating body:
Next, the relationship between the voltage condition (voltage condition 5) of the vibrator bias voltage V _B , the drive signal bias voltage V _OB and the AC signal V _A in Example 3 and the amplitude A of the vibrator 4 will be described with reference to FIG.

In the voltage condition 5 of the third embodiment, the voltage of the AC signal V _A is set to 0.1 V as in the voltage condition 1 (conventional technology), the vibrator bias voltage V _B is set to −2 V, and the booster circuit This is a case where the drive signal bias voltage V _OB output from the booster circuit 18 is set to −22V by setting the boost ratio of 18 to 11 times. Since the voltage of the AC signal V _A is equal in the voltage condition 5 (Example 3) and the voltage condition 1 (Prior art), the AC signal V in the voltage condition 5 (Example 3) and the voltage condition 1 (Prior art). _The amount of interference of _{A with} the vibration detection signal V _CA is the same. On the other hand, the direct-current potential difference ΔVo between the potential of the vibrating body 4 and the potential of the drive electrode 5 is ΔVo = 20V in the voltage condition 5 and ΔVo = 2V in the voltage condition 1, and therefore the voltage in the voltage condition 5 (Example 3). Similar to Condition 3 (Example 1), it is possible to obtain an amplitude A 10 times that of Voltage Condition 1 (Prior Art). As a result, in the voltage condition 5 (Example 3), the magnitude of the vibration detection signal V _CA is ten times that in the voltage condition 1 (prior art). Therefore, assuming that the interference of the AC signal V _{A to} the vibration detection signal V _CA is the main cause of noise in the vacuum gauge, the voltage condition 5 (Example 3) is S as compared with the voltage condition 1 (prior art). The / N ratio is 10 times, and noise can be greatly reduced.

(G) In the first embodiment, two voltage sources of the vibrator bias voltage source 13 and the drive signal bias voltage source 11 are necessary. In the third embodiment, the vibrator bias voltage for generating the vibrator bias voltage V _{B is} used. Since the drive signal bias voltage _VOB is also generated by boosting the output of the source 13 with a booster circuit, the circuit can be configured with one voltage source.

(A) Example 4 of the present invention differs from the first embodiment described above, the sense bias voltage source 25 that generates a detection bias voltage V _R of the DC drive signal for generating a drive signal bias voltage V _OB DC and a bias voltage source 11, detector bias voltage V _R is applied to the capacitance-voltage conversion circuit 21A is connected to the vibration detecting electrode 6 in the vibration detection unit, the detection potential V _D of the vibration detection electrode 6 bias voltage V together becomes the voltage level of the _R, the potential V _B of the vibrating member 4 is set at the ground level, which the absolute value of the drive signal bias voltage V _OB, was made to be larger than the absolute value of the sense bias voltage V _R It is.

(B) Structure of the structure constituting the mechanical part of the vacuum gauge:
First, as the structure constituting the mechanical part of the vacuum gauge according to the fourth embodiment of the present invention, the configuration described with reference to FIGS. it can.

(C) Vacuum gauge circuit configuration:
Next, a circuit configuration of the vacuum gauge according to the third embodiment of the present invention will be described. FIG. 11 is a circuit block diagram according to the fourth embodiment of the present invention. The same reference numerals as those in FIG. 6 denote the same names as those in FIG.

  The circuit configuration of the vacuum gauge according to the fourth embodiment includes a detection bias voltage source 25 instead of the vibrator bias voltage source 13 and a capacitance pressure conversion circuit 21A instead of the capacitance pressure conversion circuit 21. This is different from the first embodiment.

Sense bias voltage source 25, and generates a sense bias voltage V _R of the DC.
In addition, the capacitance-voltage conversion circuit 21A is a vibration detection circuit in the vibration detection unit of the vacuum gauge, and converts a change in electrostatic capacitance between the vibrating body 4 and the vibration detection electrode 6 into a change in voltage. be one that outputs a _CA, but its circuit configuration is the same as the capacitance voltage conversion circuit 21 of example 1, differs in that sense bias voltage V _R to the non-inverting input terminal of the differential amplifier 22 is applied and, by this, the voltage V _D of the vibration detection electrodes 6 also has the same voltage level as the detection bias voltage V _R.

