Basic Electricity 1:2
CP 1 – Cathodic Protection Tester Course Manual
© NACE International, 2000
02/01/05
Common symbols for voltage are:
emf electromotive force - any voltage unit
E or e voltage across a source of electrical energy (e.g.
battery, pipe-to-soil potential)
V or v voltage across a sink of electrical energy (e.g. resistor)
You will be concerned with voltage when making various
measurements in cathodic protection work. Among these are pipe-to-
soil potential measurements, voltage drops across shunts or along
pipelines (a method of measuring current explained in Chapter 4),
and the voltage output of a cathodic protection rectifier.
Current
Current is the flow of charges along a conducting path and is
measured in amperes. Current is frequently abbreviated as amps,
milliamps, or microamps. In corrosion work we use all three units.
The following shows their relationship:
Ampere = the common unit of current = a flow rate of charge of 1
coulomb per second. One coulomb is the unit of charge carried by
6.24 x 10
18
electron charges.
1,000 amperes = 1 kiloampere
1.000 ampere = 1000 milliamperes
0.100 ampere = 100 milliamperes
0.010 ampere = 10 mil1iamperes
0.001 ampere = 1 milliampere
0.000001 ampere = 1 microampere
Common symbols for current flow are:
I any amperage unit
mA milliamperes or milliamps
µA microamperes or microamps
Direct current flows constantly in one direction in a circuit.
Alternating current regularly reverses direction of flow, commonly
100 or 120 times per second.
To Next Page
Loading...