Strain gauges

Hello,

I'm currently using strain gauges for my graduation project and I'm required to install the strain gauges into concrete surface and on the rebars inside the concrete.

  1. What do you advice me to take care of ? As i'm afraid that pouring the concrete on the strain gauges inserted on the steel rebars imbedded inside the concrete will ruin the strain gauges!!

  2. Is there any calibration steps i need to do before i start the actual code for the readings i wanna obtain from the strain gauges? I will be using Arduino mega

  3. How do i obtain what's called " strain gauge factor " ? Is it different for each strain gauge ? ( as i have 120 strain gauges to use ) and when i obtain that factor what should i do with it exactly ? Does it have to be included in the arduino coding?

Thanks,

That is a pretty specialized project. I'm comfortable putting strain gauges on metal but not on concrete.

Concrete is very corrosive. Once the strain gauges are on the steel you will want to cover them with a waterproof protective layer. The strain gauge suppliers I have seen will sell several products for this. Then any wires leaving that protection should have no joins until they are outside the concrete and any future environmental moisture. (Keep the rain off the joins.)

I'm not sure about concrete. I would however first research what you expect the concrete to do. i.e. what do you plan on measuring.

For the Rod, I would wrap the strain gauge in plastic. Food wrap might be too thin, perhaps a piece of 2 mil dropcloth might work. Or the inner bag of cereal (I've seen the Cheerios and the bag appears to be HDPE and pretty rugged.

Then I would wrap it with a thin layer of packing foam. Maybe 1/8 thick. My guess is the wires will be fine if you leave them with slack at regular intervals. In addition, I would install 2 strain gauges, right near each other in case one breaks.

As for the actual mounting, I would check with Omega. They are specialists and can provide a wealth of data. I would guess if you called their tech support they could give you better recommendations than I.

For the measurement you will need one of these for each Strain gauge. Strain gauge amp

As for calibration. What can you do at school? Can you stretch a piece of rebar.

Gauge Factor. Again see the Omega website. They explain it much better than I.

Arduino coding: I would send the raw data from the boards through a UART (serial port) and capture it on a PC. Do any post calculations in Excel. I've learned over the years that trying to scale or convert data in an app is a problem waiting to happen. With the raw data you don't have to worry about using the wrong scale factors or loosing some resolution due to an type conversion etc.

Good luck

Thank you so much!

I already bought the strain gauges welded to the amplifiers.

As for the calibration, i will refer back to my supplier as you mentioned.

I just need help with the coding, I will apply loads on different specimens and I’m trying to measure the change in dimensions due to the impact of these loads ( lateral loads). That’s just as simple as that, i only need to read the values of strains for the different dimensions of the specimens. Do you have any tips on what i should use in my code?

Thanks and best regards,
You’ve really been a great help!