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(-Planning Exercise - Strain gauge Coursework Help -)

by Jack_Legacy
Tags: coursework, exercise, gauge, planning, strain
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May10-04, 11:38 AM
P: 3
My Physics plan is supposed to be in tommorrow, if I don't do it, im in deep ****.

All I know is that a strain gauge has a resistance of approximately 100 ohms. It is 15mm long and inside it is a looped copper/nickel foil. Newton weights must be hanged off the end of the wire the strain gauge is attached to, we would need to plot a graph of force against resistance with various forces applied on the wire e.g fron 5-15 newtons. The actual value of resisivity of a strain gauge is 2.

For the resistance to vary, the strain gauge must be really stuck to the wire so that any change in the length of the wire, will strech the copper/nickel foil inside the strain goauge, making the foil longer, therefoer it's resistance increases. But, the change in resistance is too small to be measured with a standard classroom ohmeter, an alternative needs o be used, and I don't know what!! Something about a wheatstone bridge, anyone heard of that??

IF anyone has any details, plllleeeeeeeeeeeaaaaaaassssssseee fill me in!
May10-04, 04:00 PM
P: 5
you have to use something called a wheatstone bridge circuit, to measure the resistance accurately. look it up, it is too complicated to explain. look in and u need to attach the gauge to foil, i think. what i am worried about is how u apply the force to the foil in measurable amounts.
May10-04, 04:23 PM
P: 3
You guys are lucky! For some reason, my head of physics decided it would be a great idea for me to resit my waves/practical paper even though I got a B, so not only do I have to do this one, but I have to do the A2 one as well! And you know what? The A2 one looks so much nicer than this one...

Mine has to be done in class tomorrow or something, I duno, I wasn't listening, but there are some great sites on strain gauges if you just search "strain gauges" on, within the first 6 or so pages.

Good luck guys n gals.
May10-04, 05:15 PM
P: 4
im totally stuck. i havent got a clue how strain gauge work. i only know about resistivity something to do with this formula R = pL/A.
May10-04, 05:52 PM
P: 2
The day is over and i have put a completely wrong answer down on the paper and handed it in and felt stupid!! I just hope that you guys and gals have sum good look and learn how to do it by your deadlines and do well!1 I have no hope now but i hope you get really good grades!! Thanks for all the help and next year when the A2 one comes out we will all probably meet again

Thanks again
See ya next year
May11-04, 05:32 AM
P: 12
Well thanks! i now think i have a bit of a clue as to what to do, which is good! i am at college know doing the whole thing in rough! due in tomorrow!!
May11-04, 05:50 AM
P: 5
i don't have a clue what to do? can anyone explain a bit.
May11-04, 05:55 AM
P: 12
well the strain gauge is exactly like it is in the paper! im sure all you have to do is apply a load by using a wire and pulley. when you know what you're doing its not that bad!
May11-04, 05:58 AM
P: 12
but you need to make sure it wont move, just stretch. 1 thing im not sure of is the dimensions of the material, or the actual material, but as far as i can see it doesn't seem to have that much effect!!
May11-04, 06:01 AM
P: 5
do you have to use a wheatstone bridge
May11-04, 06:07 AM
P: 12
oh, ive just found out maybe all you have to do is put the force on top of the gauge, but maybe this wont measure the strain. i dunno what dyu think? oh no, it says tensile stress, this is not right then is it?

i don't really know what a wheatstone bridge is and so i don't think im using 1, 4 that fact!
May11-04, 06:10 AM
P: 5
could you not use an ammeter and voltmeter to work out the resistance using R=V/I
May11-04, 06:12 AM
P: 5
if you apply the force on top of the guage then how will the gauge strech
May11-04, 06:20 AM
P: 12
yeah! that would work, i think. so then what about the size of the voltage in the circuit? would it make a difference if it was low or high?
May11-04, 06:20 AM
P: 1
what about the ranges of different measurements used?
May11-04, 06:21 AM
P: 12
the gauge would be compressed! i realised this wouldnt b a tensile force then! god this stuff is stressin me! bug style!
May11-04, 06:23 AM
P: 12
which measurements/ the voltage and current? i think by adding a range of loads, the measurements can be made each time another is added.
May11-04, 06:24 AM
P: 12
hey. i'll leave you to it. i gotta go watch a film for english so... hope i have helped. good luck with it.

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