JPS61277030A - Apparatus for calibrating vacuum gauge - Google Patents

Abstract

PURPOSE:To make it possible to perform the calibration and capacity measurement of a vacuum gauge in a pressure region lower than 10<-4>Torr with good accuracy, by correlating the hydrogen transmissivity of a nickel membrane with the temp. dependency of hydrogen transmissivity. CONSTITUTION:A current is supplied to a heater 16 to adjust the temp. T of a nickel membrane to predetermined one and, after said temp. T reached the predetermined one, the opening degree of a flow control valve 17 is regulated to allow the pressure of the calibration gas in a heating chamber to reach predetermined one on the basis of the indication of a pressure gauge 38 and, thereafter, a flow control valve 17 is closed and the flow control valve 18 and check valve 19 in the side of a vacuum chamber 17 are perfectly closed. Next, the hydrogen partial pressure P1 of the calibration gas in the heating chamber is calculated by a static equilibrium method and the calibration of a high pressure gauge to be calibrated is subsequently performed. After preparation has been finished, the calibration of the high vacuum gauge 1 to be calibrated is performed. An ion pump 26 is started and the flow control valve 18 is opened to set the vacuum chamber 7 to a dynamic equilibrium state, that is, a state having the flow of gas. Next, when the temp. T of the nickel membrane is changed while the vacuum chamber is held to a dynamic state, calibration is enabled by the pressure P3 of the vacuum gauge part to be calibrated and the output of the high vacuum gauge 1 to be calibrated.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a vacuum measurement instrument that can measure high vacuums better than 10"3 Torr, and is particularly suitable for automatic calibration and performance measurement of vacuum measurement instruments for high vacuum measurements. This article relates to an automatic vacuum gauge calibration device.

[Background of the invention]

In the conventional method, as described in JISZ-8750, 28752km, a predetermined pressure was obtained by adjusting the flow rate of the calibration gas flowing into the measuring section using a flow control valve. However, in the above method,
The amount of change in the flow rate is larger than the change in the opening degree of the flow control valve, and it is difficult to adjust the flow control valve so that the measuring section has a predetermined pressure.

[Purpose of the invention]

The purpose of the present invention is to improve the accuracy of l
It is an object of the present invention to provide a device that can automatically and accurately calibrate and measure the performance of a vacuum gauge or a pressure gauge in a pressure region smaller than 0-4 Torr.

[Summary of the invention]

A problem in calibrating a vacuum gauge that measures pressure in a region smaller than 10-' Torr is that a predetermined pressure required for calibration cannot be created arbitrarily.

By the way, there is a method to measure the hydrogen partial pressure in a fluid using the hydrogen permeability of a nickel thin film, but this involves introducing a fluid containing hydrogen onto one side of the nickel thin film, leaving the other side in a vacuum, and then passing through the nickel thin film. This method determines the hydrogen partial pressure by measuring the pressure on the vacuum side due to the hydrogen coming in with a vacuum gauge. Here, since the hydrogen permeability of the nickel thin film has temperature dependence, by changing the temperature, it is possible to change the hydrogen permeable membrane and control the pressure on the vacuum side.

This device was invented by combining the two items listed above.

[Embodiments of the invention]

The present invention will be explained in detail below.

FIG. 1 shows the first example. In Example 1, a mixed gas of hydrogen and argon is used as the calibration gas, and a nickel thin film is used as the permeable membrane. Note that the calibration gas may be any gas as long as its relative sensitivity with other gases is known and there is a permeable membrane that allows only that gas to pass through.The hydrogen permeable membrane is not limited to nickel, but may also be a membrane that permeates hydrogen such as palladium. Anything is fine.

The functions of each device in FIG. 1 will be explained below.

