Rockwell Automation 20B PowerFlex 70, PowerFlex 700 Reference Manual - Manual (Page 158)

Skip Frequency
158 Rockwell Automation Publication PFLEX-RM001H-EN-P - June 2013
Skip Frequency
Figure 31 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 31 .
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 (C) in
Figure 31 .
Frequency
Time
(A) (A)
(B)
(B)
Skip Frequency
Command
Frequency
Drive Output
Frequency
Skip + 1/2 Band
Skip – 1/2 Band
35 Hz
30 Hz
25 Hz