The Use of Sound Level Meters in the Automotive Industry - The Automotive Industry
The structure and working principle of the sound level meter sound level meter is a kind of industrial noise, life 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 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. Since the 70s, some countries have introduced four types of sub-methods, namely, type 0, type 1, type 2 and type 3. Their accuracy were ± 0.4dB, ± 0.7dB, ± 1.0dB and ± 1.5dB. According to the different power supply used by the sound level meter can also be divided into two categories of AC and DC sound level meter with dry battery, the latter can also become portable. Portable has the advantages of small size, light weight and easy to use on site.
Generally consists of microphone, amplifier, attenuator, weighting network, detector, indication table 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 capacitive type and other forms.
Moving-coil transducer consists of a vibrating diaphragm, a movable coil, a magnet and a transformer. The vibrating diaphragm starts to vibrate after being pressurized by the sound wave, and drives the movable coil installed with it to vibrate in the magnetic field to generate an induced current. The current varies according to the size of the acoustic pressure on the vibrating diaphragm. The greater the sound pressure, the greater the current generated; the smaller the sound pressure, the smaller the current generated.
Capacitive sensors are mainly composed of a metal diaphragm and metal electrodes that are very close together, which is essentially a flat capacitor. The metal diaphragm and the metal electrode constitute the two pole plates of the flat capacitor. When the diaphragm is subjected to sound pressure, the diaphragm is deformed, so that the distance between the two plates changes, the capacitance also changes, thus generating an alternating voltage, whose waveform is proportional to the sound pressure level within the linear range of the microphone and realizes the effect of transforming the sound pressure signal into a voltage signal.
Condenser microphone is a more ideal microphone in acoustic measurement, with a large dynamic range, frequency response flat, high sensitivity and good stability in the general measurement environment, and thus widely used. Since the output impedance of the capacitive sensor is very high, it is necessary to transform the impedance through the preamplifier, which is installed inside the sound level meter near the part where the capacitive sensor is installed.
(2) Amplifier and attenuator
Currently popular many domestic and imported in the amplifier circuit are used in two-stage amplifier, namely, the input amplifier and output amplifier, its role is to amplify the weak electrical signals. Input attenuator and output attenuator is used to change the amount of attenuation of the input signal and the amount of attenuation of the output signal, in order to make the meter pointer in the appropriate position, the attenuation of each block of 10 dB. The attenuator adjustment range used for the input amplifier is the bottom of the measurement (e.g., 0 to 70 dB) and the attenuator adjustment range used for the output amplifier is the measurement (70 to 120 dB). Input and output two attenuator dials are often made of different colors, the current black and transparent pair more. As many sound level meter high, bottom to 70 dB as the limit, so when rotating to prevent exceeding the limit, so as not to damage the device.
