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strain gage calibration using Signal Express

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Hi,

 

First time asking. Thanks in advance.

 

I am using NI DA system to record strain of a 350 odm 1/4 straiN gage. The connection chain would be strain gage-------->SCXI 1314 (Terminal Block)-------------->SCI 1520 ( 2nd block). I connected the lead wire to the S-, P+, and QTR pins of SCI 1314. The value of strain do display in LABVIEW EXPRESS. Now, I need to calibrate the strain gage( OFFSET NULLING and SHUNT CALIBRATION). I am stucked... I have two specific questions:

 

1. When I just check ' Offset nulling' in ' calibration' tab. error-200380 orrcurs. Can you nice people help me out?

 

2. I noticed that there were pins specific for shunt calibration in SCXI-1314. If I wanted to do shunt calibration, do I need to change my wiring, so that the 100k odm resistor can be included in the circuit?

 

Thank you so much.

IMG_0619.JPG

IMG_0620.JPG

IMG_0621.JPG

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Hi Vtttt, 

 

It looks like the issue you are seeing is addressed in this KnowledgeBase article. Read through it, make any necessary changes, and let me know if you have any other questions. 

 

 

Best Regards,

Thomas B.
National Instruments
Applications Engineer
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Thanks rich. Reading and trying!

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Hi Sir,

 

I have tried according to the knowledge base you posted. I can Zero the gage now. However, I still need help for shunt calibration. I am using a Mirco-measurments 1/4 bridge strain gage. Here is how I did the wiring:

QQ截图20130801152149.jpg

 

Here is what the error looks like:

 

IMG_0631.JPG

IMG_0632.JPG

 

Thank you so much.

 

 

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Hi Vtttt, 

 

I have looked through the knowledge base articles posted on ni.com and think I have found another document that might be helpful for you. This KnowledgeBase article addresses the specific issue you are seeing. Take and look and see if the suggestions it makes are helpful, and let me know if you have any other questions. 

Best Regards,

Thomas B.
National Instruments
Applications Engineer
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Hi Thomas,

 

I am afraid that solution does not work. I am a thought. If I includ a 100k ohm resistor in the circuit, as by the definition of 'shunt calibration'. A 1.65e-3 'virtrual' strain was simulated, as shown in my second posting. But measured strain was still near zero--91.19e-9, also in my second posting. Does that mean the 'shunt resistor' was not included in the circuit correctly?

 

Thank you so much.

 

 

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Solution
Accepted by vtttt

In your first post you have the signal wire from the gage going to S-. My first suggestion is to move your signal wire from S- to S+ if you havent done that already. When shunting 1/4 bridge you only have access to R3 and R4 which are on the + side of the bridge. That high of an error on your gain stage is usually a wiring issue or you're shunting the wrong arm of the bridge. In the Calibration wizard switch between R4 and R3 and see what happens.

 

Hows your gage wired?

From your gage you should have 3 wires. Vex+ (red) on one tab of the gage and shunt cal and sig. (tied together) on the other tab of the gage. See my attachment for a view of how I wire my system. Other than the colors the screen shot of your wiring diagram looks like it should work. The difference being, my sig+ is green and shunt is brown; where your's seems to be white and black. Either way, double check your gage and be sure the leads going back to your terminal block are where they need to be. Default shunt resistors in the 1314 are all 100k ohm so unless something changed in your system you should be fine.

Can you attach a copy of the .seproj file or screen capture the "Settings" tab of your Strain gage configuration window. Things like excitation value gage factor and resistance will affect your calibration output as well.

SCXI- 1000 Chassis w/ 1346 adapter
PCI 6281 DAQ card
SCXI- 1520 Bridge Board w/ 1314 Terminal Block (x2)
SCXI- 1180 Feedthrough Panel w/ 1302 Block
Signal Express 2014.
Win7 Enterprise
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Hi OKers,

 

Problem solved. Thank you very much. The figure really helps. It turned out that my wiring was wrong somehow. 

 

I really appreciate your kind help.

 

P.S.

 

Though I could zero and shunt calibrate most of the strain gages, there was one of which error still poped up. When shunt calibrated, the reading of this gage differed very much from the simulated strain( they should be close, as far as I know). Does that mean this paticular gage is broken? (I do have strain readings on screen and I can zero this paticular gage).

IMG_0631.JPG

 

Again, thanks rich for you precious time.

 

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Unplug your gage from the SCXI and ohm the gage out. between the two solder tabs you should see 350 ohms. Then ohm it between one of the solder tabs and ground (just touch the DMM lead to the part somewhere), check that your gage is not grounding out.

Next, plug that gage into another known good channel and see if it cal's (I just sent a 1520 in for repair because of a bad channel, so it could be hardware related).

Its pretty rare that a gage is "broken" yet still outputs a strain signal to your DAQ like you're describing. If its broken they usually appear OPEN where the signal output is maxed out or "to the rail" and unchanging in value.  That or its not bonded properly; in which case you'd get erroneous readings... but it should still cal.

 

Double/triple check your wiring and be sure you're shunting the correct side of the bridge. If all that checks out, my guess would be you're gage is grounding out or you have a bad hardware channel.

one last thing. remove the 1314 terminal block and look very carefully for bent pins on the 1520 module.

hope that helps!

SCXI- 1000 Chassis w/ 1346 adapter
PCI 6281 DAQ card
SCXI- 1520 Bridge Board w/ 1314 Terminal Block (x2)
SCXI- 1180 Feedthrough Panel w/ 1302 Block
Signal Express 2014.
Win7 Enterprise
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