Tags: block, conditioner, connector, experiment, gage, gages, labview, measurement, programming, scxi-1000, scxi-1317, signal, strain, working

strain gage experiment

On Programmer » LabVIEW

8,273 words with 8 Comments; publish: Wed, 07 May 2008 00:06:00 GMT; (200156.25, « »)

Hello All,

I am working on strain measurement experiment using strain gages. I am using

SCXI-1000 signal conditioner, SCXI-1317 connector block. I have a plate sup

ported on 4 sleeves. 2 strain gages are attached to each sleeve. When I conn

ect 4 strain gages one from

each sleeve to the connector block and apply a force of 200lbs on the

plate and do a test run in labview, the strain values I am getting are way o

ff. Here the details of inputs

Lead Resistance: 0Gage Resistance: 120Gage factor: 2Strain range max = 1M&nb

sp; min = -1MV(initial) : 0V(exe) : 5VV(exe) Source:

ExternalSrian gage config: Quarter Bridge 1

The Strain values I expected to be around 50 microstrain.The vlaues I am get

ting are 180, 520, 370 microsrtain, fluctuating +/- 50 microstrain to the ab

ove vlaues. The fourth strain gage is reading -75microstrain and is stable.

I tried changing V(exe) but

nothing really chaged in readings except the fourth strain gage but it alway

s was a negative valve.

I could not figure what am I doing wrong. If anyone in the group has any exp

erience with this please help me out.

Thank you

Mekdeng

All Comments

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  • 8 Comments
    • Hi Mekdeng,

      I will attempt to answer your question, but i also advise that your queries

      on SCXI in the Signal conditioning Discussion forum board.

      Here it looks like you are using External Excitation instead of internal exc

      itation that your SCXI 1521 module is capable of sourcing.

      so, check how you have wired on your sensor to the SCXI 1317 Terminal block.

      plus your max min range settings 1M ( is it 1000000 micro strain?) seems to

      be too high, so check it.

      Regards

      Dev

      #1; Wed, 07 May 2008 00:08:00 GMT
    • Thank you Dev,

      Yes, I also have SCXI-1521 module along with SCXI-1317 and SCXI-1000. When I

      select internal source I get a error message that source is not connected s

      o I selected external source and did a trial run.

      My strain gages have 3 lead wires and I connected then to the connector bloc

      k as per the manual. 2 wires coming out of one leg of the strain gage were c

      onnected to the AI and QTR, and one wire coming out of the other leg to the

      Ex+ just as per the SCXI-13

      17 manual.

      I'll decrease the max and min range of the input and try the experiment.

      Thanks once again.

      Hari

      #2; Wed, 07 May 2008 00:09:00 GMT
    • Hari,

      Are you using a LabVIEW example for reading SCXI-1521 strain gages?

      What are the details of the error that you get when you try to use the

      internal excitation? This module is designed to use internal

      excitation, so your strain measurements won't work unless you select

      the internal option.

      Are you or the exmple that you are using perform an Offset Null and

      Shunt Calibration? These are important for making sure that your strain

      measurements are accurate. When you perform these calibrations you must

      ensure that your strain gage is in it's resting state.

      I hope this helps.

      -Logan

      #3; Wed, 07 May 2008 00:10:00 GMT
    • Hari,Are you using a LabVIEW example for reading SCXI-1521 strain gages? Wha

      t are the details of the error that you get when you try to use the internal

      excitation? This module is designed to use internal excitation, so your str

      ain measurements won't work

      unless you select the internal option.Are you or the exmple that you are usi

      ng perform an Offset Null and Shunt Calibration? These are important for mak

      ing sure that your strain measurements are accurate. When you perform these

      calibrations you must ensu

      re that your strain gage is in it's resting state.I hope this helps.-Logan

      Thank you Logan,

      Iam using LabVIEW for reading strain. I could not read anything of my

      strain gages when I select internal excitation. But when I select external I

      could read some values though they are not what I am expectiing.

