(-Planning Exercise - Strain gauge Coursework Help -)

[arizonian]

Stress is a load applied to an object. Strain is the deformation of the object under stress. Pull a taffy candy strip lengthwise. The pull is the stress and the lengthening of the candy is the strain. Both can be quantified. The load divided by the cross sectional area gives pounds per square inch (psi). The (final length of the candy strip being deformed minus the original length) divided by the original length is the percentage of deformation.
Now that you know stress and strain, you need to take readings with your multimeter while applying different loads and at different locations. The different locations will change the loading on a cantilever beam suspended by a cable. Use trigonometry to calculate the loading in the cable.

On edit, I did not realize that there were 4 pages of posts. I hope this helps those that still have time.

 

[the fugitive]

erm...ell not reali coz it all so complicated n u jus made everyone elses suggestinos that me has had (that sounded good) sound crap...n especially as me understood those ones lolzzzzzz fuk it me jus na stik to wot me originally thought

 

[Fireball]

at the end of the strip...ther gna be a hole for a weight hanger to han g from it n then aply 0.1 kg weights to it one by one...is that stupid or ok?

Thats what I'm thinking of doing and I'm supposed to be doing it this afternoon!

 

[CKLi]

Hi! Try this website to find out more about Strain gauges. www.dur.ac.uk/richard.scott/gauges.html[/URL]

 

[devil_uk]

coursework

i have until wednesday 19th to get mine in, and i am cluless to what to do...i know what a strain gauge is and that the crain has nothing to do with it, but i have no idear how big the gauge is, or how we have/allowed to apply the force to the material, which i have no-idear to what I am using.....lol.....we are all doomed.....

 

[Fireball]

Hi! Try this website to find out more about Strain gauges. www.dur.ac.uk/richard.scott/gauges.html[/URL][/QUOTE]
Thanks for that link, I had no idea what this was all about :confused: before but reading that sorted everything out in my head and helped me to understand the theory behind it all. i now know exactly what I have to do! :smile: :biggrin: :approve: :smile: :smile:

 

[ashpot86]

I have to write mine up in exam conditions tomorrow(13/5/04), I am trying to plan it now but not much luck, the question asks for any relationship between the force applied to the surface and the electrical resistance, so all that strain and stress doesn't need to be worked out I don't think. I said to use a standard metre rule made of beech wood (i think). Whenever you look for a relationshipe between two things it means plot them in a graph, so i guess that will be a good idea to include. My idea for how the strain gauge is attached to the surface, i just think using a strong adhesive will suffice. For plotting a graph you want a good range of forces to apply, however you want to keep other variables constant. The only thing I haven't thought about yet is what safetly precautions to include. Ah well...

 

[firstkings]

the experiment is in two parts...

stretch a piece of wire . Add a mass, measure the resistance of the strain gauge. No wheatstone bridge, no crane. Glue (superglue) the strain gauge to the wire. keep adding masses (weights), keep measuring V and I. etc

 

[ibnwando]

Thanks for that site CKLI .iT WAS totally relevant!
Im in the same situation as well. Whats wrong with these OCR people??

 

[m0dm0]

Done mine today. thanks for the help everyone!

 

[marieke]

how do you attach the weight to the strain gauge and connect it to the circuit at the same time? is there a paritcular way to plug wires in a strain gauge? please answer quickly!

 

[Morph]

hiya I am doing this exp too. I think ur meant to use some kind of epoxy adhesive. But first u apply some of it to the metal ruler, then stick down a piece of felt for insulation.Then add another layer of epoxy adhesive and stick down the strain gauge. Correct me if I'm wrong people!

 

[MightyMeanie]

the experiment is in two parts...

stretch a piece of wire . Add a mass, measure the resistance of the strain gauge. No wheatstone bridge, no crane. Glue (superglue) the strain gauge to the wire. keep adding masses (weights), keep measuring V and I. etc

Is what you mentioned both parts of the experiment?

 

[ibnwando]

Is there anyone who still has tim left?? I've got a lot of tips for u:-
precautions-safety goggles,in case something snaps
use a low voltage
make sure the metal rod doesn't slip
repeat reading to get an average
air the room to prevent temperature from rising too much

 

[James101]

Hey i am doing this experiment as well and have got to hand it in for wednesday has any1 got any idea of then range of the meters we need to use? or the dimensions of a strain gauge and the material on which u mount it? This is all sssssssssooooooooooooo confusing?

