Development Of A Miniaturized Ratio-Frequency Power For Quadrupole Mass Spectrometer

Mass spectrometry is a modern analysis method used for measuring the mass-tocharge ratio of ions.The mass spectrometer can separate material according to the different mass-to-charge ratio,which is widely used in scientific research fields such as physics,chemistry,biology,and astronomy.The mass spectrometer is composed of inlet,ion source,mass analyzer,detector,data system,RF power,vacuum system,thereinto the quadrupole mass analyzer is composed of four centrosymmetric electrode rods.As one of the most commonly used mass spectrometers,quadrupole mass spectrometer has many advantages,such as simple structure,fast scanning speed,no hysteresis,high resolution,good adaptability,and so on.There will be a hyperbolic electric field in the quadrupole by applying RF high voltage signal to quadrupole structure.By varying the electric field,the input ions with different trajectories can be filtered owing to their different mass-to-charge ratios.As an important part of the quadrupole mass spectrometer,the RF power supply is used to provide high-frequency and high-voltage signals to the quadrupole structure.To meet the demands of localization and portability,an RF power supply was designed in this thesis work.The working principle of quadrupole mass spectrometer and stable motion conditions of ions were introduced briefly,and the input and output conditions were determined based on the actual workflow.An overall design scheme of the RF power system was given detailed in this thesis.Our RF power supply is composed of signals modulation module,RF amplifier module,DC control module,DC amplifier module,transform,envelope extraction module,feedback circuit,and monitoring module.The RF amplifier module is composed of an amp and a power tube,which has the advantages of convenient debugging and no distortion.The transformer is realized by interwinding which can produce a high output voltage with a small volume and a high resonance frequency.A four-layer board is designed in this thesis work according to the scheme.The PCB layout design,mechanical structure,and heat dissipation were described briefly.Circuit simulation and system testing were finished and the output specifications of the power were tested.The output specifications include output voltage,symmetry,envelope with step,power consumption,monitoring signal,etc.In the actual test,the RF power supply could output an amplitude-modulated RF high-voltage signal that the peak-to-peak voltage is higher than 3.3k V.In this situation,the resonance frequency of the circuit is 1.330 MHz.According to the calculation,the power consumption of the device is 32 W and the standard deviation of the U/V ratio is 0.00104366.In this thesis,the RF power supply applied to the portable quadrupole mass spectrometer has been designed and the correctness of the circuit was verified through simulation,theoretical calculation,as well as experiments.The debugging port was reserved for adjustment and expansion.Simple structure,small size of the transformer and portability are the characteristics of our RF power supply.The output signals are stable and the fluctuation is small.In general,the design has high practical value and meets design requirements.