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    Quote Originally Posted by TGTool View Post
    Mount a small vibrator on the case to do the automatic thumping for you.
    Well may you laugh, but that's what is fitted in analogue aircraft instruments, exactly for that purpose. I kid you not.

    13.5 V is near enough to 13.8 V for warfies' work! 13.8V power supplies are a dime a dozen.

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    Nate,
    Great post -- always like to know how fundamental things are measured. I can't quite make out in the photos what f
    Federal used to hang the pendulum.
    Is it some sort of Mylar film tape like thin recording tape or is it metal. Someone mentioned it was hung by 3 bands? That would make sense since it would make sure the pendulum always had constant force on the bands no matter any thermal twisting etc.

    I noticed some surface bubbles on the oil, I think they could cause repeatability problem from variations in surface tension between the support bands.

    Please describe the pendulum hanging system, width and thickness etc.

    I saw a gravity experiment once that demonstrated the force between two masses one of the masses was hung from about 10' with audio recording tape. The mass was two steel balls with a shaft between hung in the center by the tape. So any unbalanced force pulling on one ball would rotate the assembly and twist the tape. A mirror was glued to the tape just above the balls and alight beam used to detect any rotation of the mass. The entire thing was in a draft proof housing. The second mass was a large box of sand on a dolly. As you moved the box close to one of the balls the light beam would move as the mass in the box rotated. I must have been 10 at the time but it impressed me. The resisting force needed to twist 10' of mag tape must have been so very very small.

    Cool stuff

    Craig

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    It's been a while.

    I have been working a bit more on my testing of LVDT as a sensor for an electronic level.

    I have found (trial and error) that a LVDT that I have salvaged from a federal unit, can be interfaced into a gauge amplifier.

    The LVDT works with the setup I have made for testing. With ~ .030" of lateral movement (.015" either way from center) I can get the Amp to register a total of three hash marks when set to the least resolution setting. Oddly, the higher res settings give me less movement of the needle. Regardless, the sensor works with the amp, and now its time to mount the sensor in a level body of some type for testing.








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    well, playing with the connections a bit, I am able to get a much more drastic spread on the amplifier dial. This is great, but I need to figure out what the gage amplifiers outputs and inputs really are.

    Anyone good at reading schematics? if so, could you look at the last page in this PDF, and let me know what the input/output connections are for this amp? I have put my meter to them, but have not been able to make heads or tails of the readings.

    Since LVDT's require AC voltage to the center coil, I believe that the federal amp must be outputting a very low voltage AC. Sadly my meter cannot read this. 2 of the connections on the amp must be return from the other two coils, and one ground coming out of the amp. Any thoughts?

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    Default How the LVDT works

    Quote Originally Posted by NateA2 View Post
    well, playing with the connections a bit, I am able to get a much more drastic spread on the amplifier dial. This is great, but I need to figure out what the gage amplifiers outputs and inputs really are.

    Anyone good at reading schematics? if so, could you look at the last page in this PDF, and let me know what the input/output connections are for this amp? I have put my meter to them, but have not been able to make heads or tails of the readings.

    Since LVDT's require AC voltage to the center coil, I believe that the federal amp must be outputting a very low voltage AC. Sadly my meter cannot read this. 2 of the connections on the amp must be return from the other two coils, and one ground coming out of the amp. Any thoughts?
    An LVDT is really just 2 transformers hooked up to oppose each other. The center transformer coil is used to excite the
    other two coils. The input is AC, and like any transformer, the output is AC. When the slug, the moving iron part, is
    centered between the two output coils, each coil receives the same amount of excitation and they cancel each other
    out. When the the slug has been move to a position away from center, one coil effectively gains some windings and the
    other coil effectively looses windings, thus the coil with more windings has more output than the other and the output
    is the difference between the two coils.

    A transformer works by magnetic induction. If there is no iron, there is no magnetic induction. If you have a coil with
    ten windings, but there is iron only on/around five of those windings, then effectively five of those winding do not get
    get any magnetic induction. The amount of signal you get is proportional to the winding ratio. If a transformer has two
    windings in the primary coil, and only one winding in the secondary coil, you get a step-down transformation IE:
    10VAC on the input gives you 5VAC on the output.

    So lets say you have an LVDT with 100 windings on the primary/input coil and 100 windings on each of the two
    measurement/secondary coils - now you put a 10VAC signal into the primary coil, and move the slug to center
    position between the two secondary coils. Each of the two coils have half of their coils windings able to support magnetic
    induction because the iron slug only covers half of each coil (50 windings). So, each coil puts out 5VAC, and they cancel each other out. Now move the iron slug to the far end of it's travel, and now one coil has no magnetic coupling (no iron), and the other has all 100 windings magnetically coupled and so puts out 10VAC. If you move the slug to the opposite end the other
    coil will now put out the same 10VAC but with opposite polarity.

