Precision Electronic Levels - summary

They can do that but they're surprisingly pricey.

Are you planning to try it? Btw, thanks for the list of patents.

Wes

-- "Additionally as a security officer, I carry a gun to protect government officials but my life isn't worth protecting at home in their eyes." Dick Anthony Heller

Have you considered the liquid type? They claim 5 arc second repeatability.

Best regards, Spehro Pefhany

I got two of these Lucas liquid levels on eBay for something like $75. Before I had a chance to do anything with them, I stumbled onto the Talyvel on eBay and snapped it up. If anyone wants these Lucas units, and I have the docs with them, too, let me know. I'll make you a good deal.

Jon

I am thinking about making a level. Don't know if I'll really do it. Probably depends on how practical an approach I can dream up.

The big issue to be figured out is how to handle temperature variations.

The original Wyler unit (described in 4,023,413) may be made of fused quartz, which would be easy for a big company like Wyler to do, but a problem for me. I know how, but it would be far too much work. The patent mentions quartz as a suitable material. So, the question is if quartz is really necessary. Symmetry may suffice.

The subsequent patent (5,022,264) mentions that the diaphram mass is made of 0.003" brass foil, which is easy to get and to photoetch. One can also use stainless steel, but it must be non-magnetic so the Earth's magnetic field doesn't cause false tilt readings.

Joe Gwinn

PS. The German book came, and I was able to read it well enough to see that it wasn't all that useful. Most or all circuit diagrams in the book were clearly wrong (in the sense of being impossible), so I assume that the authors had no idea how these things actually work. JMG

Yes, I did consider electrolytric types (a bubble level vial with electronic readout). The pendulum units are a factor of ten better in resolution and repeatability, 0.1 or 0.2 arc seconds versus 5 arc seconds. Long term drift is also an issue. It sure would be easier if the electrolytic sensors were better than they are.

Joe Gwinn

fused quartz is a good choice. The quartz you can get from burnt out halogen bulbs. Procedures in experimental Physics by Strong has info on fused quartz. In another life I made coil springs out of fused quartz.

Dan

snip

If I wanted to make a precision level today - more precise than a starett/vis master level, then I think I'd do the following

1. drop a penduluum from the perpendicular - longer is better so long as the perpendicular in fact remains perpendicular

2. place a mirror at the end of the penduluum, and arrange mirrors along the base to direct beams from a low powered laser. Mirror at base shoudl have an angled and a straight part

1. use an interferrometer to measure the final centering of the penduluum - first, just use the laser to roughly center by using the angled mirror to form an optical amplifier and use a wall, maybe 20 feet away to get the thing aproximately centered (this should get you to a micro inch or so). After that, use interferrometry, this will get you to 1/2 wavelenght - so depending on your choice of emitter, somewhere in the 200 to 500 angstrom range. With a 1 meter perpendicular, that should give you what .... inverse sine of 1E-8=?? - well, using small angle aproximation, 1e-8 radians

Is that good enough?

I have read Strong's book, which is quite good.

One can buy fused quartz from glass suppliers, and work it like glass. It is possible for an amateur to make lenses and mirrors, and many people made their own telescopes. Willmann-Bell publishes books on how to do this. I can see how to wet grind the fused quartz to make the spherical depressions in the flat plates of the sensor assembly, and to drill the holes for the connections to the electrodes. However, vacuumn depositing the electrodes would have to be sent out. Wet silvering could be used, but that's another whole process.

For the record, the usual way to grind the depressions would be to use a machined cast iron tool charged with carborundum grit (or diamond grit) held in a machiine the moves the tool such that its surface describes a sphere. Mor modern would be a diamond cup curve-generation tool in a similar machine.

But I don't have the equipment to handle this, and don't want to get it for a one-off project. So, I'm thinking of alternatives like two glass sheets, two brass electrodes, a brass shim diaphram, and a pair of machined ceramic spacers, assembled with epoxy. Or, two circuit boards with metal faces inward, two brass spacers, and a brass sheet, assembled with epoxy. And so on. The temperature and humidity coefficients of the dielectrics are the big issues, as metals are far simpler.

Joe Gwinn

It's about 100 times better than the Wyler and Taylvel units, which are only good to one microradian, but portability and applicability to lathe beds and surface plates could be a challenge.

Perhaps a Sagnac interfereometer would be a suitable tiltmeter? There is a nice one in a deep bomb shelter and command center in New Zealand:

Joe Gwinn

Hi Joe, forgive my ignorant rantings here, but I see there would be a much more simple way of doing this.... If you don't want to worry about absolute accuracy, ie when leveling a lathe bed where you are only concerned with differences, then what about...

Use the capacitance method, ie to each side of centre - a bit of double sided circuit board would suffice. Suspension for the pendulum could be out of one of those $1 battery clocks in the junk shops - use 2 capacitance meters, one each side, set balance. (or use a comparator, depends on how fancy you want to go)You could do this every time you use it so drift/temp. compensation would not be a problem.