The vacuum gauge 1 to be calibrated is a high vacuum vacuum gauge that is calibrated using this device, and the low vacuum vacuum gauge 2 is a reference vacuum gauge for measuring the absolute value of hydrogen partial pressure in the heating chamber. be. These gauge signals are input to the computer 29 through transmission lines 4 and 5. The vacuum chamber 7 for setting a predetermined pressure for calibrating the high vacuum gauge 1 to be calibrated includes:
Exhaust pump 24 and ion pump 2 as exhaust pumps
6 is installed, a flow control valve 18 is installed in front of the ion pump 26, and the opening degree can be adjusted by a computer 29 by driving a motor.The heating chamber 6 is directly injected with a zero calibration mixed gas, which is different from the vacuum chamber They are separated by a thin nickel film 8 that transmits only hydrogen. A temperature probe 9 is installed on the nickel thin film 8 to detect its temperature, and its signal is inputted to an adder 11 and a calculator 29 through a temperature transmitter 10. The output of the adder 11;:b is input to the power controller 14 through the PID controller 12 and the APPS 13, which controls the output of the heater 16 in the heating chamber to control the temperature of the gas in the heating chamber and the nickel thin film 8. Note that the nickel thin film temperature can be set to any desired temperature by setting a target value from the computer 29. Further, the heater power source 15 is a power source for the heater 16. The heating chamber 6 is provided with a calibration gas injection section and an internal exhaust section. The calibration gas injection part is a hydrogen gas container 30. An argon gas container 31, a calibration gas adjustment chamber 28 that mixes appropriate amounts of hydrogen gas and argon gas to create a calibration gas, a pressure gauge 3 that measures the pressure therein, and a heating chamber 6 from the calibration gas adjustment chamber 28. It is composed of a flow control valve 17 that adjusts the amount of gas inserted. The internal exhaust section.

It is composed of an exhaust pump 25 and an ion pump 27. A pressure gauge 38 is also installed in the heating chamber to measure internal pressure.

Describe the principle and method of calibration using this device below. The basic principle of this device is that since the hydrogen permeability of the nickel thin film is temperature dependent, the amount of hydrogen permeation can be controlled by controlling the temperature, and the pressure before and after the nickel thin film can be set arbitrarily. The details will be explained below with reference to FIG.

The lower part of Figure 3 is a simplified version of the main part of Figure 1.
The upper part of the figure is a graph of the hydrogen pressure distribution inside. In the model shown in the lower part of Figure 3, the following equation holds.

Qvr='Tm+'A=-(Pt""
P z"")・A...(1)q, ;Hydrogen permeation amount per unit area of nickel thin film (Torr 6cxl/s
ac, cxl) A; Nickel thin film area (al) K; Nickel thin film hydrogen permeability (Torr-al/5e
e) d; Nickel thin film thickness opening) QweP1#P2; Refer to figure symbol explanation Also, since the hydrogen flow rates per unit time in the vacuum gauge part and the ion pump part are equal, Q m = S3・p, = s4・P4...
・(2) S,,p,,S,,P,: See diagram symbol explanation Similarly, the hydrogen flow rate between the nickel thin film and the vacuum gauge and the hydrogen flow rate between the vacuum gauge and the ion pump are equal to Q, so QW = css ( pi p-) = 034 (Pa - P4) ... (3
) C2s * C34: Refer to figure symbol explanation The following formula is derived from the above formulas (1), (2), and (3) Cps (C34+S4J Here, A, d, S,, C2,, C,, are constants. Yes, P
If □ is constant, by changing the nickel thin film hydrogen permeability K, the vacuum gauge part pressure P3 can be changed as shown in the upper part of Figure 3.
can be expressed as P,'.

On the one hand, it is a function of temperature and can be expressed by the following formula.

K= a −exp (−E/ RT) ・b−P,
""=45)R; gas constant (cal/mo12-k)
T: Nickel thin film temperature (K) E: Activation energy (cal/mo Q)a;
Constant b, rrt; constants (4), (5) related to pressure dependence
) From the formula, the vacuum gauge part pressure P3 is determined by the nickel thin film temperature T.
It can be seen that it can be controlled by

The specific procedure for calibrating the vacuum gauge in this device will be explained below with reference to FIG.

