Flowserve MX-100 Field Unit - Manual (Page 12)

MX/DDC-100 Field Unit Installation and Maintenance FCD LMENIM2329-01 – 03/11
12
2.2.5 Network Cable
The network consists of a shielded, twisted-pair cable that connects all field units and the host/Master Station II. The
cable is normally connected in a loop fashion so that any single break or short will not disable communication.
Figure 2.5 – Redundant connection operation in redundant host loop topology
The network cable connects the field units to the host controller or Master Station II. Belden 3074F, 3105A, or 9841
shielded, twisted-pair cable should be used. The use of other cables may result in a reduction of internodal distances
or increased error rate, and is the user’s responsibility.
Belden 3074F Specifications
Total cable length between repeaters or nodes with repeaters, up to 19.2 kbps: 5000 ft (1.52 km) For loop •
mode, this is the total length between operating field units. If a field unit loses power, then the relays internal
to the field unit connect the A1 Channel to the A2 Channel, which effectively doubles the length of the cable
(assuming a single field unit fails). To ensure operation within specifications in the event of power failure to
field units, this consideration must be added. Example: To ensure operation within specification when any two
consecutive field units lose power, the maximum length of cable, up to 19.2 kbps, should not exceed 5000 ft
(1.52 km) per every four field units. See Section 3.1.2.3, Network Cable Connection to Host Controller or
Master Station II.
Key Specifications
Resistance/1000 ft = 18 AWG (7 x 26) 6.92 ohms each conductor (13.84 ohms for the pair) •
Capacitance/ft = 14 pF (conductor-to-conductor) •
Capacitance/ft = 14 pF (conductor-to-shield) •
Signal initiated from host fails to reach
field unit which is located after fault... Instead, signal routes to field unit using
other side of the loop cable and
completes connection.