JP7534198B2 - Diaphragm Vacuum Gauge - Google Patents

Description

The present invention relates to a diaphragm vacuum gauge.

Pressure sensors such as vacuum gauges used in semiconductor manufacturing facilities use a variety of types of products that use different measurement principles depending on the required pressure range. For example, one such type is the capacitance-type diaphragm vacuum gauge, in which a movable diaphragm is subjected to pressure and the amount of deflection is detected as a capacitance value (see Patent Documents 1 and 2). Diaphragm vacuum gauges are often used in process equipment, including semiconductor film formation and etching processes, because the flow measurement value is less dependent on the type of gas.

Diaphragm vacuum gauges usually have a minimum full-scale pressure range of around 1.3 Pa. The reason for the 1.3 Pa limit is that the measurable pressure range is determined by the thickness of the diaphragm due to the structure of the vacuum gauge. In other words, in order to measure pressures lower than normal, the diaphragm needs to be made thinner. Conversely, for higher pressures, the gauge is designed to accommodate the specifications by making the diaphragm thicker.

When the diaphragm of a diaphragm vacuum gauge is made thicker to measure higher pressures, the pressure sensitivity may be insufficient. Specifically, the relationship between the pressure p applied to the diaphragm and the vertical displacement w of the diaphragm is expressed as in equation (1), and it can be seen that the pressure sensitivity of a diaphragm vacuum gauge decreases inversely proportional to the cube of the diaphragm thickness h.

In equation (1), r is the radial distance from the center of the diaphragm, E is the Young's modulus of the diaphragm, v is the Poisson's ratio of the diaphragm, and a is the radius of the diaphragm.
In addition, if the diaphragm is made thicker, the displacement of the diaphragm when pressure is applied becomes minute, so a highly accurate measurement circuit is required to detect the minute displacement of the diaphragm. Although there is a structural upper limit to the practical pressure measurement range of a diaphragm vacuum gauge, in some situations it may be necessary to measure beyond this upper limit while maintaining pressure sensitivity, and improvements are required.

JP 2009-210482 A JP 2002-328045 A

The present invention has been made to solve the above problems, and aims to provide a diaphragm vacuum gauge that can expand the upper limit of the pressure measurement range.

The diaphragm vacuum gauge of the present invention comprises a pressure adjustment chamber provided to communicate with a measurement chamber via a piping, a pressure measurement chamber provided to communicate with the pressure adjustment chamber, a pressure receiving section configured to change in capacitance in response to displacement of a diaphragm due to the pressure of a measurement medium in the pressure measurement chamber, a cooler configured to cool the pressure measurement chamber, a first temperature sensor configured to measure the temperature of the measurement medium in the pressure measurement chamber, a pressure measurement section configured to convert the capacitance into a pressure measurement value, and a pressure correction section configured to correct the pressure measurement value based on the temperature measured by the first temperature sensor and the temperature of the measurement medium in the measurement chamber, and is characterized in that the temperature difference between the temperature of the measurement medium in the pressure measurement chamber and the temperature of the measurement medium in the measurement chamber is converted into a pressure difference to correct the pressure measurement value.
In one configuration example of the diaphragm vacuum gauge of the present invention, the pressure adjustment chamber and the pressure measurement chamber are arranged in series, and the medium to be measured flows into the pressure measurement chamber via the pressure adjustment chamber.
In one configuration example of the diaphragm vacuum gauge of the present invention, the pressure adjustment chamber and the pressure measurement chamber are arranged in parallel, and the medium to be measured flows into the pressure adjustment chamber and the pressure measurement chamber via the piping.

In one embodiment of the diaphragm vacuum gauge of the present invention, the pressure adjustment chamber and the pressure measurement chamber communicate with each other via a throttle, and the throttle is a fixed throttle or a variable throttle.
In addition, one configuration example of the diaphragm vacuum gauge of the present invention is characterized in that it further includes a second temperature sensor configured to measure the temperature of the measurement medium in the pressure adjustment chamber, and a temperature estimation unit configured to estimate the temperature of the measurement medium in the measurement chamber from the temperature measured by the second temperature sensor.
In addition, one configuration example of the diaphragm vacuum gauge of the present invention is characterized in that the temperature of the medium to be measured in the measurement chamber is obtained from a second temperature sensor provided in the measurement chamber.

Furthermore, the diaphragm vacuum gauge of the present invention comprises a pressure measurement chamber provided to communicate with a measurement chamber via a pipe, a pressure receiving section configured to change in capacitance in response to displacement of a diaphragm due to the pressure of a measurement medium in the pressure measurement chamber, a cooler configured to cool the pressure measurement chamber, a first temperature sensor configured to measure the temperature of the measurement medium in the pressure measurement chamber, a pressure measurement section configured to convert the capacitance into a pressure measurement value, and a pressure correction section configured to correct the pressure measurement value based on the temperature measured by the first temperature sensor and the temperature of the measurement medium in the measurement chamber, and is characterized in that the temperature difference between the temperature of the measurement medium in the pressure measurement chamber and the temperature of the measurement medium in the measurement chamber is converted into a pressure difference to correct the pressure measurement value.
Moreover, one configuration example of the diaphragm vacuum gauge of the present invention is characterized in that it further comprises a heat flow sensor configured to measure a heat flow in the piping, and a temperature estimation unit configured to estimate a temperature of the measurement medium in the measurement chamber from the heat flow measured by the heat flow sensor.
In addition, one configuration example of the diaphragm vacuum gauge of the present invention is characterized in that the temperature of the medium to be measured in the measurement chamber is obtained from a second temperature sensor provided in the measurement chamber.

In addition, one configuration example of the diaphragm vacuum gauge of the present invention is characterized in that it further comprises a control unit configured to control the cooler to remove heat so that the temperature difference between the temperature of the measured medium in the pressure measurement chamber and the temperature of the measured medium in the measurement chamber becomes a predetermined value.
In one configuration example of the diaphragm vacuum gauge of the present invention, the pressure receiving unit is composed of a first electrode formed on a base, the diaphragm disposed across a gap from the base, a second electrode formed on the diaphragm so as to face the first electrode, a third electrode formed on the base outside the first electrode, and a fourth electrode formed on the diaphragm outside the second electrode so as to face the third electrode, and further includes a capacitance calculation unit configured to calculate a first capacitance between the first and second electrodes, 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, and 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 the pressure measurement unit converts the corrected first capacitance into the pressure measurement value.
In one configuration example of the diaphragm vacuum gauge of the present invention, the pressure correction section corrects the pressure measurement value only when the pressure measurement value exceeds an upper limit of a specified pressure measurement range.

The diaphragm vacuum gauge of the present invention further comprises a first pressure measurement chamber provided to communicate with a measured chamber via a pipe, a second pressure measurement chamber provided to communicate with the measured chamber via the pipe and to communicate with the first pressure measurement chamber, a first pressure receiving section configured to change in capacitance in response to the displacement of a first diaphragm due to the pressure of a measured medium in the first pressure measurement chamber, a second pressure receiving section configured to change in capacitance in response to the displacement of a second diaphragm due to the pressure of a measured medium in the second pressure measurement chamber, a cooler configured to cool the first pressure measurement chamber, a heater configured to heat the second pressure measurement chamber, a first temperature sensor configured to measure the temperature of the measured medium in the first pressure measurement chamber, a second temperature sensor configured to measure the temperature of the measured medium in the second pressure measurement chamber, and the cooler. The pressure measuring unit is configured to convert the capacitance of the first pressure receiving unit into a pressure measurement value in a first measurement mode in which the heater is in operation and the cooler is not in operation, and to convert the capacitance of the second pressure receiving unit into a pressure measurement value in a second measurement mode in which the heater is in operation and the cooler is not in operation; and a pressure correction unit is configured to correct the pressure measurement value based on the temperature measured by the first temperature sensor and the temperature of the medium to be measured in the measurement chamber in the first measurement mode, and to correct the pressure measurement value based on the temperature measured by the second temperature sensor and the temperature of the medium to be measured in the measurement chamber in the second measurement mode, and is characterized in that the temperature difference between the temperature of the medium to be measured in the first pressure measurement chamber or the temperature of the medium to be measured in the second pressure measurement chamber and the temperature of the medium to be measured in the measurement chamber is converted into a pressure difference to correct the pressure measurement value.

