Sound level meter

Sound level meter is the most basic noise measuring instrument, it is an electronic instrument, but it is different from the objective electronic instrument such as voltmeter. When the sound signal is converted into an electrical signal, the time characteristics of the response speed of human ear to acoustic wave can be simulated; The characteristics of different sensitivity and the intensity characteristics of different loudness change characteristics. Sound level meter is a kind of subjective electronic instrument.

According to the sensitivity of the sound level meter, there are two methods for classification of sound level meter: one is ordinary sound level meter, which requires less on microphone. The dynamic range and the frequency response are narrow, and generally, the band-pass filter is not configured for the connection; The other is precision sound level meter, whose microphone requires wide frequency response, high sensitivity, good long-term stability, and can be used with various band-pass filters. Amplifier output can be directly connected with level recorder and recorder, and can display or store noise signal. If the microphone of the precision sound level meter is removed, the vibration meter can be used for vibration measurement by replacing the input converter and connecting the accelerometer.

According to the national standards gb/t 3785.1-2010 and IEC 61672-1:2013, sound level meters are divided into class 1 sound level meter and level 2 sound level meter according to the accuracy. The technical indexes of class 1 and level 2 sound level meters have the same design objectives, mainly because the maximum allowable error, working temperature range and frequency range are different, and the maximum allowable deviation required by level 2 is greater than level 1. The operating temperature range of the second level sound level meter is 0 ℃ ~40 ℃, and the first stage is -10 ℃ ~50 ℃. The frequency range of level 2 is generally 20hz-8khz, and the frequency range of level 1 is 10Hz-20kHz.

Sound level meter is the most basic instrument in noise measurement. Sound level meter is generally composed of capacitor microphone, preamplifier, attenuator, amplifier, frequency meter weight network and effective value indicator. The principle of sound level meter is: the sound is converted into electrical signal by microphone, and then impedance is transformed by preamplifier to match microphone and attenuator. The amplifier adds the output signal to the weight network, calculates the frequency weight (or external filter) of the signal, then amplifies the signal to a certain amplitude through attenuator and amplifier, and sends it to the effective value detector (or external press level recorder), and gives the noise sound level value on the indicator head.

The frequency weighting network in sound level meter includes three standard weight network, i.e. a, B and C. A network is a response of 40 square pure sound in the human ear equivalent sound curve. Its curve shape is opposite to that of 340 square, which makes the high frequency segment of the electrical signal attenuated greatly. Network B is a simulation of the response of human ear to 70 square pure tone, which makes the high frequency segment of the electrical signal attenuated. C network is a simulation of human ear response to 100 square pure sound, and has a nearly straight response in the whole range of audio frequency. The sound pressure level measured by the frequency weighting network is called sound level. According to the different weight calculation network used, it is called A-level, B-level and C-level respectively.

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