Technical data

Service and Maintenance 8
Common Mode Current Noise
E364xA User’s and Service Guide 201
Common Mode Current Noise
The common mode current is the AC current component
which exists between the output or output lines and chassis
ground. Common mode noise can be a problem for very
sensitive circuitry that is referenced to earth ground. When
a circuit is referenced to earth ground, a low level
line- related AC current will flow from the output terminals
to earth ground. Any impedance to earth ground will create
a voltage drop equal to the output current flow multiplied
by the impedance.
1 Turn off the power supply and connect a 100 kΩ resistor
(R
S
) and a 2200 pF capacitor in parallel between the (–)
terminal and chassis ground at the rear output terminals.
2 Connect a digital voltmeter (DVM) across R
S
.
3 Turn on the power supply. Select the low voltage range
(8 V/3 A)
[1]
, enable the output, and set the display to the
limit mode. When the display is in the limit mode,
program the output to the full- scale rated value (8.0 V
and 3 A)
[1]
.
4 Record the voltage across R
S
and convert it to current by
dividing by the resistance (DVM reading/100 kΩ). Note
that the current is less than 1.5 μA.
[1] For the E3640A model. For other models, refer to Tabl e 8 -5 .