22 IM805 Operating Instructions Revision R032306
23
IM805 Operating Instructions Revision R032306
S e l e c t i n g a n O p t o S u p p l y
R u l e s o f W i r i n g a n d S h i e l d i n g
Noise is always present in a system that involves both high power and
small signal circuitry. Regardless of the power configuration used for your
system, there are some wiring and shielding rules that should be fol-
lowed to keep the noise-to-signal ratio as small as possible.
R u l e s o f W i r i n g
n
Power supply and motor wiring should be shielded twisted
pairs run separately from signal carrying wires.
n
A minimum of 1 twist per inch is recommended.
n
Motor wiring should be shielded twisted pairs using 20-
gauge wire or, for distance greater than 5 feet, 18 gauge or
better.
n
Power ground return should be as short as possible to estab-
lished ground.
n
Power supply wiring should be shielded twisted pairs. Use
18 gauge wire if load is less than 4 amps, or 16 gauge for
more than 4 amps.
n
Do not “Daisy-Chain” power wiring to system components.
R u l e s o f S h i e l d i n g
n
The shield must be tied to zero-signal reference potential.
In order for shielding to be effective, it is necessary for the
signal to be earthed or grounded.
n
Do not assume that earth ground is true earth ground. De-
pending on the distance to the main power cabinet, it may be
necessary to sink a ground rod at a critical location.
n
The shield must be connected so that shield currents drain
to signal-earth connections.
n
The number of separate shields required in a system is equal
to the number of independent signals being processed plus
one for each power entrance.
n
The shield should be tied to a single point to prevent ground loops.
n
A second shield can be used over the primary shield, how-
ever, the second shield is tied to ground at both ends.
R e c o m m e n d e d P o w e r S u p p l y C a b l e s
Power supply cables must not run parallel to logic level wiring as noise
will be coupled onto the logic signals from the power supply cables. If
more than one driver is to be connected to the same power supply, run
