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I have built an instrumentation amplifier using an LM348N quad op amp, supplied with ±9V. A simulation of the circuit is done as in the link - Simulation:

schematic screenshot

But when I connect the circuit accordingly, there is no variation in the output voltage as input is varied. The input differential voltage varies when I probe the non inverting terminals of the op amp, but I don't see any variation when I probe across the inverting terminals and the outputs of the op amps respectively. What am I doing wrong?

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  • \$\begingroup\$ Please include the image inline in your post. That way we can understand the question without following a link and the question will make sense when the link dies. \$\endgroup\$
    – Transistor
    Commented Apr 4, 2020 at 9:16
  • \$\begingroup\$ @Transistor done that for him just as you typed ;) \$\endgroup\$
    – Marcus Müller
    Commented Apr 4, 2020 at 9:16
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    \$\begingroup\$ You don't have a reference ground terminals, which means input bias currents will saturate the inputs. LM324 is not LM348. \$\endgroup\$
    – Neil_UK
    Commented Apr 4, 2020 at 9:17
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    \$\begingroup\$ hey, blazingcannon: chances are 70% that you schematic would work, but you made a small wiring mistake somewhere. Clean up your schematic! The "knot" of batteries in the center of your image is really confusing. Also, this is just a simulation, so use a single 24V source instead of two 12V sources V1 and V2. I really believe that tidying up your schematic has a good chance of solving this problem! \$\endgroup\$
    – Marcus Müller
    Commented Apr 4, 2020 at 9:19

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You need a ground between the two input voltage sources as @Neil says and you also need to ground the point between the two 12V sources.

The models used in this simulation must have some hidden 10G or whatever resistors because SPICE will fail to find a solution without a ground reference.

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