In the fourth embodiment, unlike the first embodiment, the potential V _B of the vibrating body 4 is set to the ground level. Therefore, in the fourth embodiment, the DC voltage difference? Vr between the potential vibration detection electrode 6 and the potential of the vibrator 4 has a? Vr = -V _R. Then, the absolute value (| V _R |) of the direct current potential difference ΔVr is such that the vibration body / detection electrode potential difference condition value | ΔVr | max (= E) is such that the vibration body 4 and the vibration detection electrode 6 do not contact with each other due to electrostatic attraction. _It suffices if it is set to be smaller than _P ).

In the fourth embodiment, the drive signal bias voltage V _OB corresponds to the relationship between the vibrating body / vibrating electrode potential difference condition value and the vibrating body / detection electrode potential difference condition value described in (F) below. of set larger than the absolute value of the absolute value detection bias voltage V _R, thereby, the DC potential difference ΔVo between the potential of the vibrating electrode 5 of the vibrator 4 is vibrating body 4 potential as vibration detection electrodes 6 The DC potential difference ΔVr from the potential is made larger.

The circuit configuration of the vacuum gauge according to the fourth embodiment is the same as that of the first embodiment except for the points described above.
(D) Excitation operation of the vibrator:
The vibrating operation of the vibrating body in the fourth embodiment is performed in the same manner as in the first embodiment.

(E) Pressure measurement operation:
The pressure measurement operation in the fourth embodiment is performed in the same manner as in the first embodiment.
(F) Relationship between the voltage conditions of each part and the amplitude of the vibrating body:
Next, the relationship between the voltage conditions (voltage condition 6) of the drive signal bias voltage V _OB , the detection bias voltage V _R, and the AC signal V _A in Example 4 and the amplitude A of the vibrating body 4 will be described.

In the voltage condition 6 of the fourth embodiment, the voltage of the AC signal _VA is set to 0.1 V as in the voltage condition 1 (conventional technology), the drive signal bias voltage V _OB is set to −20 V, and the vibrator bias voltage is set. V _B is set to 0V, and the further sense bias voltage V _R is when set to 2V. Since the voltage of the AC signal V _A is equal in the voltage condition 6 (Example 4) and the voltage condition 1 (Prior art), the AC signal V in the voltage condition 6 (Example 4) and the voltage condition 1 (Prior art). _The amount of interference of _{A with} the vibration detection signal V _CA is the same. On the other hand, the direct-current potential difference ΔVo between the potential of the vibrating body 4 and the potential of the drive electrode 5 is ΔVo = 20V in the voltage condition 6 and ΔVo = 2V in the voltage condition 1, so that the voltage in the voltage condition 6 (Example 4). Similar to Condition 3 (Example 1), it is possible to obtain an amplitude A 10 times that of Voltage Condition 1 (Prior Art). As a result, in the voltage condition 6 (Example 4), the magnitude of the vibration detection signal V _CA is 10 times that in the voltage condition 1 (conventional technology). Accordingly, assuming that the interference of the AC signal V _{A to} the vibration detection signal V _CA is the main cause of noise in the vacuum gauge, the voltage condition 6 (Example 4) is S compared with the voltage condition 1 (prior art). The / N ratio is 10 times, and noise can be greatly reduced.
(F) Relationship between the DC potential difference between the vibrating body and the excitation electrode and the DC potential difference between the vibration body and the detection electrode:
The structure constituting the mechanical part of the vacuum gauge according to the present invention includes a position where the vibrating body 4 faces the excitation electrode 5 and a position where the vibrating body 4 faces the vibration detection electrode 6 as shown in FIGS. Further, the opposed area So between the vibrating body 4 and the excitation electrode 5 is more than the opposed area Sr between the vibrating body 4 and the vibration detection electrode 6. The structure is reduced. In the present invention, as a configuration suitable for such a structure, a DC potential difference ΔVo (= V _B −V) between the potential of the vibrating body 4 (DC potential V _B ) and the potential of the excitation electrode 5 (DC potential V _OB ). _OB ) is made larger than the DC potential difference ΔVr (= V _B −V _R ) between the potential of the vibrating body 4 (DC potential V _B ) and the potential of the vibration detection electrode 6 (DC potential V _R ).

