Figure 9-3 Contact Noise Suppression - Honeywell UDC3300 Product Manual

9.6 Noise Suppression at the Source,
Contacts
1/01
When a contact interrupts an inductive load, a certain amount of energy is
stored in the load. An MOV or RC circuit in parallel with the load
provides a place where this energy may be dissipated. However, if there is
no MOV or RC circuit, the energy may create a visible electrical arc
across the open contacts. This, in turn, results in electrical noise as well as
damage to the contacts.
One way to eliminate this arc is to connect a resistor and capacitor across
the contacts (see Figure 9-3). A combination of 47 ohms and 0.1
microfarads (1000 Vdc) is recommended for circuits up to 3 amps and 300
Vac. For voltages above 2000 Vac, an MOV across the contact may be
added for extra protection.
Figure 9-3 is an illustration of a resistor and capacitor connected across a
contact to eliminate electrical noise.
Figure 9-3 Contact Noise Suppression
A.C.
supply
For large load currents, a rule of thumb is to size the capacitor so that the
number of microfarads equals the number of amperes in the load current,
and the resistor has the same resistance value as the load. The objective is
to eliminate the visible arc.
Either discreet resistors and capacitors or packaged RC networks may be
used. An RC network (47 ohms and 0.1 microfarad) is available as part
number 30371852-001. Similar RC networks are available from
Electrocube Inc. (part number RG1782-3) and from Industrial Condensor
Corporation.
UDC3300 Limit Controller Product Manual
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MOV
R
C
Inductive
load
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