Before calibration, d, A, C, , C, 4, S4. Measure the constants b and m in advance. In particular, since there is an instrumental error in P due to the nickel thin film, a calibrated high vacuum gauge is used in this device to accurately measure the pressure P. (4).

From formula (5), calculate the values of m and m of the nickel thin film to be used. Also, d, A, C, ,C,, are determined mechanically, and S
4 can also be measured by the orifice method using an orifice and a high vacuum gauge. The calibration procedure is shown below.

1. Close the stop valves 20 and 21, open the flow control valve 17 and the stop valves 22 and 23, and exhaust the inside of the heating chamber 6 with the exhaust pump 25. The ion pump 27 is used to exhaust the air, and the wall is thoroughly baked to degas the wall surface.

2. Similarly, vacuum chamber 7 is evacuated and baked to maintain a high vacuum.

3. Store the calibration gas in the calibration gas adjustment chamber by operating the stop valves 20 and 21.

4. With the stop valves 22 and 23 and the flow control valve 17 closed, the heater 16 is energized to keep the nickel thin film temperature T at a predetermined temperature.

5. After reaching the predetermined temperature, adjust the opening degree of the flow control valve 17 so that the calibration gas pressure in the heating chamber becomes the predetermined pressure according to the indication from the pressure gauge 38. However, since only the hydrogen in the calibration gas is involved in the calibration of the high vacuum gauge to be calibrated in the vacuum chamber, the partial pressure ratio of hydrogen to argon in the calibration gas is reduced to 1/1.
00 or 61/1000, and furthermore, the pressure ratio should be 1/10" to 1/10' before and after the nickel thin film.
The target pressure of the calibration gas injected into the heating chamber can also be made higher than atmospheric pressure. Further, since the accurate setting of the calibration pressure is performed by controlling the amount of hydrogen permeation through the nickel thin film, high accuracy is not required, and it is sufficient that the pressure is within a certain range.

6. When the calibration gas pressure reaches a predetermined pressure, close the flow control valve 17.

7. At this time, the flow control valve 18 on the vacuum chamber 7 side. The stop valve 19 is left fully open.

8. After determining the hydrogen partial pressure P1 in the calibration gas in the heating chamber by the static equilibrium method, the high vacuum gauge to be calibrated is calibrated. Then, the partial pressure of hydrogen in the calibration gas in the heating chamber 6 and the partial pressure of hydrogen in the vacuum chamber 7 reach equilibrium and become P, =P, , =P□, so Pl can be measured by measuring P3. Note that the static equilibrium pressure here is in the range of 1 to I x 10 Torr, and a vacuum gauge that measures this range can be calibrated with high accuracy using conventional methods, so the hydrogen partial pressure in the heating chamber can be calibrated with high accuracy. The accuracy of measurement also increases.

9. After completing the above preparations, calibrate the high vacuum gauge 1 to be calibrated. First, the ion pump 26 is activated and the flow control valve 18 is opened to bring the vacuum chamber 7 into a dynamic equilibrium state, that is, a state where gas flows. Then, a pressure distribution as shown in the graph at the top of FIG. 3 occurs in the vacuum chamber. In addition, flow control valve 1 at this time
The opening degree of No. 8 may be any opening degree as long as the conductor tube C34 can be determined, and it is also possible to stabilize the exhaust speed by using an orifice.

In addition, since the hydrogen gas in the vacuum chamber is exhausted, the partial pressure of the hydrogen in the heating chamber that supplies hydrogen to the vacuum chamber may decrease. Increase the melting ratio in the chamber. Alternatively, adjust the opening of the flow control valve 17 or install an orifice to replenish the heating chamber with calibration gas at a constant rate.
It is also possible to prevent l from changing. Further, in order to remove disturbance factors in the vacuum chamber, the low vacuum vacuum gauge 2 is stopped.

10. When the nickel thin film temperature T is changed while the vacuum chamber is kept in a dynamic state, calibration is performed using the pressure P3 of the vacuum gauge part to be calibrated determined from equations (4) and (5) and the output of the high vacuum gauge 1 to be calibrated. becomes possible.

