C-8 Measurement Considerations
Shielding
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 C-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.
WARNING Do not float input LO more than 30V rms, 424V 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.
Figure C-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.
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