4
INSTALLATION GUIDELINES FOR REDUCED NOISE INTERFERENCE
I. General Comments
SLO-SYN Micro Series drives use modem solid-state electronics such
as microprocessors to provide the features needed for advanced
motion control applications. In some cases, these applications pro-
duce electromagnetic interference (EMI, or electrical “noise”) that
may cause inappropriate operation of the microprocessor logic used
in the Micro Series product, or in any other computer-type equip-
ment in the user’s system.
This guide is aimed toward helping users avoid such problems at the
start by applying “good engineering practices” when designing their
systems. Following these guidelines will usually prevent EMI noise
from interfering with drive operation.
II. Noise Sources
What causes electrical noise? In general, any equipment that causes
arcs or sparks or that switches voltage or current a high frequencies
can cause interference. In addition, ac utility lines are often “pol-
luted” with electrical noise from sources outside a user’s control (such
as equipment in the factory next door).
The following are some of the more common causes of electrical
interference:
•
power from the utility ac line
•
relays, contactors and solenoids
•
light dimmers
•
arc welders
•
motors and motor starters
•
induction heaters
•
radio controls or transmitters
•
switch-mode power supplies
•
computer-based equipment
•
high frequency lighting equipment
•
dc servo and stepper motors and drives
III. Mounting Location
When selecting a mounting location, it is preferable to keep the drive
away from obvious noise sources, such as those listed above. If
possible, locate the drive in its own metal enclosure to shield it and
its wiring from noise sources. If this cannot be done, keep the drive
at least three feet from any noise sources.
IV. Wiring Practices - “Dos and Don’ts”
Do
the following when installing or wiring your drive or indexer:
•
Do
keep the drive and its wiring as far away; from noise sources
as possible
•
Do
provide a good, solid ground connection to the ac system earth
ground conductor. Bond the drive case to the system enclosure.
•
Do
use a single-point grounding scheme for all related compo-
nents of a system (this looks like a “hub and spokes” arrange-
ment).
•
Do
keep the ground connection short and direct.
•
Do
use a line filter on the ac input (Corcom type 10B1, 10S1 or
10K1 or equivalent) for noisy ac lines. Particularly bad ac lines
may need to be conditioned with a ferroresonant type isolation
transformer to provide “clean” power to the drive or indexer.
•
Do
keep signal and drive wiring well separated. If the wires must
cross, they should do so at right angles to minimize coupling. Power
wiring includes ac wiring, motor wiring, etc. and signal wiring in-
cludes inputs and outputs (I/O), serial communications (RS232
lines), etc.
•
Do
use separate conduits or ducts for signal and I/O wiring. Keep
all power wiring out of these signal line conduits.
•
Do
use shielded, twisted-pair cables for indexer I/O lines.
•
Do
ground shields only at one end, the indexer/drive end.
•
Do
use twisted-pair, shielded cable for the motor wiring.
•
Do
use solid-state relays instead of electromechanical contact
types wherever possible to minimize noise generation.
•
Do
suppress all relays to prevent noise generation. Typical sup-
pressors are capacitors or MOV’s. See manufacturers literature
for complete information.
•
Do
use shielded, twisted-pair cable for connection to RS232 se-
rial port.
Do Not
do the following when installing your drive or indexer:
•
Do not
install sensitive computer-based equipment (such as an
indexer/drive) near a source of electromagnetic noise.
•
Do not
bundle power and signal lines together.
•
Do not
bundle motor cables and signal lines together.
•
Do not
fail to use shielded, twisted-pair cables for signals.
•
Do not
fail to properly connect the system grounds.
•
Do not
use “daisy-chained” grounds.
•
Do not
fail to ground signal cable shields at only one end.
•
Do not
assume that power from the ac line is adequately “clean”.
V Troubleshooting Guide
Electrical interference problems are common with today’s computer-
based controls, and such problems are often difficult to diagnose
and cure. If such a problem occurs with your system, it is recom-
mended that the following checks be made to locate the cause of the
problem.
1. Check the quality of the ac line voltage using an oscilloscope
and a line monitor, such as Superior Electric’s VMS series. If line
voltage problems exist, use appropriate line conditioning, such
as line filters or isolation transformers.
2. Be certain all of the previous Dos and Don’ts are followed for
location, grounding, wiring and relay suppression.
3. Double check the grounding connections to be sure they are good
electrical connections and are as short and direct as possible.
4. Try operating the drive with all suspected noise sources switched
off. If the drive functions properly, switch the noise sources on
again, one at a time, and try to isolate which ones are causing
the interference problems. When a noise source is located, try
rerouting wiring, suppressing relays or other measures to elimi-
nate the problem.
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