Universal testing machine

[jit_singh_tara]

Dear friends ,

I want to design software for universal testing machine ,i have to plot the graph of stress vs elongation . Please suggest me any ideas how to proceed ,Any prior experience regarding the design is welcome.

- Please suggest which adc to use for measuring the stress and how .do we need a high speed adc or what , any practical experience would be helpful.
- Whats the best way to measure correct elongation(or linear distance travel ) .
- how do i plot this graph in real time on pc screen , do i need to transfer the readings from uc to pc through uart , recieve in excel and plot a graph from there, the same gui should be able to operate the machine also(i.e starttest , stop test and other data etc).


Thanks and regards
Jitender

 

[Kurenai_ryu]

i got this!

-the best way is to use a load cell to measure the stress-compression... LIKE THIS ONES according to your requirements: say you need to measure up to 10000 Newtons (10kN) you will need a 1000kg load cell (remember 1kgf = 9.8N)
then, you need an resistor bridge ADC (or some kind of high precision ADC) i suggest the AD7714 (mmm i have seen one with this ADC) or the AD7730 (i'm planning to use it in next projects) or any ADC with mV differential input, and over 16 bits of resolution (sadly this is the MOST DIFFICULT PART of the project, to get tha ADC to work with minimal noise and error).... (having readings of 20ms or more (up to 250ms) will give you enough data samples for many material tests

-to measure the elongation, we used part of the mechanism, so we setted a rotary encoder, in a way that any linear movement will make the encoder to rotate... it exactly measured the amount of rotation that the motor gave to the load cell, and thus the amount of distance traveled (we got some error by mechanical loss but it was affordable)

- yeah, as the amount of data is huge, we got a microcontroller to read the ADC, count the pulses and send them to a PC, where they could be stored, and you can manage the sample number, test results and so... also the microcontroller managed a VFD to control an small AC motor.



Sorry it's in spannish, but i can give you a document where i just analysed one of this machines and got all this info, and a few photos of that machine:

 

[jit_singh_tara]

Thanks a lot kurenai_ryu ,

The information u gave was really useful , I would be really thankful to you if you could provide me with some more information regarding this project in english form , please send me all the details which you have.

Thanks buddy....