Contemporary-control-systems USB222 Adapters Instrukcja Użytkownika Pobierz pdf (Strona 6)

TD040900-0II

-4000 AC-Coupled EIA-485

The AC-coupled EIA-485 transceiver offers advantages over the DC-

coupled version. No bias adjustments are needed and wiring polarity is

unimportant. Much higher common mode voltage levels can be achieved

with AC coupling because the transformer coupling has a breakdown

rating of 1000 VDC.

However, AC-coupling also has disadvantages. AC-coupled segments

are shorter (700 feet max) and are limited to 13 nodes compared to 17 for

DC-coupling. Also, AC-coupled transceivers operate only at 1.25, 2.5,

5.0 and 10 Mbps, whereas DC-coupled transceivers function over all

standard data rates.

Two models support AC-coupled EIA-485 segments. The USB22-4000

provides dual RJ-45 jacks, whereas the USB22-4000/S3 offers a 3-pin

screw terminal.

Cabling rules are similar to those for DC-coupled NIMs. Wire nodes in a

daisy-chain fashion. Refer toFigure 1 Figures 1 and 2 for connector pin

assignments. Termination should only be applied to devices located at

the two ends of the segment. Do not mix AC-coupled and DC-coupled

devices on the same segment; however, bridging the two technologies is

possible with active hubs that have appropriate transceivers.

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Contemporary-control-systems USB222 Adapters Instrukcja Użytkownika Strona 6