1.1           Term definitions

Causality

Causality is the relation between cause and effect - it describes the sequence of interrelated incidents and states.

Causal relation = Cause and effect relation (C&E relation)

·            Monocausality

One cause results in either one or several effects.

·            Causal chain

Strictly temporal sequence of sequential causalities.

One cause results in several sequential effects; such as dominoes falling down one after another.

·            Multicausality

Several causes interact or act independently at the same time and result in several effects.

Voting

For process flows, the functional safety must often be guaranteed. For this purpose, several functionally identical devices or systems are installed in parallel.

Via the voting, you can define how many of the devices or systems installed in parallel must be fully functional to ensure the functional safety. If several of the devices or systems installed in parallel are detected to be defective, the overall system (overall process) must be shut down.

The voting is also used to, for instance, check or evaluate the measured values of sensors. In that case, you can, for instance, define how many of the sensors installed in parallel must indicate the same measured value.

·            1oo1: Single-channel processing (there is no parallel installation of functionally identical devices). If the single device fails, the overall system must be shut down.

·            1oo2: Redundant processing with cross-diagnosis. For two functionally identical devices installed in parallel, the overall system is shut down if one device is defective.

·            2oo2: Redundant processing. For two functionally identical devices installed in parallel, the overall system is shut down if both devices are defective. If one device is found to be defective, the intact device is used instead.

·            2oo3: Threefold processing with use of the majority result: Voting (selection of ‘2 out of 3’). If three functionally identical devices are installed in parallel, the overall system is shut down if two devices are found to be defective.

·            For instance, if three functionally identical sensors are installed in parallel, you can define via this voting that two out of the three measured values must be identical for a specific action to take place.

·            2oo4: The system remains stable if two devices fail at the same time.