383
Noise Countermeasures
Equivalent circuit for a noise contamination route
Device under measurement
Measurement module
Enm'
r
1
r
2
Vin
Z
1
Z
2
Z
3
iearth
Zearth
Ecm
Zearth Zearth
Coupled impedance
Inverter or commercial
power supply
Electromagnetic coupling
Ground impedance
i
2
i
1
Grounding
resistance
Other device’s leakage current or earth current
that ows due to dierence in grounding potentials
Grounding
resistance
Voltage produced by earth current
(Common-mode voltage)
Rs
Es
Noise such as the following directly aects measured values as normal-mode
voltage.
• Electromagnetic induction noise that occurs when an alternating eld 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
Capacitive
coupling
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
1
, i
2
) ow to coupled impedances (Z
1
,
Z
2
) between the measurement module’s positive and negative input terminals and the ground.
Since the voltage occurs between the input terminals, measured values are directly aected.
Knowledge and Information
www.GlobalTestSupply.com
Find Quality Products Online at: sales@GlobalTestSupply.com
To Next Page
Loading...
Need help?
General
