Technical data
www.westermo.com Theoretical and general applications 5
Data communication is extremely important
in order to increase productivity ......................................................................................................................................................... 24–55
Interface ...........................................................................................................................................................................................................................................
24
The most common interfaces
..............................................................................................................................................................
24–25
Signals in V.24/RS-232-C ................................................................................................................................................................................... 25
Cable configuration ..................................................................................................................................................................................................
26
Key to the most important signals
............................................................................................................................................................ 27
ASCII
....................................................................................................................................................................................................................................................
28
Industrial interfaces ............................................................................................................................................................................................... 29–30
RS-422
.......................................................................................................................................................................................................................................
29
RS-422 on 4-wire
.........................................................................................................................................................................................................
29
RS-485
.......................................................................................................................................................................................................................................
29
Termination and Fail-Safe
................................................................................................................................................................................ 30
Polarity
....................................................................................................................................................................................................................................... 30
RS-232/V.24 to RS-422/485 converter – RTS support
....................................................................................... 30
Installation of RS-422 and RS-485
.................................................................................................................................................
31–32
General recommendations for installation ............................................................................................................................. 31
Range and short-haul modems .............................................................................................................................................................. 31
20 mA current loop (TTY)
.........................................................................................................................................................................
31
10 mA balanced current loop (W1) ............................................................................................................................................. 32
Consequently the 10 mA balanced current loop
is less sensitive to external sources of interference
.................................................................................................. 32
Network
.............................................................................................................................................................................................................................. 33–34
Topology .............................................................................................................................................................................................................................. 35–36
Serial point to point
............................................................................................................................................................................................... 35
Star network
.....................................................................................................................................................................................................................
35
Ring network
....................................................................................................................................................................................................................
35
Bus network ....................................................................................................................................................................................................................... 36
Combined network
................................................................................................................................................................................................ 36
Mesh network .................................................................................................................................................................................................................
36
The Problem of Interference ................................................................................................................................................................. 37–42
Lightning, machinery and fluorescent lamps
............................................................................................................. 37–38
Overvoltage protection and lightning protection
............................................................................................
38–39
Earth Loops
........................................................................................................................................................................................................................
39
Reducing Interference .......................................................................................................................................................................................... 40
Balanced Signals
............................................................................................................................................................................................................ 40
Isolation ....................................................................................................................................................................................................................................
40
Ground networks ......................................................................................................................................................................................................
41
Shielding
...................................................................................................................................................................................................................................
41
Short Connections without a modem ........................................................................................................................................ 41
Telecom modems and interference
................................................................................................................................................. 42
Fibre cable
............................................................................................................................................................................................................................ 42