Watlow Series 94 - Manual (Page 25)

W a t l o w S e r i e s 9 4 A p p e n d i x ■ A . 1
Appendix
Noise and Installation Guidelines
For wiring guidelines, refer to the IEEE Standard No. 518-1982, available
from IEEE, Inc. 345 East 47th Street, New York, NY 10017.
Noise Sources
• Switches and relay contacts operating inductive loads such as motors,
coils, solenoids, and relays, etc.
• Thyristors or other semiconductor devices which are not zero crossover-
fired (randomly-fired or phase angle-fired devices).
• All welding machinery and heavy current carrying conductors.
• Fluorescent and neon lights.
Decreasing Noise Sensitivity
• Physical separation and wire routing must be given careful consideration
in planning the system layout. For example, ac power supply lines should
be bundled together and physically kept separate from input signal lines
(sensor lines). A 12" (305 mm) minimum separation is usually effective.
Keep all switched output signal lines (high power level) separate from
input signal lines (sensor lines). Cross other wiring at 90° angles whenev-
er crossing lines is unavoidable.
• Look at the system layout; identify and locate electrical noise sources such
as solenoids, relay contacts, motors, etc. Route the wire bundles and cables
as far away as possible from these noise sources. Don't mount relays or
switching devices close to a microprocessor control. Don't have phase
angle-fired devices in the same electrical enclosure or on the same power
line with the control.
• Shielded cables should be used for all low power signal lines to protect
from magnetic and electrostatic coupling of noise. Some simple pointers
are:
◊
Whenever possible, run low level signal lines unbroken from signal
source to the control circuit.
◊
Connect the shield to the control circuit common at the control end only.
Never leave the shield unconnected at both ends. Never connect both
shield ends to a common or ground.
◊
Maintain shield continuity at daisy chain connection points by recon-
necting the broken shield.
◊
Assume no electrostatic shielding when using the shield as a signal
return. If you must do this, use triaxial cable (electrostatically shielded
coaxial cable).
A
Appendix