This application note tells you information related to time measurements, ping sensor circuit, ping ultrasonic detector, and detector. In the application note you can read things related to sensor, distance, and measurements.
Many explanation around echo time measurements, the ping sensor, and ping sensor are described inside this application note. The following are grabbed from the application note:
Ping))) sensor sends a brief chirp with its ultrasonic speaker and makes it possible for the BASIC Stamp to measure the time it takes the echo to return to its ultrasonic microphone. The BASIC Stamp starts by sending the Ping))) sensor a pulse to start the measurement. Then, the Ping))) sensor waits long enough for the BASIC Stamp program to start a PULSIN command. At the same time the Ping))) sensor chirps its 40 kHz tone, it sends a high signal to the BASIC Stamp. When the Ping))) sensor detects the echo with its ultrasonic microphone, it changes that high signal back to low.
In addition, this application note explains info around ultrasonic detector, wiring diagram, and ultrasonic.