I need guidance not in detail of course to design a liquid level controller based on 8951. How can I use a potentiometer attached to a floater in system to sense the level of liquid? the system must read (get) desired levels from a keypad and system adjusts the level in 8 tanks to match these desired levels? (we want to have 4 levels only. 25% 50% 75% 100% which is 00 01 10 11 binary). When the level liquid reaches the desired level the system must turn on a LED of the corresponding tank.

 

You would need to rig up a pulley above the tank. The system would need to have good bearings and be protected from dust and moisture. A wire would be attached to a float that rests on top of your liquid. The wire would go up the tank and around the pulley, down the outside of the tank to a potentiometer - no wait. A pulley on the potentiometer that would wind up would be too big so attach the potentiometer to the pulley at the top of the tank. You may need two pulleys at top - one directly above the float the other offset beside the tank. On the other end of the cable put a weight to put tension on the float cable.

So as the float cable moved the potentiometer would turn. You would need about 12VDC into the pot and you would get a proportional reading out or you can easily convert that to a 4-20 mA signal. With voltage out you could use a millivolt scale to see the reading as well as covert it.

Since you are only after point levels it would be lot cheaper to go with a simple multi-point level sensor like at: http://www.almegcontrols.com/multi-level_large_size.htm and then just use an LED to show when the switch points have been hit. The switches are either on or off and will run an LED without complicated circuitry.

Thanks
Bob Hogg