Tektronix TCPA300 SERIES, Instruction Manual

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Reference Notes
3- 2
TCPA300/400 Amplifiers and TCP300/400 Series Current Probes Instruction Manual
Measuring Differential Current
You can place two conductors in a current probe to provide differential or null
current measurement. This avoids the necessity of using two current measure-
ment systems with a differential oscilloscope.
WARNING.
Do not put more than one uninsulated conductor at a time in the
TCP303 or TCP404XL probes. Do not put any uninsulated conductors in the
TCP305 or TCP312 probes. An uninsulated conductor is defined as any
conductor without insulation or without insulation rated for the voltage present
on the conductor under test.
An insulated conductor is defined as any conductor that is surrounded by an
insulating material that is capable of isolating the voltage present on the
conductor. Note that lacquer coatings like those typically found on transformer
windings do not provide sufficient, reliable insulation for use with current
probes. The lacquer coating can be easily nicked or damaged, compromising the
insulating capabilities of the lacquer coating.
Do not force the slide closed. Damage to the probe may result. If you cannot
close the slide around the conductor(s), either reduce the number of conductors
you are measuring, or, if possible, take your measurement on a smaller
conductor.
1. Orient the two conductors under test so that the polarities oppose each other.
Clamp the current probe around the two conductors as shown in Figure 3--1.
Be careful not to pinch a conductor in the probe jaws.
2.
Measure the current. A waveform above the baseline indicates the conductor
with the conventional current flow in the direction of the probe arrow is
carrying the greater current. Conventional current flows from positive to
negative.
3.
To adjust for a current null, adjust the current in one of the conductors until
the displayed measurement is zero.