PACSystems VersaMax Genius Network Interface User Manual Section 2
GFK-1535D Jan 2023
Installation 40
2.11.1 Using Other Cable Types
The cable types listed in the preceding table are recommended. If the
cable types listed above are not available, the cable selected must meet
the following guidelines.
1.
High-quality construction. Most important is the uniformity of
cross-section along the length of the cable. A poor-quality cable
may cause signal distortion, and increase the possibility of
damage during installation.
2.
Precision-twisted shielded wire of EIA RS422 standard type,
having a uniform number of twists per unit of length. This type of
cable may also be listed as a twin axial cable, data cable, or
computer cable.
3.
Relatively high characteristic impedance; 100 to 150 ohms is best;
75 ohms is the minimum recommended.
4.
The low capacitance between wires is typically less than 20pF/foot
(60pF/meter). This may be accomplished by inner dielectrics of
foamed type, usually, polypropylene or polyethylene, having a
low dielectric constant. Alternatively, the conductors may be
spaced relatively far apart. Lower impedance types have smaller
cross-sections and provide easier wiring for shorter total
transmission distances.
5.
Shield coverage of 95% or more. Solid foil with an overlapped
folded seam and drain wire is best. Braided copper is less
desirable; spiral wound foil is least desirable.
6.
An outer jacket that provides appropriate protection, such as
water, oil, or chemical resistance. While PVC materials can be
used in many installations, Teflon, polyethylene, or polypropylene
are usually more durable.
7.
Electrical characteristics: cable manufacturers' information about
pulse rise time and NRZ data rate is useful for comparing cable
types. The Genius bit consists of three AC pulses; the equivalent
NRZ bit rate is about three times as great.
For assistance in selecting a specific cable type, please consult your local
Emerson application engineer.
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