Semi on topic LVDT


I had to troubleshoot one of these things today. For some that frequent this
list it is
something they likely have run into or wondered about, expecially if they work in
manufacturing.
LVDT Linear Variable Differential Transformer. An interesting measurement
device. I had
assumed it was something like an inductosyn but I was mistaken.
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is the
wiki page
which is okay but after you have read that, go to
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and watch the animation that makes it clear as a bell.
I learned something today and wanted to share it.
Wes
Reply to
Wes
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device. I had
They're nice non-contact sensors. They'll get you down to the point where you have to start worrying about differential temperatures messing up your measurements, and arms cocked over by milliradians, and other really smoky stuff.
Reply to
Tim Wescott
t this list it is
ent device. =A0I had
There is an even neater and much more reliable way to read the position of an LVDT. The way shown is dependent on the amplitude for position. With DC drift you don't know where you are. And DC offset is a real problem.
You can also use a digital Sine / Cosine generator. You drive the two coils with the Sine and Cosine signals. The phase angle if the third (pickup) coil is now dependent on the position. If the Sine/Cosine generator is driven by a digital counter, you can look for the Zero Crossing point of the sense signal and latch up the current count of the free running counter that is driving the Sine/Cosine digital waveform synthesizer. This is how the Old Bendix CNC units measured the position. They were driving Resolvers. But the same principles apply to resolvers, LVDT od inductosyns. as far as decoding the position. Send out Sine/Cosine and read the phase angle of the sense signal. It is not sensitive to DC drift, it always a full strength signal and not drifting down to zero volts where you do not know if you are reading noise or the intended signal. And being full strength you can discriminate against noise much better.
Reply to
Cross-Slide
This thing is part of a system that measures a part one of our turning centers just made and also provides wear offsets to bring the next part into tolerance.
We are not doing angstroms. I take it they are pretty accurate?
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
Reply to
Wes
list it is
device.  I had
to
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That sorta sounds like an inductosyn?
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
Reply to
Wes
They can be, when they're used right.
Reply to
Tim Wescott
uent this list it is
rement device. =A0I had
An inductosyn is VERY similar to a LVDT in that there is three circuits. The LVDT is magnetically coupled, the inductosyn is inductively coupled. The electronics to drive and decode them can be quite similar. Same for the Resolver. In all cases you can either drive the Sine and Cosine and read the pickup or drive the center and decode Sine and Cosine signals from the two circuits.
Reply to
Cross-Slide
Ayup, they beat the venerable RCH all to hell, in all ways except style and, um, scent.
-- "A patriot must always be ready to defend his country against his government." --Edward Abbey
Reply to
Larry Jaques
And taste.
I am the Sword of my Family and the Shield of my Nation. If sent, I will crush everything you have built, burn everything you love, and kill every one of you. (Hebrew quote)
Reply to
Gunner Asch
centers just made
Which reminds me of the joke Q: What sound does a pubic hair make just before it hits the floor?
A:
-- Some people are like Slinkies ... not really good for anything, but you can't help smiling when you see one tumble down the stairs.
Reply to
Larry Jaques

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