Research And Design Of Hydrogen Flame Ionization Detector Based On STM32

VOC exists in all aspects of our life,promoting the development of the industry and making our life better.However the toxic gases in the factory,the pungent flavor of the new decorated house,all harm to the environment.With the haze weather appears day and day,our health threatened seriously.With the explosion of environmental protection industry and related testing institutions,a FID detector.hydrogen flame ionization detector,is designed for VOC detection.The system hardware design can be divided into four parts according to the design ideas.The first part is the power management module,which uses the PWM control chip SG3525 to produce PWM wave,and generates all kinds of voltages required by the semi-bridge switching power supply and the voltage regulator chip,then power supply to each module.The second part is the signal amplification detection part,organic compounds burnt in hydrogen flame produces a weak electrical signals.Then to the detecting amplified circuit.There are two types detecting amplifier circuit:linear amplifier circuit and a logarithmic amplifier circuit.The amplified signal is filtered by the low-noise passive low-pass filter,and the signal is collected and transmitted to the main control chip STM32F103CRT by the high precision A/D conversion chip CS5513.The third part is some control functions for the board,such as real-time acquisition,control of temperature and pressure.control functions for events,serial port communication function,and motor drive function,etc.The fourth part is drawing and making circuit boards.PCB designs six areas that isolated by transformers.The amplifying circuit make board alone,to reduce leakage current in circuit boards and other chips that may effects of weak signal.The amplifying circuits need to be block up of shielding cases.Software design is embedded in the real time operating system FreeRTOS.The main tasks of the whole design are three:sample signal collection task,temperature and pressure collection task and serial communication task.When the sample signal is collected,STM32F103CRT is required to select the collected channel.The connected A/D chip is enabled and controlled to ensure the smooth operation of the transmission data.The collected sample signal needs to be digitally filtered again to eliminate the interference and noise signal,which is to adopt the second-order active low-pass digital filter.VOC acquisition board after the test,implements the effective amplification of the weak current signal.The noise was inhibited and processed well.Also a series of control functions done.The noise of the final FID detector is less than 0.02mV,and the drift is lower than 0.4mV/h.The stability index and detector sensitivity meet the requirements of the detector.