9237 with full-bridge load cell: load cell_null_off_shuntcal.vi throws error 200077

[CFJ]

Hi,

I'm trying to use the example load_cell_null_off_shuntcal.vi  with a full-bridge load cell (Honeywell Model 31, unamplified). I am using LabView 8.6,  cDAQ-9172 and NI9237. The load cell is connected to pins 2,3,6 and 7.

The inputs for the VI front panel are: internal excitation10V; mV/V 2.1492 (calibration sheet); max weight 10 lbs; bridge resistance 350 ohms (Honeywell specs); 9237 internal shunt resistance 100 kohms; shunt location R4 (default setting). I have selected "Do offset null" and "Do shunt cal".

This is the error I receive:

Error -200077 occurred at DAQmx Perform Shunt Calibration (Bridge).vi:1 Possible reason(s):

Measurements: Requested value is not a supported value for this property.

 Property: AI.Bridge.ShuntCal.GainAdjust

You Have Requested: -61.980405e3

Valid Values Begin with: 500.0e-3

Valid Values End with: 1.500000

If the "Do shunt cal" green button is not selected, there is no error. I understand that the Gain adjust value should be approx 1, whereas the one I get is much larger. The  subVI  DAQmx PerformShuntCalibration (bridge).vi contains a "Call library function node" which I don't know how to interrogate.  

Has anyone else had experience with this error? Do you have any advice on:

1)     How to "see" the calculations being perfomed inside the "call library function node"?

2)     What the correct shunt element location for a full bridge load cell is? (although changing this location does not eliminate the error, I can't find this info).

3)     Anything I may be doing wrong with my inputs to cause this error?

Thanks,

Claire.

[kikiduu]

You should do shunt calibration only if the Shunt calibration resistors are connected(in your case pin 1 and 10).

[CFJ]

Hi Kikiduu,

My understanding is that there is an internal shunt resistor in the 9237. Pins 1 and 10 are given so that one can connect their own shunt resistor if desired (correct?). Since I am using a full bridge load cell, I believe that this resistor will be enabled via the software, which I think is done within the VI I am using. Is there a global setting to enable the shunt resistor, or is it a matter of having the software flip the switch such that the internal resistor is brought into the circuit

Thanks, 

Claire.

[kikiduu · Accepted solution]

Hi Claire,

You have to physically connect the SC terminals to one arm of the bridge (normally R3). The terminal is not provided for connecting external resistors.

See example 

C:\Program Files\National Instruments\LabVIEW 8.6\examples\DAQmx\Analog In\Measure Strain.llb\Cont Acq Strain Samples (with Calibration) - NI 9237.vi

[CFJ]

Hi Kikiduu, thanks for your patience. I don't have much experience with reading circuit diagrams and connecting the wires. I have it working now!

Thanks for your help and have a great weekend.

Claire.