Development Of Data Acquisition System Of ICP-AES Based On DMD And PMT

Inductively coupled plasma-Atomic Emission Spectrometry(ICP-AES)is favored by people inside and outside the industry because of its advantages of qualitative and quantitative analysis,arbitrary selection of spectral lines,and simultaneous detection of multiple elements.However,the core technology of ICPAES has been mastered by some countries for a long time,resulting in the high price of the instrument and the high maintenance cost.In order to meet the needs of the domestic ICP-AES market,it is urgent to carry out research and development of ICPAES.At present,the full-spectrum ICP-AES on the market mainly uses solid-state detectors(such as CCD)as detectors.However,the sensitivity of CCD in the ultraviolet region is low,the integration time cannot be adjusted according to the wavelength,and the resolution in the full spectral range cannot be ensured,which may cause spectral line interference.In addition,a water cooling device is required,which increases the volume of the instrument.The laboratory team proposes a novel detection system that uses digital micromirrors(DMD)as spatial light modulators combined with highly sensitive photomultiplier tubes(PMT).Develop a new ICPAES based on DMD and PMT,which can quickly select wavelengths in the full spectrum range for more efficient and high-sensitivity detection.In this paper,based on the above requirements,a set of embedded spectral data acquisition system is developed in order to cooperate with the normal operation of ICP-AES based on DMD and PMT in the laboratory.The data acquisition system includes the design of the ADC hardware circuit,the development of the corresponding driver,the development of the special acquisition software,and the design of the digital lock-in amplifier and the photon counting circuit to optimize the data acquisition system,and finally the test experiment is carried out.The specific work content is as follows:(1)ADC hardware circuit development and driver developmentFirstly,the ADC data acquisition system is designed,including hardware circuit and driver development.ADC hardware includes pre-processing module and ADC acquisition module,which realizes signal conversion,amplification,adjustment and acquisition.In addition,THE PL(FPGA part)of ZYNQ based on ARM+FPGA architecture is used to complete the driver design of ADC hardware circuit and realize data acquisition,processing and storage.(2)Design of digital lock-in amplifier based on DMD modulationIn order to improve the performance of ADC data acquisition system,a digital phase-locked amplifier based on DMD chopper modulation is designed.The spectrum signal to be measured formed by DMD chopper is input into ZYNQ processing system through ADC acquisition circuit,and the correlation calculation and low-pass filtering are carried out in PL of ZYNQ with DMD chopper synchronous signal(reference signal)input at the same time.Finally,dc output is achieved to achieve digital phase-locked amplification and correlation demodulation.(3)Photon counting hardware development and driver developmentIn order to improve the performance of the data acquisition system under low light,a photon counting system is designed.The hardware circuit of the photon counting system includes signal conversion and amplification module and comparison module,which can output the square wave signal of counting pulse under the condition of weak light.In the PL part of ZYNQ,the development of photon counting driver and the design of data collection and storage are completed to realize data collection,processing and storage.(4)Design of network communication and acquisition softwareIn THE PS end(ARM part)of ZYNQ,the communication protocol is formulated according to the characteristics and requirements of data,and the application program is developed to realize the communication between ZYNQ and the upper computer,and to complete the instruction receiving and data transmission.In MATLAB,the function modules of acquisition software are designed according to the actual requirements,and the ICP-AES acquisition software interface is built by using THE GUI component of MATLAB to realize the functions of user command operation,data acquisition and graph drawing.(4)Test experimentThe experimental platform was built by combining Hg(Mercury)EDL lamp with DMD and PMT medium step grating spectrometer,and the comparison experiment between direct ADC acquisition mode and phase-locked amplification acquisition mode was carried out.The data acquisition system was integrated into the ICP-AES prototype to measure the standard sample solution of cadmium(Cd).The experimental results show that compared with the direct ADC acquisition method,the SNR of the phase-locked amplification acquisition method is improved by about 3-5times at the 4×4 template reversal in the whole band range,and about 1.7 times at the1×1 template reversal at 253.65 nm.The phase-locked amplifying acquisition method suppressed the low frequency noise,reduced the influence of system drift,improved the SNR of spectral line signal,optimized the performance of the acquisition system,and improved the sensitivity of the ICP-AES principle prototype.