How do I set strain gauge resistance on 9237

[pauloeduardo@maxioncr.com.br]

Hello Everybody,

I still having some questions about the code posted here:

1) The code is perfect. The outputs are: Simulated (ue) / Ideal (ue) / % Error / Bridge Offset (V/V).

     How can I correct the values in my code, using these outputs values?

     I.E.: I´m using a 100ohms resistor with a gage factor GF=2,11

     The output values that I have for these one are:

            Simulated (ue): 0,000600489 

            Ideal (ue): 0,000568039

            % Error: 0,201548

            Bridge Offset (V/V): 0,000956972

I would like to know how can I correct my measurements based on these output values.

Thank´s all!

Paulo Paraizo.

[rex1030]

Hey Jimmy,

I am not saying I have a working program yet.... but my issues seem to be coming from other areas.

However, the strain gauge theory and equations you need to apply the values that are given can be found in "CHAPTER 4: Theory of operation" of this manual: http://www.ni.com/pdf/manuals/372583d.pdf . It discusses strain gauge theory in detail and gives all the equations you need to apply the offsets and shunt values to each measured value.

The examples people have posted here are great. I am still trying to combine them all into a program that shunts, offsets and measures continuously on all four channels, using the dma efficiently enough so that I can expand the program to put a few of the 9237 on the 9104 back plane. Which aparently is a tall order because no one seems to have achieved that yet.

None of the examples do all of that for four channels simultaneously, yet. I keep getting dma errors and stuff when I try to expand the continuous code to apply to four channels at once. Quite a nightmare for a LabView newb like me. Let me know if anyone achieves this before I do (please post your code and help out the community).


Message Edited by rex1030 on 03-04-2008 01:48 PM

[CharlieM]

My suggestion would be to ignore the Offset or auto zero all together. Software offsetting is the best method for the 9237.

An example calculation would be:

Given:

Normal reading(with no strain on your system)=1000, Shunt Reading(same system)=1050, Simulate Theory(From pure calculations)=49

Calculation:

Gain adjust = 49/(1050-1000) = 0.98

Final Strain = [(reading) – 1000]*0.98

*note that the bridge was off balance (1000) when the system was at rest. This 1000 needs to be offset from every reading so that the system at rest is zero.

[pauloeduardo@maxioncr.com.br]

Dear Everybody,

All the problems about shunt and offset nulling I have already solved. The other point is:

I’m trying to use 3 modules 9237 together and it’s performing with loss of acquisition frequency.

Why is the best way to do it without this phenomenon?

Could someone post anything about this issue?

Thanks all!

Paulo Paraizo.

[CharlieM]

Hi Paulo,

First, I’m not sure about the specifics of what you are seeing. It would be helpful if you could provide some more detail. Second and more importantly, I would strongly suggest starting a new forum thread with this question. This would invite more of the LabVIEW and cRIO community to join in. Right now, the only people who have viewed this post are those who are interested in “How do I set strain gauge resistance on 9237.”  

[pauloeduardo@maxioncr.com.br]

Hi Charlie,

Firstly thank you. I will start a new forum concerning this issue.

But, anyway, what I’m trying to say is about the response time when you are using three 9237 modules together. I have already noted that doing it I have a kind of loss of time of data acquisition.  When I use just one module, I can have acquisition of data with 1 millisecond perfectly, but when I have 3 modules working together, I just can work with near of 300 milliseconds concerning the time of acquisition data. Is there a way to reduce this effect?

Thanks again!

Paulo Paraizo.

[CharlieM]

Hi Paulo,

Try looking at the example “Synchronizing NI 923x Modules.” If you have any questions, make a new thread and add a link to that thread on this forum.

[pauloeduardo@maxioncr.com.br]

Hello Charlie,

Below you can find the address regarding the new thread that you suggested me to create.

http://forums.ni.com/ni/board/message?board.id=220&thread.id=426

I have already posted a short text about my problem, but, anyway, I looked the example that you post, but I couldn’t note any change.

Once more, thank you!

Paulo Paraizo.

[Pedromi]

Hi Everybody

I´m new in Labview 8.6 and i have the CRIO 9074.

My question is...Can i calibrate my 9237 whitout FPGA?That means, Can i use the shunt calibration in Scan Interface (Real Time only) whiout any FPJA vi?

Thanks

Pedro Faria

[speleato]

You can use

Set Shunt Calibration (Scan Interface) .vi

which is located in

<LabVIEW 8.6 Install Dir>\examples\CompactRIO\Shared

Also a note, in the future it would be appreciated if you would start a new thread to ask a new question.