What type of strain gauge load cell to use?

Discussion in 'General Electronics Chat' started by jcmpineda, Nov 5, 2018.

  1. jcmpineda

    Thread Starter New Member

    Nov 5, 2018
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    0
    Hi. I'm new here. We need to modify an apparatus for our project and it needs the use of strain gauge load cell. Based on the structure we are making, it requires a set of four load cell. The apparatus should have an accuracy of 1 gram and can weigh up to 20 kilograms. Each load cell will be placed in every corner of a frame. We are not majoring in electronics engineering so we do not know the type of load cell to use. We see different types of weight sensor and we don't have a wide understanding on these, that's why we're seeking help so we will purchase the most suitable type. Can we use the load cell that are used to improvise human weighing scale--the one that uses four load cells? Is it suitable for an apparatus that can weigh up to 20 kilograms by one gram interval? Photo attached below. Screen Shot 2018-11-05 at 5.49.54 PM.png

    Thanks in advance!
     
  2. ericgibbs

    Moderator

    Jan 29, 2010
    7,681
    1,547
    hi jcm,
    Welcome to AAC,
    A number of members have already made weighing projects that use that type of load cell along with HX711 module, connected to a Arduino.
    So your project is feasible.
    E

    Look thru this PDF.


    EDIT:
    Link to one Thread, Search the Forums for HX711 for other Threads
    https://forum.allaboutcircuits.com/posts/1162068/
     
    Last edited: Nov 5, 2018
  3. jcmpineda

    Thread Starter New Member

    Nov 5, 2018
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    But is that type of strain gauge setup capable of detecting change in weight as small as one gram?
     
  4. ericgibbs

    Moderator

    Jan 29, 2010
    7,681
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    hi,
    You say that you are going to have four transducers on the base plate of the scale, one at each corner and you want to measure a maximum of 20Kg.
    So I would choose load cells that have a maximum of 5Kg, four cells in parallel would give a maximum of 20Kg.

    Do you want a resolution of 1 gram or an accuracy of one gram.?

    E
     
  5. jcmpineda

    Thread Starter New Member

    Nov 5, 2018
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    0
    It requires a resolution of one gram. So we can only use four 5kg bending bar load cells? Or we can use any type of load cell that fits the structure of our apparatus? We just based the structure on the size of the load cells (I don’t know what it’s called) used in making improvised bathroom scale like the photo attached above. We’re not sure if that type has a resolution of one gram because each has a capacity of 50kg.
     
  6. ericgibbs

    Moderator

    Jan 29, 2010
    7,681
    1,547
    hi,
    Using four 50Kg load cells, will give a maximum capacity of 200Kg or 200,000 gms.
    I would say you will not get an accuracy near 1gm.
    If your displayed weight showed a range of 0 gm thru 200,000gm, the lowest 2 digits displayed would be meaningless.

    The HX711 can be set up to excite the bridge at 5V, but the actual internal excitation voltage is approx 3.5v.

    The HX711 full scale differential voltage for a Gain of 128 is +/-20mV.
    So 20mV has to represent 200,000 gms, thats 100nVolt/gm
    The Input offset drift is 0.2mV and the input noise is 50nVolt.

    Which type of objects are going to be weighed on the scale.?

    E
     
    Last edited: Nov 6, 2018
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