Table of Contents
Advertisement
7
Chapter 7 Tutorial
Ground Loops
Ground Loops
The signal-generation portion of the Keysight 33210A is isolated from
chassis (earth) ground. This isolation helps to eliminate ground loops in
your system and also allows you to reference the output signal to
voltages other than ground. The illustration below shows the function
generator connected to a load through a coaxial cable. Any difference in
ground potentials (V
GND
shield of the cable, thus causing a voltage drop due to the shield's
impedance (Z
). The resulting voltage drop (I
Shield
as an error in the load voltage. However, since the instrument is isolated,
there is a high series impedance (typically 1 MΩ in parallel with 45 nF)
in the path to oppose the flow of I
Keysight 33210A
50Ω
V
GEN
1 MΩ
45 nF
Ground Loop Effects
At frequencies above a few kilohertz, a coaxial cable's shield becomes
inductive, rather than resistive, and the cable acts as a transformer.
When this happens, it tends to force the shield and center-conductor
currents to be equal but opposite. For any voltage drop in the shield due
to I
, there is a similar drop in the center conductor. This is known as
GND
322
) will tend to make current I
and thereby minimize this effect.
GND
Z
Shield
V
OUT
I
GND
V
GND
flow in the
GND
x Z
) appears
GND
Shield
V
R
= V
– (I
x Z
L
OUT
GND
L
)
Shield
Advertisement
Table of Contents
