Ultrasonic leak detection is based on the principle that forcing a fluid through a small opening creates turbulence on the dow

An ultrasonic detector electronically translates the high frequency components of leak sounds into the audible range by a principle called "heterodyning". Some instruments have frequency tuning and a phased array of transducers in the leak pick-up module to allow for leak detection in the typically noisy environments of the operating plant. An ultrasonic detector is ideally suited for leak detection. It senses the turbulence of a leak, which is produced as the gas escapes.

Ultrasonic leak detection is based on the principle that forcing a fluid through a small opening creates turbulence on the downstream side. The turbulence generates "white noise" that has an extremely strong ultrasonic component (usually around 40kHz).

Since ultrasound is a high frequency signal (these instruments typically sense between 20 and 100 kHz although as the transducer is nominally rated at 40kHz this is the best frequency for air leak detection) the intensity of the leak signal tends to fall off rapidly as the sound moves from the leak site and is therefore considered "localized".

The leak sound will be heard as a rushing sound and the transducer nearest the leak will have the highest sound level.

Due to the sensitivity of some of these instruments, one will often be able to locate small leaks at great distances so precalibration of fixed systems is important.