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INA128: Wheatstone bridge

Marc_o
Prodigy 55 points
Part Number: INA128

Hi there, 

I am using an INA128 with wheatstone bridge. I use USB power supply to supply wheatstone and INA (+5V)

But my signal is very poor. Is USB power supply not good enough for INA?

Signals from wheastone are around 10mV at 5V of power supply.

Kind regards,

Marc

  • 0
    TI__Guru 67601 points

    Marc,

    Please show the entire schematic with all the component values including supply decoupling caps - showing a bridge alone tells us nothing about a potential problem.

  • 0 in reply to Marek Lis
    Prodigy 55 points

    4x Wheatstone bridge

    4x INA128

    Signal out

    USB Power supply

  • 0 in reply to Marc_o
    TI__Guru 67601 points

    Marc,

    I'm not sure what you mean by saying that "signal is very poor."  Do you mean that there is a gain error, output is noisy, or something else?  

    If the former is the case, the linear input and output voltage range of most instrumentation amplifier, including INA128, is a function of the supply voltage, gain, reference voltage and the input common-mode voltage, Vcm, due to non-linearity of the internal stages of the device.  That's why it's critical for me to understand the details about your circuit.  Since you did not provide the value for the gain resistor, I made an assumtion below that for 10mV input signal the circuit is in gain of 100.  If that is the case, the valid range of the input signal for Vcm of 2.5V is ONLY from 8mV to 15.5mV, thus resulting in the output voltage range from 800mV to 1.55V - see below.

    If on the other hand, the latter is the case and the output is very noisy, please add 0.1uF bypass decoupling capacitor between the supply pins, from V+ to GND.