Estudante

Sensor Bus Network

AS-Interface Overview
The AS-i (Actuator Sensor Interface) protocol was created in Germany in 1994 by a consortium of factory automation suppliers. Originally developed to be a low-cost method for addressing discrete sensors in factory automation applications, AS-i has since gained acceptance in process industries due to its high power capability, simplicity of installation and operation, and low cost adder for devices. Each AS-i segment can network up to 31 devices. This provides for 124 inputs and 124 outputs, giving a maximum capacity of 248 I/O per network on a v2.0 segment. The AS-i v2.1 specification doubles this to 62 devices per segment, providing 248 inputs and 186 outputs for a total network capacity of 434 I/O points. Both signal and power are carried on two wires. Up to 8 amps at 30VDC of power are available for field devices such as solenoid valves.

Conventional I/O System vs. AS-i Bus Network
AS-i is so simple and so inexpensive that it makes using traditional wiring methods difficult to justify.

CONVENTIONAL I/O SYSTEM
Advantages - Technology is already understood - Slightly lower device cost - Independent wiring from devices to the control system means wiring problems with one device don’t affect other field devices Drawbacks - Higher installed cost - Point-to-point wiring is expensive - Many wiring connections: - are labor intensive to install - create many points of failure - increase complexity when troubleshooting - require large amounts of cabinet or rack space for installation of terminal blocks - create time-consuming initial checkout and startup - Expansion requires duplicating the entire wiring scheme for each additional point

AS-i BUS NETWORK
Advantages - Technology is easy to understand - Very low device cost adder - Lower installed cost - High speed network for sensor level devices - Ability to integrate conventional devices into AS-i network - Easy addressing for devices; auto-addressing capabilities