      I tried to calibrate my strain gages using Measurement and Automation Explor

      er, but when I go to step where I have to select DAQ hardware , the program

      not detecting SCXI-1521. So unable to calibrate my strain gages.

      If you know how to make Measurement and Automation Explorer detect SCXI-1521

      please help me out

      Thank you

      Mekdeng

      #4; Wed, 07 May 2008 00:11:00 GMT
    • Hi Mekdeng,

      Try configuring/adding the SCXI chassis to the DAQ card Properly.

      These links should tell you how.

      <a href="/app/links/?link=http://digital.ni.com/public.nsf/websearch/5902345227DFCA1286256EDA0063F50C" t

      arget="_blank">http://digital.ni.com/public.nsf/we...br />

      0063F50C</a>

      <a href="/app/links/?link=http://digital.ni.com/public.nsf/allkb/445C4DF1A24A9B8B86256D8F0078E5C2?OpenDo

      cument" target="_blank">http://digital.ni.com/public.nsf/al...C2?OpenDocument</a>

      <a href="/app/links/?link=http://www.ni.com/support/scxi/scxidaq/soft.htm" target="_blank">http://w

      ww.ni.com/support/scxi/scxidaq/soft.htm</a>

      Then, see if your SCXI 1521 and its terminal block SCXI 1317 are detect

      ed by your MAX

      Then do a self test for chassis on max itself.

      If all this goes fine, you should solve the problem you mentioned.

      Hope this Helps

      Regards

      Dev

      #5; Wed, 07 May 2008 00:12:00 GMT
    • Mekdeng,

      Those documents that Dev pointed you to are good, but in your situation

      I personally think the best place to get started with configuring your

      SCXI system in MAX is the SCXI Quick Start Guide, which should have

      come in the box that your SCXI module and chassis were shipped in. Here

      is the online link to that document if you need it:<a href="/app/links/?link=http://digital.n

      i.com/manuals.nsf/websearch/A0FB7849526E33E086256F64006F628E" target="_blank

      ">

      http://digital.ni.com/manuals.nsf/w...6256F64006F628E

      </a>

      If you follow the steps in the quick start guide and still are having

      problems detecting your SCXI-1521 in MAX, then let us know the specific

      details of the problems.

      Good Luck!

      Logan

      Message Edited by Logan K on 12-02-2005 08:55 AM

      #6; Wed, 07 May 2008 00:13:00 GMT
    • Thank you Logan,

      I followed the steps in SCXI Quick start Guide and configured my hardware im

      MAX and worked fine. Now that I configured my harware I tried to calibrate

      my strain gages and the error I got is attached with this reply. I figured o

      ut that I got this error ma

      y be bacause I am trying to use 120 ohm strain gages with SCXI-1521 which wo

      rks only with 350ohm resistors as per NI application engineers. Do I really

      have to get a SCXI-1521B module which works 120ohm resistors to do my experi

      ment or get new set of 350o

      hm strain gages?

      One thing I am amazed of is why does NI makes different modules to go with d

      ifferent capacity resistors. I only know about 1521 and 1521B modules and wh

      at if anybody uses 240ohm or 1000ohm resistors.. which module should they us

      e?...

      I am wondering if anyone know of any work around for me with out changing my

      module or strain gages.

      Thank you

      Mekdeng

      calibration-error.doc:

      http://forums.ni.com/attachments/ni...ation-error.doc

      #7; Wed, 07 May 2008 00:14:00 GMT
    • The short answer is that you are correct. The SCXI-1521B must be used

      for 120ohm strain gages, and the SCXI-1521 must be used for 350ohm

      strain gages because they have fixed quarter bridge completion

      resistors built into them. If you have a non-standard or less common

      strain gage like a 1000ohm or 240ohm, then you must use a module which

      enables you to customize your quarter-bridge completion resistor, like

      the SCXI-1520 with the SCXI-1314 terminal block.

      So, unfortunately there is not a good workaround for you with this module an

      d I appologize for your inconvenience.

      Regards,

      Logan K

      #8; Wed, 07 May 2008 00:15:00 GMT