1. How does an ultrasound camera work for leak detection?

An ultrasound camera detects high-frequency sound waves generated at leak points by escaping compressed air, escaping process gases, or incoming ambient air in vacuum applications. A microphone array performs the calculation of the direction of the sound source from the microphone signals and superimposes the result as a colored heat map over a video image.

The method operates passively: The camera does not require a test gas such as helium or formier gas, but instead detects the acoustic energy generated by turbulence at the leak site. This allows leaks to be localized during operation without having to shut down large sections of the plant, dismantle equipment, or treat areas with leak detection spray.

The technical benefit lies in the combination of acoustic localization and visual identification. Users not only see that ultrasonic activity is present but can also identify in the camera image which component, valve, hose, connection, or pipe section is generating the sound pressure. This reduces search time, prevents misinterpretations, and simplifies the documentation of detected leaks.

Example: Locating an ultrasonic source on a hard-to-reach factory ceiling. The hotspot marks the acoustic source in the camera image.

In industrial leak detection, distinguishing between audible sound and ultrasound is crucial. Most production noises fall within the audible, low-frequency range. Leaks in compressed air and gas lines generate broadband turbulence with high-frequency sound components at small leak openings. Large leaks often generate additional audible sound; however, in production environments, this is frequently masked by machine noise.

The ultrasonic sound generated by a leak is not caused by the gas itself, but by the turbulence that occurs as the gas escapes. The pressure difference, leak geometry, and the shape of the exit opening determine the sound intensity and the frequency spectrum of the generated ultrasonic waves.

Higher frequencies offer better spatial resolution due to their shorter wavelength. However, as the frequency increases, atmospheric attenuation also increases, thereby reducing the achievable detection range.

The choice of measurement frequency therefore represents a trade-off between resolution, range, and interference suppression. In many industrial applications, a frequency range around 40 kHz has proven to be favorable. In environments with interference, however, a different frequency window may yield better results.

In-Depth: Leak Detection Despite Interference Sources and FFT

For CS INSTRUMENTS, compressed air is the primary application for ultrasonic leak detection. The reason is the direct correlation between leaks, consumption, compressor load, and energy costs. Any unplanned air loss increases demand on the consumer side. If the leak is repaired, less air needs to be generated, dried, and treated.

Finding leaks is the first step. Verifying the actual savings through consumption measurements before and after the repair makes this a reliable efficiency measure. The ultrasound camera, LD 500, Leak Reporter, flow measurement, and monitoring complement each other in the tasks of localization, documentation, prioritization, and validation.

The acoustic map is generated using beamforming. The microphone array detects the incoming ultrasonic signals at defined positions. Based on the differences in travel time and phase, the system performs a calculation to determine the probable position of the sound source. A sound pressure value is determined for each pixel and superimposed on the camera image as a heat map.

The heat map is not a photograph of the leak, but a visualization of the calculated sound source. By superimposing it on the camera image, the hotspot can be clearly assigned to the component causing it.

In-Depth: BeamformingExplained Simply

The detection range of an ultrasound camera is not determined by a fixed value. It depends primarily on the size of the leak, system pressure, frequency range, environmental interference, viewing angle, and atmospheric attenuation. Large leaks can be detected from a significantly greater distance than microleaks.

Acoustically, it is not the type of gas itself that is detected, but rather the ultrasonic waves generated by the gas escaping. Whether a leak can be detected depends primarily on the pressure difference, the geometry of the leak, the flow rate, the measurement distance, and the environmental conditions. The type of gas, on the other hand, is primarily relevant for the economic, safety-related, and qualitative assessment of the leak.

Many production noises fall within the audible range. However, equipment components can also generate ultrasonic signals—for example, pneumatic actuators, conveyor systems, presses, friction points, blow-off nozzles, partial discharges, or other leaks. Using FFT analysis and selecting an appropriate frequency window, such sources of interference can be identified and specifically filtered out.

Reflections occur on sound-reflective surfaces such as glass, Plexiglas, concrete, sheet metal, or smooth machine enclosures. A hotspot on a wall, floor, or other surface can therefore also be caused by an echo. The most important step in the test is to change the viewing angle: A real sound source remains localized to the component causing it, while a reflection shifts or disappears.

In-Depth: Leak Detection Despite Interference Sources and FFT