Settings And Diagnostics; Critical Speeds; Example - ABB ACS880 Firmware Manual

86 Program features
1560
1380
1 Parameter 22.52
2 Parameter 22.53
3 Parameter 22.54
4 Parameter 22.55

Settings and diagnostics

Parameters:
•

Critical speeds:

high (page 307)
• Critical frequencies:
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.
22.01 (rpm)
(output of function)
690
540
1 2
= 540 rpm
= 690 rpm
= 1380 rpm
= 1560 rpm
22.51 Critical speed function...22.57 Critical speed 3
28.51 Critical frequency function...28.57 Critical frequency
3 4 22.87 (rpm)
(input of function)