That is exactly the design used for aircraft magnetic compass repeaters. Typically they use a 400 to 600 Hz oscillator as a
reference.
Steve

"Cross-Slide" wrote in message ...
On Aug 3, 3:35 pm, Ignoramus30076 ignoramus30...@NOSPAM.
30076.invalid wrote:
This is all regarding this old Troyke CNC rotary table that I wanted
If you recall, the latest stumbling block with the rotary table was
that it was using a old technology "resolver" for position feedback.

I was able to get a hold of Joe at Harowe, who made this
resolver. Apparently, this resolver is still in surrent production and
sells for a modest sum of $1,423.00.

http://www.dynapar.com/Accessories.a...BRW-300-F10/10

Joe emailed me a diagram of this motor with all electrical
information.

http://igor.chudov.com/manuals/Harow...300-F10-10.pdf

This looks like super duper space age technology from very many years
ago and is, apparently, a high quality product that is likely in good
shape.

So, at this point, I have two routes to take:

1) Attach a shaft extension in the back and a new encoder from US
Digital
or
2) Add a resolver to encoder converter.

Both have the same cost, these ir some machining involved in both
cases. In the first I have to add a shaft extension, in the second I
have to add an enclosure for the converter and a plug/receptacle to
the rotary table. This is so, because I may need to unplug the rotary
table and remove it from the mill from time to time.

After some thinking and talking to EMC guys on IRC, I will go with the
resolver. It is, in a certain way, a better device (though far more
expensive!)

This is so because if the encoder misses a pulse due to noise, it
eventually recovers the absolute position. Plus they are more
"crap-proof".

i

Iggy,

With your background you can appreciate the electronics of the
conversion.
Some texts will tell you that the rotor is energized with a sine wave,
and the Sine Cosine outputs are quadrature decoded to find the current
position of the rotor. This sounds straightforward, but in fact by
definition the Sine and Cosine levels will rise and fall to zero as
the rotor revolves. This makes the detection circuitry susceptible to
noise.
The difference between the Sine and Cosine signals indicate the rotary
position.
Another method to read a resolver position, which I found to be
technically superior, was to drive the Sine Cosine coils with
digitally synthesized Sine Cosine signals. The rotor coil then became
the sensing element.

As the rotor rotates, the signal from the rotor coil will be a fairly
constant amplitude, but will vary in phase relationships to the Sine/
Cosine drive signals.

To summarize the circuit, there is a master counter that counts up to
the maximum resolution of the resolver, and resets. The output of that
drives the Sine and Cosine lookup ROMs which drive the D/A and drive
the Sine/Cosine Drivers to the resolver.
The rotor signal is simply fed to a Zero Crossing detector. When it
detects a Zero crossing, the current value of the free running counter
is captured, and that is the current position of the resolver.
So, it acts as an absolute encoder.
The signals from the resolver are always at full amplitude, and only
timing of the zero crossing point determines the absolute position.

I thought you would fine that interesting, from a design point of view.