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 + 0.6t (m/s)

v=ultrasonic wave propagation speed

t=ambient temperature

The basic principle of distance measurement using ultrasonic wave is:

Fig 1: Illustrating Distance Measurement Principle

Courtesy of KIA MOTORS AMERICA, INC.

• 14cm (dia.) plastic rod is used for the test target.
• The test result may differ by a different target object.
• Detection range may be reduced by dirt accumulated on sensor, and extremely hot or cold weather.
• The following object may not be detected.:
  • Sharp object or thin object like rope.
  • Cotton sponge, snow or other materials absorbing sonic wave.
  • Smaller objects than 14cm (dia.), 1m length.