In one configuration example of the diaphragm vacuum gauge of the present invention, the first pressure measuring chamber and the second pressure measuring chamber communicate with each other via a throttle, and the throttle is a fixed throttle or a variable throttle.
In addition, one configuration example of the diaphragm vacuum gauge of the present invention is characterized in that it further includes a temperature estimating unit configured to estimate a temperature of the measured medium in the measured chamber from the temperature measured by the second temperature sensor in the first measurement mode, and to estimate a temperature of the measured medium in the measured chamber from the temperature measured by the first temperature sensor in the second measurement mode.
Moreover, one configuration example of the diaphragm vacuum gauge of the present invention is characterized in that the temperature of the measurement medium in the measurement chamber is obtained from a third temperature sensor provided in the measurement chamber.
In addition, one configuration example of the diaphragm vacuum gauge of the present invention is characterized in that it further comprises a control unit configured to control the cooler to remove heat so that the temperature difference between the temperature of the measured medium in the first pressure measurement chamber and the temperature of the measured medium in the measured chamber becomes a first predetermined value in the first measurement mode, and to control the heater to generate heat so that the temperature difference between the temperature of the measured medium in the second pressure measurement chamber and the temperature of the measured medium in the measured chamber becomes a second predetermined value in the second measurement mode.

In one configuration example of the diaphragm vacuum gauge of the present invention, the first pressure receiving portion is composed of a first electrode formed on a first pedestal, the first diaphragm disposed across a gap from the first pedestal, a second electrode formed on the first diaphragm so as to face the first electrode, a third electrode formed on the first pedestal outside the first electrode, and a fourth electrode formed on the first diaphragm outside the second electrode so as to face the third electrode, a fifth electrode formed on a second pedestal, the second diaphragm disposed across a gap from the second pedestal, a sixth electrode formed on the second diaphragm so as to face the fifth electrode, a seventh electrode formed on the second pedestal outside the fifth electrode, and an eighth electrode formed on the second diaphragm outside the sixth electrode so as to face the seventh electrode, and calculates a first capacitance between the first and second electrodes in the first measurement mode, The pressure measuring device further includes a capacitance calculation unit configured to calculate a second capacitance between the fifth and sixth electrodes in a second measurement mode, a capacitance difference calculation unit configured to calculate a value obtained by subtracting a third capacitance between the third and fourth electrodes from the first capacitance in the first measurement mode, and to calculate a value obtained by subtracting a fourth capacitance between the seventh and eighth electrodes from the second capacitance in the second measurement mode, and a capacitance correction unit configured to correct the first capacitance by the third capacitance based on a calculation result of the capacitance calculation unit and a calculation result of the capacitance difference calculation unit in the first measurement mode, and to correct the second capacitance by the fourth capacitance based on a calculation result of the capacitance calculation unit and a calculation result of the capacitance difference calculation unit in the second measurement mode, wherein the pressure measuring unit converts the corrected first capacitance into the pressure measurement value in the first measurement mode, and converts the corrected second capacitance into the pressure measurement value in the second measurement mode.
In one configuration example of the diaphragm vacuum gauge of the present invention, the pressure correction unit corrects the pressure measurement value only when the pressure measurement value exceeds an upper limit of a specified pressure measurement range in the first measurement mode, and corrects the pressure measurement value only when the pressure measurement value falls below a lower limit of a specified pressure measurement range in the second measurement mode.

According to the present invention, the upper limit of the pressure measurement range of the diaphragm vacuum gauge can be expanded (the upper limit can be raised) by converting the temperature difference between the temperature of the medium to be measured in the pressure measurement chamber and the temperature of the medium to be measured in the measurement chamber into a pressure difference and correcting the pressure measurement value.

In addition, in the present invention, the first pressure measurement chamber is cooled in the first measurement mode, and the temperature difference between the temperature of the medium to be measured in the first pressure measurement chamber and the temperature of the medium to be measured in the measurement chamber is converted into a pressure difference to correct the pressure measurement value, and the second pressure measurement chamber is heated in the second measurement mode, and the temperature difference between the temperature of the medium to be measured in the second pressure measurement chamber and the temperature of the medium to be measured in the measurement chamber is converted into a pressure difference to correct the pressure measurement value, thereby making it possible to expand the upper limit of the pressure measurement range in the first measurement mode (raise the upper limit) and expand the lower limit of the pressure measurement range in the second measurement mode (lower the lower limit).

FIG. 1 is a diagram for explaining the principle of the diaphragm vacuum gauge of the present invention. FIG. 2 is a diagram showing an example of the pressure difference between a chamber to be measured and a pressure receiving part of a diaphragm vacuum gauge. FIG. 3 is a diagram showing the results of an analysis of the relationship between the pressure of the measurement target and the pressure measurement value of the diaphragm vacuum gauge. FIG. 4 is a diagram showing the ratio of the pressure of the measurement object caused by the temperature difference between the measurement object and the diaphragm vacuum gauge to the pressure measurement value of the diaphragm vacuum gauge. FIG. 5 is a block diagram showing the configuration of a diaphragm vacuum gauge according to a first embodiment of the present invention. FIG. 6 is a cross-sectional view showing the configuration of the main part of the pressure receiving part of the diaphragm vacuum gauge according to the first embodiment of the present invention. FIG. 7 is a block diagram showing the configuration of a circuit section of a diaphragm vacuum gauge according to a first embodiment of the present invention. FIG. 8 is a block diagram showing the configuration of a signal detection section of a diaphragm vacuum gauge according to a first embodiment of the present invention. FIG. 9 is a flowchart for explaining the operation of the calculation processing unit of the diaphragm vacuum gauge according to the first embodiment of the present invention. FIG. 10 is a block diagram showing the configuration of a diaphragm vacuum gauge according to a second embodiment of the present invention. FIG. 11 is a block diagram showing the configuration of a diaphragm vacuum gauge according to a third embodiment of the present invention. FIG. 12 is a block diagram showing the configuration of a circuit section of a diaphragm vacuum gauge according to a third embodiment of the present invention. FIG. 13 is a flow chart for explaining the operation of the calculation processing unit of the diaphragm vacuum gauge according to the third embodiment of the present invention. FIG. 14 is a block diagram showing the configuration of a diaphragm vacuum gauge according to a fourth embodiment of the present invention. FIG. 15 is a cross-sectional view showing the configuration of the main part of a pressure receiving portion of a diaphragm vacuum gauge according to a fourth embodiment of the present invention. FIG. 16 is a block diagram showing the configuration of a circuit section of a diaphragm vacuum gauge according to a fourth embodiment of the present invention. FIG. 17 is a flow chart for explaining the operation in the second measurement mode of the calculation processing section of the diaphragm vacuum gauge according to the fourth embodiment of the present invention. FIG. 18 is a block diagram showing an example of the configuration of a computer that realizes the arithmetic processing unit of the diaphragm vacuum gauge according to the first to fourth embodiments of the present invention.

[Principle of the Invention]
The inventors noticed that the temperature of the gas to be measured is an element that can change the measurement conditions without improving the structure of the diaphragm vacuum gauge itself. They then came up with the idea that by cooling the gas supplied to the diaphragm vacuum gauge to a specified temperature near or inside the gauge, the pressure can be reduced to a measurable range (within the upper limit) and measured, and the pressure value can be converted based on the temperature difference caused by cooling, so that the upper limit of the pressure measurement range can be equivalently expanded. The conversion may be based on physical principles, or may be performed by experimentally determining in advance the relationship between the pressure difference caused by the temperature difference.

[First embodiment]
Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In this embodiment, a system is assumed in which a diaphragm vacuum gauge is connected to a chamber to be measured via piping. It is known that the diaphragm vacuum gauge is self-heated to prevent the accumulation of foreign matter, and since the temperature of the diaphragm vacuum gauge is different from that of the chamber to be measured, a pressure difference occurs between the two spaces due to thermal transition.

Assuming that two chambers 200, 201 are connected by a pipe 202 of diameter d as shown in Figure 1, approximate equations have been proposed for the relationship between pressure and temperature for both intermediate flow (equation (2)) and molecular flow (equation (3)).

