Measurement Principle
Back warning system (BWS) is a complementary device for reversing. BWS detects objects behind vehicle and provides the driver with buzzer alarm finding objects in a certain area, using ultrasonic wave propagation speed and time.
The propagation speed formula of ultrasonic wave in air is following :
v = 331.5 + 0.6 t (m/s)
v = ultrasonic wave propagation speed
t = ambient temperature
The basic principle of distance measurement using ultrasonic wave is: