PASCO ES-9060 Charge, Equipotential and Field Mapper - Manual (Page 18)

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Model No. ES-9060 Charge, Equipotential, and Field Mapper
17
By touching the proof plane
to a surface, the proof plane
will acquire the same charge
distribution as the section of
the surface it touched (See
Figure 11). By measuring
the charge on the proof
plane, the charge density on
that part of the surface can
be determined. The greater
the charge on the proof
plane, the greater the charge
density on the surface where the proof plane made contact.
When a proof plane is touched to a conductive surface, the proof plane
becomes part of the conductive surface. If the effect on the shape of the
surface is significant, the sampling of the charge density will not be
accurate. Therefore, always touch the proof plane to the conductor in
such a way as to minimize the distortion of the shape of the surface.
Figure 12 shows the recommended method for using the proof plane to
sample charge on a conductive sphere.
NOTE: The proof planes can be used to test for charge polarity on
conductors of any shape. However, if you want accurate readings of
charge density, the conductor surface sampled has to be considerably
larger than the disk of the proof plane and have a relatively large radius
of curvature at the point of contact.
in sampled area
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area sampled
Figure 11: Conductive Sphere
plane equals charge
charge in proof
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surface of the proo f
plane IS tangent
to the surface
of the conductor
surface of the proof
plane IS NOT tangent
t o the surface of the
conductor
charge conductive
Figure 12: Proper use of a Proof Plane to Sample Charge
spheres