Monroe Electronics Electrostatic Voltmeter - Isoprobe® - model 244A - Manual (Page 17)

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APPENDIX I
MODEL 1017 PROBE MOUNTING
The Monroe Electronics, Inc. Model 1017 Miniature Probe is intentionally constructed
with no mounting devices as any such mounting device would serve only to enlarge the
physical dimensions. It is, therefore, left to the user to devise a method of mounting the
probe to suit his individual needs and to realize the fullest potential of the inherently
small size.
As supplied, the probe is partially jacketed by a length of irradiated polyolefin shrinkable
tubing. This jacket provides insulation of sufficient dielectric strength that the probe may
be hand-held or clamped using light pressure for use within the operating range of the
Model 244A ISOPROBE Electrostatic Voltmeter.
This tubing is otherwise not essential to the operation of the probe. IT MAY BE
REMOVED AND DISCARDED, IF DESIRED. It must, in fact, be removed if the probe is
to be disassembled for any purpose such as cleaning (in those procedures involving
removal of the case). A sharp model maker's knife may be used to slit the tubing using
CAUTION to assure that the cable jacket is not nicked or slit.
If replacement is required, a 2 5 /s inch length of ALPHA FIT221- 3 /s or equivalent is
recommended. Apply heat only long enough to shrink the tubing in place as damage to
the sensitive electronics and adhesives within the probe may result from prolonged
elevated temperature on the outside of the case.
When devising fixturing for the Model 1017 probe, consideration must be given to the
fact that the normal operating range of the Model 244A ISOPROBE
® Electrostatic
Voltmeter is ±3000 volts and that the probe assumes the potential of the surface under
measurement within these limits. The probe, therefore, must be insulated from other
parts of the system.
Choice of insulating materials, although not critical in many applications, should be
limited, if possible, to "leaky" dielectric materials with relatively low volume resistivities
(in the general order of 10
10
ohm-cm) as opposed to those such as polystyrene which is
a very good insulator. Example of "leaky" insulators are the phenol- ics. The primary
purpose in this is to provide a discharge path for the insulator which has a short
relaxation time. This is especially important in the vicinity of the sensitive aperture.
The Model 244A is capable of driving a capacitive load of several hundred picofarads
without severe degradation in performance. It is possible, therefore, to attach the probe
to some fixed portion of the apparatus via a metal clamp, so long as the metal clamp is
insulated from the remainder of the apparatus.
In any friction clamp design, the pressure (unit force) on the probe case should be kept
low, thus over as large an area of the case as possible as distortion of the gold plated
brass may otherwise occur.