Keithley 8009 Instruction Manual - page 25
Volume Resistivity:
Volume resistivity is defined as the electrical resistance
through a one-centimeter cube of insulating material and is expressed in ohm-
centimeters. Likewise, the electrical resistance through a one-inch cube of
insulating material is expressed as ohm-inches.
Volume resistivity (
ρ
) is measured by applying a voltage potential across
opposite sides of the insulator sample, measuring the resultant current through
the sample (see Figure 3-1), and then performing one of the following
calculations:
or
Where:
ρ
is the volume resistivity of the sample.
V is the applied voltage from the Electrometer.
t
c
is the average thickness of the sample in centimeters.
t
i
is the average thickness of the sample in inches.
I is the current reading from the Electrometer.
Surface Resistivity:
Surface resistivity is defined as the electrical resistance of
the surface of an insulator material. It is measured from electrode to electrode
along the surface of the insulator sample. Since surface length is fixed, the
measurement is independent of the physical dimensions (for example, thickness
and diameter) of the insulator sample.
Surface resistivity (
σ
) is measured by applying a voltage potential across the
surface of the insulator sample, measuring the resultant current, and then
performing the following calculation:
Where:
σ
is the surface resistivity of the sample.
V is the applied voltage from the Electrometer.
I is the current reading from the Electrometer.
e
ate
resistivity and Figure
made up
s to
ohms) from where the drawn line inter-
tage of
line intersects
ρ
22.9V
t
c
I
---------------ohm-centimeter
=
ρ
3.55V
t
i
I
---------------ohm-inches
=
σ
53.4V
I
---------------ohms
=
14
15