Sharp Infrared Range finder problem

Hi,
I brought a sharp 10-80 cm analog range finder . I connected the output to a voltmeter and got a highly nonlinear output as is common in these range finders.At 80 cm from obstacale the voltage output drops to 0.88V.Now when I tried to move the obstacale further than 80cm the output voltage starts rising again. In the datasheet there is no mention of what might happen if the object lies out of range. Is it normal to get such high output voltage when the object is out of range?

It should drop to zero out of range.

I brought 3 of these sensors GP2Y0A21YK0F but all of them have same output.

Strange. I've not noticed anything like that. Maybe it's the way they are, but from the two I worked with I didn't notice anything like that.

can you please give me the model number you used.I will try one of those.

Have you campared it to the voltage distance graph in the data sheet?

Thanks guys for your answer I figured out my problem actually it was the supply voltage. It was too low, I rechecked the supply voltage tried it with 5.1 volt supply and it worked excatly as the datasheet says.
Thanks