Shielded Fixture Construction; Figure 11-7 Electrometer Input Circuitry (External Feedback Mode) - Keithley 6514 Instruction Manual

11-12 Digital I/O, Analog Outputs, and External Feedback
Figure 11-7
Electrometer input
circuitry (external
feedback mode)
Shielded fixture construction
Since shielding is so critical for proper operation of external feedback, it is recommended that
a shielded fixture similar to the one shown in Figure 11-8 be used to house the feedback element.
The fixture is constructed of a commercially available shielded fixture modified with the stan-
dard BNC connectors replaced with triaxial female connectors. For convenience, a banana jack
can be mounted on the box to make the necessary preamp out connection.
Alternately, a wire could be run through a rubber grommet mounted in a hole in the side of
the box. Note that input low is connected to chassis ground within the shielded box. This con-
nection can be made by using a small solder lug secured with a screw.
100MΩ
HI
Input
LO
<1Ω
Common
Preamp Out
(Chassis)
C
FB
R
FB
Zero Check
Op Amp
To Ranging
Amplifier
S