Keithley 6514 Instruction Manual page 41

2-4 Measurement Concepts
Input configurations
As shown in Figure 2-1, the input connector can be configured in two ways. With guard off
(Figure 2-1A), input low is connected to the inner shell of the connector. This configuration is
used for Amps, Coulombs, unguarded Volts and unguarded Ohms measurements.
With guard on (Figure 2-1B), the driven guard is connected to the inner shell of the triax con-
nector. Input low is accessed via the COMMON terminal through an internal 0.1Ω fuse. This
configuration is used for guarded Volts and guarded Ohms measurements only. The GRD key
toggles guard on and off.
NOTE
Figure 2-1
Input connector
configurations
The state of guard (on or off) has no affect on the Amps and Coulombs functions. The
unguarded configuration is always selected for the Amps and Coulombs functions.
INPUT
250V PEAK
Volts, Amps, Ohms & Coulombs
A. Unguarded (GRD off)
Input High
Guard
Chassis
Ground
INPUT
250V PEAK
Volts and Ohms only
B. Guarded (GRD on)
Input High
Input Low
Chassis Ground
<1Ω
Fuse
COMMON
Input Low