JPS5945935B2 - Vacuum measurement method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to a force method for measuring the degree of vacuum aimed at improving the S/N ratio.

Conventionally, to measure the degree of vacuum in high vacuum or ultra-high vacuum, an ionization vacuum gauge is used to ionize the residual gas in the vacuum, the generated ions are extracted as an ion current through an ion collector, and the current value is measured in the vacuum. The most commonly used method was to convert it into degrees, but in this method there were various electromagnetic devices near the measurement system, or the measurement bulb and its power source (the DC amplifier for the ion current) were separated. However, there is a problem in that various electrical after-sounds are mixed into the ion current, making accurate measurement impossible.

Furthermore, if the measuring ball is installed in an atmosphere where charged particles exist in vacuum, such as in an accelerator or plasma generator, noise caused by the charged particles will be mixed into the ion current, making accurate measurement even more difficult. I was making it into something.

However, the present invention modulates the electron current of the measuring bulb (the current flowing to ionize residual gas) in the ionization vacuum gauge, and detects the amplified ion current extracted from the ion collector in synchronization with the electron current. By smoothing this, the electrical noise was removed, so Oki 1
This enables accurate measurements even when there are various types of electromagnetic equipment around the fixed system or when the measurement bulb and power source are far apart.

In addition to the above method, an electrostatic shield was placed to cover the electrodes to prevent noise from charged particles entering through the electrodes of the measurement bulb. They also succeeded in removing noise caused by particles.

That is, to explain this invention with reference to an embodiment, a measurement system consisting of an ionization vacuum gauge measurement bulb 1 and its power source is constructed as shown in FIG.

In the figure, 2 represents a filament, 3 represents an anode, and 4 represents an ion collector. An electronic current controller 5 is interposed in the filament 2, and a filament heating power source 6 is connected to the filament 2.
The filament 2 is grounded via the battery 7 (20~60cm) and the resistor 8, and the anode 3 is connected to the battery 9 (150~2cm).
00V) to form an electronic current circuit between the filament and the anode.

The electronic current controller 5 obtains information (voltage) corresponding to the electronic current value from the resistor 8, controls the current flowing through the filament 2, and functions so that a desired constant electronic current flows.

In order to modulate this electronic current so that it includes an alternating current component, a modulation signal 11 taken out from an oscillator 10 is given to the electronic current controller 5.

On the other hand, a current/voltage converter 12 and an amplifier 13 are connected in series to the ion collector 4 through a capacitor 14, and the output of the amplifier 13 and the addition circuit 150 are connected to the analog gate 1.
6a as well as the waveform inversion circuit 17 and the analog gate 16b.
A low frequency wave generator 18 and an ammeter 19 are connected in series to the output of 5.

Said analog game) 16a. The gate opening/closing signal for the analog gate 16b is passed through the phase shifter 20, which is the output of the oscillator 10, and the waveform shaping circuit 21 that outputs a rectangular wave.
At the same time, the opening/closing signal is inverted by the inverter 22 and applied to the analog game N6b.

In the above measurement system, the electron current flowing between the filament and the anode is modulated by the modulation signal 11, and as a result contains an alternating current component.

Therefore, the 7'Cl current generated by the electron current also flows to the 4-on collector 4 in a state containing an alternating current component.

After this ion NEW is converted into a voltage by a current/voltage converter 12, only its alternating current component is given to an amplifier 13, where it is amplified.

The amplified ion current is applied to the adder circuit 15 in a waveform with positive and negative symmetry, and an analog gate 16at16b is interposed on the line, and the analog gate 16a,
16b is arranged to open and close alternately at every phase shift angle of 7 radians in synchronization with the signal modulating the electron current, so that the ion current appearing at the output of the amplifier 13 is synchronously detected. appears at the output of the adder circuit 15.

Since changes in the ion current usually have a slight delay with respect to the modulation signal of the electron current, this discrepancy is caused by the phase shifter 20.
Adjust when measuring.

The detected output of the adder circuit 15 is smoothed by the low-frequency r wave generator 18 to become a DC current from which noise components have been removed. Based on the indication from the ammeter 19 that operates with this current, the detection output of the system in which the measurement bulb 1 is attached is determined. The degree of vacuum can be determined.

