Beijer-electronics T15BR EN Manual de usuario descargar pdf (Pagina 27)

Additional Installation Tips

6.7 CableandBusTerminationRS485

• Use shiel ded and twisted pair cable. The pair c apacitance may not exceed

52.5 pF/m and area at least 0.25 mm

(AWG 24), if you want to use the

maximum transfer distance and maximum transfer speed.

• 0 V, the reference voltage for communication should be includ ed in

the cabling. With two-way communication use two pairs; one pair for

communication and one pair for 0 V.

• The shield mus t be grounded at one end. The other end is usually grounded,

but with longer distances or when there is a difference in the ground potential,

theshieldshouldbeconnectedtothegroundvia0.1μF/250Vplastic

capacitor to prevent ground current in the braided shield. A number of

manufacturers recommend that the shield be grounded at each node. Various

manufacturers have different systems for bus termination.

Depending on the recipients’ design, the bus wires may be on the same level or

require pull-up or pull-down to ensure that no faulty signals are detected w hen the

bus is in resting mode (all transmitters are disconnected).

6.8 COMPortCommon-ModeVoltage

The COM port I/Os have special restrictions for common-mode voltage with

respect to ground.

COMPort MaximumCommon-ModeVoltageRange

COM1 - RS232 -15 V to+15 V

COM2 - RS422/RS485 -7 V to+7 V

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Beijer-electronics T15BR EN Manual de usuario Pagina 27