Measuring resistance

[Zeria]

For my science fair project this year I'm measuring the effect of temperature of a wire on resistance. The circuit I made is working, but when I try to use the ohm meter it doesn't display the resistance. Does anyone know what I could do?

 

Images: http://imgur.com/a/nV7hM

[Externet]

Hi.

First confirm that when joining the probes of the multimeter, the OF overflow changes to a near zero reading.

If yes, check the alligator clips are secured to its wire and to the item biten, not to its insulation.

 

Minimize the number of jumpers in the test. Those pictured are well known to fail the chinese way.

If there is a bad jumper, you can find which with the multimeter.

Edited January 15, 2015 by Externet

[studiot]

Well I would say your meter is indicating 'overflow' because the resistance is so high that it can't be measured.

I would say that is because it looks like (in photo1) you have only connected your croc clips to the insulation around your wire, not to the wire itself.

 

BTW I'm not sure you will get enough variation with temperature to show on your meter. I would think you would need several hundred metres to see any effect with the sort of wire that appears in your photo.

 

 

Edited January 15, 2015 by studiot

[Sensei]

Do you realize how small resistance has plain metal wire, copper, aluminum, iron?
Check out on table
http://en.wikipedia.org/wiki/Electrical_resistivity_and_conductivity

Cheap multimeter has resolution maybe 0.1 ohm (check in instruction).. And you have maybe 1 m length? Did you exactly measured diameter and length of wire?

Edited January 15, 2015 by Sensei

[Zeria]

It's 5 meters in length, and .5mm in diameter. What is the best way to go about removing the insulation on the ends of the wire without damaging it? The circuit itself runs by the way, so there are no problems with the jumper cables.

 

Also, the instruction booklet lists it as able to record up to 60MΩ.

Edited January 16, 2015 by Zeria

[studiot]

Wire is specified by it's cross sectional area, not its diameter.

Even electricians often get diameter and cross sectional area mixed up.

 

0.5mm² is the lowest European and UK standard mains wire size and carries a 3 amp rating and this lamp or bell wire looks rather like yours so I guess you have 5m of standard bell wire.

 

This calculator shows that 5m of this wire has a resistance of nearly 0.2 Ohms so measuring this on the 60 Megohm range is inappropriate.

You need a low ohms range and not all meters will go that low, which is why I said you need a longer wire.

 

http://www.epanorama.net/index.php?index=calc_cable

 

Note in the screenshot that they call it wire diameter (wrongly) like many electricians, but they have the correct units of cross sectional area.

 

 

 

For stripping the insulation off the wire if your school has that meter, does it not have wire strippers?

 

Alternatively try nail clippers. Use these lightly to only cut the insulation, not the wire.

 

I won't recommend a knife as they can be dangerous to use.

[swansont]

What's the component in the last picture, that's held in the alligator clips?

[Externet]

Just hit my head against my brick wall.

A correctly posted first post, showing good skills of keyboard massaging; picture taking, editing, uploading, composing, attaching...

 

Asking how to remove the insulation on a wire.

 

Kids in these days have a different set of expertise from when we were 11 or so. Impressive. Well, we were kids learnig once too, and someone may have had such opinions from us then.

 

Zeria : complement your experiments with a little reading of electrical theory; and keep going with your curiosity, that the road in front of you is loooong. Visit a friendly old fart and learn/observe handywork from him.

Suggest you check youtube for removing insulation on a wire; it may serve your question on a better way.

[Greg H.]

Kids in these days have a different set of expertise from when we were 11 or so. Impressive. Well, we were kids learnig once too, and someone may have had such opinions from us then.

 

Off topic, but this reminded me of the first time my daughter saw a rotary dial telephone.

[John Cuthber]

I'd also like to know what's between the green and black croc clips in the last picture.

But it won't really help.

Stripping the wire will, at least, make a circuit that you can get some sort of resistance measurement of.

but the effect of temperature is small and the meter will not be sensitive enough to detect it.

Either you need a much more sophisticated measurement, or (more realistically) you need a much longer or thinner wire.

 

Enthalpy, if you look at the meter it only has one resistance range and the display says it's auto-ranging, but overloaded.

so it's not meaningful to say it's on a 60 MOhm range.

[Externet]

 

Off topic, but this reminded me of the first time my daughter saw a rotary dial telephone.

Off topic, wait until she sees a real typewriter...