problem in strain measurement using SCXI module 1520,1314 terminal block

[r@123]

Hi,

I am using the SCXI modules from NI for the first time.I'm currently trying to ,measure strain using rosette triaxial (0/45/90)strain gauges .

I'm using XP, LabVIEW 8.6, NIDAQmx 8.7.

SCXI chassis- 1001

DAQ device- 1600

module-1520

terminal block-1320

Quarter bridge-I configuration

I have connected the device in Quarter bridge-I type configuration. The modules are being detected. The problem right now is that while the computer recognizes the device and is getting output from it, I'm getting a constant negative voltage (-4.2milliV). Even when the strain is supposed to change the values are not changing. It remains a constant. I even tried connecting a rheostat in place of the strain gauge, still the result is the same. I tried connecting to different channels of the terminal block, but no luck. I feel the connections done are correct for the quarter bridge-I connection. but, cant understand why the values are not changing.

 I tried the same using DAQmx and LabVIEW but results obtained remain same ie; the output voltage values remain same always.

please help me out, and let me know if there is anything i have missed out to do.

[John_P1]

Hi r@123,

Your post mentions the 1320 terminal block, but I'll assume you're using the 1314 as mentioned in the title of the post (the 1320 is indended for temperature measurement modules).

Here's a screenshot from 1520 User's Manual showing how to connect QB I, please make sure you have your circuit wired exactly as shown:

In the above, diagram, R3 is the QB completion resistor--the 1314 is the only terminal block that would have this built-in (1314T does not provide R3).

So, after you verify that you are using the 1314 and it is conected as above, I would check your software configuration of the 1520.  For example, are you on the lowest voltage range setting (-10 mV to 10 mV)?  Is the excitation set for 10V?  Again, I would refer to the 1520 manual for a more information about all of these settings. 

There is something that isn't quite adding up, if the above suggestions don't help could you please post your software configuration so we can investigate further.

-John 

[Rajan_77]

Hello

I am also having similar kind of prob, i am getting a value of -300m. I just want to know what is this value, "Volts"?, or something else. If it is volts, then how do i get the strain value.

[OKors]

As John stated above, each channel inside of the 1314 terminal block has to be manually configured (wired) for the specific bridge type you're plugging in.

For single 1/4 bridge strain gages you must jumper together QTR/SCA and P-/SCA at the terminal blocks. Do this for each 1/4 bridge sensor you're pluggin in.  

Also check to make sure there are no bent pins on the back of the 1314 terminal block.

I use Signal Express so I'm not familiar with your procedure to shunt strain channels. In SigEx there's a strain gage wizard that shows whether the shunt calibration and null offset was sucessful or not. Are you getting any other errors during your shunt cal?