125
ECLYPSE APEX
Data Bus Shields: Twist
together and Isolate
with electrical tape
Typical BACnet 24VAC-
Powered Controller
Data Bus Shield:
Isolate with
Electrical Tape
Typical BACnet 24VAC-
Powered Controller
Data Bus: Shielded Twisted Pair Cable
N
ET
+
N
ET
-
N
ET
+
N
ET
-
Typical BACnet 24VAC-
Powered Controller
N
ET
+
N
ET
-
Data Bus Shield:
Isolate with
Electrical Tape
Typical BACnet Line-
Powered Controller
N
ET
-
N
ET
+
C
O
M
Electrical
System
Ground
The shield of the data bus must be connected to
the electrical system ground at one point only –
usually at the Building Controller, when present
RS-485
-
+
S
ECLYPSE
Data Bus Shields:
Twist Together
and Connect to
‘COM’ Terminal
Data Bus Shield
Connect to the ‘S’
terminal
Figure 100: Typical Cable-Shield Grounding Requirements for a BACnet MS/TP Data Bus Segment with an ECY
Series Controller located in the Middle of the Data Bus
Using Repeaters to Extend the Data Bus
A BACnet MS/TP data bus segment can be up to 1220 meters (4000 feet) long with up to a maximum
of 50 devices. When a greater length is required, a solution is to use a repeater. A repeater increases
the maximum length of the data bus.
Using a Repeater to Extend the Length of the BACnet MS/TP Data Bus
Repeaters can be used to extend a BACnet MS/TP data bus up to 3660 meters maximum total length.
Do not use more than two repeaters on a BACnet MS/TP LAN.
A BACnet MS/TP repeater is a bi-directional device that regenerates and strengthens the electrical
signals that pass through it. It creates two electrically-isolated BACnet MS/TP data bus segments that
transparently enable devices on one side of the repeater to communicate with any device on the other
side. The two BACnet MS/TP data bus segments have the same requirements of an ordinary BACnet
MS/TP data bus segment; that is, each BACnet MS/TP data bus segment:
£
Can be up to 1220 meters (4000 feet) long.
£
The first and last device on the data bus must have End-of-Line (EOL) termination resistors con-
nected across the two data lines/wires of the twisted pair.
£
Must respect the maximum limit for
.
£
Will have the same network number as they remain part of the same network or LAN.
It is recommended that you connect no more than 50 of our ⅛ or ½-load devices on all BACnet MS/TP
Data Bus repeater segments when a baud rate of 19 200 or higher is used (preferably 38 400 baud).
This is to ensure that the BACnet MS/TP Data Bus has enough bandwidth to efficiently communicate
network variables between controllers.
Do not use more than two repeaters on a BACnet MS/TP data bus.
A repeater can only connect two BACnet MS/TP data bus segments even if it has ports to support more than two
BACnet MS/TP data bus segments.
A repeater can be added anywhere to a data bus segment including the end of the segment as shown
below.
END
EOL ON
EOL Externally Set
ECLYPSE
Figure 101: Using a Repeater to Extend the Range of the LAN
BACnet MS/TP Communication Data Bus Fundamentals
Содержание ECLYPSE APEX
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