Re: [CAD_CAM_EDM_DRO] Newall sperosyn encoders

Les Newell wrote:

> This was my first impression but LVDTs produce a varying voltage, dependent
> on the position of the core. According to the documentation the output of
> the spherosyn sensor is a pair of sine waves of varying phase. They also
> mention that the sensor has six coils. I wonder what they are doing.
> The phase comparator circuit must be pretty clever as well. It has to have a
> resolution of better than 1/1000th of a degree.

6 coils, but I'll bet they are wired together, so there is really one drive
coil, and
2 sense coils. they may be paired up to get more signal, reject noise, or
average over two sets of balls to reject small imperfections in the magnetic
characteristic of individual balls. (Apparently, anything magnetic in the area

drives these sensors nuts, and passing powerful magnets near the tube
will magnetize the balls and make the scale malfunction until the balls are
demagnetized.)

The phase sensor only needs to be able to detect 0 or 180 degree phase
angles. the magnitude of the signal is where the information is, so the phase
detector doesn't need much resolution, just sensitivity (near the zero
crossing,
the signal is real small).

An LVDT, if you made one with several cycles, would also have phase
reversals. There are devices called resolvers, which are basically an
LVDT that has been wrapped around a circle. There are also inductosyns,
which are ironless resolvers, often made into linear scales.

Jon