SCXI-1314 wiring

[RobTom]

Hi, I am trying to measure votalge ouput from a strain gauge attached to a cantilever beam. My problems are that I am confused on how to exactly wire my strain gauge to the SCXI-1314 and properly calibrate it.

Thanks

[RavensFan]

Which SCXI module are you plugging the 1314 into?

I use the SCXI-1520 and its manual provides wiring diagrams located here http://www.ni.com/pdf/manuals/372583d.pdf

Look into the manual for your signal conditioning module.  If you still have issues, then please post back here with specific questions.

[RobTom]

Ravens Fan, this is sort of an unrelated question, but I was wondering if you could help me. The experiment I am doing involves finding the forces on a spinning baseball at different orientations. The baseball is attached to a motor which is coupled to a .5" square cantilever beam (lexan). I plan on attaching a strain gauge to the cantilever beam and backing out the forces from the voltage output. The problem is that I don't believe the beam will experience a force greater then 8 grams. Does this mean I have to get a strain gauge with a very high sensitivity, if so, what type should I be looking for?

Thanks 

[JK1]

Hai,

SCXI 1314 is the connector block where you wire the strain gauges in quarter/half/full bridge configuration.

Inorder to find out whether the setup will suit to the measurements or not give in detail about the strain gauge you are using, sensitivity, bridge configuration you are using.

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The problem is that I don't believe the beam will experience a force greater then 8 grams.

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What is the maximum force you are expecting out of your setup.

Post with details so that we can work that out.

[RobTom]

As, I said before, the setup involves the baseball attached to a motor which is coupled to a .5" square cantilever beam made out of lexan. The motor weights close to 3 pounds, so we will have to calibrate the meaurents for that weight at the end. The max lift force I expect to be on the ball is about 10 grams. I was wondering type of strain gauge I need to measure such a slight change in force on the beam? In other words, after calibrating the system, can I get a strain gauge that ouputs a different voltage for each gram of force is put on the ball?

[JK1]

Hai,

Visit the this link to get ideas on selecting the strain guage http://www.vishay.com/strain-gages/knowledge-base-list/technotes-list/

Strain guages gives the output in mV/V.  They respond to minute changes in the surface and can be used for your application. 

Regarding the sensitivity:Higher the sensitivity higher the resolving capability.  So selecting higher sensitivity will help detecting very small changes [it can detect mgram change in force] and will not expand your range of measurement [0-8 grams to 0-10grams.

Play with excitation voltage and bridge configuration to arrive at setup that works.

Post back for queries.

[RobTom]

JK1, what do you mean it won't expand my measurements?

Also, what type of sensitvity (gauge factor) do you think I should be looking for in order to see milligram changes?

Thanks for the help 

[JK1]

Hai,

 In all the applications i developed the gauge factor was selected as 2.0 [this is the typical value that will be selected in general)

What is the formula you are using to convert the microstrain units to force units.

When you select a SG with high sensitivity its ability to resolve minute changes increases.  But if you want to increase or expand the measurment range or span you have to select a SG that has can cover a wide range not only high sensitivity.

Just search in ni website for the definition of sensitivity and range so that you can get a clear idea.

hope this helps.

Message Edited by JK1 on 03-24-2009 12:29 AM

Message Edited by JK1 on 03-24-2009 12:29 AM

[RobTom]

I used this website's equation http://www.engineersedge.com/strain_gage/half_bridge_straingage.htm, to predict what type of strain I would see from a 10 gram force. Using an aluminum arm, I found the strain to be 3 x 10^-7 and with an lexan arm, I found the strain to be 9.3x10^-6. 

I was wondering, do strain gauges work well on plastic material like lexan? Also, would a full bridge configuration be just as effective as one highly sensitive strain gauge for measursing such small forces? 

[JK1]

Strain gauge respond to changes on the meterial it is placed.  Ensure proper bonding (pasting) meterial is used to stick the strain gauge to the surface and it should work fine.

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Also, would a full bridge configuration be just as effective as one highly sensitive strain gauge for measursing such small forces?

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Are you trying to compare a full bridge and quarter bridge configuration.  What is that exactly you are looking at?