According to the characteristics of the transmitted ultrasonic energy, the expression of the energy of each cycle of the received signal is obtained. It is assumed that the sine wave in each cycle is a standard sine wave and the transmitting head vibration plate has not yet reached a stable vibration state. During the measurement, once the interferer obstructs the travel path of the ultrasonic wave to the wall, the signal returned by the wall will be weakened. If the threshold value is too high, wall echo signals may not be detected. The dynamic threshold cannot be used due to irregularity, so the threshold value is With a small fixed value, the peak value of the noise in the received signal is relatively stable, and the fixed threshold takes a noise peak of 3 to 5 times.
Since the wall echo signal changes indefinitely, the oscilloscope acquires the signal when calibrating the measurement parameters, and takes the 0.5 times of the peak value of the received signal envelope (that is, the time at n = 4 or 5) as the distance information. The purpose of this processing is that even if the received signal is too strong or too weak, the ranging error is always within 3 to 5 cm. When N is too large, the blind zone will increase and the measurement accuracy will decrease.
Ultrasonic waves generated by the ultrasonic envelope head of the receiving signal will encounter echoes in different media, and the receiving head will convert the echo into electric energy to generate a received signal. The received signal when the ultrasonic wave is incident perpendicularly to the wall surface is analyzed, and the ultrasonic envelope of the received signal is composed of a start-up phase and an attenuation phase.
The system hardware series microcontrollers have a wealth of analog, digital peripherals and a variety of bus interfaces, support online programming, is the first choice for many measurement and control systems. There are 5 timers, 5 PCA channels, and 4 directions of ultrasonic sensor transmitter heads can share a 40kHz square wave signal to implement synchronous transmission; 4 receiver heads can access 4 channels of PCA. The amplification of the signal amplifier circuit is around 800. Even if the received signal passes through a band-pass filter, the noise peak reaches 30mv.