Keysight E3631A, Service Manual

Page: 65 / 131

Calibration Procedures 3
Keysight E3631A Service Guide 63
Figure 3-4 RMS ripple/noise measurement setup
Common mode current noise
The common mode current is that ac current component which exists between
any or all outputs 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 k W resistor (RS) and a 2200 pF
capacitor in parallel between the (-) terminal and chassis ground for +6V
output or between the (COM) terminal and chassis ground for ±25V outputs.
2 Connect a digital voltmeter across R
s
.
3 Turn on the power supply and select the output to be tested using the meter
and adjust selection key on the front panel. Enable the outputs and set the
display to the limit mode. When the display is in the limit mode, program the