Vivax Metrotech vLocDM, Руководство пользователя

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8.1 Introduction
Using the vLocDM system can quickly and efficiently assess the general coating of a pipeline network. It can
help identify defects and possible shorts to other structures. It can be used as a tool to prioritise and plan work
on the network. However, unless care is taken when interpreting the results, misinterpretation can lead to
unnecessary work and expenses.
8.2 Sources of Error
Most errors are either caused by carelessness in taking readings or by interference (or distorted signal field).
8.2.1 Operator Error
It is essential that care is taken when taking readings. Great care should be taken to pinpoint the position of the
pipeline before a measurement is taken. The locator must be aligned and held vertically. The measurements are
only as good as the care taken to obtain them.
The sensors used to detect the low frequency vLocDM profiling signal are very sensitive to low frequencies.
Moving the instrument whilst the unit is calculating the information will cause the strong earths magnetic field to
induce an interfering signal into the sensors resulting in errors. The vLocDM must be kept absolutely still whilst it
is taking measurements.
8.2.2 Interference (Distorted Fields)
The vLocDM evaluates the electromagnetic field signal radiating from a pipeline to determine the information
required. It assumed that the field is radiating from the pipe in an uniform way. Unfortunately the field is prone to
being distorted and this can lead to errors.
8.2.2.1 Source of Interference (Distorted Fields)
There are many sources of field distortion but this handbook lists some of the more common sources of distortion:
i) Changes in Pipeline Direction
ii) Adjacent Pipes or Cables
iii) Cross Bonding
iv) Passing Vehicles
v) Pipe Sleeving
i) Changes in Pipeline Direction
Whenever there is a change in pipeline direction there will be some field distortion. See diagram below. The
sharper the change, the bigger the distortion. Avoid taking measurements at these points.
Interpreting Results
8 Interpreting Results