Is my Ping sensor broken?


I'm working towards a close deadline for an installation where I was planning to use a Ping sensor with an Arduino. The sensor seemed to be ok with initial testing, but now I can't get anything sensible out of it for ranges from 50 cm and up. I get a lot of noise, mostly maximum value readouts. Closer then 50cm it seems to work reliably. Is my sensor broken, or is it really that flaky above this range? I need to detect the distance to a human body with it.

I'm testing it by hovering with my hand above it, but I've tried bigger objects without much luck. It seems that if I use something flat like a book, and I make sure the surface is ortogonal to the direction of the sensor it is not giving me noise, but how is that useful in real-life situations? :-/

I need to decide within 12h if I have to order a new one or ditch the sensor all together, so I'm getting nervous by these recent findings. I know there are better more accurate ones with larger ranges as well, but they use a I2C interface which will add a lot of extra work for someone with my experience I fear.

What are your experiences with the Ping sensor?