Strain Measurement NI 9237 Setting

[tonger]

Hi all,

I have been using the NI 9237 to measure a strain gauge rosette. Three NI 9944 were setup as quarter bridges to go into NI 9237.

While doing the testing, I also put an extensometer on my samples. The results from the strain gauge do not agree with the extensometer. But I know that my sample (carbon fibre) should fail around 1% strain.

Here is the strain gauge result.

And the extensometer's.

This is the NI 9237 FPGA settings.

Do you guys know if this is the correct setting?

Best wishes,

Tong

[Marshall_B]

Hi Tong

From the look of your code there isn't anything that stands out immediately as being incorrect.  One thing I had thought about was that you are setting the "Half-Bridge Enable" property rather than a "Quarter-Bridge Enable" property but without physically having a Wheatstone bridge set up to interface with LabVIEW FPGA, I am currently unable to check that this is an option.  

Could you clarify for me what the axis are in each of the graphs?  I suspect you are plotting stress along the x-axis and strain along the y-axis.  For my own understanding of the problem, would I be right in saying that the extensometer is producing the results that you are expecting whereas the strain gauge set up is not?  

One thing that is worth checking is that you calibrated the device correctly in Measurement & Automation Explorer.  Please let me know if you have already done this.

Thanks

[Marshall_B]

Hi Tong

Have you now been able to obtain accurate measurements from your NI 9237?

Please let me know if you need any further help.

Kind Regards

[etuzuner1]

Hi Marshall,

The question may be off topic but I didn't want to create a new discussion.

I have cRIO 9024, 9074 Chassis and NI 9237. I'm getting results both in Scan interface and FPGA interface with a loadcell having 2 mV/V sensitivity but there is a problem. When I choose the excitation voltage to be 2.5 V, 3.3 V or 5 V in properties menu, I can read the exact voltage values from pin 6 and 7 by using multimeter. When I choose 10 V, I read 7.82 V. Do you think this is normal?

After running the vi, I read 0.0095 V/V with full load and 0.00745 V/V with no load. When we multiply the output value with excitation voltage value, maximum voltage value is nearly 20 mV which is correct. The loadcell capacity is 300 kg. This means that I should read 0.067 mV per 1 kg, right?

Here is my second question. Although I change the excitation voltage values of NI 9237 from properties menu, how can I get the same voltage range which I wrote above?

Thanks in advance,

Best regards,

Emre

[Marshall_B]

Hi Emre,

Thank you for your post. I would however advise that you do create a new thread for this so that your post is included with all of the latest forum posts.  This will ensure that more users will read your post and reply with their answers.

If you would like, you could also link to this forum post as part of a more generic 9237 thread.

Kind regards,

[Strain-Measurement]

We have already purchase NI Labview and their various modules.Now I want to know how to do programming on NI 9237,NI9236.Please help in this regards.