A few questions about Load Cell calibration

[IamRubber]

I'm taking some measurements using some load cells.  I have calibration data from the vendor that I'm entering into Labview, but I'm new to this and had a few quesitons.

Here's the data I recieved.

Force (lbs)   Unit Data (mVdc)    Normalized Data

    0.00               0.054                         0.000

   12.50              9.181                          9.127

   25.00             18.322                        18.268

   12.50              9.187                           9.133

   0.00               0.055                          0.002

Balance:  0.054 mVdc

Sensitivity: 18.268 mVdc

In Resist: 377.20 Ohms

Out Resist:  351.990 Ohms

59K Shunt:  14.838 mVdc

Calibration Factors:

Sensetivity = 1.827 mV/V

59K Shunt = 1.484 mV/V

Also, I am using 10V External Supply Excitation

My questions are:

1. In the DAQ assitant under Configuration > Settings it asks for "Bridge Resistance".  Do I enter the "In Resist", "Out Resist", or the sum of the two?

2. In the DAQ assitant under Configuration > Settings > Configure Scale > Scale Type I have selected Table.  I assume that works.  Under "Electric Units"  the unit listed is "mV/V", but the units in the table for the sensor are in "mVdc".  Is it correct to use these corresponding "mVdc" and Force in LBS values in this table?

3.  In the DAQ assitant under Configuration > Settings > Configure Scale > Scale Type I am using the "Unit Data", not the "Normalized Data".  I think that's right but just want to double check.

Thanks!

[Patrick_NI]

Hello IamRubber, 

1. In the DAQ assitant under Configuration > Settings it asks for "Bridge Resistance".  Do I enter the "In Resist", "Out Resist", or the sum of the two?

The input resistance of the load cell circuit is measured at the excitation terminals with no load applied.  The output resistance of the load cell circuit is measured at the signal terminals with no load applied.  Since we are measuring from the signal terminals of the device we will want to use the Out Resist value as the bridge resistance in DAQ Assistant.

2. In the DAQ assitant under Configuration > Settings > Configure Scale > Scale Type I have selected Table.  I assume that works.  Under "Electric Units"  the unit listed is "mV/V", but the units in the table for the sensor are in "mVdc".  Is it correct to use these corresponding "mVdc" and Force in LBS values in this table?

For bridge circuits, DAQ Assistant tasks expect a value in mV(signal)/V(excitation).  In order to use the right values in this table, you will need to divide the unit data by the excitation voltage.  So the unit data in mV/V will be 0.0054 mV/V, 0.9181 mV/V, ect

3.  In the DAQ assitant under Configuration > Settings > Configure Scale > Scale Type I am using the "Unit Data", not the "Normalized Data".  I think that's right but just want to double check.

Yes, you are correct.  In the normalized data the load cell manufacturer just subtracted a 0.054 mV offset.  The unit data will more closely match what you should be expecting to see from the load cell.

For more information, please see this document:

http://digital.ni.com/public.nsf/allkb/D02125BF0BFC6130862576650001F14C?OpenDocument

Hope this helps!