Help An issue with a cantilever tube instrumented with strain gauges.

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Discussion Overview

The discussion revolves around issues encountered with a cantilever tube instrumented with strain gauges, focusing on the measurement of strains and the sensitivity of the gauges to applied loads. The conversation also touches on programming challenges related to data acquisition and file handling in C++.

Discussion Character

  • Technical explanation
  • Homework-related

Main Points Raised

  • One participant describes the setup of a cantilever tube with strain gauges and notes an unexpected high output when a small load is applied, raising questions about potential causes such as lead wire resistance and soldering issues.
  • Another participant suggests checking the zero load null and the gauge factor input into the readout system as initial troubleshooting steps.
  • A participant expresses a need for assistance with programming in C++ to handle data from two DAQ cards, indicating a lack of experience in this area.
  • One response indicates a lack of programming knowledge, specifically in C++, and suggests that the participant seek help in a dedicated programming sub-forum.

Areas of Agreement / Disagreement

The discussion includes multiple topics, with some participants focused on the technical issues of the strain gauges and others on programming challenges. No consensus is reached on the causes of the strain gauge sensitivity or the programming inquiries.

Contextual Notes

Participants have not fully explored the implications of lead wire resistance or soldering on the strain gauge readings, and the programming question remains open-ended without specific guidance provided.

Who May Find This Useful

Individuals working on strain gauge instrumentation, those troubleshooting measurement systems, and beginner programmers looking for resources on data acquisition in C++ may find this discussion relevant.

babistopher
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I am working on the development of an instrument which can be simply thought of as a cantilever tube. This tube is instrumented with strain gauges to measure the X/Y strains and two sets of rosettes, each consisting of two strain gauges at 45 degree. Note that the X/Y are 3-wire half bridge and the rosettes (for torque) are full bridge. I have been having several issues with this instrument and I am trying to figure them out one at a time.

First of all, when I apply a small load (around 1 N) I get an output of around 12 N if not more. Would anyone know why the gauges seem to be so sensitive to the loads? I have taken into consideration the gains of the amplifier and filter in the circuit. Would lead wire resistance be the culprit despite it being a 3-wire connection (which apparently negates its effect)? What about soldering? That's my first of many questions! Any help is appreciated!
 
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The first things I would look at are your zero load null and the gauge factor input into your readout system.
 
Sorry I didn't reply back. I had to work on something else for the past couple of weeks. Thanks for that. I'll look into those things whenever I can.

I do, however, have a more urgent task at hand and was hoping you could help me out. I am supposed to write a program using C++ that will take data collected by two separate DAQ cards and save them as either a text or spreadsheet file. Now, I'm still new at C++ and I do not even know where to begin. I have been looking for some literature or tutorials that might guide me online but I have had no luck. Would you know of any sites I could look into for that? Thanks.
 
Sorry. I am not a programmer. I haven't done anything outside of Labview when it comes to DAQ. I don't even think I could tell you what the first line of C++ code should say.
 
babistopher said:
I have been looking for some literature or tutorials that might guide me online but I have had no luck. Would you know of any sites I could look into for that? Thanks.

Try the Programming sub-forum...

https://www.physicsforums.com/showthread.php?t=15689
 

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