05-07-2013, 12:10 PM
AUTOMATIC REVERSE BRAKING AND DISTANCE MEASUREMENT USING ULTRASONIC
AUTOMATIC REVERSE.docx (Size: 25.98 KB / Downloads: 48)
INTRODUCTION
Until well into the twentieth century, most devices developed for measuring distance worked on the same principle. The measured distance is compared with a standard unit of length. Other means are available. One of these is the measurement of time taken by the sound wave to cover a certain distance. This sound normally lies beyond human hearing. The ultrasonic sensor is used to measure the distance in digital form and also automatically braking the vehicle when the obstacle closer to the vehicle.
DESCRIPTION
The transmitter element emits bursts of 12 pulses at a frequency of about 40 kHz. This frequency is roughly identical with the resonance frequency of the two transducers, so that some sort of selectivity is obtained at the sensing element. As soon as the first burst is emitted, a bistable is activated which enables the counter. Immediately after the burst has been emitted, the unit is switched to reception.
The sensitivity of the receiver is a function of time. During and immediately after emission of the burst, the sensitivity is low. The crosstalk between the transduction and sensing elements has, therefore, no effect on the operation on the unit. If an echo is received very soon after cessation of the emitted burst, it will be sufficiently strong to be processed by the receiver in spite of the very low sensitivity. An each that takes a longer time to reach the sensing element will be weaker, but by then the sensitivity of the receiver has become higher. The upshot of this arrangement is that reliable measurements, unaffected by spurious reflections and crosstalk, may be made with relatively simple means. At the instant the echo is sensed, the bistable is reset and the counter state transferred to the output latch.
Since the clock frequency is 17.05 kHz and the velocity of sound under normal atmospheric conditions may be taken as 341 m/s, the period of the clock is equal to the time taken by the burst to travel 2 cm, i.e., 1 cm forward and 1 cm back. This means that the number of clock pulses counted between the onset of emission of the burst and the sensing of the echo is equal to the number of centimeters between the transducers and the reflecting surface.
APPLICATIONS
It is used to measure the distance between two blocks (bellow 6 meter).
Depth measurement.
Length Measurement.
Height Measurement.
Automobile Application