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Hi,

I need a circuit to measure the input voltages (VM5) and the output voltages (VM6) of an operational amplifier (OA1) by adjusting the voltage supply with a potentiometer (R3). (Because, I need to draw a graph where the input and the output voltage dependencies are shown)

The problem: the potentiometer (R3) doesn't works exactly the way I intended. No matter how I adjust the controller, the output voltage of the op amp remains constant.

Notice: The op amp should take a ± 10 V operational voltage. The inputs should take a voltage approximately between + 10 mV and - 10 mV.

Either:

i) connect slider of R3 to one or other end of R3;

or

ii) connect non-inverting (+) input of opamp to slider of R3.

Beware:

https://www.circuitlab.com/forums/analog-design/topic/b95fc6f8/can-a-voltmeter-be-given-infinite-resistance-for-education/

Wow, now the graph with the output voltage "Ausgang" looks nearly similar to the characteristic curve of an typical op amp.

But, there is still a little problem.

When I'm plotting the graph with the input voltage "Eingang", it shows me a line with a slope of 0. This can't be. The input voltage should be changing to as the potentiometer values change.

But as the potentiometer changes value, ground does not.

Remove the "Eingang" label from ground where you have it now, on to the net connected to the slider of R3.

Note that if you edit the circuit you have originally posted (as you are), the original picture moves further away from your original question and so makes the thread hard to follow for newcomers.

It is good practice to save and post edited versions under new names to avoid this confusion.

:)

@signality, it works!!! Many thanks!

And also thanks for the advice with saving re-edited versions under new names to avoid confusion. I will notice that when I'm posting the next time.