Monroe Electronics Electrostatic Fieldmeter - Portable - model 257D - Manual (Page 9)

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mounted by means of two threaded inserts installed in the back plate. Please refer to
outline drawing Figure 6-1 for location. Care must be exercised when selecting screw
length. The tapped holes in the inserts are blind holes. They will accommodate five full
#4-40 threads. Some additional mounting options are friction clamps, adhesives or
double-sided tape. The metal body of the probe is internally connected to instrument
ground and should not normally be connected to any other ground.
D. Geometry:
All type 1036 probes are shipped from the factory standardized in a "perfect parallel
field" using a fixture similar to that shown in Figure 6-2 consisting of two flat rigid metal
plates which are parallel and separated by a distance "d" and have side dimensions of
at least 5d. The ground plate has a hole in its center just large enough to provide
clearance around the probe so that the probe does not make contact with the plate. A
calibrating voltage is applied to the gradient plate to establish a reference field in the
volume between the plates. Once standardized in this manner, they may be
interchanged at will.
Since a true uniform field does not usually occur in most practical measurement
situations, partly due to the introduction of the grounded probe itself, one must either:
1. Attempt to better the geometry by establishing a grounded plane, through which
the fieldmeter probe can view the field under consideration,
2. Establish a correction factor for the data, or
3. Accept relative data. In many cases, this is perfectly acceptable practice once a
fixed geometry is established.
Figure 6-2