Building differential electronic levels?

[John Garner]

1. I'll suggest checking with Federal about the damping oil . . . twenty, maybe thirty, years ago, someone -- I'm pretty sure a Federal rep -- told me that the damping oil was USP Mineral Oil.

2. I'll also suggest that anyone thinking of building a roll-yer-own electronic level take a good look at the websites of the two major US makers of electrolytic level sensors, Spectron and Fredericks.

Tilt Sensor and Inclinometer Design and Manufacturing - Spectron

The Fredericks Company - Electrolytic tilt sensors, vacuum measurement devices, and precision custom glass components for OEM customers.

3. Here in the US, both Sperry TILT sensors and Applied Geomechanics tilt sensors were based on the Spectron / Fredericks electrolytic level sensors, and I think (old recollection) that the original ELECTROLEVEL sensor (referenced by link in RC99's post 57, above) was one company's tradename for an electrolytic level sensor.

4. I have first-hand knowledge of damaged "suspension ligaments" in precise self-leveling optical equipment being successfully replaced with plastic film strips made by removing the adhesive from pressure-sensitive Mylar/polyester or Kapton/polyimide tape. Those repairs were what the military might call "field-expedient", but they worked until the equipment could be returned to a repair shop for the installation of factory parts. Based on that experience, I can also add that selective, educated, non-removal of the tape's adhesive can make installation of the improvise parts easier than installing OEM ligaments.

John

 

[NateA2]

I hope to take the level unit apart again now that I have made it functional. It does not repeat as well as I wish it would at the .5AS resolution.

My suspicion is that the 3 brass shims, suspending the pendulum are not positionally correct. I suspect they need to be set very carefully to have the pendulm not be influenced by them.

Additionally, I don't understand why they used 3 instead of 4. was a triangle layout more stable rotationally than 4? I also want to mic them and get the OA measurements.

The transformer (LVDT) looks to be very similar to whats inside federal electronic indicators. Federal made LVDT's like these, they are pictured in the scan of the manual. One is also for sale on ebay at this time. Federal Electronic Gage Head Model Ehe 1049 Used | eBay

the LVDT is sealed with clear epoxy.

Nothing complex in these units folks, and I dont see any reason to (at this time) explore all sorts of other sensors. The LVDT's clearly work, are available and their interface with amplifiers is understood.

I wonder why the pendulums length was not made greater? it could give greater resoloution to the degree that .1AS could be repeatably obtained without too much trouble.

For instance: the 20AS resoloution repeats spectacularly. 1AS is significantly worse. .5AS is not good at all. Tapping the unit seems to bring it into compliance (most of the time)

If I built one that had a longer length of the pendulum suspension bands, I should be able to read .5AS more reliably. I believe...

 

[NateA2]

"Tilt Sensor and Inclinometer Design and Manufacturing - Spectron"

The datasheet containing rg33a, shows a .1AS resolution. Sadly, the repeatability is .0008Deg or a bit over 2AS. if this is the case, that means they can measure sub AS, but the measurement is useless, if I cant repeat it.

 

[John Garner]

NateA2 --

Can't honestly answer your question about Federal's use of three suspension bands instead of four, but I suspect your three-is-more-stable speculation is definitely barking up the right tree. I know, from experience with optical equipment, that four suspension members can cause a bi-stable condition in the suspended member, and I can easily imagine that the Federal pendulum rocking across the short-band diagonal could subtly change the location of the pendulum's LVDT loop.

John

 

[John Garner]

A couple more thoughts:

1. The significantly-better-resolution-than-repeatability level / tilt sensors work very well, when bolted in place and both mechanically and thermally protected, for monitoring a structure (including bridges and dams) over long periods of time. Although those applications are not "obvious" machine-tool applications, I have heard that modern very-large machine tools often have built-in level sensors and temperature sensors that enable cutter-position adjustment relative to the machine structure to compensate for thermal distortions of the machine structure. I have also been told, by someone I consider to be technically competent, that the Spectron / Fredricks electrolytic level sensors noise floor is greatly reduced if higher-grade electronics are used to evaluate the bubble position.

2. Wyler AG of Switzerland, the very-highly-regarded maker of both bubble and electronic levels, publishes a "Compendium The Secrets of Inclination Measurement" that is VERY WELL worth studying: http://www.wylerag.com/fileadmin/pdf/compendium/Compendium_eng_2013.pdf

John

 

[gernoff]

John;

Thank you you for your wealth of information.

Erik

 

[Demon69]

I have to draw attention to how irresponsible and thoughtless it is of you to have posted the pdf link below, as it keeps folks wot know nuffink but have an almost obsessional need to learn sumffink very busy!

The Secrets of Inclination Measurement" that is VERY WELL worth studying: http://www.wylerag.com/fileadmin/pdf/compendium/Compendium_eng_2013.pdf

John

Id also like to thank you very very very much!

 

[John Garner]

For those who are seriously into do-it-yourself, and want to try making a Brunson-type electronic level based on differential capacitance sensing of bubble position within a vial, here's a couple of links that can get you started on the vial grinding:

NavList Message (photos to illustrate text, linked immediately below)

NavList Message (text to explain photos, linked immediately above)

After you've made the vial -- and assuming that your Google-fu is better than mine -- the basics of applying the sensing electrodes and the circuitry to turn bubble position within the vial into voltage can be found in "A Simple Tiltmeter", published in the Fall/Winter 1981 issue of NASA Tech Briefs. The Ames Research Center document number of "A Simple Tiltmeter" is ARC-11344.

