Floating Signal Generators
Many applications require a test signal which is isolated from earth
ground for connection to powered circuits, to avoid ground loops, or to
minimize other common mode noise. A floating signal generator such as
the 33120A has both sides of the output
BNC connector isolated from
chassis (earth) ground. As shown in the figure below, any voltage
difference between the two ground reference points (V
ground) causes a
current to flow through the function generator’s output common lead.
This can cause errors such as noise and offset voltage (usually power-
line frequency related), which are added to the output voltage.
The best way to eliminate ground loops is to maintain the function
generator’s isolation from earth ground. The function generator’s
isolation impedance will be reduced as the frequency of the V
ground
source increases due to low-to-earth capacitance Cle (approximately
4000 pF for the 33120A). If the function generator must be
earth-referenced, be sure to connect it (and the load) to the same
common ground point. This will reduce or eliminate the voltage
difference between devices. Also, make sure the function generator and
load are connected to the same electrical outlet if possible.
R
L
R
L
Load
V
gen
R
i
>10 G
W
C
le
V
ground
50
W
R
L
= Lead Resistance
Common
Chapter 7 Tutorial
Floating Signal Generators
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