High Impedance Measurement Techniques; Figure 4-2 High Impedance Current Measurements - Keithley 6514 Instruction Manual

High impedance measurement techniques

Significant leakage could occur across a high impedance (≥1GΩ) DUT through the insulators
as shown in Figure 4-3A where R
ing just the current (I
measured by the ammeter is I
By connecting ammeter input LO to the metal mounting (guard) plate as shown in Figure
4-2B, the leakage current (I
ter. Therefore, the ammeter only measures I
Figure 4-2
High impedance
current measurements
) through R, you are also measuring the leakage current (I
R
+ I
R
) is shunted to ammeter input LO and is not measured by the amme-
L
R
L1
E
Metal Mounting Plate
A. Unguarded
R
L1
E
Metal Guard Plate
*R = ≥1GΩ
B. Guarded
and R represent the leakage resistance. Instead of measur-
L1 L2
.
L
.
R
I
I
R
HI
R*
R
I
L2
L
Insulators
I
R
HI
R*
I
L
Amps Measurements
). The current
L
= I + I
M R L
LO
A
6514
I = I
M R
LO
A
6514
4-5