Signal processing method for ultrasonic ranging sensor

Views: 22 Author: Site Editor Publish Time: 2018-08-29 Origin: Site

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There are many methods for measuring distance ultrasonic sensors, and the most used ones are Pellam and Galt in 1946.The pulse echo method proposed in the year, the working principle of the ultrasonic probe is excited by the ultrasonic frequency pulse to radiate the ultrasonic wave outside, and the ultrasonic wave reflected from the measuring object is received, and the ultrasonic wave is transmitted to the receiving echo by detecting or estimating. The time period elapsed (referred to as the range time), and then the ultrasonic probe and the measuring object are calculated as follows, and the speed of sound propagation when the temperature e of the propagation medium changes. It also changed. Therefore, temperature probe is built in the ultrasonic range finder to detect the temperature of the sound propagation medium in real time to compensate for the influence of the ambient temperature on the ranging accuracy.

In order to improve the performance of the ultrasonic ranging system, it is not enough to start the hardware of the system. It is also necessary to study the measurement information processing method that is compatible with the hardware system. in this end, national and foreign scholars have studied many special ultrasonic ranging methods or time delay estimation algorithms, such as variable closed-valued amplitude estimation, cross-correlation function method, spectral line analysis method, phase detection method and adaptive time delay estimation. In the actual ultrasonic range finder, a variety of measurement algorithms are often applied in the combination. Of course, these algorithms are closely related to the acoustic and electrical characteristics of the ultrasonic transducer.

Ultrasonic ranging system adopts the simplest "zero-crossing" detection method, and its working process is as follows: 1 When the controller starts the clock counter, it sends out a fixed-time ultrasonic frequency pulse signal. Sending ultrasonic waves to the outside . 2 If there is a target in front of the transducer, the reflected ultrasonic wave must act on the transducer to generate a weak electrical signal. After the signal is amplified by the receiving circuit, it is greater than the preset threshold voltage to terminate the counting.which causes the output signal of the comparator to go high. 3 The high level signal enables the counter to enable the gate, and the value in the memory allows the microcomputer to query the end counting signal on the parallel input port, and read the clock to calculate the relationship between the target and the transducer according to the equation. Incidentally, the product of the duration of the sound wave transmitted by the transducer and the speed of sound is the blind spot of the ultrasonic transducer sensor.

Since the amplitude of the echo signal is inversely proportional to the distance of the target, the farther distance between the target and the transducer is the smaller the output of the ultrasonic receiving circuit is, and the longer the corresponding range time is. Therefore, in the ultrasonic ranging system, a receiving circuit transducer distance sensor is having a fixed closed value or a gain which is generally not employed, but a receiving circuit is having a time-variable value or a time-gain variable is employed. The former makes the closed value decrease exponentially with the extension of the range time, and the latter increases the amplification factor of the receiving circuit exponentially with the extension of the range time. As long as the time constant of the exponential function is properly adjusted, it is ensured that the distance of the target is accurately measured within the specified range.

The measurement process is as follows: first, the transducer transmits 1016 cycles of high frequency ultrasonic waves and then transmits 4-18 cycles of low frequency ultrasonic proximity sensors. For close-range targets, because the transducer transmits high frequency ultrasonic waves first, the high frequency echo first arrives at the receiver; for long-distance targets, the high-frequency ultrasonic energy is greatly attenuated by the air absorption, The wave signal has only low frequency ultrasound. In this way, by separating the remote ranging from the short range ranging, the inherent contradiction between the ranging range and the ranging accuracy can be overcome. Of course, the dual-frequency ultrasonic ranging method has the premise that the transducer must have two resonant frequencies, Since the detection method cannot accurately determine the occurrence time of the echo front, it is difficult to accurately estimate the actual range time. Several calculation methods for analyzing and extracting is the frontier of echo envelope are proposed. The paper gives the concept of coarse and two range ranging method: firstly send an ultrasonic ranging pulse for coarse ranging, and use microprocessor to back The wave signal is analyzed and processed, and a reasonable amplitude value is automatically set, and then another series of ultrasonic ranging pulses are transmitted, and the signal of a certain fixed position of the echo front edge is captured according to the closed value previously, thereby achieving accurate purpose of ranging.