Skip frequency – Rockwell Automation 20M LPM15 Liquid-Cooled Adjustable Frequency AC Drive FRN 2.xxx User Manual
Page 119
Application Notes
D-9
Skip Frequency
Figure D.5 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
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
Acceleration and deceleration are not affected by the skip frequencies.
Normal accel/decel will proceed through the band once the commanded
frequency is greater than the skip frequency. See (A) & (B) in
This function affects only continuous operation within the band.
Skip Frequency Examples
The skip frequency will have
hysteresis so the output does not
toggle between high and low
values. Three distinct bands can
be programmed. If none of the skip
bands touch or overlap, each band
has its own high/low limit.
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
0 Hz
Skip Frequency 2
Skip Frequency 1
Max. Frequency
Skip Band 1
Skip Band 2