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Tacho or encoder?

P

Pubo

Jan 1, 1970
0
Would like to know how a tacho is used for feedback n control the speed

which is better to use a tachogenerator or an encoder?

what is the diff for cost n size?
 
Pubo said:
Would like to know how a tacho is used for feedback n control the speed

which is better to use a tachogenerator or an encoder?

what is the diff for cost n size?

Encoders are more reliable and cheaper, as long as your drive supports
them thats the way to go.
 
Pubo said:
Would like to know how a tacho is used for feedback n control the speed

which is better to use a tachogenerator or an encoder?

what is the diff for cost n size?

Probably the cheapest and smallest solution today (when building in
quanitity from the ground up) is to use a motor withough a commutator,
with a driver circuit that switches the phases at the desired speed,
possibly with some feedback detection from the same coils. I think
this is what you will find in modern disk drives, for example.

For a one-off, use whatever you can get your hands on surplus - tacho,
surplus encoder which could be quite coarse, even one pulse per
revolution if the speed is high, etc.
 
N

Naebad

Jan 1, 1970
0
Probably the cheapest and smallest solution today (when building in
quanitity from the ground up) is to use a motor withough a commutator,
with a driver circuit that switches the phases at the desired speed,
possibly with some feedback detection from the same coils. I think
this is what you will find in modern disk drives, for example.

For a one-off, use whatever you can get your hands on surplus - tacho,
surplus encoder which could be quite coarse, even one pulse per
revolution if the speed is high, etc.
You have to be careful about the number of pulses per rev - I think you will
find if there are not enough pulses then your phase amrgin will suffer. Also
what's teh point in an encoder if you are using analogue control? You would
need to convert back to analogue.

Naebad
 
F

Frank Bemelman

Jan 1, 1970
0
Pubo said:
Would like to know how a tacho is used for feedback n control the speed

which is better to use a tachogenerator or an encoder?

what is the diff for cost n size?

Depends on the application.
 
P

Pubo

Jan 1, 1970
0
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 )

Thanks
 
F

Frank Bemelman

Jan 1, 1970
0
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 ;)
 
J

Joseph2k

Jan 1, 1970
0
Pubo said:
Would like to know how a tacho is used for feedback n control the speed

which is better to use a tachogenerator or an encoder?

what is the diff for cost n size?
I vote for the encoder. If the control system is analog you only need to
feed the encoder output (1 bit for unidirectional systems, 2 to include
direction) to a little logic and a "F to V" converter. benefits: better
linearity (over almost 4 decades of speed), and retains analog control
system (if that is a requirement). for digital control systems it is
obviously no contest in favor of the encoder; you could also get as many
bits absolute position as you can pay for. speed would be taken from the
top three bits to include measure of acceleration.
 
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