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3.3
Resistivity nomographs
With test voltage and measured current (and sample thickness for volume
resistivity) known, resistivity can be approximated by using the appropriate
nomograph. Figure 3-2 shows the nomograph for surface resistivity and Figure
3-3 shows the nomograph for volume resistivity.
Surface Resistivity: The surface resistivity nomograph (Figure 3-2) is made up
of three scales; voltage, resistivity and current. Perform the following steps to
determine resistivity:
1. Plot the test voltage value on the voltage scale.
2. Plot the measure current value on the current scale.
3. Draw a straight line connecting the plotted voltage and current values.
4. Read the surface resistivity value (in ohms) from where the drawn line inter-
sects the resistivity scale.
An example is shown in the graph. The dashed line connects a test voltage of
200V to a measured current of 3 × 10
the resistivity scale at just under 4 × 10
Figure 3-2
Surface resistivity (σ) nomograph
-10
amps (0.3nA). The dashed line intersects
13
¾ (3.56 × 10
13
¾ by calculation).
15
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