3.4 Connection of DUT
3-18 ZM2376
Cable routing and electromagnetic induction
Presence of noise sources such as motors or power transformers that generate large magnetic field
near the device causes a noise to get mixed in due to electromagnetic induction. To avoid this,
perform the wiring so that a large loop is not made.
If electromagnetic induction occurs between current cable and voltage cable, an error will increase in
the low impedance measurement or an error will vary with the movement of cables. Twisting two
cables each between current cable and current cable, and between voltage cable and voltage cable, or
twisting four cables together so that the voltage cables are arranged diagonally and also the current
cables are arranged diagonally as viewing the cross section can reduce an error due to
electromagnetic induction between cables.
Noise mixing in due to electrostatic coupling
If inner conductor of L
CUR
and L
POT
cables are exposed, a noise will mix in due to electrostatic
coupling with noise sources. Provide an electrostatic shield or keep peripheral potential constant.
Be sure to connect the ZM2376 case to the ground. Using 3-pole power cord, connect ZM2376 to
the 3-pole power outlet having a protective grounding contact, so that the device is connected to the
ground. Unless grounded, not only a hazardous situation occurs but also the potential of case varies
according to the power frequency or line noise, thus allowing a large noise to mix in.
Avoidance of 2-termianl connection
Connecting between L
CUR
and L
POT
cables or between H
CUR
and H
POT
cables in the middle of wiring
disables the 4-terminal connection. Since such a connection is equivalent to the 2-terminal
connection, it is affected by the contact resistance. In the measurement of low impedance or
measurement of small dissipation factor D (or small equivalent series resistance ESR), when the
contact resistance is not negligible, connect four connection cables independently to the DUT.
Influence of contact resistance
An error caused by the contact resistance with DUT can be restricted by 4-terminal connection, but
since the input impedance of voltage measurement terminals is not infinite, there may be some
influence. Particularly when the contact resistance exceeds 10Ω, prior evaluation of additional error
should be made before use.
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