In equations (2) and (3), P ₁ and P ₂ are the gas pressures in the chambers 200 and 201, T ₁ and T ₂ are the gas temperatures in the chambers 200 and 201, and a, b, and c are coefficients depending on the gas type and temperature.
It has been reported that, based on the relationship between equations (2) and (3), the pressure difference between the chamber to be measured and the pressure-receiving part of the diaphragm vacuum gauge is as shown in FIG. 2 (see the literature "Yasushi Yoshikawa et al., "Development of a Sapphire High-Temperature Diaphragm Vacuum Gauge", azbil Technical Review, Azbil Corporation, January 2011").

In the example of Fig. 2, the gas type is _N2 , the gas temperature _T1 in the measured chamber is 25°C, and the diameter d of the pipe connecting the measured chamber and the diaphragm vacuum gauge is 12.7 mm. The horizontal axis of Fig. 2 is the gas pressure _P1 in the measured chamber, and the vertical axis is the pressure difference between the measured chamber and the pressure receiving part of the diaphragm vacuum gauge. 203 in Fig. 2 shows the characteristics when the self-heating temperature of the pressure receiving part of the diaphragm vacuum gauge is 125°C, and 204 shows the characteristics when the self-heating temperature is 200°C.

Figure 3 shows the results of an analysis of the relationship between the pressure _P1 of the gas in the measurement target (measured chamber) and the pressure measurement value _P2 of the diaphragm vacuum gauge based on these approximate relationships. Here, the temperature difference between the temperature _T1 of the gas in the measured chamber and the cooling temperature _T2 ( _T1 > _T2 ) of the pressure receiving part of the diaphragm vacuum gauge is set to 100°C. In Figure 3, 300 shows the relationship between the pressures _P1 and _P2 , and 301 shows the relationship between the pressures _P1 and _P2 when there is no thermal transition between the measured chamber and the diaphragm vacuum gauge. In Figure 3, A1 is called the viscous flow region, A2 is called the intermediate flow region, and A3 is called the molecular flow region.

3, it can be seen that the pressures _P1 and _P2 are different in the intermediate flow and molecular flow regions, which are pressure ranges frequently used in semiconductor film formation and etching processes, and a pressure difference occurs due to thermal transition. The pressure difference reaches about 20% of the pressure measurement value _P2 .
Specifically, as shown in FIG. 4, when there is a thermal transition (when the temperature difference between the measured chamber and the diaphragm vacuum gauge is large), the gas pressure _P1 in the measured chamber is actually higher than the pressure measurement value _P2 of the diaphragm vacuum gauge.

Therefore, the pressure measurement value _P2 of the diaphragm vacuum gauge is usually corrected so that it approaches the actual pressure _P1 of the chamber being measured. That is, in order to consider the phenomenon of thermal transition as an error factor, the pressure measurement value _P2 of the diaphragm vacuum gauge is corrected and changed by a correction calculation. Specifically, as shown in Figure 3, the pressure measurement value _P2 of the diaphragm vacuum gauge, which is 0.004 Torr, is corrected to 0.01 Torr.

In this embodiment, by actively utilizing the relationship shown in Figure 3, it is possible to perform measurements up to a higher pressure range while maintaining measurement accuracy without exceeding the physical measurement limit of the diaphragm vacuum gauge. In this embodiment, the measured temperature data on the measured chamber side or the measured temperature data on the diaphragm vacuum gauge side that can predict the measured temperature data is used as a parameter. A correlation table between this temperature parameter and the actual pressure value is created when the diaphragm vacuum gauge is calibrated, and the output of the diaphragm vacuum gauge is determined based on this correlation table.

By cooling the diaphragm gauge to a low temperature and setting the temperature difference between the chamber being measured and the diaphragm gauge to 100°C, the pressure range can be expanded by approximately 36% even to the 133 kPa pressure range, which was previously difficult to measure, while maintaining the same pressure sensitivity (same diaphragm thickness as before). In concrete terms, it becomes possible to measure chamber pressures up to 207 kPa.

In this embodiment, the temperature of the chamber to be measured must be accurately known, but in semiconductor manufacturing equipment and the like, the chamber to be measured is usually temperature controlled, so the temperature measured in the chamber to be measured can be used. Alternatively, a temperature sensor or heat flux sensor that can predict the temperature of the chamber to be measured can be installed on the diaphragm vacuum gauge side, and the calculated value (e.g., integrated value) can be used. Note that in cases where the temperature cannot be accurately known, a minimum calibration may be performed at the time of shipment.

The diaphragm vacuum gauge of this embodiment will be described in more detail below. Fig. 5 is a block diagram showing the configuration of the diaphragm vacuum gauge according to this embodiment. The diaphragm vacuum gauge includes a pressure adjustment chamber 1 provided to communicate with a measurement chamber 12 via a pipe 2, a pressure measurement chamber 3 provided to communicate with the pressure adjustment chamber 1 via a throttle 4, a pressure receiving portion 5 whose capacitance changes according to the displacement of a diaphragm (diaphragm) due to the pressure of a measurement medium (e.g., process gas) in the pressure measurement chamber 3, a cooler 6 for cooling the pressure measurement chamber 3, a temperature sensor 7 for measuring the temperature _T3 of the measurement medium in the pressure adjustment chamber 1, a temperature sensor 8 for measuring the temperature _T2 of the measurement medium in the pressure measurement chamber 3, and a circuit portion 10 for converting the capacitance of the pressure receiving portion 5 into a pressure measurement value.

Figure 6 is a cross-sectional view showing the configuration of the main parts of the pressure-receiving part 5 of the diaphragm vacuum gauge. A recess is formed in the center of the base 50 of the pressure-receiving part 5. A diaphragm 51 that is configured to be deformable in response to the pressure P of the medium to be measured is bonded to the surface of the base 50 on which this recess is formed. The recess of the base 50 forms a reference vacuum chamber 52 together with the diaphragm 51.

A fixed electrode 53 is formed on the surface of the base 50 facing the reference vacuum chamber 52, and a movable electrode 54 is formed on the surface of the diaphragm 51 facing the reference vacuum chamber 52 so as to face the fixed electrode 53. In this way, the fixed electrode 53 and the movable electrode 54 are arranged to face each other across a gap. When the diaphragm 51 is deflected by the pressure P of the medium to be measured in the pressure measurement chamber 3, the distance between the movable electrode 54 and the fixed electrode 53 changes, and the electrostatic capacitance between the movable electrode 54 and the fixed electrode 53 changes. From this change in electrostatic capacitance, the pressure P of the medium to be measured received by the diaphragm 51 can be detected.

A fixed electrode 55 is formed on the surface of the base 50 on the reference vacuum chamber 52 side outside the fixed electrode 53. A movable electrode 56 is formed on the surface of the diaphragm 51 on the reference vacuum chamber 52 side outside the movable electrode 54 so as to face the fixed electrode 55. The fixed electrode 55 and the movable electrode 56 are formed on the edge of the diaphragm 51. Even if the diaphragm 51 is deflected by the pressure P of the medium to be measured, the edge of the diaphragm 51 is hardly deformed, so the capacitance between the movable electrode 56 and the fixed electrode 55 is unlikely to change. This capacitance is provided to eliminate measurement errors due to temperature changes inside and outside the sensor and humidity changes in the reference vacuum chamber 52. The diaphragm 51 and the base 50 are made of an insulator such as sapphire.

The medium to be measured introduced through the pipe 2 flows into the pressure adjustment chamber 1 , passes through the throttle 4 and then flows into the pressure measurement chamber 3 .
Providing the orifice 4 makes it possible to change the diameter d of the pipe. By acquiring data (temperature, pressure) associated with multiple diameters d, it is possible to grasp many parameters, mainly in the intermediate flow region. In other words, the inclusion of the orifice 4 can improve the measurement accuracy. The orifice 4 may be a fixed orifice with a fixed hole diameter, or a variable orifice whose hole diameter can be changed externally. In the case of a variable orifice, the degree of orifice can be adjusted.

