NAND Gate
The NAND gate functions like a combination of an AND gate and a NOT gate. The NAND gate is used to indicate that the output occurs when at least one of the input events is absent.
Summary of Logic:
If there is at least one FALSE event, the output is TRUE.
A truth table for a NAND gate follows. The Boolean equation for a NAND gate is T = ~(A * B) = (~A) + (~B).
Example
When at least one generator is operating, adequate power is supplied for the system. If both of these generators fail, no power is supplied to the system.