1-4 Functional Description
7000-TD002A-EN-P – September 2007
Speed Command (cont.) Three skip speeds Skip Speed 1(49), Skip Speed 2 (50), Skip Speed 3
(51) are provided to prevent the drive from continuously operating at
a certain speed. This feature is sometimes needed to avoid mechanical
vibrations occurring in a drive system at certain speeds. The skip
speed zone around each Skip Speed is specified by the parameter
Skip Speed Band1 (53), Skip Speed Band2 (54), Skip Speed Band3
(55) If the desired Speed Command lies in a given skip speed zone,
the Speed Command is clamped to the lowest value in the zone.
Example
If Skip Speed 1 is 45 Hz with Skip Speed Band1 as 1 Hz, then the
skip speed range extends from 44.5 Hz to 45.5 Hz. If the desired
speed command is set to 45 Hz, then the drive will avoid this speed
and run at 44.5 Hz.
The final stage in processing the command is the whether the drive
has been requested to run forward or reverse. The sign is changed if
reverse rotation is selected. The Speed Command is set to zero if the
drive is stopped.
Speed Reference The function of the Speed Reference block is to determine the Speed
Reference (278) from the desired Speed Command (277). PF7000
provides two options:
• S-curve
• Linear Ramp
To select, S curve a non-zero value of S curve Percent (475) is
selected. Using parameter S curve Acc1 (481), the drive
automatically calculates the linear and the non-linear portions of the
S curve as shown in Figure 1.2. Following example shows how to
use S curve parameters:
Example
If S curve Accel 1 is set for 20 sec with 20% in S curve Percent, then
the total acceleration time is increased by 0.2 x 20 = 4 seconds. The
total acceleration time will now be 24 seconds with 4 seconds in the
non-linear portion of the S curve. Since the curve is symmetrical,
each of the segments will be of 2 seconds duration.
The parameters for deceleration are calculated using parameter S curve
Decel 1 (479) and S curve Percent (475) and shown in Figure 1.2.
Linear Ramp is enabled if the S curve Percent is set to zero.
Independent four section ramps are provided for acceleration and
deceleration. The ramp is specified by 4 Ramp Speeds, 4 Accel and
Decel times and is shown in Figure 1.3.
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