1730
Users Manual
10
Thin-Flexi Current Probe
The Thin-Flexi Current Probe works on the Rogowski coil
(R-coil) principle that is a toroid of wire used to measure
an alternating current through a cable encircled by the
toroid. See Figure 4.
i(t)
v(t)
A
r
10 k
R3
330 k
R1
10 nF
C1
LF347
UI:A
1
GND
2
114
3
V
in
V
out
hcf028.eps
Figure 4. R-Coil Operation Principle
The R-coil has many advantages over other types of
current transformers:
• It is not a closed loop. The second terminal is passed
back through the center of the toroid core (commonly a
plastic or rubber tube) and connected along the first
terminal. This allows the coil to be open-ended,
flexible, and able to be wrapped around a live
conductor without disturbing it.
• It has an air core rather than an iron core. It has a low
inductance and can respond to fast-changing currents.
• Because it has no iron core to saturate, it is highly
linear even when subjected to large currents, such as
those used in electric power transmission or pulsed-
power applications.
A correctly formed R-coil, with equally spaced windings, is
largely immune to electromagnetic interference.
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