Configure a Load Cell connected to Multifunction DAQ

[David_Troike]

I am attempting to connect an Omega LCHD 10K Load Cell through a Dataforth SCM5B38-37 Strain Gauge module then to AI0 on a USB-6251 Multifunction DAQ.

In addition to the load cell the application will use a pressure sensor with a strain gauge bridge module connected to AI1 to read the hydrulic pressure.  Using the pressure transducer a force measurement will be calculated and compared to the load cell readings.

Currently the USB-6251 is setup to read the analog voltage on AI0.  Scaling is then done using Linear Fit.VI. 

Reviewing the example Bridge -Continuous Input shows some additional controls that might increase the accuracy of the reading.  

Unfortunately attempting to use the DAQ asistant only added to my confusion of the best pratice in acquiring a signal from a load cell.

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These are some of the questions I have........

What is the best pratice to setup a load cell using a full bridge strain guage conditioning module labview?  

What is shunt calibration?  Is this specfic to the DAQ modules similar to the USB-9237?

How do you know if your load cell is configured as a full bridge, half bridge, etc, the load cell document does not indicate this?

Can you use the DAQmx Perform Bridge Nulling VI?

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I not sure I understand all the informaiton from the calibration sheet either.  

Why is there input and output resistance values?

What is signafiance of the Zero Balance Value?

Load Cell Specfications

Lbs              mV/V

0                  0.000

2000            0.598

4000            1.201

6000            1.804

8000            2.404

10000          3.002

Excitation:                           10 VDC

Input Resistance:                350.41 Ohms

Output Resistance:             352.08 Ohms

Zero Balance:                      0.01 mV/V

[warEagle12 · Accepted solution]

Hello!

I have been looking in to your question and found a few links that might help as you set up your system. The first is a White Paper that discusses some of the fundamental concepts of strain gauges and using them with LabVIEW, shunt calibration, and also covers some of the resistance values that you see:

http://www.ni.com/white-paper/3642/en/

As you can see from this article, we have some specific hardware built for the kind of measurements that you are taking. Since these devices are made specifically for this application, they would provide better and more reliable results. That being said, you can set up your system with your USB-6521, it just might not be as accurate as one of these systems. In order to set up your measurement system, rather than setting the analog input as a strain measurement, you will want to use the Custom Voltage with Excitation option. The following article discusses this further:

http://digital.ni.com/public.nsf/allkb/C66F92BDE229F45A86257B6D004D6033

You we get your measurement data in a Volts/Volts form (this document talks more about Bridge Sensor scaling: http://zone.ni.com/reference/en-XX/help/370466W-01/measfunds/bridgescaling/), but you will need to make sure that you normalize this value to the excitation. Devices such as the NI 9237 provide the excitation voltage and can take this known value in to account within the program, however you may have to do this manually for your application. Here is additional information on the NI 9237 and the way that it is set up to read strain gauge information:

http://digital.ni.com/public.nsf/allkb/892C84122A6501AE86257547007E5C53?OpenDocument

As far as the load cell configuration and information, you might try contacting the manufacturer for additional information!

Thanks!