Automatic Water Distribution System Using PLC

You clearly need the retro encabulator from Rockwell Automation. Just kidding!! Check out the Allen Bradley site as well check out inductive proxies and the Honeywell site.

Depends on how you intend to implement the capacitive sensor? I'd be inclined to use RF capacitance operating on the principle that the capacitive level between a +ve probe and the appropriate ground will increase as the tank level rises. The capacitance change is measureable using an invasive probe connected to the appropriate electronics. For non-conductive fluids, the ground is the tank wall. With conductive fluids an insulated probe is used and the capacitance through the probe insulation is used as a measure of the level. For non-contact sensing, you can mount an ultrasonic transducer above the maximum fluid level in the tank. The emitted pulses reflect and return to the transducer, which translates the time elapsed into a measure of distance

How about an ultrasound sensor, I think is a good way to measure the level, I think the geometry of the tank is simple, doesn't it?, may be is a little bit ore expensive but is very accurate and could be connected to a PLC. Good luck!!

If the water in the tank can tolerate bubbling air through it, a really cheap way to measure level is to do it pneumatically. If there is temperature control (TC) compressed air in the plant, tie into the regulated main air supply, run it through a restrictor designed for a TC device, a $2 item, then to poly tubing that extends to the bottom of the tank (you could attach a length of poly to a weight and drop it into the tank). The pressure build up in the tubing after the restrictor will be equal to the water column height. A $30 4-20 ma pressure tranducer can tee'd into the line to be used to input to a PLC. With the right restrictor, not much air is used, about 1 standard cubic foot per hour (about 1/30 of a cubic meter). If you only have process air available, run the line through a filter first to keep the restrictor from getting clogged and you may need a small pressure reducing valve to get a constant pressure of about 20 psi (about 1.5 bar). A cheap inline automobile gas filter can work for the filter. If your tank is cylindrical and on its side or is spherical, and if you want to know the amount of water in the tank in liters at any level, you will need to have a PLC with trigonometric functions (i.e. arcsin)to calculate it from the height of the column.

I suggest to use Mitsubishi PLC.