Strain measurement

[BMaria91]

Hello,

I acquired data from asphalt strain gages by using NI 6251. The problem is that I don't understand what is the order of magnitude of my data: ε, mε, µε?

I attached a picture of my task, with the characteristics of one of my sensors.

Since the "scaled units" is strain, I suppose that the data are in ε. But I have some doubts because they are higher than my expectations.

Can someone help me to figure out how I can get this information?

[GerdW]

Hi Maria,

as soon as you provide substantial information…

[BMaria91]

I tried to attach a document to the first message, but I failed.

The picture below is to show you my task. My quesion is: if I put these information, what is the "unit" of the strain that I acquired? ε, mε or µε?

[GerdW]

Hi Maria,

why don't you just read "raw" voltages from your strain gauges? (You use an external power/excitation supply!)

Read voltages and scale them on your own according to the spec sheet of your sensors - should be as easy as it sounds…

Btw. do you really want to read 6000 samples at 675 Hz? Waiting ~9s for new data?

[BMaria91]

I am not an expert and it's the first time that I deal with LabView. So actually I was helped to connect my sensors to NI 6251 and to prepare this task. Can you please give me a suggestion about the samples to read?

In addition, indeed it would be easier to read a voltage and to manipulate it directly, but however can you tell me how I can find an answer to my question?

[GerdW]

Hi Maria,

I would read 675 samples at a rate of 6k…

[BMaria91]

Thank you very much for your answers.

Best regards,

Maria.

[arteitle · Accepted solution]

I haven't used LabVIEW to measure strain, but we can probably figure out the answer to your units question by looking at the units of the parameters you entered, and this document: http://www.ni.com/white-paper/3642/en/

What were the units on the gage factor you entered, 5.61525? The white paper says that GF for metallic strain gauges is typically around 2, and is the ratio of fractional resistance change to strain:Since yours is in the same order of magnitude, I'd guess that yours is also based on strain, not milli- or microstrain. What kind of readings are you getting from your strain gauges? If they're on the order of 1 x 10^-3, presumably they're in units of strain.

[BMaria91]

Yes, I've already read that document and it was really useful.

Well, the units of the gage factor is V/V/ε and this let me think that I am reading in the units of strain.

But I have a question: does the software go from V/V to ε or from mV/V to ε?

I'm getting readings on the order of 1*10^-4, but if they are in the units of strain, they are higher than my expectations.