"Jon Elson" wrote in message
...
DoN. Nichols wrote:

Looking at the wires, and assuming that ground is carried by the
shield, while the red is likely the power to drive the LEDs -- also out
of period with the packaged circuits, which were from the 1950s IIRC.
No, these packaged things look so much like Sprague parts, made in the
mid-late 60's, just before integrated circuits took over. The rest of
that module DOES look newer than that, however.

But, the MAGnescale is magnetic, so there would be no LEDs. It has a
smooth
stainless rod with SOMETHING inside.


I think you'll find that the SOMETHING'S inside are precision ground
bearing balls.

there is a British manufacturer who still makes them like that. They were
fearured in "Model Enginners Workshop"
a year or two ago









There is an
excitation coil and two pickup coils, so the signal scheme is exactly like
a resolver or inductosyn. You excite with a sine wave at some modest
frequency like 400 Hz, and as the head is moved, the signal on each pickup
coil rises, falls and then reverses polarity with respect to the
excitation. The two coils pick up this signal in quadrature. The
converter box interpolates the signal to increase resolution.

I played with a damaged one of these units at a shop in Wichita. I got
fairly good
signals out of it after repairing some TOTALLY hair-thin wires in the
head, but we never got a decent signal out of the converter box.

Jon