Nace CP 1, Course Manual

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Field Measurements 5:9
CP 1 – Cathodic Protection Tester Course Manual
©
NACE International, 2000
02/01/05
ammeter. If a circuit is broken with current flow and your hands act as the
connectors, then your heart acts as a shunt for the external current flow.
Work safely!
Current Flow Sign
If an ammeter is connected into an external circuit such that external
current flow goes into the positive terminal of the meter, then the display is
positive. If the display shows a negative sign, current is flowing into the
negative terminal. Since the direction of current flow in cathodic protection
work is as important as the magnitude, you should anticipate the direction
of the current before connecting the meter into the circuit. Figure 5.6
depicts direction of current flow in an ammeter measurement. Current is
flowing from the anode, through the soil, to the pipe, and then through the
meter, back to the anode. Note that the current is entering the meter on the
negative terminal, hence the negative reading on the meter display.
ANODE
PIPE
+
_
AMPS
10 mA
Figure 5.6 Direction of Current Flow in an Ammeter Measurement
Current Range
The most common DC current scales on meters are as follows:
•
200 microamps
•
2 milliamps
•
20 milliamps
•
200 milliamps
•
2 amps
•
10 amps