Figure 7 is a block diagram showing the configuration of the circuit section 10 of the diaphragm vacuum gauge. The circuit section 10 includes a signal detection section 100 that outputs a signal with an amplitude proportional to the capacitance between the movable electrode 54 and the fixed electrode 53, and a signal with an amplitude proportional to the capacitance between the movable electrode 54 and the fixed electrode 53 minus the capacitance between the movable electrode 56 and the fixed electrode 55, an AD conversion section 101 that converts the outputs of the signal detection section 100 and the temperature sensors 7 and 8 into digital signals, an arithmetic processing section 102, a memory 103 that stores a program for the arithmetic processing section 102, a power supply 104 that supplies power supply voltage to each section of the circuit section 10, and an interface section 105.

Figure 8 is a block diagram showing the configuration of the signal detection unit 100. The signal detection unit 100 is composed of a signal generator 1000, amplifiers 1001 and 1002 each consisting of a capacitance Cf and an operational amplifier A1, a subtractor 1003, differential input type low-pass filters 1004 and 1005, a switch 1006 provided between the amplifier 1001 and the low-pass filter 1004, and a switch 1007 provided between the subtractor 1003 and the low-pass filter 1005. In Figure 8, the capacitance between the movable electrode 54 and the fixed electrode 53 is represented by Cx, and the capacitance (reference capacitance) between the movable electrode 56 and the fixed electrode 55 is represented by Cr.

During pressure measurement, the signal generator 1000 applies a sinusoidal sensor drive signal E sin (2πft) to the first electrode (e.g., fixed electrode 53) and the third electrode (e.g., fixed electrode 55) of the pressure receiving unit 5 and to the switches 1006 and 1007. E is the amplitude, f is the frequency, and t is the time.

The amplifier 1001 converts the current output from the second electrode (e.g., the movable electrode 54) of the pressure receiving unit 5 into a voltage, amplifies the voltage, and outputs a signal with an amplitude proportional to the capacitance Cx. The amplifier 1002 converts the current output from the fourth electrode (e.g., the movable electrode 56) of the pressure receiving unit 5 into a voltage, amplifies the voltage, and outputs a signal with an amplitude proportional to the capacitance Cr.
The subtractor 1003 subtracts the output signal of the amplifier 1002 from the output signal of the amplifier 1001 .

The switch 1006 and the low-pass filter 1004 constitute the synchronous detection unit 1008. The cutoff frequency of the low-pass filter 1004 is set to pass the sensor drive signal Esin (2πft). The synchronous detection unit 1008 demodulates a signal synchronized with the sensor drive signal Esin (2πft) from the output of the amplifier 1001.

Specifically, when the sensor drive signal Esin (2πft) output from the signal generator 1000 is positive, the switch 1006 connects the output terminal of the amplifier 1001 to the non-inverting input terminal of the low-pass filter 1004. Also, when the sensor drive signal Esin (2πft) is negative, the switch 1006 connects the output terminal of the amplifier 1001 to the inverting input terminal of the low-pass filter 1004. This makes it possible to demodulate a signal synchronized with the sensor drive signal Esin (2πft) from the output of the amplifier 1001.

On the other hand, the switch 1007 and the low-pass filter 1005 constitute a synchronous detection unit 1009. The cutoff frequency of the low-pass filter 1005 is set so as to pass the sensor drive signal Esin (2πft). The synchronous detection unit 1009 demodulates a signal synchronized with the sensor drive signal Esin (2πft) from the output of the subtractor 1003.

Specifically, when the sensor drive signal Esin (2πft) output from the signal generator 1000 is positive, the switch 1007 connects the output terminal of the subtractor 1003 to the non-inverting input terminal of the low-pass filter 1005. Also, when the sensor drive signal Esin (2πft) is negative, the switch 1007 connects the output terminal of the subtractor 1003 to the inverting input terminal of the low-pass filter 1005. This makes it possible to demodulate a signal synchronized with the sensor drive signal Esin (2πft) from the output of the subtractor 1003.

The AD conversion section 101 converts the outputs of the signal detection section 100 (the outputs of the synchronous detection sections 1008 and 1009) and the outputs of the temperature sensors 7 and 8 into digital signals.
As shown in FIG. 7, the calculation processing unit 102 includes a temperature estimation unit 1020 , a control unit 1021 , a capacity calculation unit 1022 , a capacity difference calculation unit 1023 , a capacity correction unit 1024 , a pressure measurement unit 1025 , and a pressure correction unit 1026 .

9 is a flow chart for explaining the operation of the calculation processing unit 102. The temperature estimation unit 1020 estimates the temperature _T1 of the measurement medium in the measurement chamber 12 from the temperature _T3 measured by the temperature sensor 7 (step S100 in FIG. 9). The relationship between the temperature _T3 of the measurement medium in the pressure adjustment chamber 1 and the temperature _T1 of the measurement medium in the measurement chamber 12 has been confirmed by a prior test. The temperature estimation unit 1020 may calculate _the temperature _T1 from the temperature T3 using a preset formula, or may obtain the value of the temperature _T1 corresponding to the temperature _T3 from a preset table.

The control unit 1021 supplies power to the cooler 6 to remove heat so that the difference T ₂ -T ₁ between the temperature T ₁ estimated by the temperature estimation unit 1020 and the temperature T ₂ measured by the temperature sensor 8 becomes a predetermined value (e.g., -100°C) (step S101 in FIG. 9). In this way, the pressure measurement chamber ₃ is cooled so that the temperature difference T ₂ -T ₁ between the temperature T ₂ of the measurement medium in the pressure measurement chamber 3 and the temperature T _{1 of the measurement medium in the measurement chamber 12 becomes a predetermined value. The predetermined value that determines the temperature difference T 2 -T 1 can} be set arbitrarily within the range of -200°C to 0°C. The cooler 6 can be, for example, a heat pump or a Peltier element.

The capacitance calculation unit 1022 calculates the value of the capacitance Cx from the amplitude of the output signal of the synchronous detection unit 1008 (step S102 in FIG. 9).
The capacitance difference calculation unit 1023 calculates the value of the capacitance difference (Cx-Cr) from the amplitude of the output signal of the synchronous detection unit 1009 (step S103 in FIG. 9).

The capacitance correction unit 1024 calculates a value (Cx-Cr)/Cx obtained by correcting the electrostatic capacitance Cx using the reference capacitance Cr based on the calculation result of the capacitance calculation unit 1022 and the calculation result of the capacitance difference calculation unit 1023 (step S104 in FIG. 9).
The pressure measurement unit 1025 converts the capacitance (Cx-Cr)/Cx calculated by the capacitance correction unit 1024 into a pressure measurement value _P2 (step S105 in FIG. 9).

The pressure correction unit 1026 obtains a value obtained by correcting the pressure measurement value P2 based on the temperature _T2 of the measurement medium in the pressure measurement chamber ₃ measured by the temperature sensor 8 and the temperature _T1 of the measurement medium in the measurement chamber 12 estimated by the temperature estimation unit 1020 (step S106 in FIG. 9).

Specifically, a correlation table that associates temperatures _T2 , _T1 , pressure measurement value _P2 , and actual pressure value _P1 of the measurement medium in the measurement target chamber 12 is created when the diaphragm vacuum gauge is calibrated and set in the pressure correction unit 1026. The pressure correction unit 1026 obtains the pressure value _P1 corresponding to temperatures _T2 , _T1 , and pressure measurement value _P2 from the correlation table. In this way, the pressure measurement value _P2 can be corrected to be close to the actual pressure value _P1 of the measurement target chamber 12.

Then, the pressure correction unit 1026 outputs the calculated pressure value _P1 to, for example, a higher-level device via the interface unit 105 (step S107 in FIG. 9).
The calculation processing unit 102 performs the processes of steps S100 to S107 for each measurement period, for example, until the pressure measurement operation is ended by a user instruction (YES in step S108 in FIG. 9).

In this way, this embodiment makes it possible to expand the upper limit of the pressure measurement range of the diaphragm vacuum gauge.

[Second embodiment]
Next, a second embodiment of the present invention will be described. Fig. 10 is a block diagram showing the configuration of a diaphragm vacuum gauge according to the second embodiment of the present invention. The diaphragm vacuum gauge of this embodiment includes a pressure adjustment chamber 1a, a pressure measurement chamber 3a, a pressure receiving portion 5, a cooler 6, temperature sensors 7 and 8, and a circuit portion 10.

