Before Measurement - Iwatsu SS-281A-H Instruction Manual

Chapter 4 Measurement

4.3 Before Measurement

This section describes notes on accuracy and the handling of the Rogowski
Coil Sensor when measuring the current using this instrument.
4.3.1 To Achieve Accurate Measurement
As explained in Chapter 3 "Measurement Principle," the Rogowski Coil is a
wire rod wound tight around a tube-like wick material, as illustrated in Figure
3.1. The coil formed into a ring body detects a change in magnetic flux
caused by the current passing through the inside of the coil. The evenly
wound coil causes no error even when the current to be measured does not
flow through the center of the coil. In addition, each turn of coil enables the
cancellation of external magnetic fields.
However, it doesn't become constructional and a complete ring compound
because there is a connecting part in the Rogowski Coil.
For reference, Figure 4.3 shows the position of the connection part of the
Rogowski Coil.
Figure 4.3 Rogowski Coil Connection Part
The connection part of the Rogowski Coil is in the center of the dotted circle.
It is known that a larger measurement error is caused as the current to be
measured comes closer to this part because the variation of the magnetic
flux that cannot be detected increases. Avoid measuring current in the dotted
area, because a measurement error of −4% or more may be caused by the
measurement performed in the area. In addition, there is a possibility that the
measurement error grows because of an external magnetic flux that similarly
hangs to the connecting part. Before measuring current, place conductors in
which current flows other than the conductor to be measured away from the
Rogowski Coil connection part as much as possible.
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