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INA826: Current Meter position

Milav Soni
Intellectual 455 points
Part Number: INA826


Hello,Guys

This is Milav Soni.

In one of my project I have used INA826AIDGKR instrumental Amplifier.

I required high input impedance >66MOhm.

I want to just know the current meter direction when we apply Following Supply to the INA.

-> At positive Terminal Give +5V supply.

-> At Negative Terminal Give -5V supply.

So Question is , What is the current meter Direction in both +ve and -ve branch? 

in both case is it from source to INA? or is different in both the branch?

I asked this question , because I got Input Impedance is less than 66Mohm. 

Here I have attached the screen shot of my Setup.

 

I got Negative Value of "AM2" and From definition of Differential current Id = AM1 - AM2 

 = 4.95 - (-5.01)

= 9.96 uA

so Id is increase in this situation and Input impedance is decrease. I have also attached the result screen shot.

Please help me to sort out this problem.

Thank you

Milav Soni

 

  • 0
    Guru 140200 points

    Hi Milav,

    Does this answer your question?

    Kai

  • 0 in reply to kai klaas69
    Intellectual 455 points
    Hello, Kai

    I am not sure which is right method to put the current meter in which place?

    please let you know which is right condition to put the current meter?

    as per my knowledge , if we want to measure input impedance of INA826, we may consider the current following from external circuit.

    please let you know is this external circuit is calculate in Input impedance ?

    Thank You...

    Milav
  • 0 in reply to Milav Soni
    Guru 140200 points
    Hi Milav,

    why not just trusting the specifications given in datasheet? These data were obtained by using state-of-the-art measurement equipment.

    Which input impedance shall be >66M? The common mode input impedance or the differential input impedance? The 4k7 and 1M resistors come from your application circuit? And the INA826 shall not distort these impedances?

    Kai
  • 0 in reply to kai klaas69
    Intellectual 455 points
    Yes, The datasheet said....20Gohm. that is right.

    we measure differential input impedance. and 4k7 and 1M resistor are the part of our application circuit.

    so if we consider the external circuit , than which current i measure?

    Thank You
  • 0 in reply to Milav Soni
    Guru 140200 points

    Hi Milav,

    to make the DC input offset current cancel out, I would measure the voltage drop VM1 across one 4k7 resistor with +10V and -10V differential input voltage:

    Then, take the average of both measurements and calculate the differential input resistance. To refine the result repeat the measurement with other input voltages. This should give you an adequate estimation of the differential input resistance of INA826.

    Kai

  • 0 in reply to kai klaas69
    TI__Genius 11135 points
    Milav

    We haven't heard back from you so we assume this answered your questions. If you need more assistance just post another reply below.

    Thanks
    Dennis