tach vs encoder

I guess in principle the tach is for velocity characteristics and the
encoder is for position, but internally some types can share some circuit
similarities (ignore that last remark if it just confused things...it's a
'chicken & egg' thought).

My guess is how they detect the rotation and how they process the output.

Tachometer typically has a voltage/rpm output signal.

Encoder has a # of pulses/rev output signal.

A motor with both is apparently being used in an application where both
velocity and position are important control parameters.

The reason I said there can be internal similarities is that some tach
circuits internally look like encoders - they start out producing at a
certain number of pulses per turn, but have a detector circuit that gives an
indication of how many of those pulses occurred in a given time and
'displays' that with a voltage proportional to how fast those pulses occur -
a frequency to voltage converter, if you will.

I had some stepper motors with a confusing device on them - it looked
internally like a single-ended (non-quadrature) encoder, but maybe it was a
tach. Mariss voted for single-ended encoder, and he would know better than
me.

Murray