That is, in the structure as shown in FIGS. 1 and 2, as described in the above section (d), the direct-current potential difference ΔVr between the potential of the vibration body 4 and the potential of the vibration detection electrode 6 is the vibration body 4. Vibration / detection electrode potential difference condition value | ΔVr | max (= E _P ) (about 3.1 V in the case of the vibration body 4 with the design value illustrated in FIG. 3). It is necessary to make it smaller. On the other hand, the vibrating body / vibrating electrode potential difference condition value | ΔVo | max that the vibrating body 4 and the vibrating electrode 5 do not come into contact with each other due to electrostatic attraction is larger than the above-described vibrating body / detection electrode potential difference condition value | ΔVr | max. large (20 times of the vibrating member 4 in the E _P design values illustrated in FIG. 3).

Therefore, corresponding to the relationship between the potential difference condition values as described above, the direct current potential difference ΔVo between the potential of the vibrating body 4 and the potential of the excitation electrode 5 is changed to the vibration body / excitation electrode potential difference condition value | ΔVo | max. in a range satisfying, by a value larger than the DC potential difference ΔVr between the potential of the vibration detecting electrodes 6 of vibrator 4, it is possible to increase the electrostatic driving force F _O, electrostatic required If the magnitude of the driving force F _O is the same can be suppressed lower the voltage of the drive signal AC component V _a, thereby the interference amount to the vibration detection signal V _CA of the drive signals through stray capacitance It can be further reduced.
(G) Other configuration examples in the embodiment of the present invention:
In the first to fourth embodiments described above, as the pressure measurement operation, the magnitude of the AC signal (drive signal AC component) V _AP in the drive signal V ₀ (= V _AP + V _OB ) applied to the excitation electrode 5 is determined. to be constant, and performing control for adjusting the gain of the amplifier in the voltage control circuit 10 for shifting the signal V _CAP of the phase of the vibration detection signal V _CA in phase shift circuit 9 from the capacitance-voltage conversion circuit 21,21A state, converted into a pressure measurement signal V _P corresponding to the pressure P values the amplitude a of the vibration member 4 which changes in correspondence to the Q value of the vibrator 4 (the magnitude of the vibration detection signal V _CA) with a pressure converter 31 This is an example of a method (a constant drive voltage method).

However, the pressure measurement operation in the present invention is not limited to the above-described constant driving voltage method, and the amplitude A of the vibrating body 4, that is, the magnitude of the vibration detection signal V _CA from the capacitive voltage conversion circuits 21 and 21A is not limited. _Applied to the excitation electrode 5 in a state in which the gain of the voltage control circuit 10 is controlled to be adjusted with respect to the signal V _{CAP obtained} by shifting the phase of the vibration detection signal V _CA by the phase shift circuit 9 so as to be constant. Applying a method (hereinafter also referred to as “constant amplitude method”) for measuring the pressure P based on the magnitude of the AC signal (drive signal AC component) _VAP in the drive signal V ₀ (= V _AP + V _OB ) Is also possible.

As the method of converting the magnitude of the drive signal AC component V _AP at a constant amplitude method described above pressure P value to the (pressure measurement signal V _P), the magnitude of the drive signal AC component V _AP is converted into the Q value Further, this Q value may be converted into a pressure P value (pressure measurement signal V _P ), and the magnitude of the drive signal AC component V _AP is directly measured without passing through the Q value. You may make it convert into P value (pressure measurement signal _VP ).

Here, as described in the section (c) above, for example, when the vibrating body 4 is the design value shown in FIG. 3 and the material is a vibrating body made of silicon, the vibration direction shown in FIG. In the vibration direction perpendicular to the wide surface), the relationship between the Q value and the pressure P value (Q value-pressure characteristics) is a high pressure region (about 0.1 Pa or more) as shown in FIG. Then, the amplitude is approximately inversely proportional to the pressure, and on the low pressure side, the amplitude is saturated toward its maximum limit value. Corresponding to such Q value-pressure characteristics, the relationship (drive voltage-pressure characteristics) between the magnitude of the drive signal AC component _VAP and the pressure P value in the constant amplitude method is about 0.1 Pa. the magnitude of the drive signal AC component V _AP in response to the pressure level decreases at low pressure side toward its minimum limit value with the above) the high pressure region is substantially proportional to the pressure magnitude of the drive signal AC component V _AP The saturation region becomes saturated.