In the first embodiment, the pressure adjustment chamber 1 and the pressure measurement chamber 3 are arranged in series, and the medium to be measured that flows into the pressure adjustment chamber 1 flows into the pressure measurement chamber 3 through the orifice 4 .
In contrast to this, in this embodiment, the pressure adjustment chamber 1a and the pressure measurement chamber 3a are arranged in parallel. A baffle 9 is provided between the pressure adjustment chamber 1a and the pressure measurement chamber 3a and the piping 2a. The measurement medium introduced from the measurement chamber 12 through the piping 2a hits the surface of the baffle 9 and is introduced in equal amounts into the pressure adjustment chamber 1a and the pressure measurement chamber 3a through the gap around the baffle 9. The pressure adjustment chamber 1a and the pressure measurement chamber 3a are also connected via a restrictor 4a.

The configurations of the pressure receiving section 5, the cooler 6, and the circuit section 10 are the same as those of the first embodiment. Since the structure of the pressure adjustment chamber 1a is different from that of the first embodiment, it goes without saying that the relationship between the temperature _T3 of the measurement medium in the pressure adjustment chamber 1a and the temperature _T1 of the measurement medium in the measurement chamber 12 is calibrated for this embodiment. Using this relationship, the temperature estimation section 1020 of the circuit section 10 can estimate the temperature _T1 of the measurement medium in the measurement chamber 12 from the temperature _T3 measured by the temperature sensor 7. Similarly, it goes without saying that the correlation table used by the pressure correction section 1026 of the circuit section 10 is also calibrated for this embodiment.

In this way, this embodiment can obtain the same effect as that of the first embodiment. In the first and second embodiments, the temperature _T1 of the measurement target medium in the measurement target chamber 12 is estimated by the temperature estimation unit 1020, but if a temperature sensor is provided in the measurement target chamber, the value of the temperature _T1 may be obtained from this temperature sensor.

[Third Example]
Next, a third embodiment of the present invention will be described. Fig. 11 is a block diagram showing the configuration of a diaphragm vacuum gauge according to the third embodiment of the present invention. The diaphragm vacuum gauge of this embodiment includes a pressure measurement chamber 3b that is provided to communicate with a measured chamber 12 via a pipe 2b, a pressure receiving portion 5, a cooler 6, a temperature sensor 8, a circuit portion 10b, and a heat flow sensor 11 that measures the heat flow in the pipe 2b.

In the first and second embodiments, pressure adjustment chambers 1 and 1a were provided, but in this embodiment, the medium to be measured is introduced directly from the chamber to be measured 12 through pipe 2b into the pressure measurement chamber 3b. In this case, the chamber to be measured 12 serves as the pressure adjustment chamber, and pipe 2b serves as a throttle.

The pressure receiving unit 5 and the cooler 6 are the same as those in the first embodiment. Fig. 12 is a block diagram showing the configuration of a circuit unit 10b in this embodiment. The circuit unit 10b includes a signal detection unit 100, an AD conversion unit 101, an arithmetic processing unit 102b, a memory 103b, a power supply 104, and an interface unit 105.
The signal detection section 100 and the AD conversion section 101 are as described in the first embodiment.

As shown in FIG. 12, the calculation processing unit 102b includes a temperature estimation unit 1020b, a control unit 1021, a capacity calculation unit 1022, a capacity difference calculation unit 1023, a capacity correction unit 1024, a pressure measurement unit 1025, and a pressure correction unit 1026b.

Fig. 13 is a flow chart for explaining the operation of the calculation processing unit 102b. The temperature estimation unit 1020b estimates the temperature _T1 of the measurement medium in the measurement chamber 12 from the heat flow measured by the heat flow sensor 11 (step S200 in Fig. 13). The relationship between the heat flow in the pipe 2b and the temperature _T1 of the measurement medium in the measurement chamber 12 has been confirmed by a prior test. The temperature estimation unit 1020b may calculate the temperature _T1 from the heat flow using a preset formula, or may obtain the value of the temperature _T1 corresponding to the heat flow from a preset table.

If the heat flux obtained by converting the heat flow rate measured by the heat flow sensor 11 into an area is taken as q (W/ ^m2 ) and heat transfer is assumed to be by convection, the relationship between the heat flux q, the temperature _T2 measured by the temperature sensor 8, and the temperature _T1 of the medium to be measured in the measurement chamber 12 is expressed by the following equation.
q=k(T ₁ - _{T 2} )...(4)

In formula (4), k is the heat transfer coefficient. Using formula (4), the temperature _T1 can be calculated from the heat flux q and the temperature _T2 .

The operations of the control unit 1021, the capacity calculation unit 1022, the capacity difference calculation unit 1023, the capacity correction unit 1024, and the pressure measurement unit 1025 (steps S201 to S205 in FIG. 13) are the same as those in the first embodiment.

As in the first embodiment, the pressure correcting unit 1026b obtains a value obtained by correcting the pressure measurement value _P2 based on the temperature _T2 of the measurement target medium in the pressure measurement chamber 3 measured by the temperature sensor 8 and the temperature _T1 of the measurement target medium in the measurement target chamber 12 estimated by the temperature estimating unit 1020b (step S206 in FIG. 13). Specifically, the pressure correcting unit 1026b obtains the pressure value _P1 corresponding to the temperatures _T2 , _T1 and the pressure measurement value _P2 from a preset correlation table. It goes without saying that the correlation table is calibrated for this embodiment.

Then, the pressure correction unit 1026b outputs the calculated pressure value _P1 to, for example, a higher-level device via the interface unit 105 (step S207 in FIG. 13).
The calculation processing unit 102b performs the processes of steps S200 to S207 for each measurement period, for example, until the pressure measurement operation is ended by a user instruction (YES in step S208 in FIG. 13).

In this way, the present embodiment can obtain the same effects as those of the first embodiment. In this embodiment, the temperature estimation unit 1020b estimates the temperature _T1 of the measurement target medium in the measurement target chamber 12, but if a temperature sensor is provided in the measurement target chamber 12, the value of the temperature _T1 may be obtained from the temperature sensor.

In the first to third embodiments, the pressure measurement value _P2 is constantly corrected by the pressure correction units 1026 and 1026b, but this is not limited to the above. That is, the pressure correction units 1026 and 1026b may normally output the pressure measurement value _P2 as the pressure value _P1 without correcting it, and may correct the pressure measurement value _P2 by the processing of steps S106 and S206 only when the pressure measurement value _P2 exceeds the upper limit of the specified pressure measurement range.

[Fourth embodiment]
Next, a fourth embodiment of the present invention will be described. Fig. 14 is a block diagram showing the configuration of a diaphragm vacuum gauge according to the fourth embodiment of the present invention. The diaphragm vacuum gauge of this embodiment includes pressure measurement chambers 3c, 3d provided to communicate with a measurement chamber 12 via a pipe 2c, a pressure receiving section 5 whose capacitance changes according to the displacement of a diaphragm caused by the pressure of a measurement medium in the pressure measurement chamber 3c, a cooler 6 for cooling the pressure measurement chamber 3c, a temperature sensor 8 for measuring the temperature of the measurement medium in the pressure measurement chamber 3c, a circuit section 10c, a pressure receiving section 13 whose capacitance changes according to the displacement of a diaphragm caused by the pressure of a measurement medium in the pressure measurement chamber 3d, a temperature sensor 14 for measuring the temperature of the measurement medium in the pressure measurement chamber 3d, and a heater 15 for heating the pressure measurement chamber 3d.

In this embodiment, two pressure measurement chambers 3c, 3d are arranged in parallel. A baffle 9 is provided between the pressure measurement chambers 3c, 3d and the pipe 2c. The measurement medium introduced from the measurement chamber 12 through the pipe 2c hits the surface of the baffle 9 and is introduced into the pressure measurement chambers 3c, 3d in equal amounts through the gap around the baffle 9. The pressure measurement chambers 3c and 3d are also connected via a throttle 4c. As in the first and second embodiments, the throttle 4c may be a fixed throttle or a variable throttle.
The configurations of the pressure receiving portion 5 and the cooler 6 are similar to those in the first embodiment.

Figure 15 is a cross-sectional view showing the configuration of the main parts of the pressure-receiving part 13 of the diaphragm vacuum gauge. A recess is formed in the center of the base 130 of the pressure-receiving part 13. A diaphragm 131 that is configured to be deformable in response to the pressure P of the medium to be measured is bonded to the surface of the base 130 on which this recess is formed. The recess of the base 130 forms a reference vacuum chamber 132 together with the diaphragm 131.

