Probably really a designer problem
I am trying to use a TL082 FET Op Amp to amplify a DC signal into a range useable by an A/D device. I have breadboarded the op amp as a non-inverting amplifier using two resistors to determine the gain. The circuit is the basic one that is shown in most op amp discussions. The resisters are measured at 9.82M, connected between the output and the inverting input, and 32.6K, connected between the inverting input and ground. These are the only components in the circuit. Calculated gain of ~ 302.
My input signal varies from ~ 8 mv to 11.8 mv. The signal positive is connected to the non-inverting input, the signal negative is connected to ground. I have two 9V batteries supplying +/- 9V, with ground connected to the signal ground.
My measurements show that a 8 mv input yields a 3.34V output, while an 11.8 mv input yields a 4.49V output. The gains are 417.5 and 380.5 respectively.
I'm obviously not using the op amp correctly. The gains are wrong, but even more important, they are not the same. Varying the input signal results in varying gains, which definitely isn't right.
All I want was a simple signal conditioner circuit, seems my very simple circuit is not very stable. Any advice ?
Thanks,
Bob
I am trying to use a TL082 FET Op Amp to amplify a DC signal into a range useable by an A/D device. I have breadboarded the op amp as a non-inverting amplifier using two resistors to determine the gain. The circuit is the basic one that is shown in most op amp discussions. The resisters are measured at 9.82M, connected between the output and the inverting input, and 32.6K, connected between the inverting input and ground. These are the only components in the circuit. Calculated gain of ~ 302.
My input signal varies from ~ 8 mv to 11.8 mv. The signal positive is connected to the non-inverting input, the signal negative is connected to ground. I have two 9V batteries supplying +/- 9V, with ground connected to the signal ground.
My measurements show that a 8 mv input yields a 3.34V output, while an 11.8 mv input yields a 4.49V output. The gains are 417.5 and 380.5 respectively.
I'm obviously not using the op amp correctly. The gains are wrong, but even more important, they are not the same. Varying the input signal results in varying gains, which definitely isn't right.
All I want was a simple signal conditioner circuit, seems my very simple circuit is not very stable. Any advice ?
Thanks,
Bob