SCXI 1000 Chassis with SCXI 1600 USB, SCXI 1520 strain gauge module and SCXI 1314 strain terminal block

[gammalight]

Hello all,

Let me first say I am new at using hardware to measure a strain signal.  I have all of my hardware hooked up together and can see it in MAX.  I have my tasks configured the way I want them.  I do not yet have my gauges that I will be using so in the mean time I am using a DC power supply to hook up to my first channel to see what signal I get and see if things are working like I expected.  When I am in MAX looking at my tasks and I run the "test panel" to input my signal I am not getting the response I thought I would.  As I increase the voltage on my power supply my signal decreases.  I thought as I increased the voltage my signal would increase as well.

Am I going about this the right way to verify the tasks I set up?  Is this the response I should be seeing?  If you need more info I would gladly give it to you.

Thank you

[RT4CY]

Thanks for posting on the NI forums!  I understand you are trying to read a voltage signal using the SCXI 1520 module.  In addition to the discussion forums, another great resource on ni.com is our KnowledgeBase articles.  Take a look at the following article, and post back if you have any issues.

[gammalight]

Hey,

Thanks for the reply.  My problem was I was trying to read in a voltage but my channel was configured for strain.  After making this change I had better results.

[RT4CY]

To be clear, in addition to creating a voltage task you also need to ensure your input configuration is differential.  Also, under the Device tab configure the Auto Zero Mode as None and the Lowpass Filter Cutoff Frequency as Disable Filter.  This is outlined in the linked KnowledgeBase article in my previous post. 

[gammalight]

AHHHHHH, I see now I need a custom voltage with excitation task for this job...  This gives me what I need.

[RT4CY]

A Custom Voltage with Excitation task is used to measure a full bridge absolute transducer.  You mentioned before that you are simply trying to measure a DC voltage.  To do this, you would use a Voltage task.  The following procedure is outlined in the KnowledgeBase article I linked in my first post.

1.   Create a Voltage Analog Input Task or Global Channel in Measurement and Automation Explorer (MAX).

2.   Under the Settings tab configure the Terminal Configuration as Differential and the Input Range as the voltage range you expect.

3.   Under the Device tab configure the Auto Zero Mode as None and the Lowpass Filter Cutoff Frequency as Disable Filter.

4.   Connect the positive lead of your input signal to the S+ termin 

[gammalight]

See I was trying it out before I got my cables and tranducers so I was inputing a straight DC voltage to see how it would respond, but I had a strain task and the signal kept going negative when I increased the voltage.  I then created a voltage task and read in the voltage just fine.  When I got my cables and tranducers the signal wasnt correct, I then tried a strain task and it wasnt correct either.  This is where I stumbled across the Custom Voltage with excitation task and then it worked correctly.  So now you see the progression of my work.  I guess I dont have a true strain gauge, it is actually a pressure gauge.

[RT4CY]

Ah, thanks for the clarification.  Your pressure gage actually does use strain gages internally.  This is common with many transducers such as load cells, torque sensors, etc.  There is also a KnowledgeBase which describes how to measure these transducers using the 1520 module.