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I have ordered some load cells from a Chinese supplier, and I asked for a load/output calibration report. The chart they sent me looks like this...

Load cell response curve

Correct me if I'm wrong - but this is supposed to be a 5kg load cell - so it should be linear between 0 and 5kg, right?

How am I supposed to used one that is so obviously non-linear??

Thanks

EDIT: Specifications

  • Capacity 5kg
  • Accuracy 0.1%FS
  • Rated output 1.0±0.15mv/v
  • Operating voltage 6~12V
  • Input resistance 1000Ω
  • Output resistance 1000Ω
  • Electrical connection Excitation red Signal+ blue Signal- white
  • Cable φ0.8×350mm
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  • \$\begingroup\$ What is the linearity specification on these load cells? \$\endgroup\$ – Spehro Pefhany Jun 24 '14 at 2:56
  • \$\begingroup\$ All the specifications provided have been added. My concern is that the expected linearity is a function of cost! I haven't done much in this space, but I'm guessing that the curve we see above is an indication of a very poor sensor. \$\endgroup\$ – Adam Jun 24 '14 at 3:06
  • \$\begingroup\$ I can't see how they could make it that bad. Perhaps it is exaggerated to show the typical shape.. But you never know. \$\endgroup\$ – Spehro Pefhany Jun 24 '14 at 3:19
  • \$\begingroup\$ I agree with @SpehroPefhany, it looks exaggerated to show the shape because that wouldn't match the 0.1% accuracy specified. \$\endgroup\$ – vrleboss Jun 24 '14 at 4:09
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In general, a load cell is designed to have a linear relationship between output voltage and the load applied. In this case it wasn't.

There is a specification missing from the list, the linearity spec. Typically, load cells will specify the deviation from a straight line as a percent of full scale. For example +- 0.2% FS. All that is specified is the Full scale (or endpoint) value which says nothing about the linearity.

The load cell's output is monotonic, so it is usable. Depending on your products price and accuracy requirements, this load cell can be used and linearized in firmware by look up tables or a couple of piecewise best fit equations. Alternatively, use a higher quality load cell.

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