Introduction to Noise Meters
Noise meter, also known as (noise meter, sound level meter) is the most basic instrument in noise measurement. The sound level meter is generally composed of a condenser microphone, a preamplifier, an attenuator, an amplifier, a frequency meter network, and an RMS indicator. The working principle of the sound level meter is: the sound is converted into an electrical signal by the microphone, and then the impedance is transformed by the preamplifier to match the microphone and the attenuator. The amplifier adds the output signal to the network, performs frequency weighting on the signal (or an external filter), and then amplifies the signal to a certain amplitude through the attenuator and amplifier, and sends it to the RMS detector.
Principle of noise meter
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 tone in the equal-loudness curve. Its noise meter curve shape is opposite to the 340-square equal-loudness curve, so that the middle and low frequency bands of the electrical signal have greater attenuation. The B network simulates the response of the human ear to a 70-square pure tone, which makes the low frequency band of the electrical signal attenuated to a certain extent. The C network simulates the human ear's response to a 100-square pure tone, with a nearly flat response over the entire audio frequency range. The sound pressure level measured by the sound level meter through the frequency weighting network is called the sound level. According to the different weighting network used, it is called the A sound level, the B sound level and the C sound level, and the unit is denoted as dB(A) , dB(B), and dB(C). At present, the sound level meter used to measure noise, the meter response can be divided into four types according to the 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, "fast". The time constant of the meter head is 125ms, which is generally used to measure unstable noise and traffic noise with large fluctuations. Fast gear is close to the human ear's response to sound.
3. "Pulse or pulse hold". The rise time of the needle is 35ms, which is used to measure pulse noise with a long duration, such as punches, hammers, etc. The measured value is the maximum effective value.
4. "Peak Hold". The rise time of the needle is less than 20ms. Used to measure short-duration impulse sounds, such as guns, cannons and explosions, the measured value is the peak value. i.e. the maximum value.
The sound level meter can be connected to an external filter and recorder to perform spectrum analysis on noise. The domestic ND2 type precision sound level meter is equipped with an octave page filter, which is easy to carry to the scene and perform spectrum analysis. Sound level meters can be divided into precision sound level meters and ordinary sound level meters according to their accuracy. The measurement error of a precision sound level meter is about ±1dB, and that of an ordinary sound level meter is about ±3dB. Sound level meters can be divided into two categories according to their use: one is used to measure steady-state noise, and the other is used to measure unsteady noise and impulse noise. The integrating 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, mainly used to measure noise exposure. Impulse sound level meter is used to measure impulse noise, this kind of sound level meter accords with human ear's response to impulse sound and the average time of human ear's response to impulse sound.
Noise Meter - Standard Regulations
In order to make the measurement results of sound level meters produced in various countries in the world comparable with each other, the International Electrotechnical Commission (IEC) has formulated relevant standards for sound level meters and recommended that countries adopt them. In May 1979, the IEC651 "Sound Level Meter" was adopted in Stockholm. Standard, China's national standard for sound level meters is GB3785-83 "Sound Level Meter Electrical and Acoustic Properties and Test Methods". In 1984, IEC passed the IEC804 "Integrated Average Sound Level Meter" international standard, and in 1997 China promulgated GB/T17181-1997 "Integrated Average Sound Level Meter". They are consistent with the main requirements of the IEC standard. In 2002, the International Electrotechnical Commission (IEC) issued a new international standard for IEC61672-2002 "Sound Level Meter". This standard replaces the original IEC651-1979 "Sound Level Meter" and IEC804-1983 "Integrated Average Sound Level Meter". According to this standard, China has formulated the JJG188-2002 "Sound Level Meter" verification regulations. According to the new standard, the sound level meter can be divided into general sound level meter, integral sound level meter, spectrum sound level meter, etc. according to the purpose. The performance indicators have the same central value, only the tolerance is different, and the tolerance is relaxed as the level number increases. According to the volume can also be divided into desktop, portable, and pocket sound level meters. According to its indication method, it can be divided into analog indication and digital indication sound level meter.
Noise Meter - Classification
1. From the measurement object, it can be divided into the characteristic measurement of environmental noise (sound field) and the measurement of sound source characteristics.
2. According to the time characteristics of the sound source or sound field, it can be divided into steady-state noise measurement and non-steady-state noise measurement. Unsteady noise can be divided into periodic variation noise, irregular variation noise and impulse sound.
3. According to the frequency characteristics of the sound source or sound field, it can be divided into broadband noise, narrowband noise and noise containing prominent pure tone components.
4. According to the accuracy of measurement requirements, it can be divided into precision measurement, engineering measurement and noise census.
Noise Meter - How to Use
Whether the noise meter is used correctly or not directly affects the accuracy of the measurement results. When measuring, the instrument should choose the correct gear according to the situation, and hold the noise with both hands.
For the sound level meter used for measuring noise, the response of the meter head can be divided into four types according to the 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, "fast". The time constant of the meter head is 125ms, which is generally used to measure unstable noise and traffic noise with large fluctuations. Fast gear is close to the human ear's response to sound.
3. "Pulse or pulse hold". The rise time of the needle is 35ms, which is used to measure pulse noise with a long duration, such as punches, hammers, etc. The measured value is the maximum effective value.
4. "Peak Hold". The rising time of the needle is less than 20ms. Used to measure short-duration impulse sounds, such as guns, cannons and explosions, the measured value is the peak value. i.e. the maximum value. Distance meter, altimeter, laser line cast meter, flow meter, GPS thickness gauge, level meter, flat meter, waveform recorder, test fixture, voltage and current recorder, data set recorder, graphic recorder, flow totalizer.
Noise Meter - Sensitivity Calibration
In order to ensure the accuracy of the measurement, it should be calibrated before and after use.
Match the sound level calibrator to the microphone, turn on the calibration power, read the value, adjust the sensitivity potentiometer of the noise meter, and complete the calibration.