A fixed electrode 133 is formed on the surface of the base 130 facing the reference vacuum chamber 132, and a movable electrode 134 is formed on the surface of the diaphragm 131 facing the reference vacuum chamber 132 so as to face the fixed electrode 133. In this way, the fixed electrode 133 and the movable electrode 134 are arranged to face each other across a gap. When the diaphragm 131 is deflected by receiving the pressure P of the medium to be measured in the pressure measurement chamber 3d, the distance between the movable electrode 134 and the fixed electrode 133 changes, and the electrostatic capacitance between the movable electrode 134 and the fixed electrode 133 changes. From this change in electrostatic capacitance, the pressure P of the medium to be measured received by the diaphragm 131 can be detected.

A fixed electrode 135 is formed on the surface of the base 130 facing the reference vacuum chamber 132, outside the fixed electrode 133. A movable electrode 136 is formed on the surface of the diaphragm 131 facing the reference vacuum chamber 132, outside the movable electrode 134, so as to face the fixed electrode 135. In this way, the pressure receiving section 13 has the same structure as the pressure receiving section 5.

Figure 16 is a block diagram showing the configuration of the circuit section 10c of the diaphragm vacuum gauge. The circuit section 10c includes a signal detection section 100, a signal detection section 106 that outputs a signal with an amplitude proportional to the capacitance between the movable electrode 134 and the fixed electrode 133, and a signal with an amplitude proportional to the capacitance between the movable electrode 134 and the fixed electrode 133 minus the capacitance between the movable electrode 136 and the fixed electrode 135, an AD conversion section 101c that converts the outputs of the signal detection sections 100 and 106 and the temperature sensors 8 and 14 into digital signals, an arithmetic processing section 102c, a memory 103c that stores the program of the arithmetic processing section 102c, a power supply 104, and an interface section 105.

The configuration of the signal detection unit 106 is similar to that of the signal detection unit 100, and will be described using the symbols in FIG. 8. The signal generator 1000 of the signal detection unit 106 applies a sensor drive signal Esin (2πft) to the first electrode (e.g., fixed electrode 133) and the third electrode (e.g., fixed electrode 135) of the pressure receiving unit 13 and to the switches 1006 and 1007 during pressure measurement.

The amplifier 1001 of the signal detection unit 106 converts the current output from the second electrode (e.g., movable electrode 134) of the pressure receiving unit 13 into a voltage, amplifies it, and outputs a signal with an amplitude proportional to the capacitance Cx between the movable electrode 134 and the fixed electrode 133. The amplifier 1002 of the signal detection unit 106 converts the current output from the fourth electrode (e.g., movable electrode 136) of the pressure receiving unit 13 into a voltage, amplifies it, and outputs a signal with an amplitude proportional to the capacitance (reference capacitance) Cr between the movable electrode 136 and the fixed electrode 135.

The synchronous detection unit 1008 of the signal detection unit 106 demodulates a signal synchronized with the sensor drive signal Esin (2πft) from the output of the amplifier 1001. The synchronous detection unit 1009 of the signal detection unit 106 demodulates a signal synchronized with the sensor drive signal Esin (2πft) from the output of the subtractor 1003.

The AD conversion section 101c converts the outputs of the signal detection sections 100 and 106 and the outputs of the temperature sensors 8 and 14 into digital signals.
As shown in FIG. 16, the calculation processing unit 102c includes a temperature estimation unit 1020c, a control unit 1021c, a capacity calculation unit 1022c, a capacity difference calculation unit 1023c, a capacity correction unit 1024c, a pressure measurement unit 1025c, and a pressure correction unit 1026c.

The diaphragm vacuum gauge of this embodiment has two modes: a first measurement mode for a high pressure range similar to that of the first embodiment, and a second measurement mode for a lower pressure range than the first measurement mode. The user can select either the first measurement mode or the second measurement mode at will and instruct the calculation processing unit 102c.

In the first measurement mode, the pressure measurement chamber 3d plays the role of the pressure adjustment chamber 1a in the second embodiment. In addition, in the first measurement mode, the control unit 1021c does not operate the heater 15, and operates only the cooler 6. Since the processing flow in the first measurement mode is the same as in the first embodiment, the operation of the calculation processing unit 102c will be explained using the symbols in FIG. 9.

In the first measurement mode, the temperature estimation unit 1020c estimates the temperature _T1 of the measurement medium in the measurement chamber 12 from the temperature _T3 measured by the temperature sensor 14 (step S100 in FIG. 9). The relationship between the temperature _T3 of the measurement medium in the pressure measurement chamber 3d and the temperature _T1 of the measurement medium in the measurement chamber 12 in the first measurement mode has been confirmed by a prior test. The temperature estimation unit 1020c may calculate the temperature _T1 from the temperature _T3 using a preset equation for the first measurement mode, or may obtain the value of the temperature _T1 corresponding to the temperature _T3 from a preset table for the first measurement mode.

In the first measurement mode, the control unit 1021c supplies power to the cooler _{6 to remove heat so that the difference T2-T1 between the} temperature _T1 estimated by the temperature estimation unit 1020c and the temperature T2 measured by the temperature sensor 8 becomes a first predetermined value (step S101 in FIG. 9). The first predetermined value can be set arbitrarily within the range of -200°C to 0°C.

In the first measurement mode, the capacitance calculation section 1022c calculates the value of the capacitance Cx from the amplitude of the output signal of the synchronous detection section 1008 of the signal detection section 100 (step S102 in FIG. 9).
In the first measurement mode, the capacitance difference calculation unit 1023c calculates the value of the capacitance difference (Cx-Cr) from the amplitude of the output signal of the synchronous detection unit 1009 of the signal detection unit 100 (step S103 in FIG. 9).

As in the first embodiment, the capacitance corrector 1024c calculates a value (Cx-Cr)/Cx obtained by correcting the capacitance Cx using the reference capacitance Cr (step S104 in FIG. 9).
As in the first embodiment, the pressure measurement unit 1025c converts the capacitance (Cx-Cr)/Cx into a pressure measurement value _P2 (step S105 in FIG. 9).

In the first measurement mode, the pressure correcting unit 1026c obtains a value obtained by correcting the pressure measurement value _P2 based on the temperature _T2 of the measurement target medium in the pressure measurement chamber 3c measured by the temperature sensor 8 and the temperature _T1 of the measurement target medium in the measurement target chamber 12 estimated by the temperature estimating unit 1020c (step S106 in FIG. 9). A first correlation table that associates the temperatures _T2 , _T1 in the first measurement mode, the pressure measurement value _P2 , and the actual pressure value _P1 of the measurement target medium in the measurement target chamber 12 is created when the diaphragm vacuum gauge is calibrated and is set in the pressure correcting unit 1026c. The pressure correcting unit 1026c obtains _the pressure value _P1 corresponding to the temperatures _T2 , _T1 , and the pressure measurement value P2 from the first correlation table.

Then, the pressure correction unit 1026c outputs the calculated pressure value _P1 to, for example, a higher-level device via the interface unit 105 (step S107 in FIG. 9).
Thus, the operation in the first measurement mode can provide the same effects as those in the first embodiment.

Next, in the second measurement mode, the pressure measurement chamber 3c serves as a pressure adjustment chamber. Also, in the second measurement mode, the control unit 1021c does not operate the cooler 6, and operates only the heater 15.

17 is a flow chart for explaining the operation of the calculation processing unit 102c in the second measurement mode. In the second measurement mode, the temperature estimation unit 1020c estimates the temperature _T1 of the measurement medium in the measurement chamber 12 from the temperature _T3 measured by the temperature sensor 8 (step S300 in FIG. 17). The relationship between the temperature _T3 of the measurement medium in the pressure measurement chamber 3c and the temperature _T1 of the measurement medium in the measurement chamber 12 in the second measurement mode has been confirmed by a prior test. The temperature estimation unit 1020c may calculate _the temperature _T1 from the temperature T3 using a preset equation for the second measurement mode, or may obtain the value of the temperature _T1 corresponding to the temperature _T3 from a preset table for the second measurement mode.

