Hioki Memory HiLogger LR8401-20 Instruction Manual page 276

14
A
Appendix 8 Concerning Noise Countermeasures
Equivalent Circuit of Noise Introduction Path
Measurements are directly affected by normal mode voltages from electromagnetical-
ly induced noise resulting from electromagnetic coupling into looped HiLogger input
lines by AC magnetic fields produced by inverters and commercial power lines, as
well as the capacitive coupling that results from interline capacitance.
Inverter or Commercial
Power Supply
Signal Voltage
Ground
Resistance
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 HiLogger, 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 HiLogger as a result of the noise current (i1) and
(i2) that flows to the coupling impedance (Z1) and (Z2) between the "+" and "-" input
terminals of the HiLogger and ground. Because common mode noise is generated
between the input pins, it has a direct effect on the measurements.
Electromagnetic
Coupling
Normal Mode Voltage
Coupling Impedance
Voltage Generated by Ground Current
(common mode voltage)
Leak current from other devices and ground current
flow due to difference in ground potential.
Electrostatic Coupling
Ground Impedance
HiLogger
Ground
Resistance