Two out of three logic circuit (2/3 logic circuit) A logic circuit with three independent inputs. The output of the logic circuit is the same state as any two matching input states. For example a safety circuit where three sensors are present and a signal from any two of those sensors is required to call for a shut down. This 2oo3 system is said to be single fault tolerant (HFT = 1) in that one of the sensors can fail dangerously and the system can still safely shut down. Other voting systems include 1oo1, 1oo2, 2oo2, 1oo3 and 2oo4.