Hello elecfan,
here are some explanation:
The inverting OPamp
inverted the signal.
It's a current input.
This input is virtual grounded insides, so that the input resistor is only dependend from the connected resistor R1 in the attached circuit.
The amplification will be adjust by the ratio of R2 / R1 for R2 ≧ R1 and R1 ≠ 0 and R2 ≠ 0. The min. ampliflication Is "1".
You can use it as summing point to a lot of inputs
The amplification will be adjust by the ratio of R2 / R1. R1 of each Input can be different from each other. So you can adjust the amplification of each input.
The non-inverting OPamp
The output follows the input
The input resistance is very high and not dependend from serial resistors. The input resistance is only dependent from the parallel resistor R1 if exist.
V=1+(R3 / R2). R2 and R3 can be "0". If R2 and R3 are exist, the min. amplification will be > "1".
A special case of this circuit is show here:
In this case the amplification is "1".
Regards
Rainer