14. Appendix E
14.1. Fieldbus Wiring Considerations
514 Experion PKS Series A Fieldbus Interface Module User's Guide R400
Honeywell July 2010
Preference
Type
Description
Distance
(Meters/Feet)
Resistance
(Ohms per
km)
Attenuation
dB per km
1
#18 AWG, shielded, twisted
pair
1900/6233 22 3
2
#22 AWG, multiple-twisted,
pairs with overall shield
1200/3937 56 5
3
#26 AWG, multiple-twisted,
pairs without shield
400/1312 132 8
4
#16 AWG, multiple
conductor, no twisted pairs
with overall shield
200/656 20 8
Another rule of thumb based on Fieldbus Foundation published guidelines is for the
length of spurs and how many devices can be on various lengths of cable as listed in the
following table.
Number of Devices Maximum Spur Length (Meter/Feet)
1 to 12 120/394
13 to 14 90/295
15 to 18 60/197
19 to 24 30/98
25 to 32 No spurs allowed
ATTENTION
The spur length limitations are for spurs with one device each. Please refer to
the Fieldbus Foundation AG-140 Wiring and Installation Guide for rules on
multiple devices per spur.
Cable guidelines summary
To
tal cable length is the sum of trunk and spur lengths. If different cable preference types
are used, apportion each type against its limit and be sure the total is less than one (1).
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