op amp wheatsbrige circuit for load cell

Discussion in 'The Projects Forum' started by JamRacing, Oct 15, 2014.

  1. JamRacing

    Thread Starter New Member

    Oct 15, 2014
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    Hi,I need help with a circuit for my 350 ohm load cell for my shock testing machine.It has to read load in both directions.Not sure which circuit or resisters to use.Very new to electronics.Though this wud be easy.......not so!!!! Anyhow any help wud be good.
     
  2. Sensacell

    Well-Known Member

    Jun 19, 2012
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    Can you provide a data sheet for the transducer? and some details about your application?
     
  3. JamRacing

    Thread Starter New Member

    Oct 15, 2014
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    thanks it is a zemic l6e load cell 150 kg.full scale output is 1.991 mv output resistance is 350 ohms.I though of using a ina 125 amp and then try and feed into picaxe 08m2??thanks for ur help.
     
  4. JamRacing

    Thread Starter New Member

    Oct 15, 2014
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  5. ericgibbs

    AAC Fanatic!

    Jan 29, 2010
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    hi Jam,
    The INA125. IA would be a good choice, either dual or single supply.
    The 350R load cell signal would be amplified by the INA125.
    As you require a swing both negative and positive, suitable for a Picaxe ADC input, I would suggest that you apply a Offset voltage to the Vref pin of the INA125, so the quiescent output is Vsupply/2.

    E
     
  6. JamRacing

    Thread Starter New Member

    Oct 15, 2014
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  7. JamRacing

    Thread Starter New Member

    Oct 15, 2014
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    I have ordered a INA 125 so once I have in hand will post to help with circuit.The Picaxe runs on up to 5 v so want to run load cell and INA 125 also on 5v if possible.Thanks agin
     
  8. JamRacing

    Thread Starter New Member

    Oct 15, 2014
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    What do u thing of tlc 2252 for a op amp circuit if all else fails??
     
  9. ericgibbs

    AAC Fanatic!

    Jan 29, 2010
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    Sorry its not a Instrumentation amplifier.:(
    The AD623 IA will work from single or dual supplies.
     
  10. sirch2

    Well-Known Member

    Jan 21, 2013
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    TLC2252 would appear to be an Op Amp not an instrumentation amp. You can make an Instrumentation Amp from 3 op amps but to keep your life simple I would stick to an instrumentation amp.

    <edit> Oops, Eric beat me too it!
     
  11. JamRacing

    Thread Starter New Member

    Oct 15, 2014
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    How many will I need
     
  12. JamRacing

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    Oct 15, 2014
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  13. ericgibbs

    AAC Fanatic!

    Jan 29, 2010
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    hi Jam.
    If you want to use a 5V supply for the project, I would suggest a INA125 or AD623, followed by a rail to rail OPA, say a MCP6002.

    The reason for the OPA after the IA, is that the IA cannot swing to 0V and +5V, with a single +5V supply, the MCP6002 can swing very close to 0V and +5V.
    Also be aware of the 5V excitation of the load cell, it may be rated as 1.99mV [2mV] for say 10V ext, I would check that out.

    E
     
  14. JamRacing

    Thread Starter New Member

    Oct 15, 2014
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    Thanks cannot do much until INA125 arrives.Should be tomorrow.
     
  15. JamRacing

    Thread Starter New Member

    Oct 15, 2014
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    Hello,I have built circit around INA125 and Picaxe 08M2 for my car shock testing dyno..Works ok for my use but I get a reading of 4 even with no load.Have trimmed trim pot but still get start reading of 4.Why and what do I need to do to get zero.Not sure how to write code to minus reading so it starts at 0.Any help is welcome
     
    Last edited: Feb 7, 2015
  16. ericgibbs

    AAC Fanatic!

    Jan 29, 2010
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    hi Jam,
    Please post your latest circuit diagram so that we can check it out.

    E
     
  17. JamRacing

    Thread Starter New Member

    Oct 15, 2014
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    It is a standard Picaxe 08m2 and ina125 circuit I found on internet.I then have a 4 post 4 poll switch to swop so I get load readings on both sides of z type load cell
     
  18. ericgibbs

    AAC Fanatic!

    Jan 29, 2010
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    In order to help, a least a diagram of the load cell, INA125, power supplies and your switch wiring is required.
    E
     
  19. JamRacing

    Thread Starter New Member

    Oct 15, 2014
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  20. JamRacing

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    Oct 15, 2014
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    Pinetown-20150208-00118.jpg
     
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