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A sound level meter, also known as a noise meter, is the most basic instrument in noise measurement. A sound level meter generally consists of a condenser microphone, preamplifier, attenuator, amplifier, frequency weighting 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 transformed by a preamplifier to match the microphone with an attenuator. The amplifier adds the output signal to the weighting network, performs frequency weighting on the signal (or an external filter), and then amplifies the signal to a certain amplitude through an attenuator and amplifier, and sends it to the effective value detector (or an external level recorder). The noise level value is displayed on the indicator head. There are three standard weighting networks for frequency in sound level meters: A, B, and C. The A network simulates the response of the human ear to a 40 square pure tone in an acoustic curve, and its curve shape is opposite to the 340 square acoustic curve, resulting in significant attenuation in the middle and low frequency bands of the electrical signal. B network simulates the response of the human ear to 70 square pure tones, which causes a certain attenuation in the low frequency range of electrical signals. Temperature and humidity meter, infrared thermometer, temperature and humidity meter, infrared thermometer, oscilloscope, resistance tester
The C network simulates the response of the human ear to 100 square tones, with a nearly flat response across the entire audio frequency range. The sound pressure level measured by a sound level meter through a frequency weighting network is called sound level. Depending on the weighting network used, it is referred to as A sound level, B sound level, and C sound level, with units denoted as dB (A), dB (B), and dB (C). At present, the noise meter used for measuring noise can be divided into four types of response based on sensitivity: (1) "slow". The time constant of the meter head is 1000 ms, which is generally used to measure steady-state noise, and the measured value is the effective value. (2) Hurry up. The time constant of the meter head is 125ms, which is generally used to measure unstable noise and transportation noise with large fluctuations. Fast gear approaches the human ear's response to sound. (3) Pulse or pulse hold. The rise time of the gauge needle is 35ms, used to measure pulse noise with longer duration, such as punch presses, hammers, etc. The measured value is the maximum effective value. (4) Peak retention. The rise time of the meter needle is less than 20ms. It is used to measure pulse sounds with short duration, such as gun, cannon, and explosion sounds. The measured value is the peak value, that is, the maximum value. Sound level meters can be equipped with external filters and recorders to perform spectral analysis on noise. The domestically produced ND2 precision sound level meter is equipped with an octave band filter, which is easy to carry to the site and perform spectral analysis. Sound level meters can be divided into precision sound level meters and ordinary sound level meters based on their accuracy. The measurement error of a precision sound level meter is about 1dB, while that of a regular sound level meter is about 3dB. Sound level meters can be divided into two categories according to their purposes: one is used to measure steady-state noise, and the other is used to measure non-stationary noise and impulse noise. Integral sound level meter is used to measure the equivalent sound level of unstable noise over a period of time. A noise dosimeter is also an integral sound level meter, mainly used to measure noise exposure. Pulse type sound level meter is used to measure pulse noise, which conforms to the response of the human ear to pulse sound and the average time of the human ear's response to pulse sound.
