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Installing C.P. Components 8:4
CP 1 – Cathodic Protection Tester Course Manual
©
NACE International, 2000
07/01/04
C
P T
est
Figure 8.2 Typical Flush Mounted Potential Measurement Test Station
Post-mounted test stations are preferable to flush mounted ones because
there is less chances of losing post-mounted units. In many distributions
systems, however, it is difficult to use post-mounted test stations because of
physical restrictions and lack of available places to put the post. Where
flush mounted test stations are used; it is good practice to cast a concrete
collar around the top of the station to minimize loss of the test point.
IR (Millivolt) Drop (Current Span)
These test stations are used to measure the magnitude and direction of
current flow on a pipeline. This information is useful in monitoring the
spread of cathodic protection, locating areas of bad coating on a pipeline,
and for finding areas where short circuits may exist.
In this type of test station, the pipeline acts as a resistor; the magnitude of
the current is determined by measuring the voltage (IR) drop across the
span of the test wires. The direction of current is determined by the polarity
of the voltage.
A typical IR drop station is shown in Figure 8.3.