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load cell calibration

Hi there,

New to Labview. Working on a little college assignment and am looking for a little bit of help. I have a micro load cell hooked up to a myDAQ and I'm attempting to calibrate it to get a make-shift weighting scales. I have attached my vi below. So far I have been able to calibrate it to an extent, but the precision is quite poor. It seems to fluctuate +/- 30 grams. I've been told that the error on the load cell is +/- 5g so I would like to get it a little closer to that. Any help would be greatly appreciated.

 

Load cell

http://www.phidgets.com/products.php?product%20id=3134

 

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Lot of unknowns here.  What kind of DAQ?  What supply voltage are you using?  The load cell you indicated has a 1mv/V output.  So if you use a 24vdc input, then your output at full capacity will be 24mv.  That 1.2mv per Kg.  That's pretty darn small and may need to be amplified before going into the DAQ.  I would suspect the AI on the DAQ doesn't have the resolution for that unless you have a really high end specialty item.

 

Analyze what signals you will get and what the DAQ can work with.

Doug

"My only wish is that I am capable of learning each and every day until my last breath."
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Also, quickly looking at the specs for the load cell seems to indicate a higher error (+/-10g repeatibility error for one) than you have been told. If you are trying to read this directly, as the previous post mentions, the signal will be very small. With a supply voltage of 5V max, so the output will be very small. What are you using for Data Acquisition (DAQ)? and how are you connected?

Putnam
Certified LabVIEW Developer

Senior Test Engineer North Shore Technology, Inc.
Currently using LV 2012-LabVIEW 2018, RT8.5


LabVIEW Champion



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Add a (INAXXX)  ampifier with 100 to 400 times amplification ...

The rated output is 1mV/V so you get 5mV at max load and you also need to measure the exitation voltage .. the myDAQ spec tells that it's not exactly 5V ....

 

If you can't use an external amplifier, use the analog inputs in differential mode and 2V range, and use three 2.2k resistors to divide down (1/3)  the supply voltage.

use a low samplerate (twice your line freq) mean as much samples as possible.

Assuming that the supply is only slowly drifting, measure the supply only (50 samples), sensor only (100 samples), and supply again (50 samples)

Mean the supply and the senor output and use the ratio (U_mean_sensor/U_mean_supply) for your calibration

Greetings from Germany
Henrik

LV since v3.1

“ground” is a convenient fantasy

'˙˙˙˙uıɐƃɐ lɐıp puɐ °06 ǝuoɥd ɹnoʎ uɹnʇ ǝsɐǝld 'ʎɹɐuıƃɐɯı sı pǝlɐıp ǝʌɐɥ noʎ ɹǝqɯnu ǝɥʇ'


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Appologies. Can't get back to you re: the unknowns until I get home tonight.

 

It's strictly a LABview project so I'm not at liberty to add in extra hardware. Currently I have the NI myDAQ attached to my PC via usb so I'm assuming the supply is 5V?

 

The voltages I have set in the daq assist are +/- 10mV and it's reading in 100 samples at 1kHz.

 

Can you get access to the vi I've posted?

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Sorry, I'm still with LV2012, however what you enter in the DAQ assit and what he choose are two different things (RTFM and RTFSpec) 😉

I just give a hint how I would try it. Better use 300 Samples @ 1kHz (fit for 50Hz and 60Hz line freq.) or try as suggested... or do what you want 😉

As more you try, as more effects you might find, by finding an explanation for these effects you will learn.

 

 

Greetings from Germany
Henrik

LV since v3.1

“ground” is a convenient fantasy

'˙˙˙˙uıɐƃɐ lɐıp puɐ °06 ǝuoɥd ɹnoʎ uɹnʇ ǝsɐǝld 'ʎɹɐuıƃɐɯı sı pǝlɐıp ǝʌɐɥ noʎ ɹǝqɯnu ǝɥʇ'


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