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Appendix 8 Mitigating Noise
A20
When measuring a 1 m
Ω
resistor with 1 A, the
effect measures 0.07%. Since the detection
voltage can easily be increased for high-resis-
tance measurement, this effect does not pose a
significant problem.
The influence of electromagnetic coupling can
be reduced by keeping the noise generating
line away from the voltage detection line and
twisting the cables for each (see Fig. 2).
Induced noise countermeasures at the instrument
To counteract noise, it is
effective to attach a ferrite
core to the measurement
leads, as shown in Fig. 3-1,
or to twist the four shielded
wires and to shield the mea-
surement target with the
guard potential, as shown in
Fig. 3-2.
It is important to take similar
precautions not only for the
instrument, but also for the
noise source. It is effective to
twist nearby high-current
wires that may serve as
noise sources and to shield
high-voltage wires.
When induced noise is caused by a commercial power supply
Induced noise caused by commercial power
supplies is emitted not only by commercial
power lines and power outlets, but also from
fluorescent lights and household electronics.
Noise caused by commercial power supplies
occurs at frequencies of 50 Hz and 60 Hz,
depending on the frequency of the power sup-
ply in use.
To mitigate the effects of noise caused by com-
mercial power supplies, it is standard practice
to use a whole-number multiple of the power
supply period as the integration time (see Fig. 4).
The instrument offers four measurement speeds: FAST, MED, SLOW1, and SLOW2. Mea-
sured values may fail to stabilize during either high-resistance or low-resistance measure-
ment. If this occurs, either decrease the measurement speed or implement adequate noise
countermeasures.
If the line frequency setting is left at 60 Hz while the instrument is used in a region with a 50
Hz line frequency, the integration time will not match the power supply period, and mea-
sured values will fluctuate. Check the instrument’s line frequency setting.
Figure 2
. Twisting near
High-current Wires
Twisting
Figure 3-2
. Noise Countermeasures at the Instrument
S
ta
tic sh
ie
ld
in
g
Figure 3-1 .
Ferrite core
Figure 4
. Noise Caused by a Commercial
Power Supply
Measurement signal with super-
imposed power supply noise
Integration time
Ideal measurement signal (DC)