www.megger.comMPAC – Professional Accoustic Imaging Camera9Application and environment How loud does background noise impact functionality?The Megger instruments use advanced technology to minimise the effect of background noise, and, in the majority of cases, this will be completely effective without further action by the user. However, the instruments offer a focus mode for use where the background noise is particularly severe. This reduces the angle of response of the microphone array and thereby minimises the impact of unwanted noise.Does weather/temperature affect use cases?The operating temperature range for the instruments is -20 to +50 ºC, and their IP54 ingress protection rating means that they will not be damaged by operation in moderate rain. However, rain and high winds can affect the acoustic signals on which the instruments rely, so obtaining accurate results in adverse weather conditions may not be possible, especially when operating at large distances from the target.Can’t I just use an infrared or ultrasonic wand instead?Infrared wands operate on an entirely different principle, looking for heat generated by a fault. Most cases of PD and almost all cases of gas leakage generate no heat, so an infrared wand will not detect the problem. Ultrasonic wands respond to sounds of the same type detected by acoustic imagers but are generally designed to be used only for leak detection at short ranges. They are unsuitable for PD detection and provide no image of the equipment being examined. They are, therefore, not useful for surveying large plants for leaks.Other imagers have a frequency range of up to 100 kHz; why is yours only to 48 kHz?There are a few technical reasons why extending the frequency range up to 100 kHz does not provide meaningful advantages. Most pressurised gas leaks and electrical partial discharges emit the strongest ultrasonic signals between 20 and 45 kHz. Higher frequencies get significantly attenuated. So, the key useful signals are covered by frequencies up to 48 kHz. Background acoustic noise increases markedly above 50 kHz. Extending the frequency range above 50 kHz means that the acoustic imager sees more noise. This obscures the leak signals instead of isolating them like the advanced algorithms in our imagers, which focus on the critical lower frequency bands. The wavelength of signals significantly above 50 kHz approaches the physical distance between the camera microphone sensors. This can lead to interference and crosstalk between the sensors. In contrast, limiting the frequency response to 48 kHz ensures accurate signal separation and triangulation of the sound source.While in theory, collecting higher frequency data could provide a wider net, in practice the crucial emissions are concentrated below 50 kHz, with higher bands offering diminishing returns with lower signal strength and a higher rate of false positives. Focusing on refining sensitivity, resolution and noise reduction in the frequency band up to 48 kHz provides the best leak visibility.
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