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Amps Measurements
4-5
High impedance measurement techniques
Significant leakage could occur across a high impedance (
≥
1G
Ω
) DUT through the insulators
as shown in Figure 4-3A where R
L1
and R
L2
represent the leakage resistance. Instead of measur-
ing just the current (I
R
) through R, you are also measuring the leakage current (I
L
). The current
measured by the ammeter is I
R
+ I
L
.
By connecting ammeter input LO to the metal mounting (guard) plate as shown in Figure
4-2B, the leakage current (I
L
) is shunted to ammeter input LO and is not measured by the amme-
ter. Therefore, the ammeter only measures I
R
.
I
M
= I
R
+ I
L
HI
6514
LO
R
L1
E
R*
A
I
R
Metal Mounting Plate
Insulators
R
L2
I
L
A. Unguarded
I
M
= I
R
HI
6514
LO
R
L1
E
R*
A
I
R
Metal Guard Plate
I
L
*R =
≥
1G
Ω
B. Guarded
Figure 4-2
High impedance
current measurements
Summary of Contents for 6514
Page 203: ...14 CommonCommands...
Page 207: ...15 SCPISignalOriented MeasurementCommands...
Page 235: ...18 PerformanceVerification...
Page 254: ...19 Calibration...
Page 274: ...20 RoutineMaintenance...
Page 278: ...A Specifications...
Page 282: ...B StatusandErrorMessages...
Page 288: ...C GeneralMeasurement Considerations...
Page 294: ...D DDCEmulationCommands...
Page 299: ...E ExamplePrograms...
Page 306: ...F IEEE 488BusOverview...
Page 320: ...G IEEE 488andSCPI ConformanceInformation...
Page 324: ...H CalibrationOptions...