Viconics VT7607 Echelon Integration Guide - Manual (Page 19)

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Maximum Cable Length
The maximum length of a chain is related to its transmission speed. Using proper cable, Echelon
supports a baud rate of 78 kilobits per second for distances up to 1600-ft (500 m) in free topology and
8800 ft (2700 m) in bus topology with double terminations.
If you require a maximum network length of more than 1600-ft (500 m) or 8800 ft (2700 m), then a
repeater is required to extend the network.
Repeater
In the event that the limits on the number of transceivers or total wire distance are exceeded, a physical
layer repeater can be added to interconnect two or more network segments. A repeater will double the
overall channel capability, including node count and network extent, but not bandwidth. Note that only
one physical layer repeater should be placed in series between any two nodes on a channel. If
additional cabling or network bandwidth is required, then a LonWorks Router should be used in place of
a repeater.
Terminators
Echelon network segments requires termination for proper data transmission performance. The type of
terminator varies depending on whether shielded or unshielded cable is used. Free topology and Bus
networks also differ in their termination requirements. The following sections describe the various terminators
and terminations procedure.
Free Topology Network Segment
In a free topology segment, only one termination is required and may be placed anywhere on the
free topology segment. There are two choices for the termination:
1. RC network with Ra = 52
Ω±1%, 1/8W
2. LPI-10 Link Power Interface, with jumper at “1 CPLR” setting.
Doubly Terminated Network Segment
In a doubly terminated bus topology, two terminations are required, one at each en of the bus.
There are two choices for each termination:
1. RC network with Ra = 105
Ω±1%, 1/8W
2. LPI-10 Link Power Interface, with jumper at “2 CPLR” setting.
Only one LPI-10 interface is supported per segment. The other terminator must be an RC-type.
Grounding Shielded Twisted Pair Cable
When using Shielded Twisted Pair, terminate the twisted pair as listed in the previous section and
ground the cable shield by using a capacitor, to tie the shield to earth ground, and a large-value
resistor to bleed off any static charge on the shield. Tying the shield to earth ground through a
capacitor will avoid DC and 50/60Hz ground paths from being formed through the shield. Typical
values for resistor and capacitor are as follows:
Capacitor = 0.1
μF, 10%, Metalized Polyester, ≥ 100V
Resistor = 470k
Ω, 1/4W, ±5%
The cable shield should be grounded at least once per segment, and preferably at each node.
Grounding the shield at every node will assist in suppressing 50/60Hz standing waves.