Introducing and using noise measuring equipment
A noise meter, also known as a noise meter or sound level meter, is a fundamental instrument in noise measurement. A sound level meter generally consists of a capacitive microphone, preamplifier, attenuator, amplifier, frequency meter network, and effective value indicator head. The working principle of a sound level meter is that the sound is converted into an electrical signal by a microphone, and then the impedance is changed by a preamplifier to match the microphone with the attenuator. The amplifier adds the output signal to the network, performs frequency weighting (or external filtering) on the signal, and then amplifies the signal to a certain amplitude through attenuators and amplifiers, and sends it to the effective value detector.
Principle of Noise Meter
There are three standard frequency weighting networks in noise meters: A, B, and C. The A network simulates the response of the human ear to a 40 square meter pure tone in the equivalent response curve. Its noise meter curve shape is opposite to the 340 square meter equivalent response curve, resulting in significant attenuation in the middle and low frequency bands of the electrical signal. The B network simulates the response of the human ear to 70 square pure tones, causing a certain attenuation in the low frequency range of electrical signals. The C network simulates the response of the human ear to 100 square meters of pure tones, with an almost flat response throughout the entire audio frequency range. The sound pressure level measured by the sound level meter through a frequency weighting network is called the sound level. Depending on the weighting network used, it is called the A sound level, B sound level, and C sound level, with units recorded as dB (A), dB (B), and dB (C). At present, the sound level meters used for measuring noise can be divided into four types based on sensitivity:
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 the effective value.
2. Quick. The time constant of the meter header is 125ms, which is generally used to measure unstable noise with large fluctuations and transportation noise. Fast gear approaches the human ear's response to sound.
3. Pulse or pulse hold. The rise time of the watch needle is 35ms, which is used to measure pulse noise with a longer duration, such as punching machines, press hammers, etc. The measured value is * significant value.
4. Peak maintenance. The rise time of the watch needle is less than 20ms. Used to measure pulse sounds with short duration, such as guns, cannons, and explosions, the measured values are peak values, i.e. * maximum values.
