Help with Circuit Nodal Analysis

[ethanh100]

Summary: Perform nodal analysis on a circuit to find voltages.

For a laboratory I am trying to find the nodal voltages for a circuit we built using hand calculations. I have the answer as we ran the simulation which shows all the nodal voltages, however my nodal analysis seems to be wrong as I am getting completely different values. In the circuit I am combining nodes Vout+ and Vout- into one node to make it a bit simpler, so putting RL and R5 together as a 2k ohm, and then I can just do voltage division later to find Vout-. So I am solving for Va, Vb and Vout. Can someone explain to me what i am doing wrong.. Thank you!

 

[phyzguy]

You set it up right, you just made a mistake in your bottom equation. The coefficient of the VA term should be -0.001, and the coefficient of the Vout term should be 0.0025. If you correct those, you get the same answer as in the plot. By the way, it is a lot easier to do the math if you multiply through by 10,000 so all of the coefficients are integers.

 

[ethanh100]

Ah okay thank you, I always seem to mess up the signs and algebra in nodal analysis. Youre right it would likely be a lot easier if I just multiplied to a common base. Thank you!