OVERVIEW OF WATERLEVEL CONTROLLER.........
An analog system might use a load cell (scale) that weighs the tank, and a rate valve. The PLC could use a PID feedback loop (see section below) to control the rate valve. The load cell is connected to one of the PLC's analog inputs and the rate valve is connected to another of the PLC's analog outputs. This system fills the tank faster when there is less water in the tank. If the water level drops rapidly, the rate valve can be opened wide. If water is only dripping out of the tank, the rate valve adjusts to slowly drip water back into the tank.