Optelecom 9482-DR, Инструкция по установке и эксплуатации

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RS485 duplex 2- and 4-wire can be configured as “one- to-one“ or “one-to-many” as RS485 systems allow up
to 32 devices to be daisy-chained together in one electrical system. Markings on RS485 devices vary,
sometimes being marked the same as RS422 systems in 4-wire connection modes or marked as TD+, RD+,
TD–, and RD–. Normally the A and – signals are the – signals and the B or + signals are the + signals. In
2wire systems, there will only be a + and – signal. Care should be taken to insure the last device in a daisy
chain is terminated. Refer to the example drawings at the end of this section for examples.
Many manufacturers mark their equipment differently; read the accompanying instructions
carefully. A misunderstanding of the terminal markings and functions on data communications devices
causes most problems with data connections.
G
ROUNDING AND
S
HIELDS
The common ground/signal ground on the TKH Security USA equipment is also chassis ground. The ground
connection is required on both ends of an electrical connection when RS232 is used. Both the Tx (the output)
and Rx (the input) signals are single-ended connections (unbalanced) and are referenced to signal common.
In RS422 and RS485, the shield wire in the cable is to protect the cable from noise and electrical interference;
the + and – signals on the cable are differential (balanced) and do not require the ground be connected at
both ends. It is generally accepted practice to connect them both, however, better noise immunity may be
obtained by connecting the shield only at the end closest to true earth ground. This may also eliminate
ground loop electrical problems as well. If noise problems are encountered in a data transmission system
when RS422 or RS485 are used, try disconnecting the shield at the camera end of the data link.
E
XAMPLES OF
D
ATA
C
ONNECTIONS TO
9482D
T AND
DR
F
IGURE
5
—
D
ATA
P
ORT
1 RS232 C
ONNECTIONS