Principle of integrating sound level meter
Microphone: Electret test capacitor microphone, which converts sound signals into electrical signals and has characteristics such as good stability and wide frequency response.
Pre amplifier: With high input impedance and low output impedance characteristics, it plays a role in impedance transformation.
Frequency weighting amplification, range conversion, overload indication circuit: This part of the circuit amplifies weak signals from the preamplifier to achieve a certain amplitude. The range conversion circuit is controlled by the microprocessor to ensure that the entire amplifier can reflect the size changes of the input signal without distortion within the measurement range. When the signal exceeds the measurement range of the current range, the overload indicator circuit automatically controls the overload light indication
Logarithmic detection and DC amplification: It is the effective value detection of the AC signal corresponding to the measured sound level from the AC amplifier, and a certain proportion of amplification is performed to make the DC amplifier output a linear change in DC voltage corresponding to the measured sound level.
A/D converter, microprocessor, memory, and interface circuit: These components constitute a complete microcontroller system. The microprocessor is controlled by the program memory, and the A/D converter performs timed sampling and automatic measurement. At the same time, the measurement results are stored in the memory and output to the printer or microcomputer through the interface circuit.
Display and panel parts: The LCD display can display and output measurement marks and results such as clock, working mode, measurement data, frequency, etc. The panel part provides a manual control interface. According to measurement requirements, the working mode and control signals are input to the microprocessor to achieve noise measurement and analysis.
Reference calibration signal and power supply: Powered by a battery (or external input), a single positive voltage is converted into the required positive and negative voltage, responsible for the power supply of the entire machine. And generate a reference signal as an internal circuit correction.
The measured sound signal is received like a general sound level meter, and after passing through a weighting, amplification, and range circuit, it is converted to a logarithmic converter for logarithmic operation. Then, it is amplified by detection and A/D conversion, and sent to the microprocessor. The microprocessor performs timed sampling according to the pre programmed program and algorithm formula, calculates the Leq equivalent, and stores the measurement results in memory. The results can be displayed on the LCD screen through the display driver circuit, or output to the printer through the RS232C serial interface, automatically printing out the measurement results and spectra. The measurement data output can be transmitted to the computer through interface communication cables, achieving real-time communication output of sound pressure level Lp.
