Further, special consideration has to be given to the
pulsating torque in certain applications. For
example, large 6 pole motors driving compressors
frequently have a resonance between 60 and 80%
speed. Fortunately, it is only present during
starting. If the start-up is fast, the resonance has
little time to build up. The motor manufacturer
provides curves of the average and the pulsating
torque so that an overall system analysis can be
made. Figure 33 is a representation of a torque vs.
speed curve. Shaft sizes may be adjusted or the
coupling changed, but the pulsating torque will
still be there.