The ATC Diversified LPC Series is a conductive liquid level controller that uses two probes to sense tank level. There are two modes of operation that are user selectable. Drain Pump Down: The output relay will pick-up and the LED will turn on when the liquid level reaches the high level probe. When the liquid level falls below the low level probe the relay will drop-out and the LED will turn off.Fill Pump UP: The output relay will pick-up and the LED will turn on when the liquid level falls below the low level probe. When the liquid level reaches the high level probe the relay will drop-out and the LED will turn off.