    A long explanation, but you should get how it works, and what the signals should be. To know exactly you
    will need the windings information from the manufacturer.

    Good luck - Paul

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    Quote Originally Posted by RC99 View Post
    Talyvel 1 and 2 manual

    Dropbox - 404
    Hello; it is 5 years now, but I take my chances: I just bought an used Talyvel off Ebay and couldn't find the manual for it. Also, for some reasons, I couldn't access the link you posted here . Do you happen to have a copy of it in your computer ? Or maybe you uploaded it somewhere else too, where I could access it. Thank you very much for your time. Just in case, my email is : [email protected]

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    Default Bateri from TALYVEL 1

    I got that device but 1 battery was inside skb830 6.75V.. Anyway as you know 2 should be inside which comes to 13.5V.
    You can use 9 in series AA batteries (U=1.5V x 9=13.5V)

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    I have a Talyvel 4, which uses a 2x 9v NiCd battery internally. When they fail I plan to replace them with modern Li-ion batteries.

    In the same vein, if you connect 4 standard 18650 cells to a 4-cell charge controller/balancer board it will put out 14.8V. You can drop that to 13.5 with two silicon diodes in series. It's an inexpensive rechargeable solution that was not available 50 years ago when your Talyvel was designed and built.

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    I very much liked the idea of a DIY differential leveling system.
    Small core-less LVDT's are readily available together with cheap ADC and micro controllers for signal conditioning with infinite resolution (in theory anyway). Non-linearity is also possible to correct.

    The level can be calibrated by placing it on a straightedge resting on slip gauges.
    0,004848mm/1m of height difference equals to 1,0 arcsec.
    Using 1031mm between blocks a 0,005mm height difference is needed to achieve the same angle.

    Is it as simple as fixing the LVDT sensor to a central post and let the core move with the pendulum as proposed on the sketch?
    Did a few FEA iterations and I am now displacing 0,800-1,0μm/arcsec using 0,05x5,0mm steel ligaments.
    screenshot-1-.jpg

    What it typical thickness of the ligaments holding the pendulum?
    What kind of displacement seems to be "normal" for such equipment?
    It seems like it's a critical spot when transitioning between directions - does the commercial levels do any magic here or is it just a theoretical problem?

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    You can find the Talyvel patents online. They make interesting reading.

    The support is done with three fine copper-berillium wires. The design is clever. One of the support wires forms a "V" at the front of the pendulum, with the top ends of the V on either side and the bottom of the v in the middle of the moving carriage. A second identical support wire is at the back of the pendulum. Together these control four of the six degrees of freedom. The third wire is located at the side, and prevents rotation about the axis which passes through"tips" of the front and back Vs. The clever aspect of the design is that it controls but does not overconstrain the motion, and has zero backlash or hysteresis. When I did some adjustments to my Talyvel heads, I was terrified of breaking these wires. Later I had a phone conversation with the people at the UK home of Taylor Hobson, who do such work every day. The told me that they have seen broken suspension wires only a few times in the past decades. Apparently the designer, Richard Reason, would routinely test the read heads by knocking them from his workbench onto the floor, and wasn't satisfied with the design until they passed that test every time. You can read about him here:
    https://homepages.abdn.ac.uk/npmuseu...e/Taly2010.pdf

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    Quote Originally Posted by ballen View Post
    You can find the Talyvel patents online. They make interesting reading.

    The support is done with three fine copper-berillium wires. The design is clever. One of the support wires forms a "V" at the front of the pendulum, with the top ends of the V on either side and the bottom of the v in the middle of the moving carriage. A second identical support wire is at the back of the pendulum. Together these control four of the six degrees of freedom. The third wire is located at the side, and prevents rotation about the axis which passes through"tips" of the front and back Vs. The clever aspect of the design is that it controls but does not overconstrain the motion, and has zero backlash or hysteresis. When I did some adjustments to my Talyvel heads, I was terrified of breaking these wires. Later I had a phone conversation with the people at the UK home of Taylor Hobson, who do such work every day. The told me that they have seen broken suspension wires only a few times in the past decades. Apparently the designer, Richard Reason, would routinely test the read heads by knocking them from his workbench onto the floor, and wasn't satisfied with the design until they passed that test every time. You can read about him here:
    https://homepages.abdn.ac.uk/npmuseu...e/Taly2010.pdf
    Interesting.

    I did not find the patent however I found this link with Talyvel schematic diagram on page 19.
    https://royalsocietypublishing.org/d...rsbm.1990.0039

    You are describing three wires in total compared to the PDF which is describing five wires. I guess four of the five wires are the "V" in each end of the carriage?
    Is it only one wire on one of the sides of the carriage?
    How does it in that case control rotation in both directions?

    I seem to to failing totally in understanding the concept here

    If you have pictures to share from your Talyvel interventions it would be much helpful


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