Siemens PC 670 Using the Computing Unit in a Simatic S5 Network, Point-to-point connection, Rules

Connecting and Switching on the Computing Unit Release 04/02

3.7Using 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:

Sa V.24 connection

Sa 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.

SThe shorter the data transmission link, the higher the maximum possible transfer rate.

SIf 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.

SSignal 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).

SThe 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.

3-18 Panel PC 670 Computing Unit, Equipment Manual