Electronics Forum / Basics / May 2006

tach gives analog volts/rpm. Encoder gives A and B pulses in a 90deg
out of phase pattern, can be 16 counts/rev up to 4096 counts/rev
depending on encoder

-Tachogenerators provide an AC voltage which is proportional to speed just
like standard AC generators. The frequency of this waveform, of course, is
also proportional to speed. Having a voltage proportional to speed
simplifies analog control of a motor.

-Encoders typically provide a series of pulses proportional to rotation or
distance. Some encoders provide a binary number representation of rotation
or distance where 0001 represents position 1, 0010 represents position 2,
0011 represents position 3, etc. You can calculate system speed by measuring
the time between these pulses or positions. Having a set of pulses
proportional to distance simplifies digital control of a motor.

Dorian