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Load Cell Ratings?

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Lance:
I'm constructing a force measurement system, and I'm trying to pick a load cell that will do the job.

I'm taking a look at the following load cell:
http://www.meas-spec.com/downloads/FC22.pdf
http://search.digikey.com/us/en/products/FC2231-0000-0050-L/MSP6950-ND/809396

which I found by entering "Load Cell" into the search on Digikey. I've never really gone shopping for a load cell before, and I'm confused as to the units used to define the force ratings. It lists standard ranges as 0-10, 0-25, 0-50, and 0-100 lbf. I don't understand why the units are in foot-pounds, since that is a measurement of torque, and the cell from what I see moves linearly. I'm also failing to see how those ranges work.

Digikey also lists the "operating force" as 22.68kgf. Besides the odd mix of units, there is no "operating force" explicitly stated in the data sheet. Can someone please explain to me how load cells are rated, and what those ranges are?

Rufus:
The 'f' in those lbf and kgf is for force not foot.

The force due to gravity on a mass expressed in pounds or kilogrammes.

1 lbf is about 4.45 Newtons, 1kgf about 9.81 Newtons.

Lance:
So when it says that the operating force is 22.68kgf, does that mean that it takes 22.68kg to register 9.81 newtons of force on the load cell?

Jimmy:
What sort of force you trying to measure you may want a strain gauge not a loadcell

daedalus:
No, When it says 1kgf, it means that the sensor range is up to 9.8N (1*g). It is common for transducers for weighing applications to state their full scale range in weight units.

I only looked at the datasheet for FC22, so here goes:

This part comes in several configurations, so assuming you are going for unamplified:

Part is available in the following ranges:
0 to 10 (so full scale load is 10lbf)
0 to 25
0 to 50
0 to 100

Assume you buy the 0 to 10 part

10lbf = 44.48 newton

Span = 20mV/V
assuming you are powering the bridge with 3V3, then the output at 44.5N will be 66mV.

so ignoring the errors for now you have around 1.48N/mV response

Now assuming you have an ADC with an input range of 0-3v3, then you want a gain of 45 in order to get full scale output at max load.

assuming 12 bit ADC, your resolution works out around 10mN/lsb. As for accuracy, 1% of span on the bridge, plus whatever nonlinearity there is in your amplifier+ADC.

Thats my back of the napkin analysis, the rest is up to you.

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