What is the working principle of a noise meter:
Noise meter (also called sound level meter) is the most basic instrument in noise measurement. The noise meter is generally composed of a condenser microphone, a preamplifier, an attenuator, an amplifier, a frequency weighting network, and an effective value indication header.
The working principle of the noise meter is that the microphone converts the sound into an electrical signal, and the preamplifier then transforms the impedance so that the microphone matches 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 via an attenuator and amplifier and sends it to an rms detector (or externally Level recorder), giving the value of the noise level on the indicator head. The frequency-weighted network in the noise meter has three standard weighted networks: A, B, and C. A network simulates the response of 40 pure tones in the human ear-equivalent curve, and its curve shape is opposite to that of the 340-square equal-intensity curve, so that the mid- and low-frequency bands of the electrical signal are greatly attenuated. The B network simulates the human ear's response to 70-point pure tones, which causes a certain attenuation of the low frequency band of the electrical signal. The C-network simulates the human ear's response to 100-point pure tones and has a nearly flat response over the entire audio frequency range.
The sound pressure level measured by the noise meter through the frequency-weighted network is called the sound level. According to the weighting network used, it is called the A sound level, the B sound level and the C sound level, and the unit is recorded as dB(A). dB(B) and dB(C).
At present, for the noise meter for measuring noise, the head response can be divided into four types according to sensitivity: (1) "Slow". The head time constant is 1000 ms, which is used to measure the steady-state noise. The measured value is a valid value. (2) "Quick". The head time constant is 125ms. It is generally used to measure fluctuations in unstable noise and traffic noise. Fast approaching the human ear to the sound response. (3) "Pulse or pulse hold". The rise time of the hands is 35ms. It is used to measure pulse noise with long duration, such as punch press, hammer press, etc. The measured value is the maximum effective value. (4) "peak hold". The needle rise time is less than 20ms. Used to measure pulsed sounds with very short duration, such as guns, cannons, and explosions. The measured value is the peak value. The maximum value. The noise meter can use external filters and recorders to perform spectrum analysis on the noise. Guangzhou Hongcheng Hong Kong CEM noise meter design is small, different types of noise meter can meet all kinds of testing needs, portable design, easy to carry to the site for on-site monitoring.
Noise meter can be divided into precision noise meter and common noise meter according to the precision. Precision noise meter measurement error is about 1dB of soil, ordinary noise meter is about 3dB of soil.
Noise meters can be categorized into two types according to their purpose: one for measuring steady-state noise, and one for measuring unsteady and impulsive noise. Integral noise meters are used to measure the equivalent sound level of unsteady noise over a period of time. The noise dosimeter is also an integral noise meter that is primarily used to measure noise exposure. Pulse noise meters are used to measure impulse noise. Guangzhou Hongcheng Hong Kong CEM noise meter Different types of sound level meter can meet different types of measurement requirements.
Use of sound level meter noise meter:
Sound level meter, also called noise meter, is an instrument used to measure the sound pressure level or sound level of sound. It is the most basic and most commonly used instrument for acoustic measurement. With the development of national economy and people's material and cultural life level. The improvement of noise survey and environmental protection has been carried out in an all-round way. Noise has been taken as one of the important quality indicators of the products in the machine manufacturing industry. Buildings such as auditoriums and gymnasiums are not only required to be aesthetically pleasing but also pursue sound effects. These have led to sound level meters. The application is more and more extensive. Today, noise meters are not only used in acoustic and electroacoustic measurements, but also have been widely used in various fields such as machine manufacturing, architectural design, transportation, environmental protection, medical care, and national defense engineering, and have become an acoustic measurement that almost all departments must possess. instrument.
The correct use of sound level meter directly affects the accuracy of the measurement results. Therefore, it is necessary to introduce the use of sound level meters.
1. Selection of Sound Level Meter Use Environment: Select a representative test site. The sound level meter should leave the ground and leave the wall to reduce the additional influence of the reflection of the ground and walls.
2. The weather conditions require that the sound level meter should keep the diaphragm of the microphone clean during no rain and no snow, wind shield must be added above the third level (to avoid wind noise interference), and the wind above level 5 should stop measuring.
3, open the sound level meter carrying box, remove the sound level meter, put on the sensor.
4. Place the sound level meter in the A state, test the battery, and then calibrate the sound level meter.
5, Comparison table (commonly known environmental sound level reference), adjust the measurement range.
6, the following can be used fast (measure the instantaneous value of the environment where the sound pressure level changes greatly), slow (measuring the average value of the environment where the sound pressure level changes little), pulse (measure pulse source), filter ( Measure the sound level of the specified frequency band. Various functions to measure.
7, according to the need to record data, but also can be connected to a printer or other computer terminal for automatic acquisition. Organize the equipment and return it to the designated place
A. Sound Level Meter Usage
1, using the sound calibrator to check the sound level meter calibration
2, according to the size of the sound to be measured, the range switch is placed in the appropriate gear, if you can not estimate the size, then placed in "85-130"
3. Place the time-weighted switch at the position specified by the standard; when the sound level is relatively stable, place it at “F†(fast); if the sound level changes drastically, place it at “S†(slow).
