SEN0204 Inconsistent behaviour

Hi,

I'm trying to use the SEN0204 but I'm having inconsistent results. I have setup 6 sensors onto a square water jug (material thickness only 3mm). I'm powering up the sensors with a 6V battery supply.

What i have found that not all sensors can pick up the water (even at level 4 sensitivity setting). 2 of my sensors seem to pick up the water while the other 4 don't. If i attach a random piece of wire onto the ground of my battery (other end of wire is floating) or if i touch the 0V with my fingers, then a couple more sensors ‘seem’ to work (although not consistent).

The only thing that fixes this issue properly is connecting my 0V of the battery to electrical EARTH (in the power point). I can even drop the sensitivity of each sensor down to level 1 and they all still work.

My question is should these sensors work with a floating supply (like a battery) or does the 0V need some sort of reference (like earth).

Thanks.