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C-6 Field Control™ Genius® Bus Interface Unit User’s Manual
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October 1999 GFK-0825F
C
Using Other Cable Types
The cable types listed in the preceding table are recommended for use. If the cable types listed
above are not available, the cable selected must meet the following guidelines.
1. High quality construction. Most important is uniformity of cross section along the length of the
cable. 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. In a catalog, this type of cable may also be listed as twinaxial cable,
data cable, or computer cable.
3. Relatively high characteristic impedance; 100 to 150 ohms is best; 75 ohms is the minimum
recommended.
4. Low capacitance between wires, 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, polyethelene, 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 GE Fanuc application
engineer.
Prefabricated Cables
For applications using 150 ohm cables, prefabricated cables are available in 15" (IC660BLC001)
and 36" (IC660BLC003) lengths. These cables terminate in mating connectors that simplify wiring
between I/O blocks. The 36" cable is recommended for Field Control installations.
SHD
OUT
SHD
IN
SER
2
SER
1