4, put the reading mark switch to "5S" or "3S"
5, put the power switch to "on"; display the number when the instrument starts working
6. If the over sign “▲†(underage mark “▼â€) is displayed at the right end of the monitor, the range switch should be moved “up or down†to make the range mark disappear. If the range flag does not disappear, the measured sound level at the meter exceeds the measuring range of the instrument.
7. After adjusting the range of the sound level meter, you can read the measurement result from the display.
8, make a measurement record
9. After the measurement is completed, it is recommended to use sound calibrators to check the sensitivity of the sound level meter to ensure the accuracy and reliability of the measurement data.
10. Turn the power switch to "OFF". If the sound level meter is no longer used for a long time, be sure to remove the battery.
Two. Sound Level Meter Usage Notes
1. When measuring, the instrument should select the correct position according to the situation. Hold both sides of the noise meter on both sides. The microphone points to the sound source under test. You can also use the extension cable and extension bar to reduce the appearance of the sound level meter and the measurement of the human body. influences. The position of the sound level meter should be determined according to relevant regulations.
2, sound level meter using battery power, should check whether the battery voltage meets the requirements: the meter function switch set "battery" file, "attenuator" can be set, at this time the meter indication should be within the rated battery voltage range, otherwise Need to replace the battery. Install the battery or external Power Supply. Note the polarity. Do not connect it reversely. The sound level meter should not remove the battery for a long time so as to avoid liquid leakage damage to the instrument
3, read the instructions before use to understand the use of the instrument and precautions. Preheat according to the preheating time (eg 10 minutes) specified in the noise meter instructions
4. When the battery voltage used by sound level meter is insufficient, it should be replaced.
5, calibration amplifier gain: meter function switch set "0" file, "attenuator" switch set "calibration", then the meter pointer should be at the red line position, otherwise need to adjust the sensitivity potentiometer
6. When it is not known how large the measured sound level is, the "attenuator" must be placed at the maximum attenuation position (for example, 120 dB), and then gradually adjust to the attenuation level position of the sound level to be measured during measurement to prevent it from being measured. Sound level exceeds the range to destroy the noise meter
7. Do not disassemble the microphone to prevent it from throwing and place it properly when not in use.
8, the sensor is extremely delicate and vulnerable to the more expensive parts, pay attention to gently during the entire experimental process. After the experiment is completed, remove the sensor and place it in the designated place.
9. The instrument should be kept away from high temperature, humidity, sewage, dust, and air or chemical gases containing hydrochloric acid or alkali.
10,. Do not disassemble the noise meter. If the instrument is abnormal, it can be sent to the repair unit or the factory for inspection.
III. Calibration of Noise Meter Sound Level Meter Sensitivity A. In order to ensure the accuracy of the measurement, the sound level meter should be carefully calibrated before and after each measurement of the sound level meter.
B. Fit the sound level calibrator on the microphone, turn on the calibration power supply, read the value, and adjust the noise meter sound level meter sensitivity potentiometer to complete the calibration.
IV. Types of Sound Level Meters Sound level meters are instruments that measure the sound pressure level and sound level of a sound according to a certain frequency weighting and time weighting, and are the most commonly used basic instruments for acoustic measurements. The sound level meter can be used for the measurement of environmental noise, machine noise, vehicle noise and other various noises, and can also be used for measurements such as electroacoustics and architectural acoustics.
In order to make the measurement results of sound level meters produced by various countries in the world comparable to each other, the International Electrotechnical Commission (IEC) has established the relevant standards for sound level meters and recommended them for use by various countries. In May 1979, it passed IEC 651 Sound Level Meters in Stockholm. "Standards, China's national standard for sound level meters is GB3785-83" sound level metering, sound performance and test methods." In 1984, IEC passed the IEC 804 "Integral Average Sound Level Meter" international standard. China and 1997 issued the GB/T17181-1997 "Integral 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 IEC 804-1983 Integrated Average Sound Level Meter. According to this standard, China has formulated the JJG188-2002 Sound Level Meter verification procedures. The new sound level meter international standards and national verification regulations have been greatly modified from the old ones.
Our company's current products are in accordance with the new international standards and national metrological verification procedures for production and testing. According to the new standard, the sound level is divided into: a general sound level meter that measures the time weight of the index, an integrated average sound level meter that measures the time average sound level, and an integrated sound level meter that measures sound exposure. The standard divides the sound level meter into level 1 and level 2 according to its accuracy. The various performance indicators of the two levels of sound level meters have the same center value, only the allowable error is different, and the allowable error is relaxed as the level number increases. According to the size of the volume can be divided into desktop sound level meter, portable sound level meter and pocket sound level meter. According to its instructions can be divided into analog instructions (electric meters, sound level lights) and digital indicator sound level meter. According to the IEC651 standard and national standards, the accuracy of the two sound level meters under the reference frequency, reference shooting direction, reference sound pressure level, and reference temperature and humidity conditions (without considering measurement uncertainty)
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