Monroe Electronics Electrostatic Fieldmeter - Static Monitor - model 177A - Manual (Page 82)

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As a truly uniform field does not usually occur in most practical measurement situations
using the 1036F probes, partly due to the introduction of the grounded probe itself, one must
either:
 Improve the geometry by establishing a grounded plane (shroud) through which
the fieldmeter probe can “view” the target surface,
 Establish a correction factor for the data, or
 Accept relative data. In many cases, this is an acceptable practice once a fixed
geometry is established and that data is related to the real electric field.
Cables:
Both Models 1036E and 1036F probes are normally equipped with 10-foot-long cables and
subminiature D connectors, which mate with the Monroe Electronics Model 177A Static
Monitor. This is Option 1 of six available wiring options. See Appendix A – Probe Connection
Options for details. The first three options are for non-hazardous (non-classified) locations
where there are no Intrinsic Safety (IS) considerations. The last three options are for
hazardous (classified) locations where Intrinsic Safety must be considered as part of the
installation.
Extension cables are available from Monroe Electronics in lengths up to 1000 feet, which is
the maximum permissible length. These cables may be ordered in any length (up to 1000
feet) by part number 1036/12-nnnn, where nnnn is the length in feet.
The cable exit on the Model 1036E is through a packing gland that is screwed into a ½"-14
NPT tapped hole in a boss on one end of the housing. Inside the housing, the probe is
plugged into a terminal block to which the cable attaches. Where it is desirable or necessary
to connect Model 1036E probes to Model 177A Static Monitors using conduit, the original
cable and packing gland can be removed and the cable replaced by any length (up to 1000
feet) pulled through the conduit. Refer to Appendix A – Probe Connection Options, Options
3, 4 or 6 (depending on whether Intrinsic Safety must also be considered) for details,
including wiring information.
Purging
Any contamination present in the probe or near the measurement will have an adverse affect
on performance. When insulative particulate or liquid becomes charged and enters the probe
or attaches near the aperture of the probe, it becomes a source of measurement error and
drift. Less obvious is the influence of gaseous atmospheric constituents, including aerosols,
which contaminate the probe by altering the contact potentials
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between critical surfaces.
Constant purging of the Model 1036 probe with clean dry air or an inert gas is recommended
whenever practicable to prevent airborne contaminants from entering the aperture in the
gradient cap and being deposited on the electrode.
The air supply should meet standard ANSI/ISA-7.0.01-1996 - Quality Standard for
Instrument Air. A Koby "Junior" filter available from Koby, Inc., 299 Lincoln Street, Marlboro,
MA 01752 should meet this standard and will provide sufficient mechanical and chemical
filtration for up to four probes under most conditions.
A complete probe purge kit, Model 1017/22G, is available for the Model 1036F from Monroe
Electronics. It includes a low volume, long-life air pump, mechanical and chemical filters, and
a supply of tubing. The pump is fully capable of 24-hour-per-day operation, thus keeping the
probe ready for immediate use. A purge gas inlet tube supplied with each 1036F probe may
be installed in either of two positions, the choice of which is primarily a matter of
convenience in routing of the hose carrying the purge gas. These consist of tapped holes
that exit at 90° to each other near the probe cable. If it is desired to move the purge tube to
the other location, simply switch the purge tube with the Allen set screw plugging the other
hole.
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Contact potential between two conductors is caused by their different work functions, which are the energies
needed to remove an electron from the conductor. This gives rise to a potential (voltage) difference. This
energy is affected by the properties of the surface region. Thus, the work function is very sensitive to surface
conditioning, contamination, etc.