Design Of An On-line Atomic Spectrophotometer Element Lamp Control System

With the rapid development of chemical,biological and other fields,the problem of sewage discharge has become increasingly serious,the heavy metal elements contained in sewage will cause damage to people's body.As a kind of laboratory equipment,AAS can analyze the proportion of elements in samples under test.However,it has disadvantages such as waste of manpower,time,limitation of use site and inability to guarantee real-time data.With the increase of the use of instruments,it is very necessary to develop an AAS in line with "Internet+".The on-line AAS studied in this article has the features of remote control,while ensuring the detection accuracy and real-time.This paper mainly studies the module of elemental lamp and monochromator in AAS.The main research contents are as follows :(1)According to the functional requirements of the instrument,a hardware system for the elemental lamp module and the monochromator module is studied.LPC5411 chip was selected as the main control chip to control the operation of all modules and realize the communication between offline instruments and the cloud server.The hollow cathode lamp was used as the characteristic light source.The energy acquisition module is designed,and the characteristic light energy is collected by photomultiplier tube.The preamplifier circuit and filter circuit are improved to overcome the disadvantage of redundancy of components in the traditional circuit.A/D conversion circuit is also designed.In order to ensure the accuracy of the data,the automatic gain adjustment circuit,the zero adjustment circuit,the slit control circuit of the monochromator and the wavelength control circuit are added on this basis.The main circuit is simulated by Simulink software.(2)According to the requirements,the control scheme matching with the AAS is studied.The dual core communication mechanism of LPC5411 is described.The sampling task,the lighting task of the hollow cathode lamp,the zero task and so on were designed to make the system run stably.Combined with the slit control task,wavelength control task and elemental lamp energy task,the precision of measurement data is guaranteed.(3)Aiming at the problem of limited filtering noise of the old atomic spectrophotometer,the algorithm of data processing is improved.Using the autocorrelation detection method to process the detected data makes up for the disadvantage that the filtering effect is not ideal when the noise is large.The principle and process of the autocorrelation detection method are described,and the filtering effect before and after the improvement is compared.When the sample is not put in,the amplifier circuit output is the square wave with the amplitude of about 1V,the wave shape is stable and contains less noise after using the oscilloscope measurement.By using Matlab software test,the autocorrelation detection method can also accurately restore the wave pattern when the signal-to-noise ratio is 0.01 by test.According to the static stability of the instrument in the national standard,the instantaneous noise within 30 minutes of the baseline stability of the instrument studied in this paper is all within 0.002 Abs.The wavelength accuracy of the six groups of mercury lamp tested is 0.37375 nm with the most difference from the theoretical value.In the resolution test,the half-width of the spectral line of mercury lamp is 0.16 nm.The trough energy between the two peaks of the manganese lamp is 0.25.The above three indicators are far less than the provisions in the national standard.