3.4 Connection of DUT
3-16 ZM2371/ZM2372
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 ZM2371 / ZM2372 case to the ground. Using 3-pole power cord,
connect ZM2371 / ZM2372 to the 3-ple power socket 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-terminal connection
If L
CUR
cable and L
POT
cable are connected in the middle of cable, the measurement result
includes the contact resistance with DUT (resistance value of two paralleled contact
resistances). This is also true when H
CUR
cable and H
POT
cable are connected halfway. If the
cables on H side or L side are connected halfway, even apparent four cables are equivalent to
the 2-terminal connection. In the measurement of low impedance or measurement of small
loss D (or 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 measuring terminals is not infinite,
there may be some influence. Particularly when the contact resistance exceeds 10, prior
evaluation should be made before use.
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