Smart and Simple Level Sensing with AS-Interface bus

The adoption of digital buses in process industries is gaining traction. The Industrial-Internet of Things movement has provided a new impetus to existing digital communication technologies. Digital buses on the plant floor can take up significant resources during installation and commissioning, as it may involve trained technicians to complete the job. The industrial sites implemented Modbus, HART, Fieldbus in the plants for efficiency in operation however complexity during installation at scale, still remains a challenge. The complexity of design implies a requirement of large number of wires to connect input/output devices in process automation industries.

AS-Interface by design is a loop-powered digital bus. The 2-wire unshielded lines carry power as well as data on them. This, together with the simplicity in its operation makes it an ideal choice for quick installation. The single cabling system connects I/O devices with automation system. It supports in continuous operations by making streamlined connections, detects breakdown conditions, and reassemble the faulty device without closing power systems.

AS-Interface operates on a master-slave mechanism. This eases the protocol burden and reduces computation requirement at the nodes. The AS-Interface is noise immune which maintain better performance of networking system. Being flexible makes it movable to different locations in overall networking system. The other field devices can be integrated into existing networks via AS-Interface master. It supports in communication process by creating a network to connect various operational plants.

AS-Interface has built its significance by keeping things simple. The AS-Interface can be used along side higher-level network protocols to avail simplicity and uniformity in bus protocols. With respect to specifications other field buses seem to have an advantage. However, it is the simplicity in its installation that makes it the choice for simple low power switches.

Parameter	Modbus	Profibus	HART	AS-Interface
Maximum Cable Length	1200m	200-19.2km	2000m	100m
Communication Method	Master/Slave	Master/Slave	Master/Slave	Master/Slave with cyclic polling
Communication Speed	9.6-115.2 kbits/sec	9.6-500 kbits/sec	1200 bits/sec	167 kbits/sec
Maximum Data Size	250 bytes	246 bytes	8 bits	8 bits
Maximum stations	247 per Network	127 Devices	15 Slave	62 Slave

Point level sensing involves primarily two output states :

• Normal : The process can continue operating in this state
• Alarm : The process needs to act by either annunciation, or by triggering a filling or draining

It is essentially a binary output, AS- Interface has provision of up to 4-binary outputs per slave. Apart from single point switching AS-Interface can also be used for multi-point switching or real-time diagnostics. Using diagnostics with level sensors can ease maintenance and troubleshooting for level sensor. e.g. With Vibrating Forks, AS-Inteface can provide a diagnostic output for fork erosion which can help with predective maintenance. .

Integration of AS-Interface with level sensors makes configuration effortless which leads to cost-saving. The simplified accessibility assures installation without any specialized training.