UFC 3-570-06
JANUARY 31 2003
on milliammeter. This method requires a very specialized piece of equipment, sized to
the pipeline, and an excavation or access to the pipeline, for placement of the probe
around the pipeline.
The preferred method is to measure the actual resistance of the pipe, using
test current. This method does not require knowledge of the pipeline size or wall
thickness, and is not affected by variations in the metal due to composition or corrosion,
variations of resistance due to temperature, or inaccurate lengths of the test span. The
amount of test current required depends on the diameter of the pipeline and the
distance of the test span. The larger the pipeline, the larger the amount of current
required. The shorter the distance of the test span, the larger the amount of current
required.
Figure 7-33. Typical IR Drop Test Span Installation
V o ltm ete r
mV
+-
IR D rop
T es t S tation
P ipe lin e or ca ble
The current flowing on pipeline or cable will flow through the meter and damage could
result. If that current does not damage the meter, the measurement would not indicate
a resistance value. The voltage would be interpreted by the meter as coming from the
internal battery instead of the external electrical circuit being measured.
7-49
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