“Compressed air leakage, vacuum system leakage, partial discharge of electrical systems and other issues may cause the company to face potential risks of production shutdown and equipment replacement. In order to avoid risks in advance, the use of acoustic imagers for ultrasound imaging is an effective way to detect potential problems with equipment.
Compressed air leakage, vacuum system leakage, partial discharge of electrical systems and other issues may cause the company to face potential risks of production shutdown and equipment replacement. In order to avoid risks in advance, the use of acoustic imagers for ultrasound imaging is an effective way to detect potential problems with equipment.
Generally, this easy-to-use technology enables professionals to complete inspections 10 times faster than traditional methods. So, what aspects should be paid attention to when purchasing an acoustic imager?
Effective frequency range
The first characteristic that needs to be considered is the effective frequency range of the sound imager. You might think that the wider the frequency range, the more you can expand the range of the audio frequency. But in fact, the most effective frequency range for detecting compressed air leakage is between 20 and 30 kHz. This is because using a frequency range of 20 to 30 kHz helps distinguish compressed air leakage from background noise in the factory. Since there is a large difference between air leakage noise and background noise between 20-30kHz, it is easier to detect compressed air leakage 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 amplitude of compressed air (blue line) and mechanical noise (yellow line) both show a decreasing trend, which makes it very difficult to distinguish them. Therefore, it is more effective to work in the range of 20 to 30 kHz.
For users who detect partial discharges within a safe distance, the range of 10 to 30 kHz is the best. This is because the higher frequency range has a shorter propagation distance. In order to detect the partial discharge of high-voltage equipment in the outdoor environment, it is necessary to adjust the acoustic wave imager to a lower frequency and longer distance sound.
Optimal number of microphones
In order to capture quieter noise, the more microphones, the better. Acoustic imagers usually use dozens of microelectromechanical system (MEMS) microphones to collect and distinguish sounds. Although MEMS are small, low power consumption, and very stable, their own noise can interfere with the ability of a single microphone to record extremely quiet sounds. At this time, just double the number of microphones to increase the signal-to-noise ratio enough to eliminate 3 decibels of useless noise.
The self-noise generated by a microphone may be enough to prevent the system from recording the compressed air leakage that generates the 16.5kHz signal.
A sonic imager with 32 microphones can detect some kind of leakage, but the signal-to-noise ratio is still too low to record quieter sounds.
In contrast, a sound imager with 124 microphones can record both leaks at a frequency of 16.5 kHz and leaks at a frequency of 18.5 kHz, making it easier to detect, identify, and quantify smaller leaks.
Sound detection distance
Adding the right number of microphones to the sonic imager can also increase the probability of recording extremely quiet noise from a longer distance. This is especially important when testing high-voltage systems, because the detection of high-voltage partial discharges often requires the detection of live equipment from a safe distance. As the sound wave imager moves away from the sound source, the intensity of the sound signal drops significantly. The solution is to increase the number of microphones: increasing the number of microphones to 4 times can basically double the sound detection range.
The layout of the microphones on the sonic imager affects the way the sonic imager determines the direction and position of the sound. The sonic imager collects data from each microphone, measures the time difference and phase difference of the signal, and calculates the sound source position. These microphones need to be tightly arranged together to ensure that they can collect enough sound wave data to accurately determine the direction of the sound source.
Just like frequency, there is an optimal upper limit for the number of microphones that an acoustic imager can hold. There are potential drawbacks to setting too many microphones: each microphone needs processing power to convert the audio data signal into an image. Therefore, adding too many microphones will reduce the return. Some manufacturers balance this by reducing the resolution of the sound image pixels or “sound” pixels, but this affects the overall performance of the sonic imager. It is important to have enough sound pixels to reliably detect corona discharges and partial discharges from a certain distance and pinpoint their exact source.
FLIR Si124 has 124 microphones and advanced processing capabilities, with industry-leading detection sensitivity, excellent sound and image resolution and a large detection range, which well balances the relationship between the two.
Intelligent analysis tools
The last feature that needs to be considered is the computing power of the acoustic imager and the analysis tools and auxiliary software it carries. Acoustic imagers like FLIR Si124 provide on-board analysis tools, generate easy-to-understand reports, and use AI/web tools for predictive analysis. Inspectors can classify the severity of leakage in real time during the inspection, conduct leakage cost analysis and partial discharge mode analysis. Once the inspection is completed, the inspector only needs to connect to the Wi-Fi network and automatically upload the image to the FLIR Acoustic Camera Viewer cloud service for further analysis. Advanced artificial intelligence services assist users in calculating estimated annual energy expenditures caused by compressed air or vacuum leaks and determining whether partial discharge equipment needs to be repaired or replaced. It can also be used to create reports for sharing with maintenance teams or customers.
The ability of acoustic imaging to detect ultrasound has become an effective method for public utility organizations, industrial manufacturing and other industries to determine whether there is partial discharge and compressed air leakage.