Rockwell Automation 20A PowerFlex 70EC/700VC - Manual (Page 99)

Skip Frequency 95
Some machines may have a resonant operating frequency (vibration speed) that is
undesirable or could cause equipment damage. To guard against continuous
operation at one or more resonant points, parameters 084-086, ([Skip Frequency
1-3]) can be programmed.
The value programmed into a skip frequency parameter, 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], parameter 87. The
range is split, half above and half below the skip frequency parameter.
If the commanded frequency 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 15 .
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 15 .
Acceleration and deceleration are not affected by the skip frequencies. Normal
accel/decel will proceed through 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.
If skip bands overlap or touch, the
center frequency is recalculated
based on the highest and lowest
band values.
If a skip band(s) extend beyond
the max frequency limits, the
highest band value will be
clamped at the max frequency
limit. The center frequency is
recalculated based on the highest
and lowest band values.
If the band is outside the limits,
the skip band is inactive.
0 Hz
Skip Frequency 2
Skip Frequency 1
Max. Frequency
Skip Band 1
Skip Band 2
0 Hz
Skip Frequency 2
Skip Frequency 1
400 Hz.
Adjusted
Skip Band
w/Recalculated
Skip Frequency
0 Hz
Max.Frequency
Skip
400 Hz.
Adjusted
Skip Band
w/Recalculated
Skip Frequency
0 Hz
60 Hz. Max.
Frequency
Skip Frequency 1
400 Hz.
Inactive
Skip Band