# INA118 instrumentation amplifier

Hello,

I'm currently trying to make the INA118 (instrumentation amplifier) work, but the amplifier is not working whatsoever.

The oscilloscope measure states that the signal is just 200mV, which doesn't coincides with my calculations. That's a gain of 50. There's a small voltage difference with respect to the voltage reference, which could perfectly be amplified.

What am I doing wrong?

I don't follow your voltage divider values. R2 and R1 together should give:

5 * R2/(R2+R1) = 0.0234V, not 0.22V as you write

Similarly, R5 and R6 combine as:

5 * R6/(R5+R6) = 0.0495V and not 0.4545V as you write.

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The 0.022 is the approximate voltage I get by the multimeter, 0.023390067 is not rounder. And as I stated in the schematics, r3 and r4 should give a voltage ~ 0.045V... and the other input should be around 0.05V according to my multimeter.

Is that right no?

Remember that I won't get an exact number as the resistors have a tolerance of 5% in the first place. :)

The 0.022 is the approximate voltage I get by the multimeter, 0.023390067 is not rounder.

Yes, but your schematic says 0.22V, not 0.022V.

And as I stated in the schematics, r3 and r4 should give a voltage ~ 0.045V

No, they give a voltage ~0.455V.

You are also not really working within the allowable common-mode range of this device. If you look at the "Linear Input Voltage Range" parameter on the datasheet you see that it expects the minimum input voltage (at pins 2 and 3) to be about 1V above ground.

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