Constant Speeds/Frequencies; Critical Speeds/Frequencies - ABB ACS880 Firmware Manual

The change rate of the motor potentiometer function (page 69) is adjustable. The
same rate applies in both directions.
A deceleration ramp can be defined for emergency stop ("Off3" mode).
Settings
• Speed reference ramping: Parameters
(pages 218 and 330).
• Torque reference ramping: Parameters 01.30,
(pages 117 and 243).
• Frequency reference ramping: Parameters
(pages 252 and 330).
• Jogging: Parameters
• Motor potentiometer: Parameter
• Emergency stop ("Off3" mode): Parameter
(page 221).


Constant speeds/frequencies

Constant speeds and frequencies are predefined references that can be quickly
activated, for example, through digital inputs. It is possible to define up to 7 constant
speeds for speed control and 7 constant frequencies for frequency control.
WARNING: Constant speeds and frequencies override the normal reference
irrespective of where the reference is coming from.
The constant speeds/frequencies function operates on a 2 ms time level.
Settings
Parameter groups 22 Speed reference selection
reference chain (page 246).


Critical speeds/frequencies

Critical speeds (sometimes called "skip speeds") can be predefined for applications
where it is necessary to avoid certain motor speeds or speed ranges because of, for
example, mechanical resonance problems.
The critical speeds function prevents the reference from dwelling within a critical band
for extended times. When a changing reference
a critical range, the output of the function
reference exits the range. Any instant change in the output is smoothed out by the
ramping function further in the reference chain.
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23.11...23.19
23.20 and 23.21 (page 221).
22.75 (page 216).
(22.01 Speed ref
Program features 43
and 46.01
26.18 and 26.19
28.71...28.75 and 46.02
23.23 Emergency stop time
(page 210) and 28 Frequency
(22.87 Speed reference act
unlimited) freezes until the
7) enters