12
Installation Hints for Best Performance
This section offers several suggestions which will help you get the best performance from
your system.
RS232 and RS485 use comparitively small signals which can easily be corrupted by the
potentially high level of electrical noise which can be created by electrical machinery such as
motors, welding systems, discharge lighting, AC power inverters and solenoids. These steps
will ensure you get the best possible performance from your system.
RS232 has limited capability over long cable distances, due its low driving power (which
causes the signal to reduce in level as cable length increases) and single ended signal (which
is prone to interference by local electrical noise) , as shown below.
Maximum recommended cable distances if using LOW
capacitance screened cable such as CAT5 cable:
Baud Rate
RS232
RS485 or RS422
1200
50 m (164 ft)
1200 m (3900 ft)
9600
20 m (66 ft)
150 m (500 ft)
19200
10 m (33 ft)
75 m (250 ft)
38400
5 m (16.4 ft)
30 m (100 ft)
115200
2 m (6.6 ft)
10 m (33 ft)
1.
Use good quality screened signal cable, with twisted pairs. Screened twisted pair
CAT5 cable is ideal. The screen should be earthed at the display end only.
2.
If you are using multi-pair twisted cable, each pair should be dedicated to a single
display as shown opposite, for maximum noise immunity.This will ensure that any
electrical noise induced in the cable is properly cancelled. Mixing destinations
carelessly amongst the twisted pairs can easily corrupt data.
3.
The cable should be routed away from noisy wiring and devices such as power
feeds from inverters, discharge-lighting cables, welder cabling etc, and should
preferrably be routed in a dedicated low voltage signalling/instrumentation conduit
or cable tray.
4.
If you want to simulate data, a useful free terminal, with good flexibility is
RealTerm, available from http://sourceforge.net/projects/realterm/
Connect screen
to earth ONLY
at this end.
Do not
connect
screen at
this end.
Length of screened cable
Clean Earth
Signal Input
Logic Input
Power Input
Display connections
Sender connections
RS232 or
RS485
transmitter
