Ultrasonic sensor application

Ultrasound is a mechanical oscillation in an elastic medium and has two forms: lateral oscillation (transverse wave) and longitudinal oscillation (longitudinal wave). Applications in the industry mainly use longitudinal oscillations. Ultrasound can propagate in gases, liquids, and solids, with different propagation speeds. In addition, it also has refraction and reflection phenomena, and there is attenuation in the propagation process. Ultrasonic waves are propagated in the air with a low frequency, typically several tens of KHZ, while in solids and liquids the frequency is higher. It attenuates faster in the air, but it spreads in liquids and solids, with less attenuation and longer propagation. Utilizing the characteristics of ultrasonic waves, it can be made into various kinds of ultrasonic sensors, equipped with different circuits, made various kinds of ultrasonic measuring instruments and devices, and has been widely used in communication, medical appliances and other aspects.

The main materials of ultrasonic sensors are piezoelectric crystals (electrostrictive) and nickel-iron-aluminum alloys (magnetostrictive). Electrostrictive materials include lead zirconate titanate (PZT). An ultrasonic sensor composed of a piezoelectric crystal is a reversible sensor, which can convert electrical energy into mechanical oscillation and generate ultrasonic waves. At the same time, when it receives ultrasonic waves, it can also be converted into electrical energy, so it can be divided into transmitters or receivers. Some ultrasonic sensors both send and receive. Here only a small ultrasonic sensor is introduced. The transmission and reception are slightly different. It is suitable for propagation in the air. The operating frequency is generally 23-25 ​​KHZ and 40-45 KHZ. This type of sensor is suitable for distance measurement, remote control, anti-theft and other purposes. This species has T/R-40-60, T/R-40-12 and so on. Another type of sealed ultrasonic sensor (MA40EI type), which is characterized by a waterproof (but can not be placed in water), can be used as a material level and proximity switch, its performance is better. There are three basic types of ultrasonic applications, transmissive type for remote control, burglar alarm, automatic door, proximity switch, etc.; separate reflective type for distance measurement, liquid level or material level; reflective type for material inspection, thickness measurement, etc. .

a. Liquid Level Indicator and Controller Since the ultrasonic wave has a certain attenuation in the air, the size of the signal sent back to the liquid surface and reflected back from the liquid surface is related to the liquid level. The higher the liquid surface position is, the larger the signal is; Low signal is small. The received signal is amplified by BG1 and BG2 and rectified into D.C. voltage by D1 and D2. When the voltage at 4.7KΩ exceeds the turn-on voltage of BG3, there is current flowing through BG3. The ammeter indicates that the current is related to the liquid level. Point A is connected to point A in the above figure. When the level is lower than the set value, the comparator output is low. The BG is not conducting. If the liquid level rises to the specified position, the comparator turns over and outputs a high level. The BG is on, the J is on, and the infusion switch can be closed by the solenoid valve to achieve the purpose of control (high control).

b. Remote control switch Ultrasonic remote control switch can control household appliances and lighting. Using a small ultrasonic sensor (& PHi; 16), operating frequency at 40KHZ, remote control distance of about 10 meters. Remote control transmitter, which is an oscillator composed of 555 time base circuit, adjust the 10KΩ potentiometer, so that the oscillation frequency is 40KHZ, the sensor is connected to pin 3, and when the button is connected, ultrasonic wave is transmitted and the circuit is received. Power supply from the 220V by the capacitor buck, rectification, filtering, voltage regulator to obtain 12V working voltage. Since it is a non-isolated power supply, the entire circuit must be encapsulated with a plastic case to prevent electric shock (note also during commissioning). The signal is received by an ultrasonic receiver and amplified by Q1 and Q2 (L and C resonant tanks are tuned to 40KHz). The amplified signal triggers the bistable circuit composed of Q3 and Q4. Q5 and LED are used as trigger isolation and can display light. Since the bistable is random at startup, a clear button is added. The trigger signal output by Q5 turns on the triac and the load turns on. To disconnect the load, press the send button once.