We have a water level monitor attached to a water tank. The water monitor has an hydro-static water sensor (output 0-5 V) that goes to the bottom of the the tank (see figure).
In most cases this works OK, but for some of our clients, the water sensor burns out repeatedly.
We think this is caused by an ESD issue. By analysing the situation of these water tanks, it seems that this occurs in zinc tanks that have an internal plastic coating in some really dry and dusty areas.
Our hypothesis is that wind blows dust onto the tank, which builds a potential with respect of the water (given that the water is separated from the metal by a plastic layer) and this difference of potential gets discharged into the water sensor.
To solve this problem, we were considering switching to 4-20 mA water sensors, with ESD protection in the sensor, but we are not sure if this will be enough to solve the problem.
Additionally, we are considering grounding our device to the water tank, to prevent electric charge from building between the tank and the water. The idea is that the charge would flow with low resistance through the ground of our device and the probe.
My question would be: would this approach be correct? Wouldn't conducting the electrostatic charge to the tank create galvanic corrosion in the tank to device contact areas?
Also, maybe it is not ESD; could it be that the probe cables are acting as inductors, and creating a big potential on changes of current to the probes?
Thanks in advance.