Design And Implementation Of Cold Cathode Ionization Gauge Controller For Mass Spectrograph

It has been more than 90 years about the mass spectrograph development. At present, mass spectrograph has been widely used in basic science research, national defence, spaceflight and other fields. Therefore, it is significant to develop mass spectrograph with the independent intellectual property. This subject derives from the national natural science foundation project"Rearch of high sensitivity inside photoionization– ion trap mass spectrometer technology and key components". The research content is to develop a control unite for the cold cathode ionization gauge to measure vacuum value in the quadrupole ion trap(QIT) mass spectrograph.The mass spectrograph basiclly include the following parts: sampling system, ion source, mass analyse, ion detector and recordor. Some of the part must work under the condition of high vacuum system such as ion source, mass analyse and so on. So to measure vacuum value is one of the basic works of the mass spectrograph. Miniaturization is one of the developing directions of the mass spectrograph. Miniaturization reduces the size of the mass spectrograph itself, meanwhile reduces the size of its relevant components. For example, it requires miniature vacuum gauge to measure vacuum.There are many types of vacuum gauge products in the market. But these relevant products, all of them are either too large to posite in desktop mass spectrograph or the smaller gauges are too expensive or smaller chip gauges can not measure high vacuum. So, this paper according the features of the current inverted magnetron cold cathode ionization gauge is simple structure and no hot filament, developed a control unite for the inverted magnetron cold cathode ion gauge to measure high vacuum in the QIT mass spectrograph.The cold cathode ion gauge includes two parts: the gauge and the measure circuit. The research about the measure circuit is one of the main works of this research.The theory of cold cathode ionization gauge is to measure the cold gauge's discharge current and calculate the current to get vacuum value according to the discharge formula and then send the result to the mass spectrograph's main control system.The main hardware of this control unite including I-V convert amplifier, AD convert circuit, siginal processing and communicate circuit. Using electrometer amplifiers converts and enlarges discharge current. Using the new high integrated 16 bitΣ—ΔADC to convert the voltage into digital data. This kind of ADC only needs a few chip then can convert the weak siginal inti digital data. The data then is sent to a microprocessor according the SPI serial interface.The main job of software is to program based on MSP430, which includes control AD converter, collect data, shift measure range, processing data sending data and so on. In the data processing part, the main job is using average filter, collect data from ADC via SPI interface and calculate the data according the discharge formula, and finally get the vacuum value. At last send the vacuum value to RS232 interface which the mass spectrograph will able to read from.In the end, the paper gives the test result of the control unite, and compares the result with the commercial gauge, analyses the error, gives some advices for the forthur reseasch.