need help with load cell

Discussion in 'General Electronics Chat' started by bug13, Jan 21, 2014.

  1. bug13

    Thread Starter Well-Known Member

    Feb 13, 2012
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    Hi guys

    I have some trouble understanding a load cell, take this one for example:

    http://edg.uchicago.edu/tutorials/load_cell/FX1901.pdf

    I don't know how to work out the voltage output and force/weight ratio.

    what does mV Output: 20 mV/V Nominal mean in the datasheet? I am kind of expecting xyz Newton or Kg / mV or something.

    but all the tutorial I read need to put a known weight and work out the weight/mV ratio.
     
  2. strantor

    AAC Fanatic!

    Oct 3, 2010
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    it means at full scale, it will give you 20mV for every 1V you apply to it.

    So if your load cell is rated 200LBS max and you apply 10V of excitation current, and you load it with the full 200LBS, it will output 200mV.
    (100% load X 10V X 20mV/V)

    If you load it to 50LBS you will get 50mV
    (25% load X 10V X 20mV/V)
     
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  3. bug13

    Thread Starter Well-Known Member

    Feb 13, 2012
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    Thanks now I understand, I think you mean 10V of excitation voltage above as well?

    Another question, are all the s beam load cell expensive? I am looking for a s beam load cell, be able to handle +/-500N, they are like over $4-500, are there any sub $100 ones? I don't need very high accuracy.
     
  4. strantor

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    yes, look at ebay and amazon. I was looking at sub-$100 load cells recently
     
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  5. strantor

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  6. wayneh

    Expert

    Sep 9, 2010
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    Read note #1 in that pdf: The output is a ratio of the supply voltage. So if full scale is 20mV/V and you supply 5V, AND the full scale is 100lbs, you'll get an output of 1mV per pound.

    Oops, should've refreshed first.
     
    Last edited: Jan 21, 2014
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  7. t06afre

    AAC Fanatic!

    May 11, 2009
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    Ah yes load cells can be tricky for the beginner to understand. Load cells like the one you have have need a excitation voltage. And the output will a differential readout across the bridge. So the the 20mV/V means for each volt used as excitation voltage. The differential reading at full load will be 20mV times excitation voltage. Using 1 volt as excitation the differential output reading will be 20mV using 2 volt 40 and so on.
    http://www.sentranllc.com/pdfs/tb_accu.pdf
     
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  8. bug13

    Thread Starter Well-Known Member

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  9. strantor

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    both of those are >10X your budget
     
  10. bug13

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    Feb 13, 2012
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    :D I know, I am just curious, want to know the different why there are two type. Not that I am going to buy those.
     
  11. bug13

    Thread Starter Well-Known Member

    Feb 13, 2012
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