Baldor 18H Series Installation & Operating Manual page 99

Section 1
General Information
Electrical Noise Considerations
5-12 Troubleshooting
Continued
Combining an R-C snubber and twisted-pair shielded cable keeps the voltage in a circuit
to less than 2 V for a fraction of a millisecond. The waveform shown in Figure 5-3 in
addition to the snubber across the coil, the adjacent wire is grounded in a twisted–pair,
shielded cable. Note that the vertical scale is 1 V/div., rather than the 20 V/div. in figures
5-1 and 5-2. This shows that snubbers and twisted-pair shielded wire should be used for
sensitive circuits located adjacent to coil wires.
Figure 5-3 R-C Snubber Circuit & twisted-pair
A reverse biased diode across a DC coil achieves the same result as adding an R–C
snubber across an AC coil,
Figure 5-4 AC & DC Coil Noise Suppression
RC snubber
0.47 mF
AC Coil
33
Figure 5-4.
+
DC Coil
Diode
–
MN718