Digital Noise Meter Fundamentals:
A digital noise meter, also called a sound level meter, is the most basic instrument in noise measurement. A digital noise meter generally consists of a condenser microphone, a preamplifier, an attenuator, an amplifier, a frequency weighting network, and an RMS indicator head.
The working principle of digital noise meter is: the microphone converts the sound into an electrical signal, and then the preamplifier transforms the impedance to match the microphone with the attenuator. Amplifier will be added to the output signal weighting network, the signal frequency weighting (or external filter), and then by the attenuator and amplifier will be amplified to a certain amplitude of the signal, sent to the RMS detector (or outside the level recorder), in the indication of the meter head to give the numerical value of the noise level. The frequency weighting network in the sound level meter has three standard weighting networks: A, B and C. A network simulates the response of the human ear to the 40-square pure tones in the equal-loudness curve, which is opposite to the equal-loudness curve of the 340-square curve, thus making the middle and low-frequency bands of the electrical signals to have a larger attenuation; B network simulates the response of the human ear to the 70-square pure tones, which makes the low-frequency bands of the electrical signals to have a certain degree of attenuation. The C network simulates the response of the human ear to a 100-square pure tone, which has a nearly flat response across the entire frequency range of the sound. The sound pressure level measured by a sound level meter through a frequency weighting network is called the sound level, and according to the different weighting networks used, it is called the A sound level, B sound level and C sound level, and the units are recorded as dB(A), dB(B) and dB(C). At present, the sound level meter for measuring noise, the meter head response can be categorized into four types according to the sensitivity: (1) "Slow". (1) "Slow", with a head time constant of 1000 ms, is generally used to measure steady state noise, and the measured value is the RMS value. (2) "Fast". The time constant of the meter head is 125 ms, which is generally used for the measurement of large fluctuation of unsteady noise and transportation noise. The fast gear is close to the human ear's response to sound. (3) "Pulse or pulse hold". The rise time of the meter needle is 35ms, used for measuring impulse noise with long duration, such as punch, press hammer, etc. The measured value is the maximum RMS value. (4) "Peak hold". Table needle rise time is less than 20ms. used to measure the impulse sound of short duration, such as gun, cannon and explosion sound, the measured value is the peak value. The value measured is the peak value, i.e. the maximum value. Sound level meter can be connected to external filters and recorders, to do spectrum analysis of noise. Domestic ND2 type precision sound level meter is equipped with an octave page range filter, easy to carry to the scene and make spectrum analysis.
Digital noise meter can be divided into precision sound level meter and common sound level meter according to the accuracy. The measurement error of the precision sound level meter is about 1dB, and that of the ordinary sound level meter is about 3dB. The sound level meter can be divided into two categories according to the usage: one is used to measure the steady state noise, and the other is used to measure the unsteady state noise and impulse noise. Integral sound level meter is used to measure the equivalent sound level of unsteady noise over a period of time. A noise dosimeter is also an integrating sound level meter and is primarily used to measure noise exposure. Impulse sound level meter is used to measure impulse noise, which is in accordance with the response of the human ear to impulse sound and the average time of the human ear response to impulse sound. It is a necessary instrument for places where we usually have a noisy environment.
Noise meter is also called (noise meter, sound level meter) is the most basic instrument in noise measurement. A sound level meter generally consists of a condenser microphone, a preamplifier, an attenuator, an amplifier, a frequency meter network, and an RMS indicating meter head.
The working principle of a sound level meter is: the microphone converts the sound into an electrical signal, and then the preamplifier transforms the impedance so that the microphone matches the attenuator. The amplifier adds the output signal to the network, weights the signal for frequency counting (or external filter), and then amplifies the signal to a certain amplitude by the attenuator and amplifier, and sends it to the RMS detector.
