Pressurized gas leaks emit an audible high-frequency hiss but have even more energy at ultrasonic frequencies. Small leaks give off detectable ultrasound long before they become large enough to hear. Ultrasonic leak detectors specifically respond to ultrasonic emissions, ignoring audible sound. Because of this, leaks can be “heard” at a distance, even in noisy industrial environments.
This white paper, based on a project done years ago, explains how they work and how they are used.