For this reason, in the above-described constant amplitude method, particularly when the pressure measurement range includes the low-pressure side saturation region as described above, the pressure conversion circuit, for example, relates the relationship between the magnitude of the drive signal AC component _VAP and the pressure P value. Characteristic data of (driving voltage-pressure characteristic) is acquired, and the pressure P value is calculated from the magnitude of the driving signal AC component _VAP at the time of actual measurement by the conversion means having a storage unit storing the data table of this characteristic data. In addition, the size of the drive signal AC component _VAP at the time of actual measurement is preferably obtained by the conversion means including a storage unit storing a relational expression approximately obtained from the curve of the characteristic data. It is good also as a structure which performs conversion from a pressure P value.

Further, in the above-described constant amplitude method, the vacuum gauge controls the amplitude A of the vibrator 4 over the entire pressure measurement range, that is, the magnitude of the vibration detection signal V _CA is constant and responds to an increase in pressure. It operates so that the drive voltage applied to the excitation electrode 4 is increased. For this reason, since the magnitude of the drive voltage is relatively larger than the magnitude (amplitude A) of the vibration detection signal V _{CA on} the high pressure side in the pressure measurement range, the vibration of the drive signal is detected through the stray capacitance. There is a tendency that the influence of interference on the signal becomes larger, the S / N ratio in the vacuum gauge is further lowered, and the noise is further increased.

Here, in the present invention, the drive signal V _O (= V _A + V _OB ) obtained by adding the drive signal bias voltage V _OB to the AC signal V _A as described above is applied to the excitation electrode 5. Therefore, in the case of the above-described constant amplitude method, the vacuum gauge is controlled so that the magnitude of the vibration detection signal V _CA is constant, and the alternating current in the drive signal V _O applied to the excitation electrode 4 according to the increase in pressure. It operates so that the voltage of the signal (drive signal AC component) V _A becomes larger.

In the present invention, the drive signal bias voltage V _{OB is set} to a high voltage level to increase the DC potential difference ΔVo (= V _B −V _OB ) between the potential of the vibrating body 4 and the potential of the excitation electrode 5. The electrostatic driving force Fo (= | V _A * ΔVo |) can be increased. For this reason, in the present invention, when the required electrostatic driving force Fo is the same, the driving signal AC component V _A is increased by the amount of the DC potential difference ΔVo between the potential of the vibrating body 4 and the potential of the excitation electrode 5. Therefore, the voltage of the drive signal AC signal _VA on the high voltage side of the pressure measurement range can also be suppressed to a lower voltage level. Therefore, according to the present invention, in the constant amplitude method, the magnitude (amplitude) of the vibration detection signal V _{CA having} the magnitude of the drive voltage, that is, the magnitude of the voltage of the drive signal AC component V _A is also measured on the high pressure side of the pressure measurement range. Since the relative size with respect to A) can be made smaller than before, the influence of interference on the vibration detection signal of the drive signal through stray capacitance etc. can be made smaller, and the S / N ratio in the vacuum gauge can be made higher. In addition, noise can be further reduced.

Further, in the present invention, the DC potential difference ΔVo (= V _B −V _OB ) between the potential of the vibrating body 4 and the potential of the excitation electrode 5 can be increased by setting the drive signal bias voltage V _OB to a high voltage level. since it is possible to suppress to a low voltage level direction of the vibrating body bias voltage V _B, which makes it possible to prevent contact by the vibration detection electrode 6 transgressions electrostatic attraction and the vibration member 4.

  Thereby, the vacuum gauge according to the present invention reduces interference with the vibration detection signal of the drive signal and prevents contact between the vibrating body 4 and the detection electrode 6 due to electrostatic attraction even in the above-described constant amplitude method. The atmospheric pressure P can be measured with sufficient accuracy up to a high pressure.

