An acoustic sensor is a type of sensor used for flow detection. It can be energized during wiring and operates in high/low sensitivity range modes. The high sensitivity range is suitable for long and short wave signals fluctuating around 40 dB. The low sensitivity range is used for long and short wave signals fluctuating between 28 dB and 68 dB. The acoustic sensor can operate independently of the control device by providing an external power supply.
I. Working principle of acoustic sensors
The acoustic sensor is a built-in condenser electret microphone that is sensitive to sound. An electret microphone mainly consists of two parts—a sound-to-electric conversion section and an impedance section. The key component for sound-to-electric conversion is the electret diaphragm. It is an extremely thin plastic diaphragm with a layer of pure gold evaporated onto one side. After being electretted by a high-voltage electric field, opposite charges are deposited on both sides. The gold-coated side of the diaphragm faces outwards and is connected to the metal casing.
The other side of the diaphragm is separated from the metal plate by a thin insulating gasket. This creates a capacitor between the electret diaphragm and the metal plate. When the electret diaphragm vibrates due to sound waves, the electric field across the capacitor changes, generating an alternating voltage that varies with the sound wave. The capacitance between the electret diaphragm and the metal plate is relatively small. Therefore, its output impedance is very high, approximately tens of megohms or more. Such high impedance cannot be directly matched to an audio amplifier. Therefore, a junction field-effect transistor (JFET) is connected inside the microphone for impedance transformation.
II. Application Areas of Acoustic Sensors
The acoustic sensor features an analog output for use with Sitrans control equipment. Powered by an external source, it can operate independently of the control device. Its output signal is fed into a control panel, chart logger, data logger, or a programmable logic controller with appropriate inputs. It is primarily used for solid flow detection. Additionally, the device can be used to detect water pump cavitation and liquid leaks, generating a sufficient audible alarm.
