Design and Implementation of ICP-MS Data Acquisition and Processing System Based on ZYNQ

Data acquisition system is an important part of inductively coupled plasma mass spectrometer (ICP-MS). Aiming at the problem that ICPMS pulse and analog signal need to be collected synchronously and the signal-to-noise ratio is low, a data acquisition and processing solution based on ZYNQ chip were proposed. Using the characteristics of ZYNQ integrating processor and programmable logic, the FreeRTOS realtime operating system for process control and Ethernet communication was equipped on the ARM side. Three modules were designed on the FPGA side to realize data acquisition, cache, dynamic filtering and transmission, including counting module for synchronous acquisition of ICPMS pulse signal and analog signal, FIR filter module supporting online configuration based on FIR compiler IP core, and dual channel data transmission module based on MCDMA IP core. The dynamic configuration of FIR filter module was controlled by ARM, and the filter coefficients were generated by ARM calculation to improve the universality of the system. Moreover, the communication between ARM and FPGA and between modules were all based on AXI4 bus. The Modbus/TCP transport protocol was used for Ethernet communication to ensure the stability and universality of the system. The system test was divided into two steps of offline test and online test. The offline test verified the function and performance of each module in the system. The performance of the pulse count module was tested by using the pulse signal generated by the signal generator AFG320 to simulate ICPMS. After eliminating the error caused by the crystal vibration deviation, the relative error of the pulse count was less than 0000 5%. The ADC in the analog count was calibrated by using DP832 DC regulator power supply and 34401A sixbit halfdigital multimeter. The result showed that the fitting linearity is as high as 0999 98. The digital filter performance was tested by inputting sinusoidal signals of different frequencies, and the results showed that the amplitudefrequency characteristic curve is basically consistent with the theory. A standard tuning solution, tune D (Thermo Fisher Scientific), was tested in our team's selfstudy ICP-MS instrument in-house using this system. It was found that the pulse count had little noise, while the analog count had a large amount of noise thereby affecting the subsequent spectral peak feature extraction. The noise spectrum distribution in the data was analyzed by FFT analysis of the analog count results, and the appropriate parameters of FIR digital filter were selected according to the characteristics of Gaussian peaks. After filtering, the analog count spectrogram is improved significantly, the main noise intensity attenuation is greater than 40 dB, and the signaltonoise ratio of 115In peak is increased by 4959%. The filtered spectrum fully meets the requirements of subsequent peak feature extraction. The resource occupancy rate of the FPGA end of the system is less than 50%, and the total power consumption on the chip is only 2.28 W, which is conducive to promoting the miniaturization and intellectualization of mass spectrometry. In the future, algorithms can be designed at the ARM side or upper computer end to automatically adjust the filter parameters and further improve the degree of system automation.