Flowserve MX-100 Field Unit - Manual (Page 35)

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MX/DDC-100 Field Unit Installation and Maintenance FCD LMENIM2329-01 – 03/11
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3.1.2.2 Network Cable Connection to Host Controller or Master Station II
Two network topologies are commonly used and supported for the MX:
Redundant bi-directional loop (recommended) •
Daisy chain •
Redundant Bi-Directional Loop
The redundant bi-directional loop topology requires two serial communication ports on the host device.
Each field unit can be accessed by two host/master ports. •
The connections from the serial ports to the field units and connections between field units are made with •
shielded, twisted-pair cable in a loop configuration.
A single line break or short can occur while maintaining communication to all field units.
• Figure 3.8 shows the
redundant bi-directional loop network topology for a direct-to-host connection.
The redundant bi-directional loop topology is wired as follows: see Figure 3.8.
1. Connect the host device port 1, through an RS-232 to RS-485 converter if required, to the first field unit port
A1 at MX terminal block numbers 4 and 5.
2. Connect the port A2 at MX terminal block numbers 14 and 13 to the next field unit’s port A1.
3. Each subsequent field unit is connected in the same manner – receiving data through its port A1, then passing
the data out through its port A2 to the next field unit.
4. The last field unit’s port A2 is connected to the host device’s port 2. The host device should be configured to
ignore messages that it sends out when it returns to its other port.
The direction of data flow can be reversed because of the bi-directional capability of the serial ports.
a. Communications can be initiated by connecting host port 2 to first field unit port A2.
b. Port A1 of the first field unit is then connected to port A2 of the next field unit.
c. Port A1 of the last field unit is then connected to host port 1.
In either direction, the signal is regenerated in each field unit to permit long-distance communication with reduced
noise sensitivity and improved reliability.