In the second measurement mode, the control unit 1021c supplies power to the heater ₁₅ to generate heat so that the difference T ₂ -T ₁ between the temperature T ₁ estimated by the temperature estimation unit 1020c and the temperature T 2 measured by the temperature sensor 14 becomes a second predetermined value (step S301 in FIG. 17). In this way, the pressure measurement chamber 3d is heated so that the temperature difference T ₂ -T ₁ between the temperature T 2 of the measurement medium in the pressure measurement chamber 3d and the temperature T _{1 of the measurement medium in the measurement chamber 12 becomes the second predetermined value. The second predetermined value that determines the temperature difference T 2 -T 1 can be set} arbitrarily within the range of 0°C to 500°C.

In the second measurement mode, the capacitance calculation unit 1022c calculates the value of the capacitance Cx from the amplitude of the output signal of the synchronous detection unit 1008 of the signal detection unit 106 (step S302 in FIG. 17). In the second measurement mode, the capacitance difference calculation unit 1023c calculates the value of the capacitance difference (Cx-Cr) from the amplitude of the output signal of the synchronous detection unit 1009 of the signal detection unit 106 (step S303 in FIG. 17).

As in the first embodiment, the capacitance corrector 1024c calculates a value (Cx-Cr)/Cx obtained by correcting the capacitance Cx using the reference capacitance Cr (step S304 in FIG. 17).
As in the first embodiment, the pressure measurement unit 1025c converts the capacitance (Cx-Cr)/Cx into a pressure measurement value _P2 (step S305 in FIG. 17).

In the second measurement mode, the pressure correcting unit 1026c obtains a value obtained by correcting the pressure measurement value _P2 based on the temperature _T2 of the measurement target medium in the pressure measurement chamber 3d measured by the temperature sensor 14 and the temperature _T1 of the measurement target medium in the measurement target chamber 12 estimated by the temperature estimating unit 1020c (step S306 in FIG. 17). A second correlation table that associates the temperatures _T2 , _T1 , the pressure measurement value _P2 , and the actual pressure value _P1 of the measurement target medium in the measurement target chamber 12 in the second measurement mode is created when the diaphragm vacuum gauge is calibrated and is set in the pressure correcting unit 1026c. The pressure correcting unit 1026c obtains _the pressure value _P1 corresponding to the temperatures _T2 , _T1 , and the pressure measurement value P2 from the second correlation table.

Then, the pressure correction unit 1026c outputs the calculated pressure value _P1 to, for example, a higher-level device via the interface unit 105 (step S307 in FIG. 17).
The calculation processing unit 102c performs the processes of steps S300 to S307 for each measurement period, for example, until the pressure measurement operation is ended by a user instruction (YES in step S308 in FIG. 17).

As mentioned above, the second measurement mode is intended for the low pressure range. Diaphragm vacuum gauges usually have a minimum full-scale pressure range of around 1.3 Pa. The reason for the 1.3 Pa range is that the measurable pressure range is determined by the thickness of the diaphragm due to the structure of the vacuum gauge. In other words, in order to measure pressures lower than normal, the diaphragm needs to be made thinner.

When the diaphragm of a diaphragm vacuum gauge is made thinner to measure lower pressures, it becomes more susceptible to the effects of disturbances, resulting in more restrictions on design and use. Specifically, the effects of residual stress from the sensor mount (package) become more pronounced, and there is a higher possibility that the measurement accuracy will deteriorate due to disturbances such as temperature and vibration when the vacuum gauge is in use. In this way, there is a structural lower limit to the practical pressure measurement range of a diaphragm vacuum gauge, but in some situations it may be necessary to measure below the lower limit.

Therefore, in the second measurement mode, the measurement medium supplied to the pressure measurement chamber 3d of the diaphragm vacuum gauge is heated to raise the pressure to a measurable range (within the lower limit) and then measured, and the pressure measurement value _P2 is corrected based on the temperature difference caused by heating.
Thus, in this embodiment, the upper limit of the pressure measurement range can be extended (the upper limit can be raised) in the first measurement mode, and the lower limit of the pressure measurement range can be extended (the lower limit can be lowered) in the second measurement mode.

In this embodiment, the temperature _T1 of the measurement medium in the measurement chamber 12 is estimated by the temperature estimation unit 1020c, but if a temperature sensor is provided in the measurement chamber 12, the value of the temperature _T1 may be obtained from this temperature sensor.

In this embodiment, the pressure measurement value _P2 is constantly corrected by the pressure correction unit 1026c, but the present invention is not limited to this. That is, the pressure correction unit 1026c may normally output the pressure measurement value _P2 as the pressure value _P1 without correcting it in both the first measurement mode and the second measurement mode, correct the pressure measurement value _P2 by the process of step S106 only when the pressure measurement value _P2 exceeds the upper limit of a specified pressure measurement range in the first measurement mode, and correct the pressure measurement value _P2 by the process of step S306 only when the pressure measurement value _P2 falls below the lower limit of the specified pressure measurement range in the second measurement mode.

This embodiment assumes a case where the temperature of the measured chamber 12 cannot be known in real time. By calibrating the vacuum gauge at the time of shipment, the thermal transition between the measured chamber 12 and the two pressure measurement chambers 3c, 3d is corrected. By using the thermal transition phenomenon between the two pressure measurement chambers 3c, 3d, it is possible to exceed both the upper and lower measurement limits. In other words, it is possible to raise the upper limit of the pressure measurement range and lower the lower limit.

In the first to fourth embodiments, the capacitance Cx is corrected by the reference capacitance Cr to calculate the value (Cx-Cr)/Cx. However, this is not limiting, and the capacitance Cx may be converted into the pressure measurement value _P2 .

The arithmetic processing units 102, 102b, and 102c described in the first to fourth 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. 18.

The computer includes a CPU 400, a storage device 401, and an interface device (I/F) 402. The cooler 6, the heater 15, the AD conversion unit 101, and the like are connected to the I/F 402. In such a computer, a program for implementing the method of the present invention is stored in the storage device 401. The CPU 400 executes the processing described in the first to fourth embodiments in accordance with the program stored in the storage device 401.

This invention can be applied to pressure measurement technology.

1, 1a... pressure adjustment chamber, 2, 2a, 2c... pipes, 3, 3a to 3d... pressure measurement chamber, 4, 4a, 4c... throttle, 5, 13... pressure receiving section, 6... cooler, 7, 8, 14... temperature sensor, 10, 10b, 10c... circuit section, 11... heat flow sensor, 12... measured chamber, 15... heater, 100, 106... signal detection section, 101, 101c... AD conversion section, 102, 102b, 102c... calculation processing section, 10 3, 103b, 103c...memory, 104...power supply, 105...interface unit, 1020, 1020b, 1020c...temperature estimation unit, 1021, 1021c...control unit, 1022, 1022c...capacity calculation unit, 1023, 1023c...capacity difference calculation unit, 1024, 1024c...capacity correction unit, 1025, 1025c...pressure measurement unit, 1026, 1026b, 1026c...pressure correction unit.

Claims (19)

