Ultrasonic rangefinder / distance measuring sensor is based on the propagation velocity of ultrasound in the air is known, the ultrasonic wave encounters an obstacle reflected back characteristics measured.Ultrasonic transmitter to transmit ultrasonic waves in one direction, and the launch timing, ultrasonic wave propagation in the air, the obstacles on the way to return immediately to the ultrasonic receiver receives the reflected wave immediately interrupt to stop the clock, and then according to the transmitting and receiving the time difference to calculate the actual distance of the emission point to the obstacle.By constantly detecting the echoes reflected by the obstacles encountered after generating wave transmitting which measured emitting an ultrasonic wave and receives the echo of the time difference T, and then calculate the distance L.Ultrasonic rangefinder / distance measuring sensorby the ultrasonic wave generating circuit, and ultrasonic reception amplifying circuit, the counting and display circuit.

Laser rangefinder / distance measuring sensoris a sensor for accurate measurement of the distance to the target using a laser.Laser rangefinder while at work to the target injection a bunch very fine laser, received by the photovoltaic element and the laser beam reflected by the target, the timer time from the emission to the reception of the laser beam was measured to calculate the distance to the target from the observer.The laser rangefinder is currently the most widely used distance sensor, laser range finder / distance measuring sensor and can be classified as two kinds of handheld laser range finder / distance measuring sensor and telescope laser range finder / distance measuring sensor.

Source:http://blog.fasttobuy.com/2012/10/18/what-is-the-difference-between-the-ultrasonic-and-laser-range-finder-distance-measuring-sensor/#.U4uAnPmSwlI