Hioki LR8410-20, Instruction Manual

Page: 332 / 364

Appendix 8 Concerning Noise Countermeasures
A
16
Equivalent Circuit of Noise Introduction Path
Common mode noise results from the interposition of ground impedance between
the ground point of the device being tested and the ground point of the measurement
units, and from capacitor coupling between the ground wire and noise source.
Common mode noise is converted to normal mode voltage (Enm) that is added to
the "+" and "-" input terminals of the measurement units as a result of the noise cur-
rent (i1) and (i2) that flows to the coupling impedance (Z1) and (Z2) between the "+"
and "-" input terminals of the instrument and ground. Because common mode noise
is generated between the input pins, it has a direct effect on the measurements.
Inverter or Commercial
Power Supply
Electromagnetic
Coupling
Signal Voltage
Normal Mode Voltage
Coupling Impedance
measurement
unit
Voltage Generated by Ground Current
(common mode voltage)
Ground

Resistance
Ground Impedance
Ground

Resistance
Leak current from other devices and ground current
flow due to difference in ground potential.
Electrostatic Coupling
Measurements are directly affected by normal mode voltages from electromagnetical-
ly induced noise resulting from electromagnetic coupling into looped measurement
unit input lines by AC magnetic fields produced by inverters and commercial power
lines, as well as the capacitive coupling that results from interline capacitance.