Appendix 8 Concerning Noise Countermeasures
A16
Running the instrument (Model LR8431-20) on battery power
When the instrument is being powered by batteries and the AC adapter is not con-
nected, the ground current loop is eliminated, making it possible to reduce the
effects o
f common mode noise.
For measurements of short duration, powering the LR8
431-20 with batteries is an
effective method for eliminating noise.
Common Mode Noise Countermeasures
Connect the chassis GND on the signal side
to a good ground with a sufficiently low
ground resistance. If there is still a large
amount of noise, it may be possible to re-
duce the effects of common mode voltage
by connecting a bypass ground wire to the
GND terminal on the instrument.
Noise current (i1) and (i2) can be sup-
pressed by suppressing the common
mode voltage with a low-resistance
ground wire or a bypass between ground
poles. This suppresses the generation of
normal mode voltages and reduces the
effect on measurements.
Inverter or Commercial
Power Supply
Electro Magnetically Induced
Noise
Electrostatic Inductance Noise
Ground Wire
Coupled Impedance
Normal Mode Voltage
Voltage Generated by Ground Current
(common mode voltage)
Ground Impedance
Device being
Tested
Instrument
Thermocouple
If it is not possible to simply ground the instrument or the signal side, connect a ground
wire between the chassis GND of the instrument and the signal side to equalize ground
potentials. A basic requirement for obtaining stable measurements is to ground the de-
vice.
Ground Wire
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