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Problem with INA 128

jm4goncalves
Prodigy 10 points
Other Parts Discussed in Thread: INA128

Hi,

im doing a project to school but im having some problems..

my project is a distance transductor with a linear potentiometer, for that i used a wheatsone bridge connected with a amplifier INA128, but the problem is that i don,t have gain in my Vout..

My source in the bridge is 5V, and i use the same 5V to connect in 7-pin,  4-pin is connected to earth as 5-pin..

To change the gain i used an potentiometer (470K) in RG, but every time that i change the value of RG my gain in the Vout dont change..

What im doing wrong??

I will appreciate any help!

Miguel

  • 0
    TI__Guru 64186 points

    Hi Miguel,

    Thanks for your question.

    For starters, can you please attach a schematic of your circuit? I'm uncertain as to whether you are using 1 or 2 potentiometers in your circuit. It sounds as if you are using one as part of your wheatstone bridge and another as your gain-setting resistor (Rg).

    I also have a couple questions about your input. What is your input voltage range to the INA128 Vin- and Vin+? What output voltage levels are you seeing? Keep in mind that, for a +5V single-ended supply (V+ = 5V and V- = GND), your input voltage range is limited from 1.7V to 3.6V. In addition, your output voltage swing is typically limited to (V+) - 0.9V, which equals 4.1V in your case.

    The INA128 allows for a wide supply voltage range, up to +/- 18V! I would suggest increasing your supply voltage first and see if that helps.

     

    Thanks and regards,