I'm looking for a sensor that will measure the distance to a water surface. Some approximate specifications are: Operating range: 0 to 2 metres Update interval: 0.1 sec (10 per second) Accuracy: 1cm Naturally it needs to be water resistant or able to be mounted in a water proof housing, and operate continuously for up to 3 or 4 hours. It will need to connect to a programable controller that will process the measurements and control an actuator depending on the distance to the water surface. I'll need to program the controller as the movements are not a simple linear or curve relationship to the distance, it will need to be able to handle velocity and acceleration as well as straight displacement as it needs to have dampening effects and filter out noise. Can someone advise of any existing hardware that fits the bill? And a suitable programmable controller that it can connect to?