 

[thespacedevil]

the experiment is in two parts...

stretch a piece of wire . Add a mass, measure the resistance of the strain gauge. No wheatstone bridge, no crane. Glue (superglue) the strain gauge to the wire. keep adding masses (weights), keep measuring V and I. etc

never use super glue! it will melt the strain gauge... that the whole point of superglue... to melt the two substances together...it will damage the gauge...trust me.....dont use superglue

 

[thespacedevil]

use a ruler clamped on a clamp stand.... masses atttached to the ruler...move the masses along bout 10cm and take a reading... again move 10 cm...another reading...repeat experiment...draw say u going to draw table and graph.....hey presto...u done it...caio

 

[devil_uk]

any 1 who carez

The material seems to be at the candidates discretion, and as to the dimensions, i have read that is only small being about 16mm long but don't quote me on that....mine also has to be in on wednesday (i go to Joeseph Ruston college in Lincoln and got an extension to the time )
i think that i will use a standard metre rule of beech wood, and mount the stress gauge with adhesive suggested earlier in this topic called cyanoacrylate, mounted at the highest stress point, this should give sufficeint strain on the gauge for decent results, i will use a 10g weight set with a hook-base attached via string through a hole in the end of the rule to apply the strain. also i will suggest saying that ur using the quarter brige wheat-stone bridge circuit with a variable resistor for adjustment and a stress gauge in the circuit for the measurement of the resistance(obvious reasons apply...lol).
Also the crain in the introduction to the question has no relevance to question.
Please if anyone has suggestions for improvement can than post them please?

 

[Morph]

hi i have until wed 19th as well, I have no clue wat a strain gauge is either!- a lot of use i am to u ey! do u no wat the dimensions r meant to be? Is that meant to be the metal ruler? the strain gauge has to be as wide as the ruler rite?

 

[Morph]

my teacher said it has to be a metal ruler instead of a beachwood one. Is that rite?

 

[longhairedbean]

i would have thought that using any kind of ruler would be less effective cos they'd have a large cross sectional area compared to something like metal foil. Considering that it doesn't state the material you need to use, and your only measuring the extension of the strain gauge applying less force, ie less weights would be easier to manage therefore a material with a low young's modilus (is that right? i can't spell) should extend more that a material with a higher young's modilus with the same force applied. the same is true with the cross sectional area.

You'd then also be able to talk about the safety aspecs of the foil/wire snapping rather than working your arse off thinking up something totally irelivant.


on a side note, our actual practical is on wednesday and neither of my physics teachers have 'made' a hassle about buying in strain gauges yet the practical will have something to do with the planning so maybe that's where the crane comes in? i don't know but it might be.

one last thing. does anyone know if we Have to use a wheatstone bridge or will it only icrease the accuracy? is it possible to measure the resistance just by measuring the voltage and the ampage?

 

[devil_uk]

as i said its at the candidates discretion, I'm already changing my plan I'm changing to a aluminium strip about 20mm x 150mm and i will attach the waits from the bottom with a drilled hole about 10mm from the bottom of the strip i will hange the strip vertically aso it dangles, and attack the gauge about mid way (the gauge doesn't have to be the same width i don't think...)

 

[longhairedbean]

a drilled hole about 10mm from the bottom

if you drill a hole then all the force will be applied on a small length of the strip. what you need to do instead is use a clip or something along the whole of the bottom of the strip so that the force is applied evenly over it. All this is just scroundging for that extra mark or two though.

 

[Morph]

seems like aluminium is the best to use then! Yes I'm going to talk about using a wheatstoe bridge. It isn't nessecary according to other people measuring the voltage and current, But I'm talking about it just for the sake of getting an extra mark or 2. I have looked on many websites, but I can't seem to find one which shows how the gauge is connected into a wheatstone bridge circuit. Or maybe its jus me being thick and not being able to understand it!
A wheatstone bridge circuit is more accurate to use coz a) it measures really precisely b) shows that the voltage which shows up to force applied. A full wheatstone bridge is always best to use for these reasons. The other ones like half, quarter etc seem to have more disadvantages for some reason, which I can't remember which helps of course!

 

[Morph]

according to my teacher, the actual practical has nothing to do with our planning exercise, strain gauges or cranes even!but has got somthing to do with stress and strain.
Anyone who has done theirs give us a hint will ya! pleeze!

 

[James101]

If you attach the gauge to a ruler and then add masses to the end of the ruler how do you work out the forces on the strain gauge??

 

[longhairedbean]

http://www.allaboutcircuits.com/vol_1/chpt_9/7.html
http://www.entran.com/gages.htm

the first of these two i found very useful, it shows how the gauge is connected but you've still got to realize that if the amage is kept constant like it is for this experiment (because your not changing the power supply) then the voltage will vary with the resistance, it also shows the full, half and quarter wheatstone bridge.

the second website is an actual strain gauge; we were all talking about them but most of use were ignorant, this page won't help most, me included but i does show that they come in packs of 4 so are designed with a full wheatstone bridge in mind, they also show that the GF is not 2 but 140 or 155 unless i can't read it properly which is very interesting seeing as we were going on about them being only 2 or so, the resistance it shows so is useful but beyond that i can't work anything what any thing means.

can't think of any questions but can't think of anything to write either so something must be wrong...ah well

ah yep; i find the starts the hardest, how are you/how have you started writing you plan cos i can't seem to manage that.

 

[longhairedbean]

this is a question for you morph; in the full-bridge, where are all of the strain
gauges attached to and WHY is this more sensitive than, say a quarter-bridge?doesthe full bridge only test for bending rather than streching because otherwise all of the strain gauges will read the same resistance and so the bridge will always stay balenced. this is just my reasoning so tell me if I'm wrong.

 

[taurinne]

does any1 know how or where to connect the ohmeter and voltmeter on the strain gauge?

 

[wolf_song]

isn't it just in a circuit, so the volt metre would be parallel