Flowserve MX-100 Field Unit - Manual (Page 13)

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MX/DDC-100 Field Unit Installation and Maintenance FCD LMENIM2329-01 – 03/11
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Belden 3105A Specifications
Total cable length between repeaters or nodes with repeaters, up to 19.2 kbps: 4500 ft (1.37 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 4500 ft
(1.37 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 = 22 AWG (7 x 30) 14.7 ohms each conductor (29.4 ohms for the pair) •
Capacitance/ft = 11.0 pF (conductor-to-conductor) •
Capacitance/ft = 20.0 pF (conductor-to-shield) •
Belden 9841 Specifications
Total cable length between repeaters or nodes with repeaters: up to 19.2 kbps: 3500 ft (1 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 3500 ft (1 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 = 24 AWG (7 x 32) 24 ohms each conductor (48 ohms for the pair) •
Capacitance/ft = 12.8 pF (conductor-to-conductor) •
Capacitance/ft = 23 pF (conductor-to-shield) •
2.3 Software
2.3.1 Modbus Protocol
The Modbus protocol was developed by AEG Modicon ® for communicating to various networked devices. The
relationship between these devices and a central controller is called a master-slave relationship in which the master
(host device) initiates all communication. The slave devices (DDC-100 field units in the actuators) respond to the
queries from the master.
Modbus only permits one device to communicate at any given time (simultaneous communication is prohibited) to
ensure process control integrity.