JPH01274353A - Quadrupole mass spectrometer - Google Patents

Abstract

PURPOSE:To enable the prevention of burning of a hot filament in a rapid increase in pressure during a residual gas analysis by providing a circuit for detecting the ion current flowing into the focus electrode constituting an ion source, and measuring the divisional pressure and the whole pressure simultaneously. CONSTITUTION:A part of the ion formed inside an anode electrode 3 is captured by a focus electrode 5. This divisional pressure is obtained by measuring the ion current flowing into a Faraday cup 9, and the whole pressure is obtained by measuring the ion current flowing into the focus electrode 5 and supplied to an I-V converter 10. Hence, the ion current is converted to an amplified voltage signal. This signal is inputted to the minus input terminal of a comparative circuit 11 and compared with a standard voltage applied to the plus input terminal. When the ion current is increased by the increase in pressure in vacuum to make the input voltage of the comparative circuit 11 lower than the standard voltage, the output of the comparative circuit 11 is changed from L to H. As a result, a relay 12 is made to shut up a filament power source circuit 13.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a quadrupole mass spectrometer for analyzing the components of residual gas in vacuum.

[Summary of the invention]

The purpose of the present invention is to prevent hot cathode filament burnout by having a means for simultaneously measuring the pressure in vacuum during analysis of residual gas, thereby activating a protection circuit against sudden increases in pressure. That is.

[Conventional technology]

A quadrupole mass spectrometer is a device that measures the spectral intensity (hereinafter referred to as partial pressure) of gas molecules with different mass numbers by applying appropriate DC voltage and high-frequency voltage to quadrupole electrodes installed in the analysis section. be. Therefore, by calculating the sum of each partial pressure, the pressure of all gas molecules in vacuum (hereinafter referred to as total pressure) can be measured. The total pressure can also be measured by applying a DC voltage of zero volts and a high frequency voltage of several volts to the quadrupole electrodes. Conventionally, these methods were used to measure the total pressure, and when the pressure exceeded a certain level, 1.
The method used was to activate the filament protection circuit and cut off the filament power supply.

[Problem that the invention seeks to solve]

However, with these methods, it is not possible to measure the total pressure at the same time as the partial pressure measurement, and therefore it is not possible to instantly detect a sudden pressure rise and activate the filament protection circuit. As a result, the hot cathode filament often burned out.

[Means to solve the problem]

In order to solve the above-mentioned problems, the present invention extracts an ion current from a focus electrode constituting an ion source.
Input to converter. The I-V converter is connected to a comparator circuit,
Its output connects to a relay drive circuit.

[Effect]

When the ionic current corresponding to the pressure required to activate the filament protection circuit is detected, the output of the comparison circuit is “L”
When the level changes to "H", activate the relay and cut off the filament power supply.

〔Example〕

Embodiments of the present invention will be described below based on the drawings. 1st
The figure is a cross-sectional view of a quadrupole mass spectrometer according to the invention. The ion source part 1 includes a hot cathode filament 2 and an anode electrode))3
, a shield electrode 4 and a focus electrode 5. When the hot cathode filament 2 is energized, thermoelectrons fly out and fly toward the grid-shaped anode electrode 3. Some of the thermoelectrons are captured by the anode electrode 3, while others pass through the grid and head towards the focus electrode 5.
is placed at a negative potential with respect to the hot cathode filament 2, the thermionic electrons are repelled and head towards the anode electrode 3 again.Thermionic electrons that have passed through the anode electrode 3 then head towards the shield electrode 4, but here too they are heated. The electrons are repelled.

In this way, the thermoelectrons flying from the hot cathode filament 2 reciprocate inside and outside the anode electrode 3, but a small portion of these thermoelectrons collide with gas molecules inside the ion source and are ionized. Ions generated inside the anode electrode 3 by the ionization action are guided to the mass spectrometer 6 by the lens action of the focus electrode 5. The mass spectrometer 6 is arranged in parallel with the 4
It consists of a quadrupole electrode 7 with a cylinder or a hyperbolic cross section, and by applying an appropriate DC and high frequency voltage to this quadrupole electrode 7, ions with a desired mass-to-charge ratio can be generated. Only the ion beam passes through the quadrupole electrode 7 and reaches the Faraday cup 9 disposed in the ion detection section 8.

By measuring the ionic current flowing through the Faraday cup 9, the partial pressure can be measured. The aforementioned focus electrode 5
has the effect of repelling thermoelectrons but trapping ions. Therefore, not all of the ions generated inside the anode electrode 3 are guided to the mass spectrometer (although some of them are captured by the focus electrode 5).The present invention focuses on this fact, and the partial pressure is By measuring the ion current flowing into the Faraday cup 9, and by measuring the ion current flowing into the focus electrode 5, the total pressure can be measured simultaneously even during partial pressure measurement. Figure 2 is a filament protection circuit diagram.The focus electrode 5 is connected to I-V by a coaxial cable.
It is connected to a converter 10, which converts the ion current into an amplified voltage signal. This signal is input to the minus input terminal of the comparison circuit 11 and compared with the reference voltage applied to the plus input terminal. When the pressure in the vacuum increases, the ion current increases, and the input voltage of the comparator circuit 11 becomes lower than the reference voltage, the output of the comparator circuit 11 changes from the "L" level to "
As a result, the relay 12 becomes in the make state and the filament power supply circuit 13 is cut off.

〔Effect of the invention〕

As described above, the present invention provides a circuit for detecting the ion current flowing into the focus electrode constituting the ion source, so that partial pressure measurement and total pressure measurement can be performed at the same time.
During residual gas analysis, even if there is a sudden pressure rise, the filament protection circuit is activated instantly and the hot cathode filament will not burn out.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a quadrupole mass spectrometer according to an embodiment of the present invention, and FIG. 2 is a filament protection circuit diagram showing an embodiment of the present invention. 2... Hot cathode filament 3... Anode electrode 5... Focus electrode 10... TV converter 11... Comparison circuit 12... Relay 13... Filament power supply circuit and above Applicant Seiko Front view of Electronic Industry Co., Ltd. En'fIL Food v Quantity Preparation Figure 1 Figure 2

Claims (1)

[Claims] In a quadrupole mass spectrometer consisting of an ion source, a mass spectrometer, and an ion detection section, an IV converter converts ions generated by ionization into a thin current flowing through a focus electrode into a voltage in the mass spectrometer. 1. A quadrupole mass spectrometer, comprising: a comparator circuit for detecting the output voltage of the I-V converter; and a comparator circuit for detecting the output voltage of the I-V converter, and the current supply to the filament is cut off based on the output of the comparator circuit.