EA002 2 / 10 / 50 CLAMP COIL ADAPTER
OPERATION MANUAL
Transmille Ltd.
Page 5
High Accuracy Design
Clamp meters can measure current by using the invisible magnetic field generated round
any conductor carrying a current. The degree of magnetic coupling between the field
produced by the conductor and the jaws of the clamp meter varies due to the position of
the conductor within the jaws - this changes the current reading. Transmille’s coil is
designed to immerse both jaws of he clamp meter in the magnetic field while allowing the
‘gap’ or opening where magnetic flux will escape to protrude through the coil and stay out
of the strongest part of the field. This makes the reading less dependent on the position of
the clamp within the coil and also the quality of the jaw closing, allowing greater
confidence in the calibration.
Calculating Clamp Meter Accuracy.
There are two contributions to the total accuracy which should be taken into account when
calibrating clamp meters using a coil. The first is the accuracy of the current produced by
the calibrator, the second is the coupling between the coil and clamp meter. These must
be combined using a
root sum of the squares
. Empirical tests made on a wide range of
clamp meters calibrated by Transmille at its laboratory have shown that
torroidal wound
current transformer
type clamps typically exhibit better performance and will give coupling
errors of 0.2% and
hall effect devices
slightly higher at around 0.4%.
Innovative Closed Construction Design
Three coils in one provide the ability to calibrate a wide range of coils, from small lower
clamps down to 10mm jaw diameter to larger 2000A clamps. The low inductance, low
resistance properties allow the calibrators to easily drive the coil, giving plenty of overhead
for calibrating older clamps. The coils are fully enclosed in a strong, robust and compact
plastic enclosure preventing mechanical damage. This rugged design is ideal for using the
coil on-site and in harsh environments.
