The sound level meter is an instrument used for noise detection and testing in public places such as work sites, squares and other public places. Higher decibel noise can even cause serious damage to the eardrum of a person, causing deafness and so on. The application of the noise tester can provide the decibel that the noise reaches in order to take relevant measures to control and reduce the noise.
In order to measure different noise requirements, ATO sells class 1/class 2 sound level meters, which have the characteristics of large dynamic range, large-screen LCD digital display, GPS positioning, and automatic measurement and storage of various data.
The sound is converted into electrical signals 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 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 press). Level recorder), the value of the noise sound level is given on the indicator head.
In order to simulate the different sensitivities of human hearing at different frequencies (20Hz-20KHz), there is a network in the sound level meter that can simulate the auditory characteristics of the human ear and correct the electrical signal to a similar value to the sense of hearing. It's called a weighted network.
The sound pressure level measured by the weighting network is no longer the objective physical sound pressure level (called linear sound pressure level), but the sound pressure level corrected by the sense of hearing, which is called weighted sound level or noise level.
Since people have different perceptions of noise in each frequency band, they are sensitive to the intermediate frequency Z of about 3 kHz, but less to low frequency and high frequency. Therefore, the unweighted signal-to-noise ratio may not be as good as the human ear's subjective perception of the noise level. match. How to integrate the measured value with the subjective sense of hearing? So there is an equalization network, or a weighting network, which moderately attenuates both low and high frequencies, so that the middle frequency is more prominent.
This weighting network is connected between the equipment under test and the measuring instrument, so the influence of the IF noise of the equipment will be "amplified" by the network, in other words, the IF noise that has the greatest impact on the sense of hearing is given a higher weight, the measured signal-to-noise ratio at this time is called the weighted signal-to-noise ratio, which can more truly reflect people's subjective sense of hearing.
The sound level meter measurement is to convert the vibration wave signal of the metal diaphragm of the microphone (microphone head) at the front of the sound level meter into an electrical signal through the vibration wave caused by the sound signal (sound wave), and then pass through the special weighting network and circuit. After the operational amplification, the noise decibel value is displayed by digital or meter.
The quality of the air is unstable. For example, the temperature, humidity, atmospheric pressure, etc. of the air will change at any time due to the influence of the environment and other factors. In this way, it is necessary to ensure the accuracy of the air vibration wave signal received by the metal diaphragm of the microphone. Adjust the sensitivity of the microphone accordingly.
The process of adjusting the sensitivity of the microphone is to calibrate the sound level meter.
The sound level meter is a basic instrument for measuring noise. It is an electronic instrument. The sound level meter is generally composed of a condenser microphone, a preamplifier, an attenuator, an amplifier, a frequency weighting network, and an effective value indicating meter. According to the sensitivity of sound level meters, they can be divided into two categories. One is ordinary sound level meters, the other is precision sound level meters. According to the purpose of sound level meters, they can also be divided into two categories: one is used to measure stability. State noise, one type is used to measure unstable noise and impulse noise.
The digital detection technology adopted by the sound level meter greatly improves the stability and reliability of the instrument. The sound level meter has the advantages of simple operation and convenient use; it has the characteristics of large dynamic range, large-screen LCD digital display, automatic measurement and storage of various data, etc.
The sound level meter can be widely used for industrial noise measurement and environmental noise measurement of various machines, vehicles, ships, electrical appliances, etc. It is suitable for factories and enterprises, architectural design, environmental protection, labor and health, transportation, teaching, medical and health, scientific research and other departments.
According to the sensitivity of the whole sound level meter, there are two types of sound level meter classification: one is the ordinary sound level meter, which does not require much microphone. The dynamic range and frequency response flat range are relatively narrow, and bandpass filters are generally not used in combination; the other type is precision sound level meters, whose microphones require wide frequency response, high sensitivity, and good long-term stability. This kind of band-pass filter is used together, the output of the amplifier can be directly connected with the level recorder and tape recorder, and the noise signal can be displayed or stored. If the microphone of the precision sound level meter is removed, replaced with an input converter and connected to an accelerometer, it becomes a vibrometer that can be used for vibration measurement.
1. Spectrum analysis function
In order to perform spectrum analysis on noise, the spectrum analysis function needs to be selected. Octave and 1/3-octave spectral analysis are the most used in acoustic measurements. In the past, spectrum analysis was realized by analog filters, but now most of them use digital technology to conduct real-time spectrum analysis through digital filters.
2. Accuracy class
Instrument Accuracy Class: Class 1 and Class 2.
When purchasing a sound level meter, you need to consider the price range of the product. The price of a sound level meter depends on many factors, including functionality, accuracy rating, number of channels, storage capacity, and more.
In the process of use, it is necessary to use a sound calibrator for sound calibration. The sound calibrator is often used as a supporting instrument of the sound level meter and becomes an integral part of the instrument. There are two kinds of sound calibrators: piston sounder and sound level calibrator. The piston sounder produces 250Hz, 124dB sound pressure level, and the accuracy level is 1 or 0; the sound level calibrator produces 1000Hz, 94dB sound pressure level, and the accuracy Level 2 or 1. Class 1 should be calibrated with a class 1 or class 0 sound calibrator, and class 2 should be calibrated with a class 2 or class 1 sound calibrator.
5. Measuring range
The measurement range sometimes needs to consider its upper measurement limit in order to measure high sound pressure levels, such as 140dB, or even more than 160dB; sometimes it needs to consider its lower measurement limit, in order to measure low sound pressure levels, such as below 20dB, usually the measurement of sound level meters The range is in the 25dB to 130dB range.
6. Number of channels
The general sound level meter has only 1 channel and only measures 1 channel sound pressure level. Sometimes it is necessary to measure multi-channel sound pressure level, and it is necessary to use multi-channel. For example, the measurement of sound intensity level requires 2 channels, and the measurement of sound power level requires more channels. The multi-channel sound level meter greatly expands the use of the instrument.
The measurement function is the most important indicator, it not only determines the application scope of the instrument, but also has the greatest relationship with the price of the instrument. According to the type of the measured signal, for the steady-state noise signal, the function of this instrument only needs to measure the instantaneous sound pressure level; for the measurement of the non-steady-state signal, it is generally required to measure the time-averaged sound level or the equivalent sound level. For analysis, choose a noise spectrum analyzer.
The current sound level meters generally contain RS232, USB and other interfaces, which are used to connect to micro-printers or computers, and users can choose according to the test needs.