Siemens PC 670 Manuel d'utilisateur télécharger pdf (Page 52)

Connecting and Switching on the Computing Unit

Release 04/02

3-18

Panel PC 670 Computing Unit, Equipment Manual

3.7 Using the Computing Unit in a SIMATIC S5 Network

Point-to-point connection

This section describes the options for connecting your computing unit to a

programming unit or an S5 programmable controller in a point-to-point connection.

A point-to-point connection is possible by connecting the computing unit to another

programming unit or a PLC via:

S a V.24 connection

S a TTY connection

Configuring notes for interfaces with current loop (TTY, 20 mA)

Different criteria have to be taken into account for reliable operation of a

connection. The maximum data transfer rate (baud rate) depends on the required

distance, the type of cable, the pin assignment of the interface and external

interference.

Rules

To reduce interference by a favorable choice and correct connection of the

cable, you should comply with the following rules:

S The shielded cable used must have a low line resistance

(< 130 W / km) and a low capacitance (< 90 pF/ m). Twisted-pair cables are less

susceptible to inductive interference. A low line resistance result in reduced voltage

excursions and shorter charge reversal times; the line resistance decreases with

increasing conductor cross-section for the same length of cable.

S The shorter the data transmission link, the higher the maximum possible transfer

rate.

S If there is an active transmitter and an active receiver at the same end of the

transmission link, the sequence of access priority to the transmission circuit must

be taken into account in order to achieve the longest possible transmission link.

S Signal lines and power lines must not be run together. Signal lines must be installed

as far away as possible from sources of strong interference (for example, 400 V

3-phase power cables).

S The active TTY interface with a 12 V open-circuit voltage has been tested on a

100 m long cable at a transmission rate of 9600 bps in an environment with normal

levels of noise (field strength < 3 V/ m). If a LiYCY 5 x 1x 0.14 shielded cable is

used, reliable transmission is possible over a distance of up to 100 m. The AS511

driver was used for testing (only one transmitter at a time).

Note

The interference field of the source of interference is reduced by the square of the

distance.

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Siemens PC 670 Manuel d'utilisateur Page 52