How to ensure load cell output symmetric about origin

[Moni98ce]

Hi, 

I am attaching a figure which contains output from two load cells under the same displacement but different inertia forces.

In the bottom figure, the force is fluctuating about 0, however, in the top figure, it is not about 0. I need to ensure all cases it is fluctuating about the origin. This data is collected from two load cells by using one VI. The black one is the subtraction of red and blue. Could anyone please help me with my problem?

Thank you.

[santo_13]

Could you please rephrase your question?

Are you asking how to solve the mechanical issue or some software you developed in LabVIEW using NI instruments or third party instruments?

If the former, you may get some guidance but this may not be the best place to ask as this is a LabVIEW board under the NI discussion forum.

If the latter, please share all information about the loadcell model, datasheet, source code of the application used to capture this signal, instruments used, connections etc.,

If you used the same exact VI but just changed the loadcell, then it looks like there is some drift.

[Moni98ce]

Hi Santo,

Thank you so much for your reply. I am attaching my VI here. My load cells are identical. I am using the same VI and hardware. I am measuring the forces simultaneously by using the same VI. My C module is NI9237, cDAQ is 9137, Load cells are LCB 500 (FUTEK) having a capacity 100LB, Output: com -0.7903mV/V @100lb, and for another load cell -0.7912mV/V @100lb.

[GerdW]

Hi Monice,

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@Moni98ce wrote:

My C module is NI9237, cDAQ is 9137, Load cells are LCB 500 (FUTEK) having a capacity 100LB, Output: com -0.7903mV/V @100lb, and for another load cell -0.7912mV/V @100lb.

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Please cleanup that VI before uploading again…

• Why do you use a TimedWhileLoop? It's next to useless on Windows targets. And it doesn't help with DAQmx readings: wire a reasonable #samples to DAQmxRead and your loop will magically read all samples!
• You forgot to attach your subVI.
• Where do you apply the different scalings for both signals? Both are multiplied by the same value…
  Why do you apply the different scalings so late in the sample analysis? You do a lot of averaging and analysis on "unscaled" values even though you know their scaling is different!
• You may apply scales when creating channels using DAQmxCreateVirtualChannel! DAQmxRead would output already scaled values…
• Why do you use SplitSignal when you should use IndexArray? Good advice: avoid using ExpressVIs and DDT wires!
• Why do you use Matrix functions to display a 1D array of data on a chart? Did you read the context help of the chart to learn which datatypes are expected by the chart? (Use BuildArray to convert the 1D array into a 2D array to display several channels on your chart…)
• Why do your charts miss their labels? Would you use label-less variables the same in text-based programming???
• Do you know you can change the number of outputs at an IndexArray node? No need to use two IndexArray nodes when one would be sufficient!
• DAQmxRead expects an integer number of samples to read: use Q&R (Quotient&Remainder) instead of simple divisions upstream…

[ASTDan]

Hello,

I would check your wiring.

See this document

https://www.ni.com/en/shop/data-acquisition/measurement-fundamentals/field-wiring-and-noise-consider...

[Moni98ce]

Hi GerdW,

Thank you so much for your time. I am using a timed loop because I need it. I am not using it in WINDOWS target. I am running the VI in a real-time target. I am attaching the subVI here. Thank you for all of your suggestions. I will try to implement it.

[santo_13]

Please help us understand how you're running on an RT target when you use a cDAQ chassis? do you connect to a PXI running RT?

[Moni98ce]

Hi Santhosh,

My cDAQ chassis is a real-time target in my case. I am not using it to collect the data also using it for numerical simulation. It is running OS Linux, not Windows.