Research On The Control Technology Of The New Type AFS’s Hollow Cathode Lamp With The Strong Short Pulse Power Supply

Atomic fluorescence spectrometer（AFS）is a detector for ultra tracing analysis,which is widely used in food hygiene,environmental monitoring,geological metallurgy and other fields.Nowadays,the structure of non-dispersive AFS is simple and Limit of Detection（LOD）is low,but it can not overcome scattering and spectral interference.Based on the project"Development and Industrialization of New Atomic Fluorescence Spectrometer"of 13^th national Five-year Plan,a New AFS applied by Digital Micromirror Device（DMD）was developed,which can effectively overcome scattering and spectral interference.Because of the ultraviolet DMD,this new AFS leads to decrease the intensity of fluorescence signal and increase LOD.Therefore,it is essential to improve the intensity of fluorescence signal and reduce the LOD.Therefore,this thesis initiate a short-strong pulse power,supplying to HCL,which can improve the intensity of fluorescence signal and reduce LOD by increasing the emission intensity of HCL in order to enhance the intensity of fluorescence signal.The main contents of this thesis are as follows:（1）Develop Hardware of HCL control system powered by strong short pulseFor realizing the application of short-strong pulse power supplied to HCL in the new AFS,HCL control system with strong short pulse power is developed,including strong short pulse power supply and high-speed acquisition system.The strong short pulse power supply,constituted by high-speed analog switch（ADG751ARTZ）,high-speed operational amplifier（AD8034）and high-speed high current N-MOS tube（STW8N120K5）,generates microsecond and ampere level of high current to supply the HCL.The shortest pulse can up to 2.5us and the maximum pulse current can reach5A.For analysing the mechanism of main and second cathode current,The accuracy of output current is tested and the rate is more than 97%.High-speed operational amplifiers（AD4817）with low noise and low input bias current designed a high speed conditioning circuit,which was simulated and verified and indicates that the cut-off frequency is 100.681k Hz.High-speed A/D acquisition chip（AD9245）designed a high-speed A/D acquisition circuit based on FPGA,converting speed can up to2MSPS.It provides a hardware platform for the follow-up experimental research and lays a theoretical foundation.（2）Research on HCL characteristics and working parameters of the new AFSFor researching on optimum working characteristics when HCL control technology applied to this new AFS,As and Bi elements were as samples to study.Firstly,the characteristic of HCL were analyzed,including the impact on cathode voltage from HCL supply voltage,study on the optimum current ratio of HCL main-auxiliary cathode,and emission intensity of different spectral lines from short-strong pulse supply to HCL.Secondly,According to the delay time generated by the fluorescence signal of HCL under the working condition of short-strong pulse,the timing sequences of DMD was designed to coordinate the power supply of HCL short-strong pulse and the high-speed acquisition system,which could achieve the maximum Signal to Noise Ratio（SNR）and rapidly quantitative detection.Lastly,Research on the impacts of pulse current in the new AFS,pulse width,supply voltage of HCL,shielding gas flow rate,atomizer height,carrier gas flow rate,detector PMT negative high voltage and other working parameters on the atomic fluorescence intensity of the new AFS.Optimize these parameters to provide the best experimental conditions for subsequent sample experiments.（3）Sample experiment and application of As and BiFor verifying the effects of HCL control technology with strong short pulse power supply,the hardware system,timing sequence on software and optimized working parameters were developed or studied,which be applied to this new AFS.For the standard sample experiment,the strong short pulse（As:2000m A/20us Bi:1500m A/20us）and conventional pulse（As:200m A/200us Bi:200m A/150us）carried out the contrast experiment.When short-strong pulse power supply to HCL,standard curve correlation coefficient As and Bi elements was up to 0.9996 and0.9997 respectively and LOD of As and Bi elements reduced 1.93 times and 2.45times respectively.For the actual sample experiment,diluted As aqueous solution with standard values of 13.0ng/m L and 38.3ng/m L were tested result of 13.30ng/m L and 38.45ng/m L respectively,which are within the error range of the actual sample standard value.