Contemporary-control-systems AI Active Hubs Uživatelský manuál stáhnout pdf (Strana 21)

TD675100-0MJ

For EIA-485 DC operation, it is very important that all devices

on the wiring segment be referenced to the same ground

potential in order that the common mode voltage requirement

(+/–7 Vdc) of the EIA-485 specification is achieved. This can

be accomplished by running a separate ground wire between all

AIs and computers (pin SH has been provided for such a

connection on the AI) or by relying upon the third wire ground

of the power connector assuming that the DC power return is

connected to chassis ground on all computers (this is the case

with the AI). Another approach would be to connect the DC

common of each computer to a cold water pipe. Connected

systems, each with different elevated grounds, can cause

unreliable communications or damage to the EIA-485

differential drivers. Therefore, it is important that an adequate

grounding method be implemented.

Figure 2-10. Each -485 hub port has provisions for

applying bias and termination. Make sure common mode

voltage (Vcm) does not exceed +/–7 Vdc.

In summary, segments of -485 (-485D) connected NIMs can be

extended through the use of active hubs. Select an AI model

with a -485 compatible port. Connect one end of the segment to

this port following the same termination rules as used for a

+5V

PIP2

TXEN

RXIN RXIN

TXEN

PIP2

Vcm

SH SH

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Contemporary-control-systems AI Active Hubs Uživatelský manuál Strana 21