Brochure/Catalogue
Surge protection fundamentals for data signals
Surge protection for data interfaces
The principles of data transmission
RS 232
Serial interface for point-to-point
connections up to 20 kbit/s
Voltage signal to earth:
logic 1 (mark) -15 V to -3 V
logic 0 (space) +3 V to +15 V
max. signal level ±15 V
Lines up to 20 m long depending
on transmission rate.
RS 232
Protection module in
terminal housing
VSSC 6 / RS232 Page D.14
RS 422
Serial uni-directional high-speed interface
for up to 10 parallel receivers
Differential voltage signal:
logic 1 (mark) A-B < -0.3 V
logic 0 (space) A-B > +0.3 V
max. signal level ±12 V
Lines up to 1200 m long
max. data rate 10 Mbit/s
RS 422
Protection module in
plug-in housing
VSPC / RS485 Page D.8
RS485
Serial bi-directional high-speed
interface for up to 32 subscribers
2- or 4-wire system
Differential voltage signal:
logic 1 (mark) A-B < -0.3 V
logic 0 (space) A-B > +0.3 V
max. signal level -7 V to +12 V
Lines up to 1200 m long
max. data rate 10 Mbit/s
RS485
Protection module in
plug-in housing
VSPC / RS485
VSPC / RS485 R
Protection module in
terminal housing
VSSC 6 / RS485
VSSC 6 / RS485 DP
Page D.8
Page D.10
Page D.14
COAX
Protective module for
BNC- and N-cables
Protective module for
F- and UHF-cables
Page D.18
Page D.19
Electrical system
MSR
0
1
2
3
4
5
SURGE PROTECTION
SURGE PROTECTION
SURGE PROTECTION
“Data transmission” is the name
given to the sending of characters,
numbers, statuses and measurements
between different, decentralised units.
Decentralised units are, for example,
controls, computers, measuring
sensors, actuators, etc. One unit
transmits the data, the second unit
receives it. This corresponds to the
simplest method of data transmission.
It is often necessary for one unit to
receive data and then send an “answer”
back to the other unit. Two data lines
in a back-to-back arrangement are
required for this, or data lines are
combined by providing each end of the
data line with a transmitter and receiver.
Structures and properties of
networks
There are various options for networking
data terminals. We distinguish between
star, ring, point-to-point and bus
networks.
Star networks
The main unit is located in the centre.
The individual data lines then radiate
out from this centre to the individual
terminals. In this system all data
terminals are connected to the central
terminal via their own cable.
Ring networks
The computers or data terminals are all
connected to each other like a chain by
means of, for example, coaxial cable.
In this case the data is passed on
from one data terminal to the next.
Therefore, the entire ring is always
under load. The advantage of the ring
network is that it can cover a larger
area than a star network because the
length of the transmission path is
only ever the distance between two
adjacent data terminals.
Point-to-point networks
These are basically networks between
two data terminals that are connected
directly with each other, e.g. an RS 232
or RS 422 link.
Bus networks
These are networks based on the
parallel connection of modules. All
components operate on one and the
same line. Therefore, only two/four
wires are required for the data bus. If
bus cabling includes branches, then
we call that a tree structure. Every bus
system includes a bus controller that
issues “transmission licences” to the
individual data terminals.
Transmission media
In order to be able to send any data at
all, data lines are necessary:
Two- and three-wire systems
Data transmissions requiring relatively
low transmission rates can make use
of two-wire systems. For example, an
ISDN system acting as an exchange
line to a building requires only two
wires.
However, there are bus systems which
also require only two or three wires.
Four-wire systems
This is the current standard for the
majority of corporate data networks.
Two wires are used for transmitting
data and two for receiving. These
cables are well shielded and can
transmit data with frequencies of up
to 500 MHz over distances of up to
100 m.
Coaxial cable
Sending data via coaxial cables is a
rather old technique. This method is
too slow and inexible and only a few
businesses are still using such systems.
Speeds of up to 12 Mbps are no longer
adequate these days. Over longer
distances, modern bre-optic cables
have been replacing this technology;
these can transmit several hundred
Mbps.
Serial interfaces
A serial interface operates with 8 data
bits (1 byte). A start bit (low bit) is
always sent before the output of a byte,
and one or two stop bits (high bits)
are appended to the end of the byte.
This encryption is critical for the data
receiver as it can then detect where
each data byte begins and ends. Serial
interfaces frequently operate with
+5 V (logical 1) and 0 V (logical 0).
Advantage: less cabling (only 3 wires).
Disadvantage: slow data transmission.
D
D.2 2028840000
Lightning and surge protection
for data interfaces