Monroe Electronics Electrostatic Fieldmeter - Portable - model 257D - Manual (Page 8)

6
Section 6
PROBE INFORMATION
A. General:
It must be emphasized that the critical elements of these probes (gradient cap and
vibrating electrode) must be kept free from contaminants, e.g., dust, adsorbents, etc.
The materials of which these elements are made were very carefully chosen to
minimize contact potential and any foreign matter which will cause relative electrical
activity when combined with relative motion will tend to cause drift and measurement
errors.
Therefore, it is recommended that:
1. Probes be constantly purged even when not in use, if this is practical.
2. Probes be kept tightly covered when not in use and are not being purged to
prevent contamination. A covering such as a plastic bag or aluminum foil may be
used. Do NOT cover the sensitive aperture with adhesive tape.
3. Probes be cleaned only to the degree and frequency necessary to achieve the
required stability.
4. Gradient caps NOT be removed for cleaning unless absolutely essential.
5. Major cleaning and reconditioning be performed by the factory.
B. Sensitivity:
Full-scale sensitivity for any properly standardized probe/instrument combination is
dependent upon the gradient cap on each probe. Thus, the full-scale sensitivity for any
given system can be determined by inspecting the gradient cap on the probe. Each
gradient cap is stamped with a number and this number can be related to the sensitivity
of the probe. With some possible exceptions, probes intended for use with the Model
257D will be stamped with the digit “5” to indicate that the sensitivity is 20 kV/cm.
Probes are standardized at the factory in a uniform electric field between two relatively
large metal plates. Once standardized in this manner, they may be interchanged at will.
C. Mounting:
Probe mounting requirements for
electrostatic field determinations will vary
somewhat with the nature of the desired
measurement. In general, it will be best to
mount the probe as near as is practical to
the surface to be monitored – so long as
the input signal remains less than the full-
scale sensitivity of the probe. For
example, mount at one centimeter, if
feasible. It is recommended that, where
possible, the probe be mounted "looking"
downward in order to minimize the
probability of contaminants entering the
aperture in the face.
The Model 1036F-5 probe may be held by
hand to make rough measurements or
Figure 6-1