Keithley 2651A Reference Manual page 216

Model 2651A High Power System SourceMeter® Instrument Reference Manual
SourceMeter
+
-
A: Unguarded
SourceMeter
+
-
B: Guarded
2651A-901-01 Rev. A / March 2011
Figure 81: Comparison of unguarded and guarded measurements
IN/OUT
A
HI
I-meter
V-source
IN/OUT
LO
GUARD
x1
A
IN/OUT
I-meter
HI
V-source
IN/OUT
LO
Insulator Insulator
I
D
DUT
R
L1
I
L
Metal Mounting Plate
I = Measured current
M
I = DUT current
D
I = Leakage current
L
Cable Shield
I
D
DUT
R
L1
0V
Metal Mounting Plate
Section 4: Theory of operation
I = I + I
M D L
R
L2
Safety Shield
Insulator
I = I
M D
Connect to earth safety ground
using #18 AWG wire or larger.
4-19