Keithley 2700, User Manual, Page: 441 / 500

E-8 Measurement Considerations Model 2700 Multimeter/Switch System 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.
2700