19
Checking for Conducted Emission with the 3M
™
ScanEM-HQC
Electromagnetic Near-Field Probe
1. Calibrate the probe by moving it away from the product and setting the
Level dial to light only green LED. Take precautions to ensure that no
extraneous RF fields are affecting the setting. A determination of this can
typically be accomplished by comparing the probe level setting at various
places within the building. If the probe level setting is unaffected or only
slightly affected, then it is unlikely extraneous fields are affecting the
probe. If you have any concern that extraneous RF fields are affecting the
probe, the computer system should be relocated to a different building and
the calibration process repeated.
2. Place the computer AC power cord longitudinally in the center of the
ferrite core as tightly as possible. Move the probe up and down the length
of the power cord. If a high energy level is detected, check the gain of the
probe and remeasure the AC power cord. If four or five LEDs light, then
the unit should be considered noncompliant. Generally, this problem can
be corrected by substituting a power supply that has a built-in RF filter. In
unusual situations, addition of ferrite beads on some or all of the power
supply output leads inside the computer case may be required to correct
the problem.
