By Megha Parolkar on January 12, 2021

Need for a Simple Digital Bus in Process Industries

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.

Actuator Sensor-Interface
As-Interface and other bus topologies

AS-Interface: A new technique of Networking

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.

Actuator Sensor-Interface Cable
AS-Interface Cable

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.

Precendence of AS-Interface over other Fieldbus

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

AS-Interface with Level Measurement: A productive Fusion

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. .

Actuator Sensor-Interface Cable
Connection of AS-Interface with Level Sensor

AS-Interface benefits with level Sensors

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


The better quality ensures the longer life span.

Cost Saving
Cost Saving

Reduction of wires leads to cost-saving.

Low Power Consumption
Low Power Consumption

Network operate at low power supply consumes less power.

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