Re: [CAD_CAM_EDM_DRO] To convert Quadrature Encoder signals to Tachogenerator signals

I assume that you have two square waves (in
quadrature) coming from your encoder and you want an
analog signal proportional to the frequency of the
square waves which is proportional to the rotation
speed of the encoder shaft. What you are looking for
is a frequency to voltage converter. Analog Devices
has an IC, the AD650, which will do what you want. You
can get specs on the IC from their web site and don't
forget to also download the Application Note AN-279
which will give you a schematic for a frequency to
voltage converter using the AD650. You can even get up
to 2 free samples of the AD650 from Analog Devices
(all this on their web site).
In addition to the IC, you will need a few resistors
and capacitors (Radio Shack, Mouser, Digi-Key) as well
as a power supply. An oscilloscope (or access to one)
will be a big help in the final tuning up.
But, in the final analysis, you are (via the AD650)
taking the average of a series of pulses derived from
the square wave from your encoder (all done inside the
AD650). As the shaft speed drops, so does the
frequency, and thus the averaged DC voltage from the
AD650 starts to get more and more ripple on it. You
can, of course, increase the averaging capacitor to
smooth this out, but at some point the response time
to spindle speed changes becomes too slow. This may
cause you problems in a feedback type of application.
I had a related situation with my 16" SB lathe in
that I wanted a tachometer for the spindle. I added an
inductive pickup to sense the teeth on the bull gear;
85 pulses per revolution. I didn't want to put in the
work to build a true frequency counter but small, LED
DC panel meters are real cheap ($10) and simple to
mount and use. I used an AD650 to convert the 85 teeth
signal to a DC voltage and then scaled it to readout
in RPMs. As there was no feedback involved, it worked
OK at slow spindle speeds.

Good luck,
Pete

--- Babar <riet91@...> wrote:

>
> Hi All,
>
> I am using a DC drive which takes analog tacho
> signals
> to run a Fanuc DC Motor which only have a Digital
> Encoder , so I need to convert the Encoder signals
> to
> Analog voltage to use this as Tacho feedback. Can
> anybody help me by suggesting a simple circuit?
>
> Regards
>
> Babar
>
>
>
>
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