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WATLOW Series 942 User's Manual
Appendix
Wiring Guide
How To Eliminate Noise
• Use "snubbers" ("QUENCHARC™") to filter out noise generated by devices
such as relays, relay contacts, solenoids, motors, etc. A snubber is a simple
filter device using a 0.1
µ
f, 600 volt, non-polarized capacitor in series with a
100 ohm, 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:
PAKTRON
P.O. Box 5439
Lynchburg, VA 24502
Phone: 804/239-6941
• 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.
Watlow stocks several MOVs. See Table 7.
• "Islatrols" and other similar power line filters are designed to carry the power
for the control circuit and "buffer" the control circuit from A.C. line noise.
Devices like the Islatrol use media (electromagnetic filtering) other than
electric circuits to filter out electrical noise. Take care in matching the power
capabilities of the filter with power demands of the circuit. Keep line filters as
close to the control as possible to minimize the area for interference pick up.
• Islatrols are available from:
Control Concepts Corporation
328 Water Street
P.O. Box 1380
Binghamton, NY 13902-1380
Phone: 607/724-2484
I - 101 (1A, 120VAC)
I - 202 (2.5A, 208/240VAC)
I - 105 (5A, 120VAC)
I - 207 (7.5A, 208/240VAC)
I - 115 (15A, 120VAC)
• The ultimate protection is an "uninterruptable" power supply. This "senses"
the A.C. power line; when the line fluctuates, a battery powered 60Hz
inverted circuit takes over, supplying power within one-half to one cycle of
the A.C. line; very expensive.
