Actuator sensor interface (AS-i) is a bit-oriented master–slave type open system fieldbus designed to be used at the device level of process control systems. It is included in both EN 50295 and IEC 62026 standards. AS-i is designed to connect binary sensors and actuators (i.e., slaves) that require very small number of bits to convey device status. Thus, this protocol is very efficient for this type of slaves. AS-i is not good enough to be connected to intelligent controllers that require information beyond the limited capacity of such a protocol.
The main design of AS-i is based on modular components. They act as bridges between the network and the binary sensors. Nodes can be added or taken out in “live” condition, i.e., while the system is running, without any kind of interruption. AS-i data capacity ranges from 1 to 16 bits per device.