Design Of Multifunctional Sound Level Meter Calibration System Based On STM32F407

The sound level meter is utilized to evaluate noises and is one of the most common instruments in acoustic measurement.It has been widely used in labor hygiene,transportation,industrial production and scientific research teaching,reflecting that sound level meters are closely related to people’s daily work and life.Thus it is extremely important to ensure that the sound level meter’s functions are complete and accurate.For the calibration of sound level meters,most of the domestic acoustic calibration instruments have the disadvantages of low calibration accuracy,single frequency and constant sound pressure while the prices of foreign instruments are expensive.In this thesis,a multi-functional sound level meter calibration system based on STM32F407 is developed.After an in-depth analysis,an effective method for reducing the error is proposed.Firstly,the background and research significance of the noise measurement are introduced,providing a theoretical basis for the multi-functional sound level meter calibration system.The basic methods of acoustic calibration are clarified and the development status of domestic and abroad acoustic calibrators is given,laying a theoretical foundation for the design of the system.According to the requirements of this subject,the main working mechanism of the multi-functional sound level meter calibration system is expounded.Secondly,in order to reduce the influence of external factors on the coupling cavity,the improved Leyte criterion is used to pre-process the sampled data.It is verified by experimental simulations that the algorithm has excellent anti-noise performance and strong resistance to external interference.Aiming at the error of the system,an improved differential evolution algorithm to optimize the digital PID is proposed and the corresponding optimization process is introduced in detail.By comparison,it has the advantages of accuracy,stability and high speed.The hardware and software implementation based on the algorithm on the acoustic calibration system is introduced.Then,the hardware system based on STM32F407,AD9910 and PCM1804 is constructed,consisting of a signal generation unit,a signal acquisition unit,a signal processing unit and a power supply unit.The working principle of each module in each unit is introduced in detail.The design flow of the hardware system PCB is outlined.Finally,the design process of the main program of the multi-functional sound level meter calibration system is introduced,and the software design of each unit is realized by the modular programming idea,including a data acquisition module,a data processing module,a data filtering module and a control algorithm module,a signal generation module and a human-computer interaction module.Test results show that the calibration frequency of the multi-functional sound level meter calibration system developed in this thesis ranges from 20 Hz to 20 kHz(±0.5 Hz),the sound pressure is 84/94/104/114 dB(±0.2 dB),with the functions of A/C frequency weighting calibration and F/S time weighting calibration.It meets the GB/T 15173-2010 "Electroacoustics-Sound calibrators" requirements for Class 1 sound level meters.In addition,this system has advantages of a friendly human-computer interaction and convenience for users.