Future Design MCTB 4.3, User Manual

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MCTB
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3.2.1 Process Loop/Limit Controller Communications
The loop/limit controls communicate with the MCTB touch screen using the RS485 communications port. This
allows up to three B42 boards (or two B42 boards and one L41 limit control) to be connected using one 2-wire
link. The controllers are wired in parallel with each one having their own communications address of 1, 2 and
3 (corresponding to loops 1, 2 and 3 or loops 1, 2 and L41 limit).
Communication wiring should be run using a minimum of 24 AWG twisted-pair, copper conductors. For short
runs (< 10 feet total), non-shielded wiring can be used as long as proper separation from power/control
conductors is maintained. For communications wiring where the total length will exceed 10 feet, shielded
twisted-pair should be used.
NOTE:
It is important to keep the power/control and sensor/communications wiring separated from one
another. Relay and/or high voltage outputs can interfere with the sensor and communication wiring
as they cycle on and off, which can cause erroneous sensor readings or communications errors.
FDC recommends the use of shielded wire for all installations in order to maintain optimum
performance and minimize the possibility of communications errors.
When using shielded twisted-pair, be sure to ground only one end of the cable, preferably at the loop controller.
Allowing any other portion of the cable shield to come in contact with ground, or grounding both ends, will cause
ground loop currents to flow in that section of the cable shield which can disrupt communications.