John

 

[RC99]

The Talyvel offered to me turned up today in the mail..The previous owner is a friend of mine and he offered it to me on the basis that if I can get it to work, I can buy it.. He purchased it off ebay but never used it.. It had no batteries with it and I believe it used mercury batteries due to their very flat voltage discharge rate..

Anyhoo, I was expecting a Talyvel 1, finest scale graduation of 2 arc seconds..

Turns out it is a Talyvel 2, which is twice as sensitive, with a one second/graduation scale..

I did read they could be powered for short amounts of time with a standard 9V battery... Installing one of them is just a simple procedure.. Doing a battery test showed it came on the lower end of the battery OK scale.. I think the mercury batteries are a higher voltage...

Anyhoo, I put it on the surface plate and switched it on, scale went to one end, so I jacked up one end with feeler gauges.... Got it zeroed on the large scale, then at least on the scale witht he finest graduation..

Wandered around the cement floor the plate is sitting on, the pointer moved 1 arc second when moving from one end of the plate to the other...

Quite impressed and quite happy... Have to pay for it now, which will be a pleasure..

I will see if I can get a manual from one of the Taylor Hobson dealers and some info about batteries..

 

[RC99]

Two pics of me at either end of the plate, showing how the needle moved..

 

[RC99]

Talyvel 1 and 2 manual

https://dl.dropboxusercontent.com/u/46279918/Talyvel 1& 2 Handbook 212-7.pdf

 

[Artemia Salina]

RC99,

If it's of any help, here is a discussion from 2009 on powering a TalyVel 1. The Mallory SKB-830 batteries are no longer available, but the discussion was able to determine the required voltage (13.5VDC for the pair). Perhaps the unit could be retrofitted with a regulated DC wall-wart power supply?

Reviving a Talyvel inclinometer

 

[RC99]

RC99,

If it's of any help, here is a discussion from 2009 on powering a TalyVel 1. The Mallory SKB-830 batteries are no longer available, but the discussion was able to determine the required voltage (13.5VDC for the pair). Perhaps the unit could be retrofitted with a regulated DC wall-wart power supply?

Reviving a Talyvel inclinometer

Thanks, yes I had read that thread in my search for information...

The manual I got from Taylor Hobson confirms the above, it says two mallory batteries at 6.7 volts each connected in series... When the batteries reach 4.5 volts each they are depleted and should not be used.. There was also a mains power supply as an optional extra... I have plenty of cheap 12V wall warts here, but wonder how ripple free their output is.. I think I would also find how much power the Talyvel consumes in operation and get an appropriate fuse if I was to use a mains supply... It is easy to see why differential levels are used when measuring very fine angles...

 

[Artemia Salina]

When the batteries reach 4.5 volts each they are depleted and should not be used..

That's pretty much confirmation that the voltage is being used as a reference, too.

There was also a mains power supply as an optional extra...

Yes, I was searching evilbay for one last night. :-) Sure would be nice to get the schematics for one. They're probably nothing too fancy, but it'd be nice to be able to build a replica.

I have plenty of cheap 12V wall warts here, but wonder how ripple free their output is..

I like the idea of a wall wart because it keeps any heat away from the unit and maintains temperature stability, but you're right about ripple. I'm not an expert on wall wart PS's but I think they may not be regulated, so that's something to check as well. Maybe make a larger case for the PS guts and add a line cord, more filtering, and an adjustable regulator. Of course if you go to that much trouble you might just as well build a PS from scratch. Then you could start with a 18V transformer and regulate down to 13.5.

I think I would also find how much power the Talyvel consumes in operation and get an appropriate fuse if I was to use a mains supply...

I think if you could find the amp/hour rating of the original battery set you could deduce the current draw from the anticipated battery life of 250 hours. I'm guessing there are no transistors in the unit so I think we're talking on the order of 100's of miliamps current.

It is easy to see why differential levels are used when measuring very fine angles...

 

[RC99]

The analogue scale meter unit on my Talyvel is sticking at various places on the scale... You slightly bump the unit and it frees itself.. i do not really want to pull it apart..

 

[TGTool]

The analogue scale meter unit on my Talyvel is sticking at various places on the scale... You slightly bump the unit and it frees itself.. i do not really want to pull it apart..

Mount a small vibrator on the case to do the automatic thumping for you.

 

[RC99]

Where would one acquire a small vibrating tool?

 

[TGTool]

Where would one acquire a small vibrating tool?

Wow, I can't pass that setup.

Around these parts there are "adult stores" that have battery powered vibrators. At least that's what I've been told. Maybe borrow from a woman friend to test proof of concept? If spouse has one I don't want to know about it.

Sorry, a little loopy this evening so maybe the de-stress is coming out. I've been seeing a friend through recovery after a major operation. Yesterday he took his own life.

 

[RC99]

In my quest to discover the sticking part of the Talyvel I did remove the analogue dial from the meter unit... It was an extremely simple thing to do... I did not remove any covers off the dial though, just the unit as it seemed free.. I wondered if the level unit was malfunctioning... I forgot to take a picture of the circuit board of the Talyvel.... Not an IC to be seen, just resistors, capacitors and these round top hat shaped metal cap things with three insulated wires coming out of them that I assume were early transistors.. Very simple electronics in todays world...

I did little to the level unit... Just took off the covers and had a look.. The pendulum is suspended by the five very fine wires that was mentioned earlier... When you put it in transport mode the weight is taken off the wires and the pendulum is forced upwards against four stops... Only four wires in the level unit.... One looks to be an earth, and an input wire and two output wires I would guess...

 

[gernoff]

Nate, you inbox is full......