Eliminating Noise - Watlow 945 Series User Manual

• Twisted pair wire should be used any time control circuit signals must travel over
two feet, or when they are bundled in parallel with other wires.
• Select the size or gauge of wire by calculating the maximum circuit current and
choose the gauge meeting that requirement. Using larger wire sizes than
required generally increases the likelihood of electrostatic (capacitance) coupling
of noise.
• Eliminate ground loops in the entire control system. You can spot the obvious
loops by studying the "as-built" wiring diagram. There are also not-so-obvious
ground loops resulting from connecting internal circuit commons in the
manufacturer's equipment.
• Do not daisy chain A.C. power (or return) lines, or output signal (or return) lines
to multiple control circuits. Use a direct line from the power source to each input
requiring A.C. power. Avoid paralleling L1 (power lead) and L2 (return lead) to
load power solenoids, contactors, and control circuits. If an application uses L1
(power lead) to switch a load, L2 (return lead) has the same switched signal and
could couple unwanted noise into a control circuit.
• Tie all ground terminals together with one lead (usually green wire) tied to ground
at one point. Don't connect ground to the control case if the control is in a
grounded enclosure (preventing ground loops).
• Do not confuse chassis grounds (safety ground) with control circuit commons or
with A.C. supply L2 (return or neutral line). Each return system wiring must be
separate. Absolutely never use chassis ground (safety) as a conductor to return
circuit current.

Eliminating Noise

• Use "snubbers" ("QUENCHARC™") to filter out noise generated by relays, relay
contacts, solenoids, motors, etc. A snubber is a simple filter device using a
0.1µf, 600 volt, non-polarized capacitor in series with a 100 , 1/2 watt resistor.
The device can be used on A.C. or D.C. circuits to effectively dampen noise at its
source.
• The general purpose Watlow snubber, described above, is 0804-0147-0000.
For other "QUENCHARC" sizes contact:
• A Metal Oxide Varistor (MOV) can be used to limit voltage "spikes" that occur on
the A.C. supply lines as a result of lightning strikes, switching large motors, etc.
The MOV is available in several varieties and for 115 or 230 volt lines. The
device dissipates the voltage "spikes" to ground and in doing so repeatedly,
deteriorates its ability to function. MOVs have a limited life. See Table 4.
Appendix
PAKTRON
P.O. Box 5439
Lynchburg, VA 24502
Phone: 804/239-6941
WATLOW Series 945 User's Manual
Noise
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