I want to measure weight, so I use load cells,
As far I know, commonly 4 load cells are used for this purpose, but I can not understand it's real purpose, maybe 2 will be more accurate than 4? Is it wrong?
Or, what is the optimum condition for it?
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\$\begingroup\$ Four supports - four cells, otherwise the position of the load on the platform varies the reading to much. (Maybe if you only need to guess the weight, but the you can also do it without a load cell :-) \$\endgroup\$– skveryCommented Mar 8, 2017 at 11:03
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\$\begingroup\$ Thank you, How can I do it without load cell? I want to measure an animal's weight whil it is walking. \$\endgroup\$– M.DioCommented Mar 8, 2017 at 12:52
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\$\begingroup\$ (Eyeballing, maybe the error will be acceptable, depends on the eyeball :-) \$\endgroup\$– skveryCommented Mar 8, 2017 at 17:34
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\$\begingroup\$ Sorry, I can not understand. Can you send me a link please? \$\endgroup\$– M.DioCommented Mar 10, 2017 at 5:41
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\$\begingroup\$ (See definition of eyeballing :-) \$\endgroup\$– skveryCommented Mar 10, 2017 at 6:15
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2 Answers
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I you have 2 load cells then the supporting area is a line, which is hard to balance an object on. If you use a separate support then you aren't measuring what part of the object is supported by that support.
So you either need to hang the load or need at least 3 load cells to have a large enough area to make the object stable.
Adding a 4th load cell is then done to make the usable area of your platform a rectangle which tends to be easier to work with.
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Depending on the mechanical structure that the loads cells support will depend on the number of load cells used. If one cell is used all good. If 4 cells are used then just parallel the cells up and treat them as a single cells from a single processing point of view :)
As for accuracy the number of cells is not as important as the resolution of the measurement electrics that converts physical weight to a voltage.
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1\$\begingroup\$ First part is correct, second paragraph is plain wrong. Of course, the accuracy, linearity and temporal stability matter a lot. You can digitize anything, but it's no use if your analog sensor has less accuracy than your ADC's resolution, which in times of 1$ MCUs with 12bit ADCs, and widely available 24bit dedicated ADCs, is the much more probable case. And: of course, with appropriate signal processing, and the fact that parallelizing multiple resistances or current sources is a summing process, with the additional benefit of the central limit theorem, will increase the accuracy. \$\endgroup\$ Commented Mar 8, 2017 at 10:06