The sound level meter is the basic noise measuring instrument, which is a subjective electronic instrument, unlike objective electronic instruments such as voltmeters. The ability to convert an acoustic signal into an electrical signal can simulate the temporal characteristics of the human ear's response to sound waves; the frequency characteristics of different sensitivities for high and low frequencies and the intensity characteristics of varying frequency characteristics for different loudnesses.
The working principle is that the sound is converted into an electrical signal by the microphone, and then the impedance is converted by the preamplifier to match the microphone with the attenuator. The amplifier adds the output signal to the weighting network, performs frequency weighting (or external filter) on the signal, and then amplifies the signal to a certain amplitude through the attenuator and the amplifier, and sends it to the RMS detector (or externally pressed) Flat recorder), the value of the noise level is given on the indicator head. However, there are some differences in the principles of different categories of sound level meters.
According to the sensitivity of the sound level meter, there are two types of sound level meter classification: one is the ordinary sound level meter, which is not very demanding on the microphone. The dynamic range and the frequency response are relatively narrow, and generally do not have a band-pass filter connected; the other is a precision sound level meter, which requires a wide frequency response, high sensitivity, long-term stability, and A bandpass filter is used together, and the amplifier output can be directly connected to the level recorder and the recorder to display or store the noise signal. If the microphone of the precision sound level meter is removed, and the input converter is connected and the accelerometer is connected, the vibrometer can be used for vibration measurement.
Moreover, different sound level meter measurement methods are also different, but the same is the sound level meter calibration method, which is to take a calibrator on the sound level meter before measurement to obtain a value. The range of values ​​should be 94.0dB plus or minus 0.5dB. If this range is exceeded, the measurement behavior will be invalid.
1, according to the use can be divided into general sound level meter, integral sound level meter, automatic monitoring (statistics, spectrum) sound level meter.
2. According to the accuracy, it can be divided into type 2 (allowable error 1 d B) and type 1 (allowable error 0.7 d B) sound level meter. ï‚·
3, by volume can also be divided into desktop, portable, and pocket sound level meter.
4. According to the indication mode, it can be divided into analog indication (pointer type) and digital indicator sound level meter.
Introduction of several typical sound level meters1. Integral sound level meter - can directly display the equivalent continuous sound level of the measured noise within a certain measurement time in digital form. For unsteady noise, the equivalent continuous sound level Leq of the measurement noise is required to be defined as: at a certain point in the sound field, using a method of energy averaging over a certain period of time, several different A-levels that will vary intermittently. , the noise level of the period of time is represented by an A sound level.
2. Digital sound level meter - A sound level meter that displays the measurement results by digital. It not only has the advantages of intuitive and accurate reading, but also can be processed by other analytical processing instruments and computers through BCD code output.
3. Pulsed sound level meter - measures the effective value of the measured signal by the pulsating characteristics of the capacitor at different times, and has a high crest factor capacity, so it can respond to pulse sounds with short duration and low repetition rate. . In life, often encounter discontinuous noise, that is, pulse sound or impact sound, such as typewriter noise, punch bed noise, guns and so on. This noise duration is very short and the recurring time can be very long, even once in a while. When measuring with a general sound level meter, there will be a large error, and a pulse sound level meter should be used.
4. Environmental automatic monitoring (noise statistics, spectrum) analyzer - can automatically collect and calculate noise data according to preset functions, and display the results directly (and store the data at the same time).
1. The sound level meter measures the vibration wave of the air vibration caused by the acoustic signal (sound wave). The vibration wave signal of the metal diaphragm of the microphone (header) at the front end of the sound level meter is converted into an electrical signal, and then the special weighted network and circuit. After the operation is amplified, the noise decibel value is displayed by digital or electric meter.
2, the quality of the air is unstable, such as: the temperature, humidity, atmospheric pressure of the air, etc. will be affected by the environment and other factors, so as 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.
3. The process of adjusting the sensitivity of the microphone is to calibrate the sound level meter.
4. The national standard stipulates: “The measuring instrument must be calibrated with a sound level calibrator before and after measurement. The deviation of the indication value of the calibrated instrument shall not exceed 0.5 dB, otherwise the test will be invalidâ€.
1. After turning on the sound level meter, there will be four options: measurement, setup, access, and calibration. The last option is the calibration option. Move the cursor to this option.
2. After entering the calibration page, there are still four options for review, calibration, application, and modification. Place the cursor on the second option calibration option and select the calibration option.
3. Insert the sensor of the sound level meter into the upgrade calibrator, then turn on the switch of the calibrator. The calibrator will emit the standard sound level. When everything is ready, press the calibration to start, and the instrument can be automatically calibrated.
4. When the data displayed by the sound level meter reaches 93.8dB(A), the instrument is calibrated.
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