Principle and application of ultrasonic position sensor

                           

  Ultrasound waves is a general term for mechanical waves whose frequency exceeds the human 's auditory frequency limit (approximately 20 kHz). Ultrasonic waves are generated by vibration transducer under the excitation of voltage. Distance measuring transducer has the characteristics of high frequency, short wavelength, small diffraction phenomenon, especially good directivity,it is capable of being ray and directed propagation. Ultrasonic transducers are also known as ultrasonic sensors or ultrasonic probes. The ultrasonic level gauge is a digital level gauge controlled by a microprocessor. In the measurement, the ultrasonic pulse distance transducer is emitted by the sensor (transducer), and the sound wave is reflected by the liquid surface and then received by ultrasonic receiver, it is converted into an electrical signal by the piezoelectric crystal or magnetostrictive device, and transmitted and received by the sound wave. The time between the calculation of the distance sensor to the surface of the object being measured. Due to the non-contact measurement, the measured medium is almost unlimited ,Ultrasonic distance measuring transducer can be widely used for the measurement of various liquid and solid materials.

  Structure of ultrasonic position sensor and its performance of ultrasonic transducer is mainly composed of piezoelectric wafers, which can emit sound waves can also receive ultrasound. Piezoelectric ultrasonic generators actually work with the resonance of a piezoelectric crystal. It has two piezoelectric wafers and a resonant piezo plate. When its two poles plus has a pulse signal whose frequency is equal to the natural oscillation frequency of the piezoelectric wafer, the piezoelectric wafer will resonate and drive the resonance plate to vibrate to generate ultrasonic waves. Conversely, if no voltage is applied between the two electrodes, when the resonator plate receives ultrasonic waves,transducer for distance will compress the piezoelectric wafer to vibrate, it is converting the mechanical energy into an electrical signal, and it will become an ultrasonic receiver.

  Low-power ultrasonic probes are mostly for detecting. They have many different structures, such as straight probe (longitudinal wave), oblique probe (transverse wave), transducer for flowmeter ,surface probe (surface wave), Lamb wave probe (Lamp wave), and dual probe ( One probe emits , one probe receives). The core of the ultrasonic probe is a piezoelectric wafer in its outer casing, and there are many kinds of materials constituting the wafer. The size of the wafer, such as diameter and thickness, is also different, so the performance of each probe is different, and its performance must be known before use. The main performance indicators of ultrasonic sensors are as follows:

1.Operating frequency. The operating frequency of Ultrasonic distance-measuring sensor is the resonant frequencyof the piezoelectric transducer. When the frequency of the AC voltage applied to both ends is equal to the resonance frequency of the transducer, the output energy is maximum and the sensitivity is the highest.

2.Operating temperature. Since the Curie point of the piezoelectric material is generally high, in particular, the ultrasonic probe for detecting distance measurement sensor has a small power, so the working temperature is relatively low and can work for a long time without failure.