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Chapter 3 Calibration Procedures
Common Mode Current Noise
56
2
Turn on the power supply. Select the 15V/7A range, enable the output, and set
the display to the limit mode. When the display is in the limit mode, program
the current to full rated value (7.0A) and the voltage to the full rated value
(15.0V).
3
The output current should be at the full-rated rating with the CC annunciator
on. If not lit, adjust the load so that the output voltage drops slightly until the
CC annunciator lights.
4
Divide the reading on the rms voltmeter by the load resistance to obtain rms
current. The readings should be within the limit of 2mA.
Common Mode Current Noise
The common mode current is that 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 impendance to earth
ground will create a voltage drop equal to the output current flow multiplied
by the impendance.
1
Turn off the power supply and connect a 100K
9
resistor (R
S
) and a 2200 pF
capacitor in parallel between the (-) terminal and chassis ground.
2
Connect a digital voltmeter across R
S
.
3
Turn on the power supply. Select the 15V/7A range, 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 rated value (15.0V and 7.0A).
4
Record the voltage across RS and convert it to current by dividing by the
resistance (DVM reading/100K
9
). Note that the current is less than 1.5
mA.