ABB ACS860, Firmware Manual, Page: 37 / 438

Program features 37
A deceleration ramp can be defined for emergency stop (“Off3” mode).
Settings
• Speed reference ramping: Parameters 23.11 … 23.19 and 46.01
(pages 157 and 240 ).
• Torque reference ramping: Parameters 01.30 , 26.18 and 26.19
(pages 96 and 181 ).
• Frequency reference ramping: Parameters 28.71 … 28.75 and 46.02
(pages 191 and 241 ).
• Jogging: Parameters 23.20 and 23.21 (page 160 ).
• Motor potentiometer: Parameter 22.75 (page 155 ).
• Emergency stop (“Off3” mode): Parameter 23.23 Emergency stop time
(page 160 ).

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 (page 149 ) and 28 Frequency
reference chain (page 186 ).

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 (
22.87 Speed reference act 7 ) enters
a critical range, the output of the function ( 22.01 Speed ref unlimited ) freezes until the
reference exits the range. Any instant change in the output is smoothed out by the
ramping function further in the reference chain.
The function is also available for scalar motor control with a frequency reference. The
input of the function is shown by
28.96 Frequency ref act 7 , the output by 28.97
Frequency ref unlimited .