On 30 Dec 2016 03:33:36 GMT, "DoN. Nichols"
wrote:

On 2016-12-29, Jon Elson wrote:
wrote:

So I was looking at some rotary encoders and a thought occurred to me
that maybe I could make a level with a digital display for checking
lathe bed twist. The highest number of pulses per revolution available
was 40,000. That works out to only .009 degrees. Seems pretty small
huh? But .009 degrees is 36 seconds! That works out to .0016" in 10
inches. My fairly inexpensive precision level shows .0005" in ten
inches. That's ten seconds resolution. And I know it's accurate
'cause I checked it with gauge blocks. I know, overkill, a feeler
gauge would be good enough. I guess I'll stick with the level and just
watch the analog bubble display.
Eric
Lucas made some liquid inclinometers that had a resistive liquid inside and
some traces on a PC board that turned it into essentially a potentiometer
with a plumb weight. Kind of worked. No friction, which is what would make
the mechanical version (weight and encoder) not work very well.

I've seen similar devices, a small metal dome with about the
curvature of a golf ball (without the dents) which has four electrical
contacts in a Bakelite insert, and a connection to the metal dome
itself. The liquid was likely something like a saline solution,
selected to not attack the electrodes or the dome. (Both appeared to be
either silver or silver plated.

The original used mercury

This was used in an old artificial horizon (gyroscopic) (and also
in a gyrocompass) to level it when it first spins up. I picked both up
about 1960 at a surplus place, so it has been around for a while.

IIRC, it was made by Sperry, and likely made for propeller
driven aircraft.

What it does is apply current to a torque motor (ring like
a hollow motor rotor in a permanent magnet field to apply torque at
right angles to the pivot of the gyro to force it to precess until
level. It has outputs on two axes, so between them can zero the gyro
properly rather quickly. (I've seen similar things working with airflow
for air powered gyros -- no electric signals there -- just breathing on
vanes. :-)

Anyway -- I doubt that the dome sensors were anywhere near as
high resolution as our serious sensitive levels, but the
electrical/electronic sensors have been around for quite a while.

The problem with really sensitive bubble levels (like master precision
levels that resolve better than an arc minute) is they take a long time to
settle, like about 30 seconds.

Taylor Hobson makes an electronic level, called the TalyVel. It resolves to
about 0.2 arc second when new, and settles completely in 2 seconds.

The technique is a very light platform suspended by 5 hair-thin wires. It
has an aluminum plate between two magnets as a damper, and a pair of
inductive proximity sensors that detect the ends of the pendulum.
Works fantastically well, but QUITE expensive. About $7000 for one sensor
and the readout box.

Jon