Noise meters - Environmental testing
Noise meters, also known as (noise meters, sound level meters) are *basic* instruments for noise measurement. A sound level meter is generally composed of a condenser microphone, a preamplifier, an attenuator, an amplifier, a frequency meter network, and an RMS indicator 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.
Noise Meter Principle
The frequency weighting network in the noise meter has three standard weighting networks, A, B and C. The A network simulates the response of the human ear to the 40-square pure tones in the equal-loudness curve, and the shape of its noise meter curve is opposite to the equal-loudness curve of the 340-square, which results in greater attenuation in the middle and low frequency bands of the electrical signal.The B network simulates the response of the human ear to the 70-square pure tones, and results in a certain degree of attenuation in the low-frequency band of the electrical signal.The C network simulates the response of the human ear to the 100-square pure tones. 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 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 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 to measure the large fluctuation of unsteady noise and transportation 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 meter is used to measure impulse noise, this kind of sound level meter conforms to the response of the human ear to impulse sound and the average time of the response of the human ear to impulse sound.
Noise Meter-Standard Requirements
