Shielding - Keithley 2750 User Manual

Model 2750 Multimeter/Switch System User's Manual

Shielding

WARNING
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 measure-
ments, rendering experimental data virtually useless.
In order to minimize noise, a closed metal shield surrounding the source may be neces-
sary, as shown in the example of
in most cases, although better noise performance may result with the shield connected to
chassis ground in some situations.
Figure E-4
Shielding example
WARNING: Safety shield required when
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 pos-
sible 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.
2750
A
HI
LO
Connect noise
shield to LO.
floating noise shield >30V rms
above chassis ground.
Measurement Considerations
Figure E-4. This shield should be connected to input LO
DUT
Noise
Shield
Safety
Shield
Connect safety shield to a
known safety earth ground
using #18 AWG wire or higher.
E-9