ABB ACS880 - Critical Speeds; Example; Settings and Diagnostics

1560
1380
690
540
1
2
3
4
22.87 (rpm)
(input of function)
22.01 (rpm)
(output of function)
Parameter 22.52 = 540 rpm1
Parameter 22.53 = 690 rpm2
Parameter 22.54 = 1380 rpm3
Parameter 22.55 = 1560 rpm4
Settings and diagnostics
Parameters:
• Critical speeds: 22.51 Critical speed function…22.57 Critical speed 3
high (page 307)
• Critical frequencies: 28.51 Critical frequency function…28.57 Critical frequency
3 high (page 353).
￭
Critical speeds
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) enters a critical range,
the output of the function (22.1) 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.
Example
A fan has vibrations in the range of 540 to 690 rpm and 1380 to 1560 rpm. To make
the drive avoid these speed ranges,
• enable the critical speeds function by turning on bit 0 of parameter 22.51, and
• set the critical speed ranges as in the figure below.
86 Program features