Can someone explain my op amp output?

op amp 0v output

Hi All,

I've just started to learn electronics in an attempt to build a small project.
I've bought a number of components and a breadboard and have been playing around. The project will need to use an op-amp to create a voltage difference amplifier. I bought a few LF351N op amps but whatever i do i'm seeing unexpected results. So i thought i'd start off really simple and go back to first principals, but again no joy! Please could someone take a look at the attached diagram and tell me what is wrong?

Basically both inputs are at ground, the supply voltage is +3V and -3V.
I confirm these with my multi meter.
So i would expect the output to be 0 when compared to ground but my voltmeter shows 2.19Volts?

I tried on several opamps and i get the same so i know its unlikely to be broken.

Any help on this or op amps in general greatly appreciated!
Thanks!

Your output is sitting at the top rail. This is because you are usin the op-amp open loop, which has very high gain, so any slight offset at the amplifiers input is going to be amplified vastly and drive the output to the rail.
add a wire between pins 6 and 2, to give yourself 100% -ve feedback (not usually recommended for stability reasons), and you'll have yourself a voltage follower, you'll have 0V at the output then.

Added after 6 minutes:

http://www.talkingelectronics.com/projects/OP-AMP/OP-AMP-1.html

the offset of the amp can cause your out to vdd or vss.

The opamp has an internal voltage gain of 100,000 to 300,000.
For its output to be saturated at 2.2V then its input offset voltage must be only 22uV or more but its max input offset voltage is 10mV.

It has two pins for a pot to null the input offset voltage.

Audioguru is right, you need to use a potentiometer to adjust the "null offset", connecting both inputs to the ground is not enough to get the 0V output. Plus, you must use a close feedback loop, do not left it open.

Everyone,

This forum is great, thanks for all the replies they have really helped.
I'm experimenting with your suggestions (when i get the time!) and things starting to become clear.

I'll probably end up asking more questions up ahead, but i'll try and find out myself before doing so!

Cheers