PARSTAT 4000 Hardware Manual
PARSTAT 4000 Hardware Manual 13
Once the instrument is completely surrounded by the shield (taking care not to unduly
restrict ventilation), the only additional requirement is to install low-pass filters where lines
pass through the shield (all openings through the shield should be as small as possible).
A capacitor between a line and the shield can function as a suitable low-pass filter. The
leads of the capacitor should be as short as possible. We suggest using coaxial feed
through capacitors.
In the case of a signal lead, it is essential that the capacitor’s value be such as to attenuate
the interference frequencies without unduly attenuating critical frequency components of
the signal itself.
NOTE: Keep the filter capacitor leads short! Long leads establish sizable ground
loops and could additionally act as radiating antennae.
Coaxial cables are a special case in that the cable shield acts as an extension of the
enclosure shield. Thus, the filter can be counted in a shielded box fitted with coaxial
connectors without undue concern for keeping the box extremely close to the enclosure.
If more convenient, it can be located at some distance from the enclosure as long as the
integrity of the coaxial shield is maintained.
The preceding techniques are extraordinary measures that should be required only in
unusual cases. If they are applied with care, RF interference should be reduced to an
acceptably low level in all but the most critical applications. Contact the Customer Service
Department for advice in the case of a problem that does not yield to these measures.
2.2.3. Transient Sensitivity
Princeton Applied Research instruments are designed and constructed to ensure normal
operation in the presence of moderate transient levels. Although these provisions are
sufficient for operation in most places where the equipment is used, it is certainly possible
for transient levels in particular environments to be so severe that they make reliable
operation uncertain. There are three general types of high-level transients:
1. Static discharge
Transients from this source generally affect input or output circuits, input circuits
that include MOS field-effect transistors to achieve high input impedance are
particularly susceptible to damage from this source. Damage typically occurs when
the charge built up on a user’s body discharges into an input or output connector
as a connection is being made. Among the factors determining the tendency for
charges to build are the kind of clothing fabrics worn, shoe materials, and the
materials in the floor or floor covering.
2. High-level transients generated internal to the place of use
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