Siemens Simatic 620 - Manual (Page 53)

Setting Up and Operating the SIMATIC Box PC 620
3-19
SIMATIC Box PC 620 Manual
A5E00131465-01
3.6 Connecting the SIMATIC Box PC 620 to other SIMATIC S5
Point-To-Point Connection
In this section, you will learn how to connect your SIMATIC Box PC 620 to a
programming device or S5 programmable logic controller using a point-to-point
connection.
You can stablish a point-to-point connection by connecting the
SIMATIC Box PC 620 to another programming device or a programmable logic
controller using
S A V.24 connection
S A TTY connection (optional product feature)
Configuring Interfaces with Line Current (TTY, 20 mA)
To ensure reliable data transfer, several factors must be taken into account. The
maximum data transfer rate (baud rate) depends on the distance, the type of
cable, the pin assignment of the interface and external interference.
You can reduce interference by choosing the right transmission cable and
connecting it properly, and by observing the following guidelines:
S Use a shielded cable with a low line resistance (130 W / km) (about 40 W kft)
and low capacitance (< 90 pF/m) (about 27 pF/ft). Twisted-pair cables are less
susceptible to noise and interference. A low line resistance results in reduced
voltage excursions and shorter charge reversal times. The line resistance de-
creases with increasing conductor cross-section for the same length of cable.
S The shorter the transmission link, the higher the maximum possible data
transfer rate.
S If there is an active sender 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 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 no-load voltage has been tested on a 100
m (1100 ft) long cable at a transmission rate of 9600 bps in an environment with
normal levels of noise fieldstrengthV/mor1V/ft).If a shielded 5 x 1 x 0.14shielded
cable is used, reliable transmission is possible over a distance of up to 100 m
(1100 ft). The AS511 protocol (only one transmitter at a time) was used for
testing.
Note
The interference field of the source of interference is reduced by the square of the
distance.