The Critical Angle of Electrical Inspection Ultrasonic Transmission Line Testing.

          Abstract

Electrical Ultrasound Inspection is one of the most unique application as it isn’t dependent on Decibels as much as the patterns the anomaly produces and its limited approaches can make it difficult to get the truest former of the Incident Wave.   

Drew Walts SME

Often when preforming Electrical Inspection we might find that we hear something and as we move around the anomaly we hear the sound characteristics actually change as we move our position. When we record these anomalies from different angles we actually see different signatures of the same event. This is because there is only one Critical Angle of the anomaly.  

 The Critical Angle of Electrical Inspection is the Angle at which we achieve the best sound characteristic and decibel of the anomaly. The most important things when it comes to Ultrasonic Electrical Inspection is Sound Analysis. Decibels can only tell us that we have found the Critical Angle of the Ultrasonic Anomaly. The Critical Angle is much like a Radio Signal your car radio receives in that it receives a strong signal when we are in line with the transmission. However when we drive into a valley or behind a mountain we start to lose signal clarity. We can still hear some of the transmission but we start losing the signal as it becomes distorted. We might still be able to pick out a voice or certain notes from an instrument, but it is not the clearest signal so we experience distortion of the signal and miss out on the fine details of the signal. As we drive back in range of the Radio Signal we achieve the Critical Angle we need to receive full signal strength so we can enjoy our radio program.

This is the same with Ultrasound Inspection of Electrical Equipment. We can often hear an Electrical Anomaly and record that anomaly for sound analysis. As we analysis that recording we find that the FFT doesn’t always show a 60 Hz Harmonic Marking in the FFT, but the 60 Hz Harmonics show up in the Time Series. This is what happens with the Sound Wave we capture when we are not at the Critical Angle. It’s not the truest form of the Incident Wave so we lose some of the resolution of the Signal and it a distortion of the signal. We however will still be able to see some indications with in the Time Series as it’s not dependent on any translation of the Signal into a Frequency of occurrence.  

This is just like your car radio when you hear some of the signal but it is distorted because we aren’t in line with Critical Angle of the Radio Transmission.  

 Here are some example of Sound Images.

Critical Angle Achieved:

  In image 1 the FFT we can clearly see the first 1st, 2nd, 3rd, 4th, 8th & 9th occurrence of a 60 Hz Harmonic. Critical Angle was achieved for this anomaly.   

In image 2 the Time Series clearly shows peaks with 60 Hz Harmonic indications.

Critical Angle not achieved:

Notice in image 3 the lack of rich 60 Hz Harmonics in this Tracking Occurrence. The Critical Angle was not achieved in this recording and as such we do not have the signal strength to show rich harmonic intervals at 60 Hz.

  Notice that in image 4 the 60 Hz Harmonics clearly show up in the Time Series but are virtual absent in the FFT.

 These are great examples of Tracking when we listen to them but its Spectralyzer that tells the tale of not having the Critical Angle of these Tracking Events. This is why it is so important to walk around and listen as you move around to try to find the Critical Angle of Anomaly. The key to this is using your Decibels as an indication of increased strength of signal. Decibels should never be used for gauging severity of Electrical Anomalies however. Decibels only indicate that we are in line with the Critical Angle.

 In conclusion it is very important that as we perform our Electrical Inspections that we take the time to note our surrounds and look before we step. We can easily get too tied up in just looking at the sound source and forget to watch our footing. We need to also insure that we are not just limiting ourselves while inspecting and only focusing on the sound and recording it. We need to also look at the display screen and what we can physically see with our own eyes. This are all important parts of any inspection program.

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