Rockwell Automation Liqui-Flo DBT Reach Drive - Manual (Page 226)

Appendix D-12 DBT Reach Drive User Manual
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. Skip Frequencies
(084-086) 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 Skip Freq Band (87). 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 D.14.
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 D.14.
Figure D.15 – Skip Frequency
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