Principle of sound level meter, calibration regulations, analysis of the internal structure of the relevant models
Noise meter is also called sound level meter, is a kind of industrial noise, living noise and traffic noise, etc., according to the human ear hearing characteristics of the approximate determination of its noise level instrument.
Noise level refers to the sound pressure level (dB) or loudness level (phon) measured by a sound level meter and corrected by hearing.
According to the sound level meter in the standard conditions to measure the accuracy of 1000Hz pure tone performance, the 60's international sound level meter is divided into two categories, a class called precision sound level meter, a class called ordinary.
Our country also adopts this method. Noise meter weighting network generally has A, B, C three kinds of A weighting sound level is simulated human ear on the frequency characteristics of low-intensity noise below 55 decibels; B weighting sound level is simulated 55 ~ 85 decibels of the frequency characteristics of medium-intensity noise; C weighting sound level is simulated high-intensity noise characteristics.
Since the 70's, some countries have introduced four types of classification, i.e. type 0, type 1, type 2 and type 3. Their accuracy is ±0.4dB, ±0.7dB, ±1.0dB and ±1.5dB respectively.
According to the different power supply used in the sound level meter, it can also be divided into two categories of AC and DC sound level meters with dry batteries, the latter can also become portable. Portable has the advantages of small size, light weight and easy to use on site.
It is generally composed of microphone, amplifier, attenuator, weighting network, detector, indicator head and power supply.
(1) microphone It is the sound pressure signal into a voltage signal device, also known as microphone, is the sensor. Common microphone has crystal type, electret type, moving coil type and condenser type and other forms.
(2) Amplifiers and attenuators Many popular domestic and imported ones use two-stage amplifiers in the amplification circuit, i.e., the input amplifier and the output amplifier, whose function is to amplify the weak electrical signals.
(3) weighting network The weighting network generally has three kinds of A, B and C. A weighting level is to simulate the human ear to the frequency characteristics of low-intensity noise below 55 decibels; B weighting level is to simulate the frequency characteristics of medium-intensity noise from 55 to 85 decibels; C weighting level is to simulate the characteristics of high-intensity noise.
(4) Detector and Indicator Meter Head In order to display the amplified signal through the meter head, a detector is also required to convert a rapidly changing voltage signal into a slower changing DC voltage signal.
