Rockwell Automation 9VT201-007HTNNN, User Manual, Page: 205 / 224

Application Notes C-9
Publication 9VT-UM001D-EN-P
Figure C.4 Skip Frequency
Some machinery may have a resonant operating frequency that must be
avoided to minimize the risk of equipment damage. To assure that the
motor cannot continuously operate at one or more of the points, skip
frequencies are used. Parameters 084-086, ([Skip Frequency 1-3]) are
available to set the frequencies to be avoided.
The value programmed into the skip frequency parameters sets the center
point for an entire “skip band” of frequencies. The width of the band
(range of frequency around the center point) is determined by parameter
87, [Skip Freq Band]. The range is split, half above and half below the
skip frequency parameter.
If the commanded frequency of the drive is greater than or equal to the
skip (center) frequency and less than or equal to the high value of the
band (skip plus 1/2 band), the drive will set the output frequency to the
high value of the band. See (A) in
Figure C.4 .
If the commanded frequency is less than the skip (center) frequency and
greater than or equal to the low value of the band (skip minus 1/2 band),
the drive will set the output frequency to the low value of the band. See
(B) in
Figure C.4 .
Skip Frequency
Frequency
Time
(A)
(A)
(B)
(B)
S kip Frequency
Command
Frequency
Drive Output
Frequency
S kip + 1/2 Band
S kip – 1/2 Band
35 Hz
30 Hz
25 Hz