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INA114: Sensing direct current in microampers

Jesus Adrian Guerra Delgado
Prodigy 50 points
Part Number: INA114
Other Parts Discussed in Thread: INA2321, INA333

Hi! I've been locking a way to sense direct current in microamperes, my idea is to use a 1 ohm shunt resistor to pass from current to voltage, amplify it and sense it with an 10bits ADC, my problem is that i don't know which amplifier to use, I've tryed with the opetarional 741, but the input current/voltage is to low, so i switch to the instrumentation amplifier INA2321 but problems is still there, I'll try with the INA114. I hope anyone have already worked something similar before, thaks a lot.

  • 0
    TI__Mastermind 22620 points

    Hello, 

    I have a few questions that would help guide us on our recommendations. 

    1. What is your supply voltage?
    2. What is the common mode voltage?
    3. What is producing the microamperes of current that you are measuring?
    4. Is the measurement a high side or low side measurement?

    Best Regards, 

    Chris Featherstone

  • 0 in reply to Chris Featherstone
    Prodigy 50 points

    Hi, 

    1.- I have 5v on v+ and  0v v- and the watermeter  with 3v

    2.- My Vdiff goes from 30uV to 70uV

    3.- Its a watermeter on stand-by, my full task y to sense the current average consumed by the meter

    4.- I've tryed both, but know I'm using high side

  • 0 in reply to Jesus Adrian Guerra Delgado
    TI__Mastermind 22620 points

    Hey Jesus, 

    The lowest input offset voltage instrumentation amplifier that we have is the INA333. The INA333 has a max specification of approximately 25 uV in high gain. This is almost 100% of the the smallest level you are trying to measure. For this reason I would recommend increasing the shunt resistor by at least 10x. The INA114 has an input offset voltage spec of approximately 50 uV in high gain.

    I have included Figure 5-3 below from the INA114 data sheet. Looking at Figure 5-3 you can see that as the common mode voltage increases above +7.5 or below -7.5V, the output voltage swing starts to reduce. For this reason I recommend using a common mode voltage of 0V on a split supply of +/-15V. This will help maximize the output swing and allow you to use higher gains on the INA.  

    Best Regards, 

    Chris Featherstone