When purchasing an ultrasonic imaging device, these 6 aspects must be considered

When purchasing an ultrasonic imaging device, these 6 aspects must be considered

Compressed air leakage, vacuum system leakage, partial discharge of electrical systems and other problems may cause the company to face the risk of potential shutdown and equipment replacement. In order to avoid risks in advance, using ultrasonic imaging equipment is an effective way to detect potential problems in equipment.

Typically, this easy-to-use technology enables professionals to complete inspections 10 times faster than traditional methods. So, what should you look for when buying an acoustic imager?

Effective frequency range

The first characteristic to consider is the effective frequency range of the imager. You might think that the wider the frequency range, the wider the range of frequencies that can be picked up. But in fact, the most effective frequency range for detecting compressed air leaks is between 20 and 30kHz. This is because using the 20 to 30kHz frequency range helps to distinguish compressed air leaks from the background noise of the plant. Since there is a larger difference between the leaking noise and the background noise between 20-30kHz, compressed air leaks are easier to detect in this frequency range than at higher frequencies.

From the above figure, we can see that in the frequency range of 30 to 60kHz, the amplitudes of compressed air (blue line) and mechanical noise (yellow line) both show a decreasing trend, which makes it difficult to distinguish them. Therefore, it is more effective to work in the range of 20 to 30kHz.

For users who are detecting partial discharge at a safe distance, the 10 to 30 kHz range is optimal. This is because the higher frequency ranges travel a shorter distance. To detect partial discharge on high voltage equipment in an outdoor environment, the acoustic imager needs to be tuned to lower frequency sounds that travel farther.

Optimal number of microphones

To capture quieter noises, the more microphones the better. Acoustic imagers typically use dozens of microelectromechanical systems (MEMS) microphones to collect and distinguish sounds. Although MEMS are small, low power, and very stable, the noise they generate can interfere with a single microphone's ability to pick up very quiet sounds. In this case, simply doubling the number of microphones can increase the signal-to-noise ratio enough to eliminate 3 decibels of unwanted noise.

The self-noise generated by a microphone may be enough to prevent the system from picking up a compressed air leak that produces a 16.5kHz signal.

A 32-microphone acoustic imager can detect some leaks, but the signal-to-noise ratio is still too low to pick up quieter sounds.

In contrast, a camera with 124 microphones can pick up both 16.5kHz and 18.5kHz leaks, making it easier to detect, pinpoint and quantify smaller leaks.

Sound detection distance

Adding the right number of microphones to an acoustic imager also increases the probability of picking up very quiet noises from a greater distance. This is especially important when inspecting high-voltage systems, where detection of high-voltage partial discharges often requires inspecting live equipment from a safe distance. As the acoustic imager moves away from the sound source, the strength of the sound signal drops significantly. The solution is to increase the number of microphones: quadrupling the number of microphones essentially doubles the sound detection range.

FLIR Si124

Microphone placement

The layout of the microphones on an acoustic imager affects how the acoustic imager determines the direction and location of a sound. The acoustic imager collects data from each microphone, measures the time and phase differences of the signals, and calculates the location of the sound source. The microphones need to be arranged closely together to ensure that they can collect enough acoustic data to accurately determine the direction of the sound source.

Microphone performance

Just like frequency, there is an upper limit to the number of microphones you can have in an acoustic imager. There is a potential downside to having too many microphones: Each microphone requires processing power to convert the audio data signal into an image. Therefore, adding too many microphones will have diminishing returns. Some manufacturers balance this by reducing the resolution of the acoustic image pixels, or "sound" pixels, but this affects the overall performance of the acoustic imager. It is critical to have enough sound pixels to reliably detect corona discharges and partial discharges from a distance and pinpoint their exact source.

With 124 microphones and advanced processing capabilities, the FLIR Si124 offers the perfect balance of industry-leading detection sensitivity, excellent audio and video resolution, and a large detection range.

Smart analysis tools

The final feature to consider is the acoustic imager’s computing power and the analytical tools and supporting software it comes with. Acoustic imagers like the FLIR Si124 offer onboard analytical tools, generate easy-to-understand reports, and leverage AI/web tools for predictive analysis. Inspectors can grade leak severity, perform leak cost analysis, and analyze partial discharge patterns in real time during the inspection. Once the inspection is complete, inspectors simply connect to a Wi-Fi network to automatically upload images to the FLIR Acoustic Camera Viewer cloud service for further analysis. Advanced AI services help users calculate the estimated annual energy cost expenditures caused by compressed air or vacuum leaks and determine whether partial discharge equipment needs to be repaired or replaced. They can also be used to create reports that can be shared with maintenance teams or customers.

Acoustic imaging, which can detect ultrasonic waves, has become an effective method used by utilities, industrial manufacturing and other industries to determine the presence of partial discharge and compressed air leaks.