Hioki MEMORY HiLOGGER LR8450 Instruction Manual page 280

Equivalent circuit for a noise contamination route
Noise such as the following directly affects measured values as normal-mode
voltage.
• Electromagnetic induction noise that occurs when an alternating field generated
by an inverter or commercial power line is coupled with an instrument's input line
loop
• Electrostatic induction noise caused by capacitive coupling between wires
Inverter or commercial
power supply
Device under measurement
Rs
Es
Z
Coupled impedance
3
Voltage produced by earth current
(Common-mode voltage)
Zearth
Grounding
resistance
Other device's leakage current or earth current
that flows due to difference in grounding potentials
Common-mode noise is caused by ground impedance that is interposed between the ground points
of the device under measurement and the measurement module and capacitive coupling between
ground lines and noise sources.
Common-mode noise is converted into a normal-mode voltage (Enm) between the instrument's
positive and negative input terminals when noise currents (i
Z ) between the measurement module's positive and negative input terminals and the ground.
2
Since the voltage occurs between the input terminals, measured values are directly affected.
Electromagnetic coupling
Capacitive
coupling
r
1
Enm'
r
2
Ecm
Zearth
Ground impedance
iearth
Noise Countermeasures
Measurement module
Vin
i i
2 1
Z Z
2 1
Zearth
Grounding
resistance
, i ) flow to coupled impedances (Z
1 2
11
,
1
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