a pressure adjustment chamber provided to communicate with the measurement chamber via a pipe;
a pressure measuring chamber provided in communication with the pressure adjusting chamber;
a pressure receiving section configured such that a capacitance changes in response to a displacement of a diaphragm caused by a pressure of a medium to be measured in the pressure measuring chamber;
a cooler configured to cool the pressure measurement chamber;
a first temperature sensor configured to measure a temperature of a medium to be measured in the pressure measurement chamber;
a pressure measuring unit configured to convert the capacitance into a pressure measurement;
a pressure correction unit configured to correct the pressure measurement value based on the temperature measured by the first temperature sensor and the temperature of the measurement target medium in the measurement target chamber,
A diaphragm vacuum gauge comprising: a pressure measuring chamber and a chamber for measuring a temperature difference between the temperature of the medium to be measured in the pressure measuring chamber and a pressure difference is converted into the temperature difference to correct the pressure measurement value. 2. The diaphragm vacuum gauge according to claim 1,
1. A diaphragm vacuum gauge comprising: said pressure adjustment chamber and said pressure measurement chamber arranged in series; and a medium to be measured flows into said pressure measurement chamber via said pressure adjustment chamber. 2. The diaphragm vacuum gauge according to claim 1,
a pressure adjusting chamber and a pressure measuring chamber arranged in parallel, and a medium to be measured flows into the pressure adjusting chamber and the pressure measuring chamber via the piping; 4. The diaphragm vacuum gauge according to claim 1,
the pressure adjustment chamber and the pressure measurement chamber communicate with each other via a throttle;
The diaphragm vacuum gauge is characterized in that the orifice is a fixed orifice or a variable orifice. 5. The diaphragm vacuum gauge according to claim 1,
a second temperature sensor configured to measure the temperature of the medium in the pressure adjustment chamber;
and a temperature estimating unit configured to estimate a temperature of the measurement medium in the measurement chamber from the temperature measured by the second temperature sensor. 5. The diaphragm vacuum gauge according to claim 1,
A diaphragm vacuum gauge comprising: a second temperature sensor provided in the measurement chamber, the second temperature sensor detecting a temperature of a medium to be measured in the measurement chamber; a pressure measurement chamber provided in communication with the measurement chamber via a pipe;
a pressure receiving section configured such that a capacitance changes in response to a displacement of a diaphragm caused by a pressure of a medium to be measured in the pressure measuring chamber;
a cooler configured to cool the pressure measurement chamber;
a first temperature sensor configured to measure a temperature of a medium to be measured in the pressure measurement chamber;
a pressure measuring unit configured to convert the capacitance into a pressure measurement;
a pressure correction unit configured to correct the pressure measurement value based on the temperature measured by the first temperature sensor and the temperature of the measurement target medium in the measurement target chamber,
A diaphragm vacuum gauge comprising: a pressure measuring chamber and a chamber for measuring a temperature difference between the temperature of the medium to be measured in the pressure measuring chamber and a pressure difference is converted into the temperature difference to correct the pressure measurement value. 8. The diaphragm vacuum gauge according to claim 7,
a heat flow sensor configured to measure heat flow in the pipe;
and a temperature estimating unit configured to estimate a temperature of a measurement target medium in the measurement target chamber from a heat flow rate measured by the heat flow sensor. 8. The diaphragm vacuum gauge according to claim 7,
A diaphragm vacuum gauge comprising: a second temperature sensor provided in the measurement chamber, the second temperature sensor detecting a temperature of a medium to be measured in the measurement chamber; 10. The diaphragm vacuum gauge according to claim 1,
a control unit configured to control the cooler to remove heat so that a temperature difference between a temperature of the medium to be measured in the pressure measurement chamber and a temperature of the medium to be measured in the measurement chamber becomes a predetermined value. 11. The diaphragm vacuum gauge according to claim 1,
The pressure receiving portion is
A first electrode formed on the base;
the diaphragm disposed across a gap from the base;
a second electrode formed on the diaphragm 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;
a capacitance calculation unit configured to calculate a first capacitance between the first and second electrodes;
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;
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,
The diaphragm vacuum gauge according to claim 1, wherein the pressure measuring unit converts the corrected first capacitance into the pressure measurement value. 12. The diaphragm vacuum gauge according to claim 1,
The diaphragm vacuum gauge according to claim 1, wherein the pressure correction unit corrects the pressure measurement value only when the pressure measurement value exceeds an upper limit of a specified pressure measurement range. a first pressure measurement chamber provided in communication with the measurement chamber via a pipe;
a second pressure measurement chamber communicating with the measurement chamber via the piping and communicating with the first pressure measurement chamber;
a first pressure receiving section configured such that a capacitance thereof changes in response to a displacement of a first diaphragm caused by a pressure of a medium to be measured in the first pressure measuring chamber;
a second pressure receiving section configured such that a capacitance thereof changes in response to a displacement of a second diaphragm caused by a pressure of a medium to be measured in the second pressure measuring chamber;
a cooler configured to cool the first pressure measurement chamber;
a heater configured to heat the second pressure measuring chamber;
a first temperature sensor configured to measure a temperature of a measurement target medium in the first pressure measurement chamber;
a second temperature sensor configured to measure the temperature of a medium to be measured in the second pressure measurement chamber;
a pressure measuring unit configured to convert a capacitance of the first pressure receiving unit into a pressure measurement value in a first measurement mode in which the cooler is operating and the heater is not operating, and to convert a capacitance of the second pressure receiving unit into a pressure measurement value in a second measurement mode in which the heater is operating and the cooler is not operating;
a pressure correction unit configured to correct the pressure measurement value based on the temperature measured by the first temperature sensor and the temperature of the measurement medium in the measurement chamber in the first measurement mode, and to correct the pressure measurement value based on the temperature measured by the second temperature sensor and the temperature of the measurement medium in the measurement chamber in the second measurement mode,
A diaphragm vacuum gauge characterized in that a temperature difference between the temperature of the medium to be measured in the first pressure measuring chamber or the temperature of the medium to be measured in the second pressure measuring chamber and the temperature of the medium to be measured in the measurement chamber is converted into a pressure difference to correct the pressure measurement value. 14. The diaphragm vacuum gauge of claim 13,
the first pressure measuring chamber and the second pressure measuring chamber communicate with each other via a throttle;
The diaphragm vacuum gauge is characterized in that the orifice is a fixed orifice or a variable orifice. 15. The diaphragm vacuum gauge according to claim 13 or 14,
a temperature estimating unit configured to estimate a temperature of the measured medium in the measured chamber from the temperature measured by the second temperature sensor in the first measurement mode, and to estimate a temperature of the measured medium in the measured chamber from the temperature measured by the first temperature sensor in the second measurement mode. 15. The diaphragm vacuum gauge according to claim 13 or 14,
a third temperature sensor provided in the measurement chamber, the third temperature sensor detecting a temperature of a medium to be measured in the measurement chamber; 17. A diaphragm vacuum gauge according to any one of claims 13 to 16,
a control unit configured to control the cooler to remove heat so that a temperature difference between a temperature of the measured medium in the first pressure measurement chamber and a temperature of the measured medium in the measured chamber becomes a first predetermined value in the first measurement mode, and to control the heater to generate heat so that a temperature difference between a temperature of the measured medium in the second pressure measurement chamber and a temperature of the measured medium in the measured chamber becomes a second predetermined value in the second measurement mode. 18. A diaphragm vacuum gauge according to any one of claims 13 to 17,
The first pressure receiving portion includes:
a first electrode formed on the first base;
the first diaphragm disposed across a gap from the first base;
a second electrode formed on the first diaphragm so as to face the first electrode;
a third electrode formed on the first seat outside the first electrode;
a fourth electrode formed on the first diaphragm outside the second electrode so as to face the third electrode;
The second pressure receiving portion includes:
a fifth electrode formed on the second base;
the second diaphragm disposed across a gap from the second base;
a sixth electrode formed on the second diaphragm so as to face the fifth electrode;
a seventh electrode formed on the second seat outside the fifth electrode;
an eighth electrode formed on the second diaphragm outside the sixth electrode so as to face the seventh electrode;
a capacitance calculation unit configured to calculate a first capacitance between the first and second electrodes in the first measurement mode and to calculate a second capacitance between the fifth and sixth electrodes in the second measurement mode;
a capacitance difference calculation unit configured to calculate a value obtained by subtracting a third capacitance between the third and fourth electrodes from the first capacitance in the first measurement mode, and to calculate a value obtained by subtracting a fourth capacitance between the seventh and eighth electrodes from the second capacitance in the second measurement mode;
a capacitance correction unit configured to correct the first capacitance by the third capacitance based on a calculation result of the capacitance calculation unit and a calculation result of the capacitance difference calculation unit in the first measurement mode, and to correct the second capacitance by the fourth capacitance based on a calculation result of the capacitance calculation unit and a calculation result of the capacitance difference calculation unit in the second measurement mode,
the pressure measurement unit converts the corrected first capacitance into the pressure measurement value in the first measurement mode, and converts the corrected second capacitance into the pressure measurement value in the second measurement mode. 19. A diaphragm vacuum gauge according to any one of claims 13 to 18,
the pressure correction unit corrects the pressure measurement value only when the pressure measurement value exceeds an upper limit of a prescribed pressure measurement range in the first measurement mode, and corrects the pressure measurement value only when the pressure measurement value falls below a lower limit of a prescribed pressure measurement range in the second measurement mode.

Images