pylon:
I don't know this sensor but the spec says the output signal range is 8-12mV, so all possible values give you a reading of 1 or 2 on your Arduino so the resolution is unusable. You have to amplify the signal before you give it to the Arduino. As the company for the datasheet, the information on that web page is not satisfactory.
As you bought a sensor from them they should be able to provide you the necessary information to use it.
Then i can't read 8-12mV with my ardunio am i right ? How can i amplify signal ?