Ebtron GTC116 Installation Manual - Ebtron
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4.2 GTC116 ‐ RS‐485 NETWORK WIRING CONNECTIONS
4.2.1 GTC116 ‐ RS‐485 Network Cable Specifications
The RS‐485 network cable shall be shielded twisted pair with a characteristic impedance of 100 to 130 ohms.
Distributed capacitance between conductors shall be less than 100 pF per meter. Distributed capacitance between
conductors and shield shall be less than 200 pF per meter. The maximum recommended length of a network
segment is 1200 meters with AWG 18 cable.
4.2.2 GTC116 ‐ Connecting to an RS‐485 Network:
Connect the NET+, NET‐ and COM terminals with shielded twisted pair cable meeting the specifications defined in
the previous paragraph (typically using two pairs; one pair for +/‐ and (at least one of) the wires in other pair for
COM when using 2‐pair cable). The connection to the network must be made in a "daisy chain” configuration. "T"
connections and stubs are NOT permitted. The shield should be terminated at one end on the network only.
*CAUTION
For ISOLATED output, the COM connection MUST BE CONNECTED to the network common for proper
operation. In addition, when the Analog Output is concurrently used with the RS‐485 Output, the Common
connection for both Analog and RS‐485 Outputs must be at the same potential.
For NON‐ISOLATED output, the COM connection MUST BE CONNECTED to the common ground that is used
by the other network devices (typically the ground side of the 24VAC supply; terminal L2 at the POWER
connector block in Figure 6). In addition, when the Analog Output is concurrently used with the RS‐485
Output, the Common connection for both Analog and RS‐485 Outputs must be at the same potential.
4.2.3 GTC116 ‐ Setting Transmitter Termination for RS‐485 Network
The GTC116 is shipped with the Termination switch set for No termination, which is the recommended setting
for devices installed on the network bus anywhere EXCEPT at the ends of the bus/segment. EBTRON
recommends the following termination strategy for devices connected at the ends of the network
bus/segment:
When the transmitter is at one end of the network, it should be terminated with “End of Line” (or 120 ohm
standard) termination, and the device at the other end should be terminated with “Fail Safe Bias”
termination. This method provides proper network termination and ensures that the bus is in a known state
during idle-line conditions (when no devices are driving the bus). EBTRON GTC116 transmitters include
three termination options for “End of Line” (standard 120 ohm) and “Fail-safe Bias” (recommended at one
end of the bus) or for “No Termination”. Termination is selected by setting TERMINATION DIP switch SW3 as
shown below.
Check the network/network segment to ensure that only one device is terminated with either method. If multiple devices
are terminated as described above, network segment operation will be adversely affected.
4.3 GTC116 ‐ Transmitter Setup for RS‐485 Network Operation
For RS-485 operation, network connections are made on the GTC116 Combination board as shown in Figure
6, and set up is as follows. Network protocol, MS/TP address, device instance number and baud rate options
are all selected with- in the NETWORK section of SETUP menu shown in Appendix A.
NOTE:
Prior to power up, network configuration and termination switches must be set as shown in Figure 6.
Wiring to the RS-485 network is accomplished after setting the GTC116 network configuration switches.
4.3.1 GTC116 ‐ RS‐485 Network Options and Communications Menu Settings
The transmitter is shipped from the factory with the protocol set for BACnet MS/TP Master, address 2, MS/TP
Device ID
2, Baud rate of 76,800 and no termination. Initial RS-485 communications settings are
accomplished within the
GTC116 NETWORK sub menu shown in Appendix A. Termination is set up by the
TERM DIP switch SW3 located on the
Combination card shown in Figure 6.
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