How Acoustek® works
Acoustek® uses a principal known as Acoustic Pulse Reflectometry (APR). According to APR theory, an acoustic wave propagating along a pipe will generate reflections whenever it encounters a change in acoustic impedance. Variations in acoustic impedance are directly related to changes in the cross sectional area of the pipe caused by the presence of blockages, holes in the pipe wall, fittings or expansions. By measuring the time of flight and with knowledge of the speed of sound in the pipe, the location of any features in the pipeline can be identified.
Detecting a feature
The pressure pulse leaves the probe and enters the pipeline, passing the microphone and generating a positive pressure pulse – ‘A’ in the diagram. The pulse then propagates along the pipe and, when it reaches the feature, some of the energy is reflected back towards the probe. The microphone then detects this reflected pulse – ‘B’ in the diagram. By knowing the time of flight and the amplitude of the reflection, the distance and size of the feature can be determined.
The top graph shows the acoustic signal travelling along the pipe and the middle graph shows the measurements hitting the microphone in the forward and backwards directions. The bottom figure distinguishes between the acoustic signals travelling in the forwards (blue) and backwards (red) directions.