length of wire by using resistance??

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Re: length of wire by using resistance??

I saw that Charlie had a respone to Steve's post and I just couldn't wait to see how profound it might be. :(
 
Re: length of wire by using resistance??

Or, if you are a littled bored, you can make up a 4 wire ohmmeter with two $50 DVM's and a D cell. Should get you down to the +or- 0.0005 ohm acuracy range or better. Not as good as a $5K DLRO, but still pretty respectable.

Copper Temp Coefficient: Yep, sure has one.

.00323/degF A 3 degF change gives about a 1% resistance change.

carl
 
Re: length of wire by using resistance??

Carl, can you really get an inexpensive DVM to come up with a 500 microOhm tolerance? I have to claim that I don't beleive you. No offence of course.
 
Re: length of wire by using resistance??

Originally posted by physis:
Carl, can you really get an inexpensive DVM to come up with a 500 microOhm tolerance?
Click to expand...
Yeah, unless I slipped a decimal or two - which has happened to me at least once before (or more). But you can't do it with one, it takes two DVMs and a pencil, a D-cell, some wire, two probes, 4 meter plugs, and a soldering iron.

I didn't have much time to look, but I checked a Newark catalog and found two meters for $39.95 that would give pretty close to .5 milliohm accuracy for a 25 milliohm resistance. Interestingly, the resolution is .001 milliohm.

I don't think I could do better on the price, but I suspect I could better the accuracy and still be under $50 each.

Originally posted by physis:
I have to claim that I don't beleive you. ...
Click to expand...
okay

carl

(Hint: It's a four wire ohmmeter and a shorted D-cell puts out about 4 amps)
 
Re: length of wire by using resistance??

I haven't seen a Newark in at least a decade. There used to be one in Hayward, Ca. My all time favorite electronics distributer.

Are they still around? Where are they?
 
Re: length of wire by using resistance??

Originally posted by physis:
... Newark ... Are they still around? Where are they?
Click to expand...
Their catalogs still are. I didn't even know they had stores. I thought they lived in the back of brown trucks. (UPS deliveries)
 
Re: length of wire by using resistance??

I'll confirm that Carl.

Edit: Are you talking about a Wheatstone bridge?

[ November 24, 2005, 02:31 PM: Message edited by: physis ]
 
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