Basic understanding of sound level meters and how to select the appropriate kind?
A sound level meter is an instrument for measuring noise. Sound level meter is an instrument for measuring sound pressure level according to certain frequency weighting and time weighting according to international standards and national standards. It is suitable for the measurement of various acoustics such as machine noise, occupational noise, environmental protection, and architectural acoustics.
Basic structure and principle of sound level meter
The components of a sound level meter are generally divided into: microphone, preamplifier, attenuator, weighted amplifier, RMS detector, A/D, CPU, digital indicator, power supply, printer, etc.
Microphone: It is a transducer used to convert an acoustic signal into an electrical signal. A test condenser microphone is generally used in a sound level meter. It has the characteristics of stable performance, wide dynamic range, flat frequency response, and small size.
Preamplifier: The main function is to perform impedance transformation. Since the capacitor microphone has a small capacitance and high internal resistance, and the input impedance of the post-stage attenuator and amplifier is not too high, a preamplifier needs to be added in the middle for impedance transformation.
Attenuator: Attenuate large signals to increase the measurement range.
Weighting amplifier: amplify the weak signal, and perform frequency weighting (frequency filtering) as required.
RMS detector: rectifies the AC signal into a DC signal, and the magnitude of the DC signal is proportional to the RMS value of the AC signal. The geophone must have certain time-weighting characteristics. In the exponential time-weighting sound level measurement, the "F" characteristic time constant is 0.125 s, and the "S" characteristic time constant is 1 s.
A/D: Convert analog signals into digital signals for digital indication or send to CPU for calculation and processing.
CPU: Microprocessor (single chip microcomputer), which calculates and processes the measured value.
Digital indicator: It directly indicates the decibel number of the measured sound level in digital form, and the reading is more intuitive.
Power supply: generally DC/DC, after the power supply (battery) is converted and stabilized, it is supplied to each part of the circuit.
Printer: print out the measurement results, usually using a miniature printer
Selection of sound level meter
There are many types of sound level meters on the market with different functions, so how do we choose a suitable sound level meter? You can choose from the following aspects:
Accuracy class
Sound level meters are divided into grade 1 accuracy and grade 2 accuracy according to different accuracy grades. The difference between level 1 and level 2 is mainly in the maximum allowable error, operating temperature range and frequency range, and the accuracy of level 1 sound level meter is higher than that of level 2. Although in general, the use of Class 2 sound level meters can meet the measurement requirements, but more and more Class 1 sound level meters are selected. According to my country's environmental noise regulations, when the noise A sound level is lower than 35 dB, it is required to use a sound level meter that meets Class 1 accuracy.
application function
According to different functions, sound level meters can be divided into conventional sound level meters for measuring exponential time weighting; integrated average sound level meters for measuring time-average sound levels; integral sound level meters for measuring sound exposure; in addition, those with noise statistical analysis functions are called noise statistical analyzers; those with collection functions are called noise collectors (recording sound level meters); those with spectrum analysis functions are called spectrum analyzers.
If you simply measure the noise A sound level, you only need to choose a conventional sound level meter. If it is necessary to measure environmental noise, it is often necessary to measure the time-averaged sound level or equivalent sound level due to the large fluctuations in environmental noise. For example, when measuring indoor noise (mainly low-frequency noise) in noise-sensitive buildings, it is also necessary to measure octave-band sound pressure levels with center frequencies of 31.5 Hz, 63 Hz, 125 Hz, 250 Hz, and 500 Hz, so a Class 1 sound level meter with octave spectrum function needs to be selected.
