I am trying to subtract a variable voltage from a sensor output voltage reading using the INA129P. I am powering the chip with a +/- 9V. A problem that I am having is that I only get the expected voltage when the Vin+ > 1.07V .
Is the offset voltage the cause of this? And is there a way to make the output proper for values around 0.60-0.70V?
Can you please post your schematic and the actual measurements of each input pin and the output pin?
Precision Analog Applications
Sorry I do not know how to draw a schematic for you to see. I'll try my best to write what I am experiencing in words.
Fixed: V+ & V- are powered by 9V ; Ref = GND (from an Arduino UNO) ; Gain ~= 1;
Vin+ = 0.70V ; Vin- = 0.30V ; Vout = 0.00-0.01V;
Vin+ = 1.30V ; Vin- = 0.30V ; Vout ~= 1.00V
If you have a program that you can suggest that would help me describe these technical details, I'd be happy to use it.
We have a free SPICE simulator that is great for drawing schematics. Here is the URL:
I have attached a TINA-TI simulation that you can use to verify your setup. Please verify your input common-mode voltage is 0V and that you have +/-9V on the supplies. The worst-case offset voltage is 1.125mV (at G=1), which is insignificant when compared to your input signals. Therefore I suspect an issue with the circuit configuration.
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