Pubo said:
How a tacho is used??
Now in my application am giving it to an opamp(error amplifier).
the application is to drive a DC servo motor(90Vmax,3A )
Yes, but do you also need to stop and hold the shaft at a fixed
position, do you need to know the exact position of the
shaft, etc.
Encoders can be used to generate a tacho-like signal, but at
very low RPM including stopped position, the signal isn't
as smooth as a true DC-tacho, and you may get small oscillations
in the shaft position and audible noise. But if you need to
know the exact position you *need* to use an encoder. I had
a system once that used both a DC-tacho and an encoder with
sine output. Tacho for velocity feedback and encoder to keep
track of position during run, and sine output was used to lock
the shaft in stopped position.
So, again, it depends on the application. You can't just
say that a tacho is better than an encoder or vice verca.
When in doubt, try both