Further, FIG. 4 shows a flowchart in the case where the steps 1 to 10 above are automated by a computer 29. Note that the computer 29 may be any type of device that can perform calculations.

Although the specific calibration procedure has been described in detail above, the advantages of this calibration method are described below.

1. The pressure inside the vacuum chamber can be controlled only by the temperature of the nickel thin film, so calibration can be easily automated.

2. If the hydrogen partial pressure in the heating chamber is fixed, there is a one-to-one correspondence between the pressure in the vacuum chamber and the temperature of the nickel thin film. Therefore, it is easy to measure the repeatability of the vacuum gauge, and furthermore, by reducing the amount of temperature change, the amount of change in the pressure in the vacuum chamber can also be reduced, making it possible to measure the dead zone of the vacuum gauge.

3. Calibration is performed while the vacuum chamber is in a dynamic state and the inside is constantly evacuated, so calibration errors due to the accumulation effect of gas emitted from the walls can be reduced.

In the above description, the ion pump used for evacuation in the high vacuum part of the heating chamber and the vacuum chamber may be any pump that can be used in the region of 10-4 Torr or less. Further, the calibration gas may be only hydrogen, or a gas such as argon and a level gas may be used from the beginning.

FIG. 2 shows one example of the application of this device, in which a vacuum gauge is calibrated using liquid metal instead of the calibration gas and hydrogen contained therein as an impurity. The configuration of the apparatus will be explained below using FIG. 2.

The vacuum chamber 7 is equipped with a vacuum gauge, a transmitter, and an exhaust pump as in Example 1. On the other hand, the heating chamber 6 separated from the vacuum chamber 7 by the nickel thin film 8 is filled with liquid metal. A temperature probe 9 is set on the heating chamber side of the nickel thin film 8, and the temperature signal is sent to the computer 2 via a transmission line 10.
9 and is used to control the output of talk 16. The heating chamber 6 is connected to the liquid metal loop 37 via a liquid metal stop valve 33,34. The liquid metal loop is equipped with a cold trap 36 and a liquid metal circulation pump 35 for controlling the amount of hydrogen dissolved in the liquid metal according to the saturation temperature. The cold trap is a device that controls the amount of dissolved hydrogen, that is, the hydrogen partial pressure P□ in the liquid metal, by utilizing the fact that the amount of hydrogen dissolved in the liquid metal changes depending on the saturation temperature. Transmitter 10. A cold trap temperature control heater 39, its power source 40, and a cold trap temperature controller 41 are provided, and the temperature signal from the transmitter 1o is input to the temperature controller 41 and also to the computer 29, and the liquid metal is It is used to calculate the hydrogen partial pressure P1 inside.

Cw=1・P, 1″...(6)C
YO; Concentration of liquid metal in water (ppm) K; 5i
everts constant (ppm/Torr L4)PI
III; Water in liquid metal partial pressure (Torr) QOgloK
, = 0.86-122.0/T・-(7)T; Nickel thin film temperature (K) 41 og. C, l = 6.067-2880/1-
(8) t ; Saturation temperature inside the cold trap (K) From the above, = (10 (s, osv-2sso/off/10 (0
, Il! -1210/T) )2 , (9) Here, since the water-in-liquid metal partial pressure pHl corresponds to the hydrogen partial pressure in the heating chamber, it can be regarded as P*w=P1. Therefore, the static equilibrium pressure P□ of the heating chamber and the vacuum chamber can be determined from equation (9). The high vacuum gauge to be calibrated can be calibrated in the same manner as in Example 1 below. Note that the liquid metal in Example 2 may be any metal containing hydrogen as an impurity, such as sodium or Na.

C. Effects of the Invention] As detailed above, according to the present invention, 1O-4Torr
This makes it possible to calibrate vacuum gauges with high accuracy even in high vacuum areas. Furthermore, since the object to be controlled is the temperature of the stagnant fluid, which has few disturbances and is easy to control, it is possible to set the target temperature within ±0.5°C and change the temperature in 1°C increments.Therefore, the target pressure can also be set within ±0.5°C. Accuracy of 5% is possible, and fine pressure changes of ±1% of the reference pressure are also possible. This makes it possible to measure instrument performance such as repeatability and dead zone, which were previously impossible to measure. Furthermore, automation is easy because the pressure is set by temperature control using an electric heater.

