I'm looking for a small(ish) non contact solution to measure an oscillating surface to within a few tens of microns over a stroke of some 50mm at a frequency of around 100Hz. I need to take measurements at 100uS intervals. Any ideas? Cost as always is a factor so anything under (say) $300 in mass production...
-- Dirk The Consensus:- The political party for the new millenium http://www.theconsensus.org
Angled laser, optics and a CMOS image sensor?
- Better than 1ppm accuracy
- Better than 100Hz bandwidth
- Measurements at 10kHz
Sure!
- price < $300
Oh dear.
Keyance makes a non-contact laser distance measuring instrument that gets your 10um accuracy over less than 1mm stroke with about 1/10th your rep rate and your full bandwidth -- they charge about $10k.
Mostly I mention the Keyance's product because you may be able to copy some of it's salient features for your application.
While you're asking your question, you may be able to significantly lower the price of your solution if
- You have control over the surface, and can either prepare it in a certain way or (better) embed something into it to make the job easier.
- The oscillating part is significantly less than 50mm stroke (I'm thinking a 2-part sensor like a capacitive or inductive proximity sensor on the end of a movable probe).
-- Tim Wescott Wescott Design Services http://www.wescottdesign.com
I'm thinking of that. Maybe some kind of interferometer setup with either fringe counting or convert the fringe rate to a velocity measurement.
-- Dirk The Consensus:- The political party for the new millenium http://www.theconsensus.org
I'm wondering whether I can get away with measuring velocity. Still, this is some time away as a project so I'm just scouting round for options. Maybe someone will come up with a really clever idea I have not even thought of.
-- Dirk The Consensus:- The political party for the new millenium http://www.theconsensus.org
production...
Is the stroke strictly one-dimensional?
production...
Pretty much so as far as I can tell.
-- Dirk The Consensus:- The political party for the new millenium http://www.theconsensus.org
Any
production...
I can get you the resolution and about half the stroke, using a capacitive measurement. Our prototype here at the University is a two opamp triangle generator, a 25 mm diameter pair of disks to make the capacitor , a one opamp preamp/clipper, a two opamp precision rectifier and a passive low pass filter. Its crude but we can see distance changes on the order of 5 nM with it. A properly shaped linear capacitor could do it with our circuit, which is by no means a origional concept. Adding a synchronous rectifer as a sort of rude lock-in would really improve things but we havent got around to that yet. Would you like a scanned diagram emailed to you?
Steve Roberts Research Associate, Polymer Science, Akron U.
-- Maybe... Are you willing to pay for it?
opps, forgot, we need a cap plate on each side, so I guess we are not non-contact.
Steve
50mm / 50um = 1000
He needs around 0.1% accuracy. Does that make it any easier?
jp
"John Fields" schreef in bericht news: snipped-for-privacy@4ax.com...
Yes,
Not the idea, but maybe the implementation.
-- Dirk The Consensus:- The political party for the new millenium http://www.theconsensus.org
Dangit.
Why yes, it does.
-- Tim Wescott Wescott Design Services http://www.wescottdesign.com
Not really since I'd already done the calcs for a 12 bit converter.
-- Dirk The Consensus:- The political party for the new millenium http://www.theconsensus.org
I don't even see accuracy requested. It might just be precision and repeatability, which could be calibrated for accuracy if needed (but not necessarily.)
Jon
Any
production...
That's very impressive. I had thought about capacitative measurement but the distance seemed too great. How would increasing the dia of the disk affect the spacing limits?
Also, this has given me a different idea. Would it be possible to put a thin film electret on the device and sense its proximity with the plate?
Anyway, I would definately like to see the circuit as I have other position measurement stuff to do that may be related. Email as above.
-- Dirk The Consensus:- The political party for the new millenium http://www.theconsensus.org
"Dirk Bruere at Neopax" schreef in bericht news: snipped-for-privacy@individual.net...
oscillating
Any
production...
Total travel per second = 100 * 100 => 10.000 mm. Travel between
100uS samples => 1mm. Accuracy 0.02 mm while object is moving... You say 'tens' not 'tenths'. I assume 'tens' not 'tenths'.Doesn't sound as a real time control of something, but just a recording/measurement apparatus. If it were a real time control, the slightest delay in processing could cause problems.
I'd try a linescan camera with ((1/0.02) * 50) => 2500 pixels, perhaps 2048 or 4192 pixels. Don't know if you can get those for
a bigger set of disks increases sensitivity. could also be used in bridge mode with a little thinking to see your electret. parts count = LM412 X 1 Lm318 X 1 2 diodes 7 caps 12 Rs 1 pot runs off +-12 V
we use a 40 Khz 5V p/p triangle as excitation
NASA used to hand out data in NASA TECH BRIEFS on something they called capaciflector which was a scaled up multiple electrode sensor that could have one side "blind" as you need,
Steve
Thanks - that is definately something I have not considered.
-- Dirk The Consensus:- The political party for the new millenium http://www.theconsensus.org
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