Precision Electronic Levels - summary

Talyvel: It turns out that there are two US patents that mostly describe at least the early versions of the Taylor-Hobson Talyvel
electronic level.
3,081,552 "Suspension Devices" to R. E. Reason, issued 19 March 1963.
3,160,237 "Damping Device" to R. E. Reason et al, issued 8 December 1964.
The fact that the above two patents "partially" describe the Talyvel is mentioned in US patent 3,902,810, so this may well be it.
The Wyler AG levels are based on capacitance. The relevant US patents are:
4,023,413 "Device for measuring Accelerations, Particularly Accelerations Due to Gravity" to Stauber, issued 17 May 1977.
5,022,264 "Instrument for measuring Accelerations, Particularly Gravitation Components for Goinometry", to Stauber, issued 11 June 1991.
Siegfried Stauber was the Chief Engineer of Wyler AG at the time.
<http://www.wylerag.com/IMAGES_2008/history.pdf
The picture of Dora Wyler scraping a surface plate reminds me of the grimy young child hidden behind the machines in in the northern brush factory.
Both instruments sense tilt by means of a pendulum swinging on a zero-friction pivot of some kind.
The Taylvel senses pendulum motion by means of variable reluctance and thus inductance. As the pendulum moves, one air gap widens while the other gap narrows. The two inductances are compared in an impedance bridge, yielding null at level. The drive frequency is about 10 KHz.
The Wyler level senses pendulum motion by means of variable capacitance. As the pendulum moves, one inter-plate gap widens while the other gap narrows. The two capacitances are compared in an impedance bridge, yielding null at level. The drive frequency is not stated, but is probably near to 1 MHz.
As for manufacture by a HSM, either approach is practical, but the Wyler approach is far simpler mechanically. In either case, the electronics part is dead simple by present-day standards, but was a big deal back in the 1960s and 1970s.
Joe Gwinn
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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
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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
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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
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In article

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
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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.
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In article
snipped-for-privacy@wia.org.au wrote:

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 *very* good, and the PIC can do no better. I was imagining a purely analog approach.

Good luck with the surgery.
Joe Gwinn
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wrote:

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.erect a perpendicular over the base material - one might use a surface plate or other optically flat material for the base.
2. drop a penduluum from the perpendicular - longer is better so long as the perpendicular in fact remains perpendicular
3. 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
4. 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?
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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:
<http://www.ringlaser.org.nz/content/c-2.php
<http://en.wikipedia.org/wiki/Sagnac_effect
Joe Gwinn
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Joseph Gwinn wrote:

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
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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
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On Sat, 04 Apr 2009 19:50:29 -0400, the renowned Joseph Gwinn

Have you considered the liquid type? They claim 5 arc second repeatability.
Best regards, Spehro Pefhany
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On Sat, 04 Apr 2009 22:23:03 -0500, Spehro Pefhany

They can do that but they're surprisingly pricey.
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Don Foreman wrote:

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
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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
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On Sun, 05 Apr 2009 13:42:14 -0400, Joseph Gwinn

Have a look at http://www.spectronsensors.com/datasheets/SDS-105-2704.pdf
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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
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On Tue, 07 Apr 2009 00:02:58 -0400, Joseph Gwinn

I thought it was better but you are correct.
2.9 arc seconds is about 14 microinches per inch or .00014" in 10". Will you post your pendulum design and results as time goes on, please? Interesting project!
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If one were to build an electrolytic level, this would be a good sensor for it. The electronics are pretty simple. But I assume that one must use only AC currents for sensing angle, a slight complication.

If I actually do it, sure.
This is one of those few areas where a dead simple gadget can achieve such precision.
An odd thought: There was a burglar alarm design sold in the 1970s that used a silicon strain gage glued to the underside of the floor (especially the joists) to detect a person walking through. The maker soon disappeared; don't really know why. May have been too fragile or too temperature sensitive to be practical. (Silicon strain gages were new then.) Or, too hard to install in an existing building. Or, too sensitive to wind induced building sway. Or merely too hard to explain. A precision tilt sensor could do the same thing, and could be installed in a closet somewhere. The big advantage was that the sensor was not easily found or approached undetected, and that one could set the sensitivity to ignore small critters scurrying about and most pets.
Joe Gwinn
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On Tue, 07 Apr 2009 09:12:18 -0400, Joseph Gwinn

Very slight. Recall that liquid crystal displays (as found in a $1.99 multimeter from HF) also require AC excitation.

I designed stuff like that in those days. Signal processessing to reject false alarms was indeed the trick before microprocessors became common. It's still a good trick, but a lot easier to implement now.
Another approach was seismic. The sensors were geophones developed for oilfield exploration, basically a dynamic mike with a slug instead of a diaphragm. We made devices that could sense a man walking from a distance of several meters, a vehicle from several hundred meters or a chopper overhead, and it could tell the difference. It used a very small number of CMOS logic chips (less than half a dozen) to do it.
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