Monroe Electronics Electrostatic Fieldmeter - Portable - model 257D - Manual (Page 10)

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E. Cables:
Probes are normally equipped with 10 foot cables and subminiature D connectors which
mate with a connector recessed in the back panel of the instrument. Extension cables
are available in lengths up to 1000 feet – the maximum length permissible. These
extension cables may be ordered in any length (up to 1000 feet) by part number
1036/12-nn, where nn is the length in feet.
F. Purging:
It can be demonstrated that any "contamination" present in the probe or in the vicinity of
the measurement will have an adverse affect on performance, which will be exhibited as
a DC offset that usually will drift with time. "Contamination", in this sense, refers to any
time varying change in contents of the local environment around the probe and surface
under measurement. Included are changes in the constituent gases of the atmosphere
as well as aerosols and airborne particles.
The nature of this contamination effect is easily understood in the case of non-
conducting solids or liquids, which can trap electrostatic charges on a sensitive surface.
Less obvious is the influence of gaseous atmospheric constituents, which "contaminate"
by altering the contact potentials between critical surfaces.
Constant purging of the type 1036 probe with clean dry air or an inert gas is
recommended whenever practicable in order to prevent airborne contaminants from
entering the aperture in the gradient cap and being deposited on the electrode thus
creating undesired voltage offsets.
The air supply should meet Industrial Standards Association standard ISA/S7.3 (1975)
or be filtered with a filter such as a Koby "Junior” filter available from Koby, Inc., 297
Lincoln Street, Marlboro, Massachusetts 01752. This filter will provide sufficient
mechanical and chemical filtration for 1-4 probes under most conditions.
A complete probe purge kit, Model 1017/22G, is available for 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, which 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 it with the Allen set screw plugging the other hole.
Gas pressure to the probe should be only great enough to produce a slight positive flow
out of the probe and in no event should it exceed 14" of water column (½ psi).
G. Cleaning:
Recommended cleaning solvent is clean technical grade isopropyl alcohol used with a
suitable applicator. Any use of non-approved solvent may degrade performance
permanently requiring factory service.
Outside surfaces of the probe should first be wiped clean using a lint-free wiping tissue
saturated in the solvent then the interior surfaces flushed through the aperture until no
dirt or dust may be seen. The probe should then be allowed to drain and dry
thoroughly. A 15 minute bake-out at 75°C is recommended to remove residual solvent.