Hioki Super megohm SM7110 - Effects of Conductive Noise

Appx.5
Countermeasures Against Noise
Countermeasures for the instrument against induction noise
Attaching a ferrite core around a measurement lead
as shown in Figure 3 is e󰀨ective.
In addition to taking the countermeasure on the
instrument the instrument, twisting the surrounding
noise-generating large current wires and shielding
the high-voltage wires are even more e󰀨ective.
Ferrite core
Figure 3 Ferrite core
If the induction noise is caused by a commercial power
Induction noise caused by a commercial power
is not only generated from commercial power
lines and power outlets, but also uorescent lights
and household electronics. Noise caused by the
commercial power depends on the frequency of the
commercial power, and is generated at a frequency
of 50 Hz or 60 Hz.
To reduce the e󰀨ect of noise caused by this
commercial power, generally the reset time is set to
an integral multiple of the power cycle (Figure 4).
Measurement signal with power
noise superimposed
Ideal measurement signal (direct current)
Integration time
Figure 4 Noise caused by the commercial power
The measurement speed of the instrument has the following ve options: FAST, FAST2, MED, SLOW, and
SLOW2. For high resistance and low resistance measurement, measured values may not be stable. In that
case, you should reduce the measurement speed or take actions against the noise.
If the instrument is operated on AC with a frequency of 50 Hz while the power frequency setting is set to 60
Hz, the reset time will not be synchronized with the power cycle, and the measured values will be uctuated.
Check the power frequency settings.
(2) E󰀨ects of conductive noise
Aside from induction noise superimposed on a measured object or measurement leads, conductive noise can
invade via another path. Conductive noise refers to noise superimposed on control lines such as power lines
and USB cables.
Various equipment is connected to a power line such as motors, welding machines, inverters, etc.
While this equipment is running, or when it is turned on or o󰀨, a signicant spike will ow through the power
line. Due to this spike current and impedance of the power line, a large spike voltage can be generated in the
power line and ground line of the power, resulting in e󰀨ects on the measurement instrument.
Similarly, noise may also be injected from control lines of the controller. Noise that penetrated from the
power of the controller, or was generated from a DC-DC converter installed the controller, penetrates the
measurement instrument through a USB cable or EXT I/O wire (Figure 5).
RS-232C
EXT I/O
USB
GP-IB
L
N
PE
The instrument
Motor
Power line
Welding
machine
Inverter
Controller
(Computer, PLC)
Figure 5 Conductive Noise Penetration
Appx.