So, set to balance/zero/whatever figures it shows at one end of the lathe, this will establish a datum point, move to the other end, note difference (in picofarads, whatever) - then use this as a measure of how far out it is, and which way to go in correcting.

Resolution - no idea. Probably someone smarter than me could do it all in a PIC micro or similar.

Now, I suspect(sigh...) you could drive a truck through my approach, but would appreciate constructive comments...

Andrew VK3BFA.

PS - will be away from the PC for at least a week (minor surgery) so will be looking forward to your reply.

I have been considering circuit board for the outer electrodes, two glass spacers with the brass shim stock diaphragm between, all held together with epoxy. (In Europe, the standard would be Araldite.)

Wyler apparently uses fused quartz and invar, but the patent does cover a design with a stack of sheets glued with epoxy.

The glass sheets can easily be drilled on a drill press with abrasives, so it will be easy to make the 1" diameter hole for the diaphragm.

That won't really work. The key innovation in the patent is the use of the perforated diaphragm as the proof mass. The diaphragm is made by photoetching, which isn't difficult.

The design in the Wyler patent (4,023,413) uses a differential capacitor, which is optimum, and is far easier than trying to measure the two capacitances independently. The classic capacitance-bridge circuit uses a centertapped transformer to generate the drives to the outer plates. The moving center plate will have zero voltage when that plate is centered. The balanced configuration causes the non-varying part of the capacitance to cancel out, allowing the varying part to come out loud and clear.

I have built such circuits before, and they are very stable and well-behaved. The transformer is easily built using a ferrite cup core, which can also be part of the drive oscillator. The exact frequency is not important.

The subsequent digital sensor from Wyler does measure the two capacitances independently, and uses their ratio. There is a patent, but I don't have the number at hand.

Initial balance of the sensor would be mechanical, being a set of leveling screws. Given the difficulty of coming up with a reference surface that's exactly horizontal (to less than 0.1 arc seconds) in a home shop, the approach will be to swap ends and adjust for equal deviations from zero. Ultimately, one can use the sensor to adjust the surface plate to exact horizontal and the sensor to exact adjustment, in a converging cyclic process.

Transformer-driven capacitance bridges with synchronous detectors are

Good luck with the surgery.

Joe Gwinn

Have a look at

Not bad. The resolution is up there, but the repeatability is 0.0008 degrees, or 2.9 arc seconds, versus 0.1 arc seconds. Better than 5 arc seconds, but still. This is why people bother with pendulum tiltmeters.

Joe Gwinn

Believe me, .1 arc seconds is AWFULLY sensitive. I can walk from one end of my Sheldon lathe to the other and tilt it a full arc second by deflecting the concrete floor. So, unless you are aligning turbo-alternator sets in nuclear power plants, you have no need for such sensitivity. Possibly because my Talyvel is old and hasn't been to the factory in 20+ years, it also drifts. If I am going to be doing anything precise, I turn it on and let it "warm up" for

Jon

The Talyvel is housed in a cast aluminum frame, with probably stainless parts inside holding the platform. The platform can be tilted with two micrometer knobs on top to compensate for intentional tilt. When you screw them both down, it locks the pendulum.

I think fused silica is totally insane, the thermal drift of my unit is really quite small.

Jon

I thought it was better but you are correct.

I assume that the foot is cast iron.

How sensitive is the unit to magnetic fields?

Are there any patent numbers on the unit or in its documentation?

Swiss precision! Must be zero drift!

Actually, making something out of fused quartz and invar is easy for an optics shop, and the Wyler tilt sensor has only three parts requiring no adjustments, so it may well be cheaper to make than the Taylvel sensor unit.

Joe Gwinn

I like it! I bet you can detect the house swaying in the wind as well.

Probably the turboalternator twists the thicker floor of the power station just as much as your lathe does to your basement floor.

One wants instruments to be at least ten times more accurate than what is being measured, so the instruments don't limit the measurement.

No, the drift is built in, a matter of temperature coefficients and residual deviations from symmetry. Aging has little to do with it. I'm glad to know the rough magnitude.

While handling, temperature gradients may be the issue, as gradients cause transient asymmetry. A wooden handle may be in order to cut down on handling-induced thermal drifts. Or at least cover the existing handle with the cloth tape used on bicycle handles.

One thing the fused-quartz Wyler unit is used for is long term monitoring of such things as bridges, where the temperature drift of the Taylvel would preclude this use.

If my only reason were to measure tilt, I would just monitor evilbay for a Taylvel. I may yet do this. (I saw three Taylvel electronics boxes yesterday, but "as is" and no sensor.)

But this is a Project, and if I am going to go to that much effort, the pendulum units are far more interesting, and accurate.

Joe Gwinn