Sound level meter, also known as (noise 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 weighting 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 weighting 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 (or external power supply). flat recorder), the numerical value of the noise sound level is given on the indicator head. The frequency weighting network in the sound level 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 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 sound level. According to the different weighting network used, it is called A sound level, B sound level and C sound level, and the unit is denoted as dB (A) , dB(B) and dB(C). At present, 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 1000 ms, 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. That is, 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.
The noise meter is mainly used to measure noise, and the classification of noise measurement mainly includes the following:
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. From 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.
How to use the noise meter in general
Whether the noise meter is used correctly or not directly affects the accuracy of the measurement results. Therefore, it is necessary to introduce the use of noise meters.
Before use, you should read the manual to understand the use method and precautions of the instrument.
. Pay attention to the polarity when installing the battery or external power supply, do not reverse the connection. The battery should be removed if it is not used for a long time, so as not to damage the instrument due to leakage.
.Do not disassemble the microphone to prevent falling, and place it properly when not in use.
.The instrument should not be placed in places with high temperature, humidity, sewage, dust and air or chemical gas with high hydrochloric acid and alkali components.
.Do not disassemble the instrument without authorization. If the instrument is not normal, it can be sent to the repair unit or the factory for overhaul.
2. Calibration of Sensitivity
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.
3. Measurement methods
When measuring, the instrument should select the correct gear according to the situation, hold both sides of the noise meter with both hands, and point the microphone to the sound source to be measured. Extension cables and extension rods can also be used to reduce the impact of the noise meter’s appearance and human body on the measurement. The position of the microphone should be determined according to the relevant regulations.
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 1000 ms, 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. That is, the maximum value. Range finder, altimeter, laser line meter, flow meter, GPS thickness gauge, level meter, flat meter, waveform recorder, test fixture, voltage and current recorder, data recorder, graphic recorder
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. Process Calibrator Temperature Calibrator Pressure Calibrator Loop Calibrator Calibration Buffer Clamp Meter Calibrator Oscilloscope Calibrator Noise Meter Calibrator Current Calibrator Multifunction Calibrator Humidity Calibrator pH Calibrator
