Inexpensive load cell/force transducer?

Discussion in 'The Projects Forum' started by summersab, Jun 16, 2010.

  1. summersab

    Thread Starter Active Member

    Apr 8, 2010
    132
    0
    Hey, all. I'm looking for an inexpensive load cell/force transducer/force cell (they go by various names). I tried yanking one from a cheap Walmart digital bathroom scale, but for some reason, I can't get much sensitivity out of it (I've tried standing on it and squeezing it with pliers, and the resistance only changes by a ten-thousandth of an Ohm). Most of the load cells I've found online are for industrial purposes, and they're like $200 and up. I'm thinking like under $20, but I've had no such luck. Where do digital scale manufacturers get their parts?

    Alternatively, I was thinking of using a force sensitive resistor such as the following:

    http://www.trossenrobotics.com/flexiforce-25lb-resistive-force-sensor-4inch.aspx?feed=Froogle

    However, the Wikipedia article on them mentions that they might be damaged by prolonged exposure to a weight, which would pose a problem for my application. Anyone have any experience with these and their durability?

    Thanks a bunch, all!!!
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    As explained before, load cells respond to applied strain, not crushing. The force causes the fixture the strain gauges are attached to to bend. Try Omega Engineering to learn how they work.
     
  3. ericwertz

    Member

    Aug 26, 2009
    14
    0
    Not sure what your app constraints/goals are, but perhaps you could kludge one out of a spring (in compression) displacing a linear potentiometer (with its own light-weight return spring) ?
     
    Last edited: Jun 17, 2010
  4. atferrari

    AAC Fanatic!

    Jan 6, 2004
    2,648
    762
    Adding a spring to a LVDT could work.

    Besides what many would say, even built by you should be not necessarily expensive.

    Calibration coukld be tricky, I admit, but doable.
     
  5. summersab

    Thread Starter Active Member

    Apr 8, 2010
    132
    0
    @beenthere, I'm a mechanical engineering student. No offense, but I understand how a load cell functions. I'm not talking about crushing strain gauges - that is not an appropriate mode of operation for them, and I fully understand that. I'm applying force in an operational manner to the load cells with an integrated strain gauge, not directly to a strain gauge.

    Springs and button cells won't work in my application. It's got to be either a load cell or something similar like a force sensitive resistor. A professor at school suggested I look into the sensors in newer car seats that enable airbags based on weight. If a small child is in the seat, the airbag won't enable, but if an adult is in the seat, the airbags turn on. Unfortunately, I don't know what mechanism is used in this application.

    Anyone know of something inexpensive along these lines?
     
  6. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    4,769
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    :p:D
    Your seach should start at Digikey.com, Mouser.com, Newark.com or Omega.com. They are not cheap when you want 1, they are much cheaper when your are Chrysler and order them by the millions. Heck walk over the the electrical engineering department and pull one from the bins of spare parts they should have.
     
  7. pilko

    Active Member

    Dec 8, 2008
    213
    20
    Google conductive foam sensor.---- there are many examples and costs next to nothing.

    Regards

    pilko
     
  8. vachhaninimit

    New Member

    Jul 7, 2010
    1
    0
    Hi,
    You can find many different types of load cell here. Of course the company dosen't hold certifications which obviously not needed in the market that company is dealing.
     
  9. forcemeasurement

    New Member

    Oct 13, 2015
    3
    0
    You can try this cheap load cell ,about 5usd/pc,capacity starts from 3kg,should be sensitive enough.
     
  10. GopherT

    AAC Fanatic!

    Nov 23, 2012
    6,016
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    Whew, that was a fast response. The previous post was barely up 2291 days before you came blazing through with an answer. Good work! Do you work at the company you recommended?
     
  11. forcemeasurement

    New Member

    Oct 13, 2015
    3
    0
    Even though it was posted years ago,but still I found this conversation on google,what's the harm to provide an applicable product or sulution to the coming pals?
     
  12. GopherT

    AAC Fanatic!

    Nov 23, 2012
    6,016
    3,789
    I think it is funny, the moderators usually don't.
     
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