AS-i functional safety

Safety at Work (SAW) has been available since 2000 as the first approved safety networking technology. SAW is an approved safety network that incorporates the required international safety approvals for functional safety. The system is certified by TUV, a Nationally Recognized Testing Laboratory that is recognized by OSHA.

Safety at Work wiring benefits

• One cable from the main control cabinet for safety wiring
• Feedback wiring is eliminated
• Eliminates the need for additional PLC cards
• M12 patch cables used for connecting safety devices to safety input modules

Operating principle

Each fail-safe AS-i slave has a unique code sequence that is 8 x 4 bits. While the contacts are in the closed position, a 32 bit number is transmitted over the AS-i cable 4 bits at a time. After eight scans, the pattern repeats. The bit pattern is referred to as a "Code Table".

The fail-safe AS-i slave responds to each cyclic data call of the AS-i master with one of the following:

• the consecutive part of its code sequence if its two channels are active (ex. - e-stop unlocked)
•  "00xx" or with "xx00" if one of its two channels is inactive
• "0000" if both channels are inactive.

The AS-i safety monitor only listens to the communication between the AS-i master and fail-safe AS-i slave. The safety monitor also knows the code sequence of each configured safe AS-i slave because it is taught during set-up. The safety monitor safely switches off its output if the code sequence is received incompletely or not at all.