Distance US3 Module not able to detect correctly distance under 15 cm

Hello all,

I’ve some issue with the distance US3 module.
I want to detect a distance between an object and the sensor. The distance is suppose to be between ~5 to 30 cm. So I decided to use the US3 module which normally able to detect distances between 2 to 400 cm according to the specifications.

My problem is that with all tests I did, the module was never able to show on the screen a distance lower than 15-16 cm even when the object is clearly closer.
I tried many things : small & big objects (walls) and with distance from 0 to 200 cm.
I got a correct answer from the module when the distance is larger than 20 cm but it never answered me anything smaller than 15-16cm even when it’s very close to a wall.

I also notice that the detection is way faster when the distance is big (1/3 sec for more than 30 cm) and is quite long when it thinks the distance is at 15cm (around 1sec).

I’m using a FEZ Spider 1.0, I also tried to use different slot for the US3 module.

I’m open to any suggestion.
Thank you.