tl;dr: I want to understand op-amps better! How do I choose the magnitude of resistors? 1k, 10k, 100k, etc.. I made a schematic to play with an In-amp to create a gain of 5.
What other considerations should I implement in a real world circuit?
–
I'm trying to learn how to use op-amps to provide a gain of Av=5
Eventually I would like to apply this knowledge to the use of strain gages in a Wheatstone configuration. That's a later thing 🙂
For now, I'm diving into it by creating a instrumentation amplifier with a gain of 5. I like this approach because as I understand it, it is a more robust solution to boosting a signal for a variety of reasons. Not to mention the gain is easily adjusted, which I may be interested in using a digital potentiometer in that location for just that reason.
This is what I have came up with so far in ltspice:
This yields what I want:
The frequency is not very relevant in my situation, the signal won't be changing very much over the course of 1 second.
So my question to you guys,
-
Why do I choose resistors in the realm of 1k? Why not 10k? or 100k?
-
How can I add some basic noise filtering?
-
Do you see any issues that may occur in applying the circuit above to real life?
I apologize for my lack of knowledge and terminology if I butchered anything! Thank you for any time you can lend me, I do circuits by hobby and want to understand more of the analog elements.
Best Answer
If you choose too low valued resistors, they would draw too much current and dissipate too much, which isn't needed. (And when they draw really too much current, the may overdrive the OpAmps as well and/or damage it).
If you choose too high valued resistors, your circuit may be prone to external noise. And next to that, the OpAmp draws a small input current as well. With too big resistors, those currents influence the circuit too much. Depending on the voltage of the OpAmps you pick the resistors.
I'd advise to start reading about RC filters and apply them.
Leaving that to others. I'm not that experienced applying them.