Introduction to and use of noise measurement equipment
Noise meters are also called (noise meters, sound level meters) are the *basic* instruments 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 indicator head. The operating principle of a sound level meter is that the microphone converts the sound into an electrical signal, and then the preamplifier converts the impedance so that the microphone is matched to 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.
Noise Meter Principle
The frequency weighting network in the noise meter has three standard weighting networks, A, B and C. A network simulates the response of the human ear to a pure tone of the 40th parallel in the equal-loudness curve, and the shape of the noise meter curve is opposite to the equal-loudness curve of the 340th parallel, which results in greater attenuation in the middle and low frequency bands of the electrical signal. The C network simulates the response of the human ear to a 100-square pure tone, which has a nearly flat response over the entire frequency range. The sound pressure level measured by a sound level meter through a frequency weighting network is known as the sound level, and depending on the weighting network used, it is known as the A sound level, the B sound level and the C sound level, and the units are recorded as dB(A), dB(B) and dB(C). At present, the measurement of noise with a sound level meter, the meter head response according to the sensitivity can be divided into four kinds:
1. "Slow". Meter head time constant of 1000ms, - generally used to measure steady state noise, the measured value for the effective value.
2. "Fast". The time constant of the meter head is 125ms, which is generally used for the measurement of large fluctuation of unsteady noise and transport noise. 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, which is used to measure the impulse noise with longer duration, such as punching machine, pressing hammer, etc. The measured value is the *larger RMS value.
4,"Peak Hold". The rise time of the meter needle is less than 20ms, used to measure the impulse sound of short duration, such as guns, cannons and explosions, the measured value is the peak value. That is, the * big 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 equipped with an octave page range filter, easy to carry to the scene and for spectrum analysis. Sound level 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 its use: one is used to measure steady state noise, and the other is used to measure 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 Meters are used to measure impulse noise, which corresponds to the response of the human ear to impulse sound and the averaging time of the human ear's response to impulse sound.
