Where leaks produce a sound that is inaudible to the human ear, or where the leak noise is low, or the background noise is high, electronics can help. These devices usually consist of a microphone, amplifier and frequency filters, seeking to amplify the leak noise whilst seeking to filter out the amplification of extraneous noise. Frequency filter selection facilities can be a great help in this regard, but sometimes the unwanted noise may have a similar frequency to that of the leak, and not all ambient noise can be isolated out. The output of the amplifier can be fed to headphones, to a loudspeaker, to an indicating meter, or to a combination of all three. An indicating meter will display a measure of the total sound intensity received by the microphone, and hence is a more sensitive method of determining the position of maximum noise intensity than the stethoscope, especially if the latter’s operator is unskilled. To further assist the electronic device, different microphones are normally available depending upon whether the sounding is done on metallic pipe and fittings, or on non-metallic pipes, or on the ground surface. Electronic devices, with ground microphones, are sometimes used as routine tools to survey areas of suspected leakage, and also as a final confirmation of leak position detected by a correlator.
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