Electric motor shaft alignment involves power
transmission couplers to be aligned in two
planes. Alignment of the electric motor shaft to
the driven equipment shaft can be checked with
a straight edge ruler. A better check of
alignment is to use dial indicators as shown,
slowly rotate the shaft that the indicator is
mounted on, and read the travel of the
indicator. Total Indicated Runout (TIR) is the
term used to describe the indicator needle
travel. The best method for measuring
misalignment uses lasers mounted on one shaft,
a complex receiver on the other, and a
microprocessor with trigonometric algorithms
for determining alignment. All three methods
are used. The two planes of alignment are basic
to all of them. Misalignment is a common cause
of destructive vibration.

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