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xtr111

Michel Stassen
Prodigy 20 points

Other Parts Discussed in Thread: XTR111, XTR101, XTR106, LM7705

Hello,

For my application (straine gauge) i need to put a op before xtr111.

when i do not have negative supply for the op can y put 3V on input 7(SET) in order to perform a zero adjust ?

thanks a lot

  • 0
    Expert 1495 points

    Hi Michel,

    I would recommend a XTR101 instead.. http://www.ti.com/lit/ds/sbos146a/sbos146a.pdf see Fig.14.

    With XTR111 you will need an op amp to convert from differential to single ended input. To answer your question, I don't think external 3V input on pin 7 of XTR111 will work.

    Hope this helps,

    JayantD

  • 0 in reply to Jayant Deshpande
    TI__Guru 64795 points

    Hello,

    Thanks for your interest in the XTR111.

    Michel,

    Jayant is correct and you can not add a +3V offset to the SET pin.  Please help us understand your system better and perhaps we can come up with a solution.  From what I understand you have a strain guage and you need to interface it with the XTR111 and your plan is to buffer / scale the strain guage signal with an amplifier before feeding it into the XTR111.  I'm not sure why you need a 3V offset in your system though so could you please elaborate?  What is the signal range of your strain guage? 

    Also, are your requirements for a remote 2-wire transmitter or a 3-wire transmitter?  If your sensor is some distance away from the main control station and a local power source is not available then you are probably interested in a 2-wire transmitter and should look at the XTR101 or a newer product such as the XTR106 which is meant for bridge sensors. 

    Jayant,

    Thank you for your help again!  I hope all has been well.  Since Michel was interested in the XTR111 which is a 3-wire transmitter let's let him explain his system so we can determine how to best help him.

    Regards,
    Collin Wells
    Precision Linear Applications

  • 0 in reply to Collin Wells
    Prodigy 20 points

    Sorry i have reply to noreply....

    Hello,

    Thanks for your response.
    I need a 3 wires system.
    I have to make a very smal pcb.
    if i put a op i cant have 0V without negative supply on the output.
    it's why i asked the question.
    i know i can put a inverter but i do not have space enough
    signal range from strain gauge is above 2 mV/V supply.
    thanks a lot
  • 0 in reply to Michel Stassen
    TI__Guru 64795 points

    Hi Michel,

    I understand your dilemna better now.  There isn't an external way to offset the input voltage by 3V as you would like.  As described in the "Level Shift of 0V Input and Transconductance Trim" adding an external reference and a resistor can help with a few 100's of mV of input offset but not 3V. 

    Perhaps you can place an OPA with a near rail-to-rail output stage and then use the level shift function described in the datasheet to overcome the small 100mV or less output offset of the OPA.

    Also, if you're in a similar situation in the future but have more room on the PCB, then consider the LM7705 which provides a -230mV output to bias the V- supply of an OPA so the output can reach 0V.

    Regards,
    Collin Wells