Tektronix TCPA300 SERIES, Instruction Manual

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Application Notes
3- 16
TCPA300/400 Amplifiers and TCP300/400 Series Current Probes Instruction Manual
Measuring Inductor Turns Count
To obtain an approximate turns count of an inductor, connect the inductor to a
current limited source, as shown in Figure 3--13. Measure the input current on
one of the inductor leads, then clamp the current probe around the inductor and
note the current value. The number of turns is equal to the ratio of coil current to
input current. The accuracy of this method is limited by the current measurement
accuracy. The following method allows more precise turns measurement.
For a more precise turns count, you need a coil with a known number of turns to
use as a reference. The measurement setup is similar to the previously described
one, except the reference coil and the test coil are inserted into the current probe
so that the currents oppose each other (see Figure 3--14). You must observe the
polarity of coil current to determine whether the test coil has more or fewer turns
than the reference coil. The turns are calculated by using the formula:
N
2
= N
1
×
I
m
I
1
where N
2
is the number of turns in the test coil, N
1
is the number of turns in the
reference coil,
I
m
is the measured coil current, and
I
1
is the input current.
Measure input current here
Coil
Clamp probe
around coil to
measure
current from
coil turns
Current flow (i)
Figure 3- 13: Measuring the number of turns in a coil