How to measure voltage changes using a NI-9219 with strain gauges and use the data in labview

[coffeyfj]

I am updating an old LabView/Data Acquisition system that uses strain gauges to measure two forces (normal and axial) as well as two moments (Pitch and Roll). I am having trouble reading the voltage changes over my strain gauges using my NI-9219 as well as filtering the data with both a lowpass and smoothing filter. The program attached has the project and should have all the sub-vi's used in the program. This program was written on LabView version 8.5 and is being updated to a 2013 version of LabView. Also, the hardware previously used was a combination of a NI SCB-68 and NI USB-6251. If anyone could help me it would be greatly appreciated! 

[wfernand]

Hi Coffeyfj,

If you are having trouble reading the acquired strain measurements you might want to refer to the one of the examples and see if you get the correct readings from the examples. Help >> Find Examples >> Hardware Input and Output >> DAQmx >> Analog Input >> Strain - Continuous Input.vi. Also refer to the following link.

Measuring Strain with Strain Gages

William Fernandez

Applications Engineering

National Instruments

[coffeyfj]

Hey wfernand,

Firstly, thanks for the reply! Secondly, I have already taken a look at that particular article. The issue arises that the program I attached in my first comment was an old program I am upgrading and the whole program uses voltage inputs. The issue I am having is that my strain gages are not responding to the forces I apply. For instance, if I run the program and I am graphing the changes in voltage over time and I apply a force to the test specimen there is no response or noteworthy change in the voltage reading. I am not 100% sure where the issue is arising in the program or hardware. If you have any insight on to where my problem might be coming from that would be great!

Thanks for the help again!

P.S. If you have any questions for me on the setup of the measurement I can definitely attach them at request.

[wfernand]

Hi Coffeyfj, 

Did you ever had this set up working? The first thing that I would do as I mentioned in the previous comment would be to use one of the LabVIEW examples. I recommended to you using the (strain - Continuous Input.vi). If you can read any voltage changes with the example vi, then we will know the problem we are having is in your code. If you cannot read any voltage changes using the example I mentioned, we can start trouble shooting the hardware connections. Are you connecting the excitation voltage? If yes, Are you making the right connections. Please refer to page 19 of the following document (half and full bridge modes)

NI 9219 Operating Instructions and Specifications 

Regards,

William Fernandez

Applications Engineer 

National Instruments