The output of Op-Amp[LM324] has error as non-inverting Amp

[booboo1]

Hi everybody
I'm a newbie and working on LM324 to learn Op-Amp. this is my circuit:



One of the resistors is 217ohm and another 978ohm. then the gain should be 4.50691 as you can see. so far so good. I know this is for ideal Op-Amp. I applied 0.15v to the input and got 0.94v in the output. then the gain is 6.26667. again I applied 0.35v to the input and got 2.03v then gain should be 5.8!?o_O
again I applied 1.86v and got 10.31 then the gain is 5.54301! holy crap!  why isn't the gain stable? because of input offset voltage? How can I stabilize it?

[mikerj]

The gain of that circuit is 1+(978/217) = 5.5.  The errors in your measured gains are likely to due to a combination of input offset voltages and output swing limitations of the LM324

[PSR B1257]

again I applied 1.86v and got 10.31

10.3V is about the maximum the LM324 can deliver it's output with 12.xxV supply voltage due to saturation.
One advantage of the LM324 you have already discovert, it can take an input signal close to GND. But too close and you might get in trouble.

If you measure a little more ponits, you end up with a graph like this.
As you can see, it is fairly linear, besides from the top and bottom end so to speak. But that's all you can expect from a LM324 anyway.