Saturday, February 14, 2015

Cable Acoustical Detector Auxiliary Device

Figure 1 is an illustration of an acoustical detector, an auxiliary device that is used with both types of thumpers. An acoustical detector has two sound transducers that are placed on the ground above a buried cable. The sound made by the cable when its insulation breaks down under the stress of the thumper’s high-voltage pulse causes an upscale deflection of the detector’s output level meter. A set of headphones can also be plugged into the detector so that the amplified and filtered sound of the breakdown can be heard.

Acoustical Localization
Figure 2 illustrates the basic method of using an acoustical detector to locate a fault in a buried cable. The pulses transmitted by the cable thumper cause the damaged insulation of the cable to break down repeatedly.

Each breakdown produces a sound. This sound can sometimes be heard above the ground. But for those cases when the sound is not loud enough to be heard, an acoustical detector is used to locate the damaged insulation.

The acoustical detector is able to distinguish the relative intensity and time delay between the arrival of the thump sound at its two pickups. The technician moves the location of the acoustical pickups until the thump sound is equal in intensity in the two earpieces of the headphones. The location of the fault is then directly below and midway between the pickups.

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