FCO770 Users Guide Issue 1
Page 17
W
W
i
i
r
r
i
i
n
n
g
g
C
C
o
o
n
n
s
s
i
i
d
d
e
e
r
r
a
a
t
t
i
i
o
o
n
n
s
s
Electrical Interference
Ignition transformers, arc welders, mechanical contact relays and solenoids are all common
sources of electrical noise in an industrial environment and therefore the following guidelines
must be followed:
Noise generating devices such as those listed should be mounted in a separate enclosure. If
this is not possible, separate them from the instrument by the largest distance possible.
Provide separate cable runs for communication lines, inputs and outputs. If they run parallel,
there should be as much separation between the groups as possible.
RS232 and RS485 connections must use shielded cable. This will reduce the level of
electrical noise induction on the wires. Lead lengths should be kept to a minimum. The shield
should be grounded at one end only.
Inductive loads
When inductive loads such as relays or solenoids are switched off, they can produce a very
large negative voltage spike (over a thousand volts!). If the cable feeding the inductive load is
bundled with other cables, the voltage can be induced into the other cable and can cause
unpredictable results. It is very important that any inductive load is suppressed to prevent
these voltages being generated.
The transistor outputs from the FCO770 are fitted with suppression diodes and it is not
necessary to add further suppression to the inductive load. However, if an inductive load is
being activated from a PLC or another relay, then suppression must be fitted. This is usually
achieved by fitting a diode in parallel with the load as shown.
DC (-)
DC (+)
PLC output
or relay contact
Inductive load
Protection diode
(Typically 1N4003)
Summary of Contents for FCO770
Page 2: ......