1 ... Weight
2 ... Beam
3 ... Vibrating body fixing part
4 ... Vibrating body
5 ... Excitation electrode
6 ... Vibration detection electrode
7,7A ・ ・ ・ Capacity pressure conversion circuit
9 ... Phase shift circuit
10 ... Voltage control circuit
11 ... Drive signal bias voltage source
12 ... Signal synthesis unit
13 ... Vibrator bias voltage source
15 ... Signal source for initial excitation
16 ... Switch circuit
17 ... Voltage divider circuit
18 ... Boost circuit
21,21A ・ ・ ・ Capacitance voltage conversion circuit
22 ... Differential amplifier
23 ... resistance
24 ・ ・ ・ Capacitor
25 ... Detection bias voltage source
31 ... Pressure conversion circuit

Claims (10)

Detecting the capacitance between the vibrating body, the vibrating electrode facing the vibrating body and driving the vibrating body by electrostatic force, the detection electrode facing the vibrating body, and the vibrating body and the detection electrode Has a vibration detection unit that detects vibration of the vibrating body and a drive signal generation unit that generates a driving signal for exciting the vibrating body, and applies the driving signal to the excitation electrode to hold the vibrating body in a resonance state. In a vacuum gauge equipped with a pressure measuring unit that measures the pressure of the atmosphere from the vibration characteristics of the vibrating body,
The position where the vibrating body faces the excitation electrode is closer to the fixed portion of the vibrating body than the position where the vibrating body faces the detection electrode,
The drive signal generation unit generates a signal obtained by adding a DC drive signal bias voltage to the AC signal as the drive signal,
A vacuum gauge characterized in that the DC potential difference between the potential of the vibrating body and the potential of the excitation electrode is larger than the DC potential difference between the potential of the vibrating body and the potential of the detection electrode. The vacuum gauge according to claim 1,
A vacuum gauge characterized in that the facing area between the vibrating body and the excitation electrode is smaller than the facing area between the vibrating body and the detection electrode. The vacuum gauge according to claim 1 or 2,
A drive signal bias voltage generator for generating a DC drive signal bias voltage; and a vibrator bias voltage generator for generating a DC vibrator bias voltage;
The vacuum gauge according to claim 1, wherein the vibrator bias voltage is applied to the vibrator, and the drive signal bias voltage is a DC voltage having a polarity opposite to that of the vibrator bias voltage. The vacuum gauge according to claim 1 or 2,
A drive signal bias voltage generation unit that generates a DC drive signal bias voltage; and a voltage dividing circuit that divides the drive signal bias voltage;
An output voltage of the voltage dividing circuit is applied to the vibrating body as a DC vibrating body bias voltage. The vacuum gauge according to claim 1 or 2,
A vibrator bias voltage generator for generating a DC vibrator bias voltage; and a booster circuit for boosting the vibrator bias voltage;
The vacuum gauge, wherein the vibrator bias voltage is applied to the vibrator, and the output voltage of the booster circuit is a direct current drive signal bias voltage. The vacuum gauge according to claim 1 or 2,
A detection bias voltage generation unit that generates a DC detection bias voltage; and a drive signal bias voltage generation unit that generates a DC drive signal bias voltage;
The detection bias voltage is applied to a capacitance voltage conversion circuit connected to the detection electrode in the vibration detection unit, the potential of the detection electrode becomes the voltage level of the detection bias voltage, and the potential of the vibration body is set to the ground level, A vacuum gauge characterized in that the absolute value of the drive signal bias voltage is larger than the absolute value of the detection bias voltage. The vacuum gauge according to any one of claims 1 to 6,
An AC signal in the drive signal generation unit is generated by changing the phase of the detection signal based on the detection signal of the vibration detection unit and amplifying the vacuum signal. The vacuum gauge according to claim 7,
The drive signal generation unit adjusts the amplification gain for the signal obtained by changing the phase of the detection signal of the vibration detection unit so that the voltage of the AC signal in the drive signal is constant,
The pressure gauge is a vacuum gauge that measures pressure based on the magnitude of the detection signal of the vibration detector. The vacuum gauge according to claim 7,
The drive signal generation unit adjusts the amplification gain for the signal obtained by changing the phase of the detection signal of the vibration detection unit so that the magnitude of the detection signal of the vibration detection unit is constant,
A pressure gauge is a vacuum gauge which measures pressure based on the voltage of an alternating current signal in a drive signal. The vacuum gauge according to any one of claims 7 to 9,
The drive signal generation unit includes an initial excitation signal source that outputs an initial excitation signal having a frequency corresponding to the natural frequency of the vibrator,
When the vibrator is initially driven, an initial drive signal obtained by adding the drive signal bias voltage to the initial excitation signal is applied to the excitation electrode instead of the drive signal based on the detection signal of the vibration detection unit as the drive signal. A characteristic vacuum gauge.