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Appx.
10
Noise Countermeasures
Using the instrument with the power supply frequency set to 60 Hz in a region with 50 Hz power will
cause measured value wobble even if the integration time is set in PLC units.
Figure 6. Noise Rejection Characteristics Using Integration
Effects of conductive noise
Conductive noise embodies a channel of potential noise introduction that is separate from induced
noise, which is superposed on measurement targets or measurement cables. Conductive noise
is superposed on power lines or control lines such as USB. Various devices are connected to
power lines, including motors, welding machines, and inverters. Large spike currents flow to the
power supply while such equipment is operating, as well as when it starts and stops. These spikes
combine with the power line’s wiring impedance to create a large spike voltage in the power line
and the power supply’s ground line, and that spike voltage may affect measuring instruments.
Similarly, noise may be introduced from the control lines of connected external devices. Noise
introduced from external devices’ power supplies and noise generated by DC-DC converters and
other components inside external devices may enter the measuring instrument via its USB or EXT
I/O wiring (see Figure 1).
RS-232C
EXT I/O
USB
GP-IB
L
N
PE
LAN
Instrument
External device
(computer,
programmable
controller)
Motor
Welding
machine
Inverter
Power lines
Figure 1. Ingress of Conductive Noise
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