# Project help!!! Pls

Discussion in 'Homework Help' started by Hunter, Aug 14, 2007.

1. ### Hunter Thread Starter New Member

Aug 14, 2007
3
0
Hello there,

I am doing a project at the moment and it is close to finish. I have build a prototype for to do the compression and shear tests on the human tissue. before the prototype being build, all the test was performed using big test rig. Then it was decide to build a prototype to test the force and i have decide to use Strain Gauge to measure the test. Can I ask a few simple questions here and hope i can get some useful information here.

1.) I am using 2 plate to perform the compression test. the top plate is driven by a cable towards bottom plate (vertically). the cable was pull using a rotary switch. - where should i attact the strain gauge to get a more accuracy reading?

2.) the bottom plate will move in horizontal direction to perform a shear movement. and this is control by a pulling rod. same question again. where should i apply the strain gauge?

3.) is it possible to have 2 strain gauge in a same circuit board to get the two reading? - I need to build a smaller circuit if possible.

Wish to have your help here as i am a medic student, dont know much about the engineering part. Thanks in advance.

Regards,
Hunter

2. ### recca02 Senior Member

Apr 2, 2007
1,211
0
i did not get the complete picture ,
but maybe this will help u
for compression test use the gauge/gauges in line with the support for the fixed
plate.
for shear u'll have to put it on the surface which is under shear.
if ur asking about getting readings on same display ,u can but it wont be possible to have both readings at once on same display.

EDIT: yup didnt make it clear the support shud also be in line(parallel) with the forces (like MR beenthere said) like in weighing m/c otherwise u wud be measuring a torque instead.(now did i need to mention that)?

3. ### beenthere Retired Moderator

Apr 20, 2004
15,815
283
In both cases, the strain guage has to be in line with the applied force for an accurate reading. If the tests run concurrently rather than simultaneously, it may be possible to use the same SG for both tests. Using a two line display may allow you to display both test results.

The mechanism for applying force is going to be interesting. How are you planning to apply force by pushing a cable? How can a rotary switch apply force? If you are tracking displacement, something more like a linear potentiometer may work better.