Voltage scaling of analog signal -10 to +10V to 0 to 3V inorder to give it as input to ADC using opamp TL082 and TL431
So you need to do two things for solving your problem.


Add a 10V DC offset so the all the voltage goes in a positive direction. you can do that easily using a voltage divider network. I have attached a circuit where I add a 2.5V voltage offset using a voltage divider network(R3 &amp; R4).
Now all the volage is range 0-20V. Then use an OP-AMP in a non-inverting amplifier for attenuating the signal to 0-3V. Remember you by doing so you just need a single supply voltage for the op-amp.