I had a doubt about designing a varible offset adjustment for a differencial amplifier (op-amp). (This question: Offset adjustment with unity-gain buffer). The solution was saved in the accepted answer and in the image from the EDITED 2 section of the question. My question now is, could I have a configuration where, using a potentiometer, I could vary gain and offset independently? Could I add to that previous design the gain adjustment now? This new design would allow me to adjust the offset with a pot and the gain, within a range, without affecting each other when varying one parameter. I can't think about this configuration. Is it possible? Is it possible just with one op-amp?
The simplest answer is no, but you can sort of come close. Add another op amp and you can do it. First, your "final" circuit needs to be changed. Ignoring the desire (for now) for an offset adjustment, you should use the classic instrumentation circuit.
See, for instance the Wikipedia article on instrumentation amplifiers for the rules on how to set the resistor values.
Rg, as you might guess, can be varied to vary the gain.
The right hand side of R6 does not need to be grounded. Varying the voltage at this point will produce an offset. However, cannot do something like
That will simply change the gain in an inconvenient fashion. You need to provide a voltage to R6. And you can't do this, either.
That will provide an offset voltage, but it will ALSO change the gain. You need to provide a voltage which doesn't change with the signal. You can do this by
Hope this helps.