Front Panel Operation
2-37
For circular electrodes:
D
0
= D
1
+ g (refer to Figure 2-34 to determine dimension
D
0
).
Volume Resistivity —
Volume resistivity is defined as the
electrical resistance through a cube of insulating material.
When expressed in ohm-centimeters, it would be the electri-
cal resistance through a one-centimeter cube of insulating
material. If expressed in ohm-inches, it would be the electri-
cal resistance through a one-inch cube of insulating material.
P
π
D
0
=
Figure 2-34
Circular electrode dimensions
D
1
- D
2
2
g =
Guarded
Electrode
Ring
Electrode
D
1
D
0
D
2
Guarded Electrode
Sample
g
Ring Electrode
D
1
D
0
D
2
D
0
= D
1
+ g
Test Fixture
Dimensions (cm)
D
1
D
0
D
2
g
Model 8009
g
2.000 in
2.125 in
2.250 in
0.125 in
Volume resistivity is measured by applying a voltage poten-
tial across opposite sides of the insulator sample and measur-
ing the resultant current through the sample as shown in
Figure 2-35. The Model 6517A automatically performs the
following calculation and displays the volume resistivity
reading:
ρ
V
= Volume resistivity.
K
V
= The effective area of the guarded electrode for the par-
ticular electrode arrangement employed.
τ
= Average thickness of the sample (mm).
R = Measured resistance in ohms (V/I).
For circular electrodes:
D
1
= Outside diameter of guarded electrode.
g = Distance between the guarded electrode and the ring
electrode.
B = Effective area coefficient.
Notes:
1. Refer to Figure 2-34 to determine dimensions D1 and g.
2. An effective area of coefficient (B) of 0 is typically used
for volume resistivity.
ρ
V
K
V
τ
-------R
=
K
V
π
D
1
2
------
B
g
2
---
+
2
=
Guarded
Electrode
Sample
Top
Electrode
Ring
Electrode
6517A
V-Source
HI
LO
HI
LO
A
6517A
Picoammeter
Guard
Figure 2-35
Volume resistivity measurement technique
