(-Planning Exercise - Strain gauge Coursework Help -)

[chidinma]

The Actual Practical Is On Moment And Electrolysis..actually This Site Helped Me a lot..i Just Started Mne Today...
Thanx To You All

 

[chidinma]

i don't undertand the two experiments...i used a metre rule and attached the strain gauge at the centre of the metre rule with the aid of a super glue..and attached a load under the gauge..i don't know whether it is right..we are told to use copper not aluminum as it gives much strain..im now asking..where do we fix the copper..do we put it round the gauge or what...
secondly,do we have to put down two drawings: that of the meter rule and also the second expt...i was told by ma teacher to use a voltmeter if using a wheatstone bridge is going to be complicated.If youve done this sort of expt let me know or youve got better idea..im stuck i need to submit it on wednesday

 

[wolf_song]

At least I'm not the only one up at this time doing the work... has anyone here finished and handed it in already?

 

[ibnwando]

So far,it seems you guys are making a mistake :surprise: . In the planning sheet it says to investigate how the resistance of a strain gauge depends on the *tensile force*
Tensile forece is:-A stretching force (tension) pulling at both ends of a component or structure along its length.

so basically ,you have to stretch the metal strip or whatever it is you are using, not bend it like in the crane .The crane was just given as an illustration of a forec but they specified what kind of force to look out for:-tensile force. So just to tell u guys not to bend ur metal strip cos it won't be giving u a tensile fore. here's a bit of my diagram tho.

And a strain gauge is a tiny thing, as small as a post stamp so u can just stick it on your surface.

 

[n1ck_w87]

If you bend a strip of material, you are still applying a tensile force along its top edge. If you hang a material like in ibnwando's diagram, you will have to use a lot of force to be able to get an appreciable change in length, and therefore resistance. Bending will be much easier in a labotary situation.

 

[Morph]

http://www.allaboutcircuits.com/vol_1/chpt_9/7.html

Well I read that the full wheatstone bridge is more sensitive on the exact same website that u mentioned. Its stated towards the end. As for how it is connected, i can't draw it 4 u at the moment my paint is ****ed so I can't draw at all which helps but I'll try & describe it to u. I am only using one strain gauge and 4 resistors. Set it up in a full bridge circuit except replace the gauges with resitors so u get r1,r2,r3,r4 and there will also be a volt meter in the middle to pick up slight changes in electrical resistance and a voltage supply. If one of the resistors experience anything, this results in an unbalance and something comes up on the voltmeter.
This probably sounds confusing but I was never good at explaining!

 

[MightyMeanie]

hmmmmmmmm

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

are you sure that will happen, as my physic's teacher hinted at using superglue , - if this is the case techniqually, would we loose marks in planning to use this as it is really just a theoretical experiment (as it were) as we arent really carrying it out... oh well i will keep it as it is for now and ask my teacher tomorow

 

[littlerich]

ibnwando's right, that's exactly how I've set out mine, and apparently that's rite, all i need to know is where i can get more info on what to attach the strain gauge to the metal strip wiv, and what are the safety precautions, if someone wud like 2 help me wiv these 2, i will be glad to email my full plan to that specific person.

 

[little me]

superglue shud be fine as it shouldn't actually get hot anyway. I thought of using epoxy adhesive but I think that it is not ok to use as it has give and is flexible. Safety precautions: safety goggles, nothing on floor to trip over, no water near electricity, use low current as less harmful but still be careful

 

[little me]

i think that some of u r making it more complicated than necessary. You don't need to worry about wheatstone bridges, a voltmeter and an ammeter will be fine and calculate the resistance from V=IR.

 

[little me]

My physics teacher has just sed that epoxy adhesive is good as it is strong but also has give which is good for this experiment! (I'm at a boardig school so my physics teacher is still here!)

 

[Morph]

Hey guys,
What did u all put down for your dimensions?
This is the only thing I am stuck on now.

 

[James101]

what ranges of forces are u using?

 

[Morph]

range of forces

As they obviously haven't stated, I'm sayin use anywhere between 1-10 N as anything bigger than this could result in whiplash- v dangerous!
what r u sayin about the dimensions?

 

[sampreet]

Can't be more then 0.1mm as strain gauge will snap

 

[tom_shardlow]

i think that some of u r making it more complicated than necessary. You don't need to worry about wheatstone bridges, a voltmeter and an ammeter will be fine and calculate the resistance from V=IR.

yeah but remember that you get awarded marks for things in your experiment that improve its accuracy and reliability

so a wheatstone bridge will give you a couple of marks id have thought

 

[little me]

yeah but then you can put the wheatstone bridge etc into the improvements section and get marks for it there.

 

[ibnwando]

But if the wheatstone bridge is too complicated for you tio make..one thing is to get it right then, a voltmeter and ammeter will do just nicely...
but u cud do the wheatstone bridge if u still have time..

 

[ibnwando]

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

u don't need n ohmeter(whatever that is)
connect an ammeter in series and a voltmeter in parallel with the ciruit

 

[tom_shardlow]

yeah but then you can put the wheatstone bridge etc into the improvements section and get marks for it there.

what improvements section?

are some of you actually doing this experiment? coz we don't have to

i only have to do the plan, with (a) to (g)

and then we have a different experiment tomorrow

 

[ibnwando]

If you bend a strip of material, you are still applying a tensile force along its top edge. If you hang a material like in ibnwando's diagram, you will have to use a lot of force to be able to get an appreciable change in length, and therefore resistance. Bending will be much easier in a labotary situation.

I agree with you, Nick but u don't have to use a lot of force to get a change in length in my diagram, instead of adjusting the force, you could adjust the dimensions of the material,and it would stretch nicely.

 

[ibnwando]

are you sure that will happen, as my physic's teacher hinted at using superglue , - if this is the case techniqually, would we loose marks in planning to use this as it is really just a theoretical experiment (as it were) as we arent really carrying it out... oh well i will keep it as it is for now and ask my teacher tomorow

I don't think superglue will melt the strain gauge cos if u do a google search, most laboraotory experments use superglue ,even in biology,when testing animals cos its a lab experiment and its only a temporary adhesive that can serve the purpose without separating the 2 surfaces in contact.

 

[chidinma]

I am submitting it tomorrow..im not scared of what I've done anyway..i know I've tried ma best...I finally saw the paper i wrote something about the strain gauge and here is the diagram of the stuff>>>>>>>>>>>
ope you will find it reasonable
Wish you all the best of luck! If you don't have any hint of what the chemistry practical is all abt...you can let me know

 

[chidinma]

I am submitting it tomorrow..im not scared of what I've done anyway..i know I've tried ma best...I finally saw the paper i wrote something about the strain gauge ope you will find it reasonable
Wish you all the best of luck! If you don't have any hint of what the chemistry practical is all abt...you can let me know

 

[James101]

what substance are you stretching?

 

[little me]

You have to write about improvements you could make even though we aren't doing the experiment.

i used polyamide as has a low yong modulus value (2.4 GPa). Most people in my college have used aluminium as also has low young modulus.

 

[Reizo]

hello everyone, I'd just like to ask, is there any way of adding an ammeter to the wheatstone bridge structure? I'm a lilttle stuck!

 

[wolf_song]

Nite nite guys. Good luck to everyone tomorrow. Thanks for all of your help!

 

[macf13nd]

Completed!

hey all,

handing mine in tomorrow. this site and specifically this thread has been pretty invaluable, so i figured i'd upload/attach my completed one. comments are appreciated, but i think it should be 100% now...

later,
macf13nd

PS: its in two parts cause the site doesn't let you upload .doc files that are > 50kb