Resistance Sensor Problem

ehsjr · 2010-12-18T17:54:24+00:00

I'm in over my head on this one. Need to sense the resistanceof a _fine_ moving wire, and control one, two or 3 of the following:Wire speed, pump volume, and pulsing sine wave amplitude. Thedesign for those 3 controls is done and they are all properlycontrollable with pots. What I don't know how to do is sense theresistance of the wire.The wire is etched to a smaller diameter by running through a chemicalbath with a 0 to 10 amp (controllable) current applied. Speed, currentand amount of chemical all affect how much material is etched away,and the final spec is ohms per foot. The wire can be either platinum,gold or copper (and maybe other material in the future - don't know),and the desired final diameter spec varies, too, but in all cases isextremely fine, almost impossible to see.How to sense the resistance of this wire at the output? It'seasy enough to do when stopped - lay it in a jig with two metalrollers and a hinged lid that, when closed, presses the wireagainst the rollers. But when running? The best I can thinkof so far is essentially the same as the jig, without the lid. __________________ wire__/0 0________wire ^ ^ | | roller rollerThe fear I have is that the rollers won't make consistent contactwith the wire as it moves across them. I can't put a lot oftension on the wire because it is so fine. So the question iswhether this approach is viable. Any ideas on the viability?Any other approaches?Thanks,Ed

Dec 18, 2010 21 Replies

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Ralph Barone 15 years ago

I would still start with separate drive and sensing, just to avoid the problem of having to filter out the drive signal from the actual oscillation of the wire (but maybe that's just because I haven't done anything like this before).

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josephkk 15 years ago

chemical

current

=20

Yeah, it is way late but; much of the wire bounce can be handled with two additional twists on the technique.

use over 180 degrees of wrap on the rollers
put some (a touch of) skew on the rollers to get wiping contact action

=20

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