Sources and Sinks

There are three kinds of external connections and devices in an ACS:

• Sensors that obtain raw observations about the state of the world used to Update Navigation Models.

• Effectors that manipulate mechanical components in accord with Action Models.

• User interfaces and instruments that display suggested Actions, Flight Objectives, and the State of the ACS, and accept pilot input for changing Modes, and Arming components.

Most source and sink components in an ACS must be designed and constructed independently from the models and transformations that interact with them. This is because, in general, there is a many-to-many relationship between devices and other components:

• A single input device may provide data used to estimate many different model properties.

• Many different input devices may provide data about the same property.

• One output device may collect, display, or use information from several models.

• A single effector setting may be transduced through several output devices (e.g., in the case of redundant hardware and parallel paths that simultaneously display and perform actions).

Design Steps

Separate device control from information flow by constructing Device Controllers. Sensor device controllers differ in most details from Effector device controllers. The control of inputs and outputs is generally device-specific, while the overall ACS Information Flow is generally estimate-specific. User interfaces and instruments are special kinds of input sensors and output effectors. (The design of user interfaces for avionics systems is not otherwise addressed in this set of patterns.)