Introduction to the test principle of the noise tester
The frequency weighting network in the noise meter has three standard weighting networks: A, B, and C. The A network is to simulate the human ear's response to the 40-square pure tone in the equal-loudness curve. Its noise meter curve shape is opposite to the 340-square equal-loudness curve, so that the middle and low frequency bands of the electrical signal are greatly attenuated. The B network simulates the human ear's response to the 70-square pure tone, and it attenuates the low-frequency band of the electrical signal to a certain extent. The C network simulates the response of the human ear to a 100-square pure tone, and has a nearly flat response throughout the entire audio frequency range. The sound pressure level measured by the sound level meter through the frequency weighting network is called the sound level. According to the weighting network used, it is called A sound level, B sound level and C sound level respectively, and the units are recorded as dB(A), dB(B) and dB(C). The sound level meter used to measure noise can be divided into four types according to the sensitivity of the meter head response:
1. "Slow". The time constant of the meter head is 1000ms, which is generally used to measure steady-state noise, and the measured value is an effective value.
2. "Quick". The time constant of the meter head is 125ms, which is generally used to measure unstable noise and traffic noise with large fluctuations. The fast gear is close to the human ear's response to sound.
3. "Pulse or pulse hold". The rising time of the watch needle is 35ms, which is used to measure the pulse noise with a long duration, such as punch press, hammer, etc. The measured value is the maximum effective value.
4. "Peak hold". The rise time of the hands is less than 20ms. It is used to measure short-duration impulsive sounds, such as guns, cannons and explosions, and the measured value is the peak value. That is the maximum value.
The sound level meter can be connected with an external filter and recorder to perform spectrum analysis on the noise. The domestically produced ND2 Haunate precision sound level meter is equipped with an octave page filter, which is easy to carry to the scene and perform spectrum analysis. Sound level meters can be divided into precision sound level meters and ordinary sound level meters according to their accuracy. The measurement error of a precision sound level meter is about ±1dB, and that of an ordinary sound level meter is about ±3dB. Sound level meters can be divided into two categories according to their uses: one is used to measure steady-state noise, and the other is used to measure unsteady-state noise and impulse noise. Integrating sound level meters are used to measure the equivalent sound level of unsteady noise over a period of time. Noise dosimeter is also an integrating sound level meter, mainly used to measure noise exposure. Impulse sound level meter is used to measure impulse noise. This sound level meter conforms to the human ear's response to impulse sound and the average time of human ear's response to impulse sound.
