Installation and Operations Guide
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Hardware installation
© Honeywell. All Rights Reserved. LT-VLXEXPAXMIOG Rev. 01
33
When connecting a VLX using MS/TP, the total number of devices on that MS/
TP should be limited to 10 or fewer. The 10-device limit is in cases where the
VLX is connected via Ethernet, and is acting as a router to other VLCs on its
MS/TP trunk. Other factors will affect network performance such as global-
controller-hosted VLC point alarms, global controller DDC references to devices
on the MS/TP, and active operator workstations requesting data from devices on
the MS/TP.
EXP/AXM I/O
This topic describes physical connections for EXP/AXM inputs and outputs. It
does not cover software configuration and use. Software configuration of inputs
is required for proper operation. See “Setting up inputs” on page 53 and “Setting
backup mode values for AOs and BOs” on page 56 for information on
configuring I/Os in software. See “VLX/ACM-VLX data, DDC, and
automation” on page 58 for information about using I/O data.
WARNING Before connecting equipment to EXP/AXM I/O, ensure that DDC
and automation features have been thoroughly tested to confirm adherence to the
engineered sequence of operations.
Binary outputs (BOs)
EXP/AXM BOs are arranged in groupings (banks). Outputs are labeled BO n.
Each output has a software-controlled, onboard connection to the HOT terminal
for its output bank. HOT terminals are labeled HOT A, HOT B, and so on.
Terminal identification HOT terminals connect to the hot leg of a 24 VAC
transformer that is used exclusively for BO power. BO terminals connect to the
Terminal identification VLX: Terminals for MS/TP are on the left and are
labeled MS/TP + and MS/TP –.
ACM: Terminals for MS/TP can be on the left
(onboard 485 ports), or the right (option card added
485 ports).
Cable type and length BACnet specifies shielded, 18AWG two conductor
twisted shield cabling with characteristic
impedance between 100 and 130 Ohms. Distributed
capacitance between conductors must be less than
30 pF/foot (100 pF/m). Distributed capacitance
between conductor and shield must be less than 60
pF/foot (200 pF/m). Foil or braided shield is
acceptable.
Maintain polarity throughout the MS/TP segment.
Terminating resistors Matched precision resistors are required at each end
of the MS/TP segment. Wire the resistors across +
and –.
Recommended 120 Ohm resistor value.
Shield grounding Terminate shield drain at one end of the MS/TP
segment to ground. Tie shield drain through with
wire nut at each intermediate device and insulate to
avoid potential ground contact. Tape shield drain
back at other end of segment.
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