A bubble level makes more sense

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
Reply to
etpm
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I did not know you were planning on checking twist with a rotary encoder.
But yes, a level sounds better. If you're going to be looking at the "analog" display, would a real old-time machinist's level be better, or are the 'lectronic ones cheaper?
Reply to
Tim Wescott
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.
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
Reply to
Jon Elson
The rotary encoder will measure tilt as will a level. The levels are much more accurate and have a much finer resolution than any comparably priced electronic level. To use a rotary encoder to measure tilt I envisioned a weighted in one spot aluminum disc between a couple damping magnets. Eric
Reply to
etpm
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"But take away the fancy GPS shells, and the AGS and its digital fire control system are no more accurate than mechanical analog technology that is nearly a century old."
--jsw
Reply to
Jim Wilkins
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.
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.
Reply to
DoN. Nichols
Why not add a 'level arm' - magnify the change easily.
"With a level I can move the world" in reverse.
Martin
Reply to
Martin Eastburn
The original used mercury
Reply to
clare
I remember hearing that not having a level is easy too. Just tie a bolt ont o string and hang it from the ceiling. There you have what is called a plu m bob. Its shadow (from the ceiling on down) is an exactly verticle line do wn, so its right angle is an exactly horizontal one.
Reply to
walter_evening
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That's PLUMB, not PLUM, the fruit, to be the pedant...
Reply to
dpb
Have you checked out
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Art
Reply to
Artemus
I remember hearing that not having a level is easy too. Just tie a bolt onto string and hang it from the ceiling. There you have what is called a plum bob. Its shadow (from the ceiling on down) is an exactly verticle line down, so its right angle is an exactly horizontal one.
=================================
A plum(b) bob won't help in an airplane because "down" during a turn isn't really vertical, and if you think it is your time will be brief.
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Large warships needed a complex instrument called the Stable Vertical to tell the gunnery computer which way is up.
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It explains the mercury.
-jsw
Reply to
Jim Wilkins
"A plum(b) bob won't help in an airplane...." Unless you're fueling it with the tanks' dripsticks. There's one in the main gear wheelwell on the keel beam.
Garrett
Reply to
Garrett Fulton
Surveying equipment all has built in levelling doo-dads. One I took apart had some sort of glass vials filled with something noxious like iodine that is used to adjust itself to a level position. There were electrodes attached to the vials but I don't recall the details.
Anybody know what this stuff was?
Reply to
Cydrome Leader
Well, yes, the ordinary "electronic levels" at the hardware store are not terribly precise.
But, Taylor Hobson also makes a high-end electronic level for millwrights and such technicians that need to align stuff to serious levels of accuracy. My Talyvel 3 will resolve .1 arc second, and is quite repeatable to 1 arc second. It easily detects me walking from one end of my 3500 Lb lathe to the other, shifts the floor about 1 arc second. The best part is it settles to a fully damped reading in less than 3 seconds after being picked up and moved to a different spot. WAY faster than a bubble level.
Jon
Reply to
Jon Elson
And way more expensive too. I could build an accurate enough level with an electrolytic level sensor but that's still way more money than a good precision level. If I leveled stuff every day I would have a fast accurate level. Eric
Reply to
etpm

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