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Well, it happens a I have a glucose test strip (One Touch Ultra) which has three electrodes (Counter, Working and Reference) and I'm guessing this electrodes are made from graphite mixed with a binder. If graphite is a conductor why the continuity tester registers there is no conduction?

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Whatever, they're made of, I don't think anyone would design a non-conducting electrode. It's difficult to answer this question without more information about how exactly you've connected the continuity tester up. –  Nathaniel Mar 1 '13 at 4:10
    
That's what I think, I was on the idea it was a conductor (like a metal) but it seems is a semiconductor, now that I've made some measurements it read 0.6V as if it were the threshold voltage of a diode, just that reads the same lecture no matter the polarity applied (i.e how I connected the continuity tester), all seems to indicate it is graphite and graphite is a semiconductor, that's why the continuity tester indicated there was no continuity since it is not a metal (conductor) but a semiconductor. –  Favner Mar 1 '13 at 4:19
    
If your multimeter reads 0.6V you are probably using the "diode test" function when you should be using the "resistance"/"ohms" function. The "continuity test" function is often at the same dial position as diode test. continuity just beeps if resistance is less than some threshold (e.g. 50 ohms). Use the "ohms" function. –  RedGrittyBrick Apr 30 '13 at 9:31
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2 Answers

graphite is only conducting 2 dimensionally, when it's stacked in layers. If your guess is correct, that the electrodes are made from graphite mixed with a binder, it is probably bunched together, and doesn't conduct nicely.

My guess is that it's not made of graphite.

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If it's not graphite, and this electrodes are exposed to make contact with the circuitry it means there must be a current flow thru them, right? They must be conductive, why the continuity tester says there is no conduction? (the current flow is generated from the reaction of blood + enzime on the reactive strip) –  Favner Mar 1 '13 at 3:26
    
This is wrong. Graphite rods conducts well. –  Anixx Mar 1 '13 at 3:47
    
Apply ~13[V] to a graphite pencil, you'll see it does conduct. The problem here is that it is a semiconductor not a conductor (as I was erroneously assuming). –  Favner Mar 1 '13 at 4:28
    
@Favner: Graphite is much more conductive than semiconductors such as silicon - see Resistivity of various materials and List of semiconductors –  RedGrittyBrick Apr 30 '13 at 9:40
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Graphite is a semiconductor, this means that its conductivity greater than of insulators but higher than that of most metals.

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Interesting, I did some measurements now that you mention it. I'm getting readings of about 0.6[V],0.7[V] on each electrode, as it it were a diode voltage threshold, just that it reads 0.6,0.7 no matter the polarity applied. –  Favner Mar 1 '13 at 4:14
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Graphite is a semimetal, not a semiconductor. –  Nicolau Saker Neto Apr 30 '13 at 4:27
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