Ultrasonic distance meter design and application analysis
1. Design principles
Ultrasonic rangefinders measure based on the characteristics of ultrasonic waves reflected back when encountering obstacles. The ultrasonic transmitter emits ultrasonic waves in a certain direction and starts timing at the same time. The ultrasonic waves propagate in the air and return immediately when encountering obstacles on the way. When the ultrasonic receiver receives the reflected waves, it immediately interrupts and stops the timing. By continuously detecting the echo reflected by the obstacle after the generated wave is emitted, the time difference T between transmitting the ultrasonic wave and receiving the echo is measured, and then the distance L is calculated. The basic ranging formula is: L=(△t/2)*C
Where L--the distance to be measured
T--The time interval between the transmitted wave and the reflected wave
C--The speed of sound of ultrasonic waves in air, which is taken as 340m/s at room temperature.
After the speed of sound is determined, L can be obtained by measuring the round-trip time of the ultrasonic wave.
2. Design goals of ultrasonic range finder
Measuring distance: within a range of 5 meters; the distance between two points can be displayed correctly through LED; the error is less than 5%.
3. Data measurement and analysis
Data measurement and analysis
Due to the limitations of the actual measurement work, six distances of 30cm, 50cm, 70cm, 80cm, 90cm, and 100cm under one meter were finally selected for measurement. Each distance was measured seven times in succession to obtain the measurement data (temperature: 29℃), as shown in the table. It can be seen from the data in the table that the measured values are generally several centimeters larger than the actual values, but the accuracy of continuous measurements is still relatively high.
Remove a maximum value and a minimum value from each set of measured data, and then find the average value, which is used as the final measurement data, and finally conduct comparative analysis. Processing data in this way also has a certain degree of scientificity and rationality. Judging from the data in the table, although the ultrasonic wave is temperature compensated, its relative error is relatively large in measurements at relatively close distances. Especially for distance measurement of 30cm and 50cm, the relative errors reached 5% and 4.8% respectively. However, judging from all the measurement results, the errors of this design are relatively small and relatively stable. The blind area of this design is about 22.6cm, which basically meets the design requirements.
Error Analysis
Ranging errors mainly come from the following aspects:
(1) There is a certain angle between the ultrasonic transmitting and receiving probe and the measured point, which directly affects the value of the measured distance; (2) The intensity of the ultrasonic echo is directly related to the distance to be measured, so during actual measurement, It is not necessarily triggered by the zero-crossing point of the first echo; (3) Due to the rudimentary tools, the actual measured distance also has errors. There are many factors that affect measurement errors, including on-site environmental interference, time base pulse frequency, etc.