Generally, the degree of vacuum determined from the current value is directly calibrated on the scale plate of the electric meter 19 so that the degree of vacuum can be directly connected.

It is of course possible to use a digital display instead of the ammeter indication.

Note that the frequency of the oscillator 10 for modulating the electronic current is preferably about 20 hertz, taking into account other electromagnetic equipment used around this measurement system.

FIG. 2 shows the ionization vacuum gauge 1 used in the above embodiment,
A filament 2, an anode 3, and an ion collector 4 are exposed within the vacuum device.

A so-called nude measuring ball is shown.

In the figure, 23 and 23 are introduction terminals that support each electrode, and 24 is a flange for attaching this measurement bulb to a vacuum device.

When such a nude measuring sphere is installed in a device where charged particles exist in a vacuum, such as an accelerator or a plasma generator, in addition to the electrical noise mentioned above, charged particles may fly into the measuring sphere. Noise from charged particles generated by this is mixed into the ionic current.

In order to eliminate such noise, the electrodes placed in a vacuum are covered with an electrostatic shield.

Figure 3 shows an electrostatic shield in which the electrodes of the filament 2, anode 3, and ion collector 4 placed in a vacuum to measure the degree of vacuum are triple-layered with metal meshes 25, 25a, and 25b formed into a cylindrical shape. It is covered with 26.

The electrostatic shield 26 grounds the inner metal mesh 25, the middle metal mesh 25aK has a negative potential (approximately 200 volts), and the outer metal mesh 25b has a positive potential (approximately 200 volts). give.

In this embodiment, the electrostatic shield 26 can repel charged particles straying toward the electrodes of the measurement bulb in vacuum and prevent them from being mixed into the ion current, so even in a vacuum where charged particles are present, Accurate measurements are possible.

Point 'L' where the electron current is modulated and the alternating current component of the ion current is synchronously detected! Same as above.

That is, according to this invention, the degree of vacuum is determined by modulating the electron current and synchronously detecting the alternating current component in the ion current and then smoothing it, thereby eliminating electrical noise around the measurement system and obtaining accurate It has various effects such as being able to perform measurements and making it possible to separate the measuring bulb from its power source.

In addition, since the electrodes of the measurement bulb are covered with an electrostatic shield, noise caused by charged particles in the vacuum can be removed, making it possible to accurately measure the degree of vacuum even during military operations such as accelerators and plasma generators. .

[Brief explanation of drawings]

Figure 1 is a block diagram of a measurement system implementing this invention, Figure 2 is a block diagram of a measurement system implementing this invention.
The figure is a partially cutaway perspective view of the same nude-type measuring sphere used in the actual measurement system, and FIG. 3 is a longitudinal cross-sectional view of the measuring sphere covered with an electrostatic shield. 1...Ionization vacuum gauge measurement bulb, 2...Filament, 3...Anode, 4...Ion collector, 5...Electron current controller,
6...Filament heating power supply, 7,9...
... Battery, 8 ... Resistor, 10 ... Oscillator, 11 ... Modulation signal, 12 ... Current, voltage converter, 13 ... ...Amplifier, 14...
... Capacitor, 15 ... Addition circuit, 16a
, 16b...Analog gate, 17...
・Waveform inversion circuit, 1801000. Low-frequency p-wave device, 19.
...Ammeter, 20...Phase shifter, 21...
... Waveform shaping circuit, 22 ... Inverter,
23...Introduction terminal, 24...Flange, 2
5.25a. 25b...Metal mesh, 26...Electrostatic shield.

Claims (1)

[Claims] 1 In a vacuum measurement method in which an electron current is passed between electrodes placed in a vacuum, and ions generated by this electron current are extracted from an ion collector as an ion current, the electrodes placed in a vacuum are covered with an electrostatic shield. One way to remove noise mixed in from the electrode part is to modulate the electron current and amplify the modulation component of the ion current, then detect it in synchronization with the electron current, and use the low-frequency P-wave detector to output the detected signal. A force method for measuring the degree of vacuum characterized by determining the degree of vacuum from the smoothed output after smoothing.