The Application of Sound Level Meters in the Automotive Industry
It generally consists of a microphone, amplifier, attenuator, weighting network, detector, indicator head, and power supply.
(1) Microphone
It is a device that converts sound pressure signals into voltage signals, also known as a microphone or sensor. Common types of microphones include crystal, electret, moving coil, and capacitive.
A dynamic coil sensor consists of a vibrating diaphragm, a movable coil, a magnet, and a transformer. After being subjected to acoustic pressure, the vibrating diaphragm begins to vibrate and drives the movable coil installed with it to vibrate in the magnetic field, generating induced current. The current varies according to the magnitude of the acoustic pressure acting on the vibrating diaphragm. The higher the sound pressure, the greater the generated current; The lower the sound pressure, the smaller the generated current.
Capacitive sensors are mainly composed of metal membranes and closely adjacent metal electrodes, essentially a flat capacitor. The metal film and metal electrode form the two plates of the flat capacitor. When the diaphragm is subjected to sound pressure, it deforms, causing a change in the distance between the two plates and a change in capacitance, resulting in an alternating voltage whose waveform is proportional to the sound pressure level within the linear range of the microphone, achieving the function of converting sound pressure signals into electrical pressure signals.
Capacitive microphones are ideal microphones in acoustic measurements, with advantages such as large dynamic range, flat frequency response, high sensitivity, and good stability in general measurement environments, making them widely used. Due to the high output impedance of capacitive sensors, impedance transformation is required through a preamplifier, which is installed inside the sound level meter near the location where the capacitive sensor is installed.
(2) Amplifier and attenuator
Many popular domestic and imported amplifiers currently use two-stage amplifiers in amplification circuits, namely input amplifiers and output amplifiers, which amplify weak electrical signals. The input attenuator and output attenuator are used to change the attenuation of the input signal and the attenuation of the output signal, so that the pointer of the meter head points to the appropriate position, and the attenuation of each gear is 10 decibels. The adjustment range of the attenuator used in the input amplifier is for measuring the bottom end (such as 0-70 decibels), and the adjustment range of the attenuator used in the output amplifier is for measuring * * (70-120 decibels). The dials of the input and output attenuators are often made in different colors, and currently black and transparent are often paired together. Due to the fact that many sound level meters have a high and low limit of 70 decibels, it is important to prevent exceeding the limit during rotation to avoid damaging the device.