[Brief explanation of the drawing]

Fig. 1 is a system configuration diagram of a vacuum gauge automatic calibration device according to an embodiment of the present invention, Fig. 2 is a system configuration diagram of a vacuum gauge automatic calibration device of another embodiment, and Fig. 3 is a diagram showing the pressure distribution within the device and simplification of the device. A diagram showing the model, FIG. 4, is an automatic calibration flowchart. 1... High vacuum gauge for calibration, 2... Vacuum gauge for low vacuum, 3... Pressure gauge, 4... High vacuum gauge transmitter for calibration, 5... Vacuum gauge for low vacuum Transmitter, 6...
・Heating chamber, 7... Vacuum chamber, 8... Permeable membrane, 9...
Temperature measuring element, 10... Temperature transmitter, 11... Heater, 12... PID controller, 13... APPS, 14
...Power regulator, 15...Heater power supply, 16...
Heater, 17...Flow control valve.・, 18...Flow control valve, 19...Stop valve, 20...
Stop valve, 21... Stop valve, 22... Stop valve, 23.
... Stop valve, 24 ... Exhaust pump, 25 ... Exhaust pump, 26 ... Ion pump, 27 ... Ion pump, 28 ... Calibration gas adjustment room, 29 ... Calculator,
30...Hydrogen gas container. 31... Argon gas container, 32... Stop valve for liquid metal, 33... Stop valve for liquid metal, 34... Stop valve for liquid metal, 35... Pump for liquid metal circulation, 36.
...cold trap, 37...liquid metal loop, 3
8...Pressure gauge, 39...Heater for cold trap, 40...Heater power supply for cold syrup, 41...
・Temperature controller for cold trap, Pl... Hydrogen partial pressure in the heating chamber (Torr), Pg... Pressure at the nickel thin film part on the vacuum chamber side (Torr), Pa... Pressure at the vacuum gauge part to be calibrated (Torr) , P, - Ion pump part pressure (Torr), S3... Vacuum gauge part pumping speed for calibration (CiI/5ac) S4... Ion pump part pumping speed (al?/see), C23... Nickel Conductance between thin film and vacuum gauge (ad/sec)
, C34... Vacuum gauge-ion pump conductance (aJ/ssc), Q-... Nickel thin film hydrogen permeation amount (Torr-cxl/see).

Claims (1)

[Scope of Claims] 1. A thin film that transmits a certain element in a container having a temperature control section and a flow rate control section, a vacuum chamber containing the thin film, a vacuum conduit and a vacuum pump that exhaust the element that has passed through the thin film, and the a vacuum system consisting of a vacuum measuring instrument for measuring the pressure inside the vacuum chamber; a fluid conduit that guides fluid to the opposite side of the vacuum chamber of the thin film in the vacuum system; and a purity adjustment section that can adjust the amount of a specific element in the fluid; A vacuum gauge calibration device characterized by comprising an injection part capable of injecting a specific element. 2. In the vacuum gauge calibration device, the concentration of a specific element in the fluid is adjusted by controlling the purity adjustment section and the injection section, and the absolute equilibrium pressure in the vacuum chamber corresponding to the concentration is changed, thereby making the vacuum measurement instrument in the vacuum chamber. 2. The vacuum gauge calibration device according to claim 1, wherein absolute calibration of the vacuum gauge is possible. 3. The pressure in the vacuum chamber is changed by changing the temperature of the vacuum thin film, thereby making it possible to calibrate and measure the performance of a vacuum measuring instrument with high precision. Vacuum gauge calibration device. 4. The target measurement quantity can be automatically measured by controlling the fluid temperature and the vacuum system valve in accordance with the measurement mode, vacuum measurement instrument output, etc. Vacuum gauge calibration device as described in section.