| Proton transfer reaction time of flight mass spectrometer(PTR-TOF-MS)is a kind of analytical instrument for determining the chemical information of different substance.The principle is that the pronton transfer reaction can occur between the ions generated in the ion source and the volatile organic compounds(VOCs)introduced into the drift tube.After focusing and cooling by the ion transport system,the particles gain the identical initial kinetic energy.However,because of the different mass charge ratios,the time required to pass through the same distance is different in the constant electric field of the mass analyzer.Based on this principle,PTR-TOF-MS can achieve the rapid qualitative and quantitative analysis of the samples.PTR-TOFMS has the advantages of wide detection range,fast scanning speed,simple instrument structure and so on.It has been widely used in environment monitoring,food safety,human health monitoring,terrorism prevention,space exploration and other fields.At present,the application fields of PTR-TOF-MS is still expanding because of the researchers’ continuous exploration.Compared with abroad,the research and development on mass spectrometry started relatively late in our country,which is at the stage of the localization of the core technology.In order to promote the development of the instrument and lay a foundation for the subsequent experimental research,the PTR-TOF-MS measurement and control system is studied in this paper according to the composition principle and structure characteristics of the instrument.The structure of the mass spectrometer is precise and complex,and there are many electical parameters and peripherals needed to be controlled manually.The users of mass spectrometers are generally not R&D personnels,thus the over-reliance on manual adjustment will be time-consuming and may induce the errors.Therefore,the instrument needs an integrated measurement and control system,which can control PTR-TOF-MS peripherals to work orderly through a friendly host computer interface.According to the structure of the mass spectrometer,the instrument control system is divided into several modules,including HVDC analyzer power supply,RF power supply,pulse power supply,medium and low voltage power supply,etc.,and each module is independent of each other.Based on this idea,the main work of this paper was as follows.(1)According to the idea of modular design,a measurement and control network based on CAN bus was proposed.Each module was connected to the measurement and control network as the node of CAN bus.The communication rate of CAN bus can reach 1 Mbps,which met the communication requirements.The modular design idea was conducive to the intelligent and standardized design of the instrument,which was convenient for the later maintenance and update of the instrument.(2)According to the functional requirements of each module,the independent control boards were designed from the aspects of hardware circuit,underlying software and performance debugging.Each control board was independent and could communicate with each other.(1)The main control board was integrated ARM processor and transplanted u C/OS-III embedded real-time operating system,which could manage multiple tasks in real time.The communication between the main control board and the upper computer was established through Ethernet,the main control board sent the control commands of the upper computer to the CAN bus network,and realized the monitoring of the ultra vacuum state(< 10-3 Pa).(2)The high-precision high-voltage power supply module was used in the control board of high-voltage DC power supply,and the power supply output and reading were realized by combining the digital-to-analog conversion chip and the analog-to-digital conversion chip.The output precision of the power supply could reach 0.1V by using the piecewise linear interpolation method.(3)RF power signal source control board was used to generate RF signal source.The output frequency range was 1~8 MHz,and the frequency setting error was less than 0.5%.When the output frequency was 3MHz,the stability of singal source within 3 hours was 0.13%.It was connected with the rear stage amplifier to improve the ion transmission efficiency of the instrument(3)Each function module was connected to the measurement and control network.The small homemade high-performance PTR-TOF-MS,which had equipped the measurement and control system,was used to test human breath.The test results showed that the overall performance of the instrument was excellent,and the operation was stable and reliable. |
