E-8 Measurement Considerations Model 2701 User’s Manual
Shielding
WARNING Do not float input LO more than 30V rms, 42.4V peak above earth
ground with an exposed shield connected to input LO. To avoid a
possible shock hazard, surround the LO shield with a second safety
shield that is insulated from the inner shield. Connect this safety shield
to safety earth ground using #18 AWG minimum wire before use.
Proper shielding of all signal paths and sources being measured is important to minimize
noise pickup in virtually any low-level measurement situation. Otherwise, interference
from such noise sources as line frequency and RF fields can seriously corrupt
measurements, rendering experimental data virtually useless.
In order to minimize noise, a closed metal shield surrounding the source may be
necessary, as shown in the example of Figure E-4. This shield should be connected to
input LO in most cases, although better noise performance may result with the shield
connected to chassis ground in some situations.
Figure E-4
Shielding example
HI
LO
DUT
A
2182
Noise
Shield
Connect noise
shield to LO.
Connect safety shield to a
known safety earth ground using
#18 AWG wire or higher.
Safety
Shield
WARNING: Safety shield required when
floating noise shield >30V rms
above chassis ground.
2701
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