AS-Interface networks up to 62 field devices onto a single pair of wires that delivers both signal and power. Actuator Sensor Interface,or AS-Interface,was developed by a group of sensor manufacturers and introduced into the market in 1994. Since that time,it has become the de facto standard for discrete sensors in process industries throughout the world. AS-Interface may be used in hazardous process environments using explosion proof,tray cable,nonincendive and for nonincendive wiring protection concepts.
- Ideally suited for on/off batch process valves and other discrete applications.
- 62 field devices per network master.
- Simple electronics for economical and robust performance.
- Transfer medium is unshielded two-wire cable for both data and power supply.
- Signal transmission has high tolerance to EMI.
- Easy to install providing the greatest cost savings with the least complexity.
- Free choice of network topology allows optimized wiring network.
- Variety of gateways available to seamlessly tie into high level bus networks.
AS-Interface economic analysis
Using a network with 16 valve communication terminals (VCTs),the following economic analysis may be performed (costs are listed in the amount per automated valve):
There is a net savings of $1, 335 per automated valve with AS-Interface communication over the conventional system (52% reduction in installed cost). This savings does not include other cost reductions due to less space consumption for wiring,conduit and I/O racks,as well as greater flexibility in adding field devices or reconfiguring later.
Standards and user groups
AS-Interface technology has been standardized in EN 50295 and IEC 62026-2. There are over 400 different products available from 50+ vendors. And,as of this writing,there are estimated to be over 12, 000, 000 installed nodes (field devices) throughout the world.
AS-Interface protocol version history and interoperability
As-I has continued to improve over the years and has resulted in several versions of the communication protocol. AS-Interface has been careful to revise the standards to allow for improvements without adversely affecting current users or products/systems that are of older versions. They have made these versions both forward and backward compatible. Here are some of the key differences:
- 2.0-This is the first version of AS-i that had significant usage in the process industries. It featured 31 device and only discrete device profiles were possible (4 bits per device)
- 2.1-This version added the capability for up to 8bits of discrete I/O and also analog I/O profiles. This version also allowed for optional extended addressing feature (A/B slaves) so that up to 62 devices could be on a single AS-interface network
- 3.0-This is the latest version. It allows for many new device profiles for greater flexibility
IEEE Standard for a Smart Transducer Interface for Sensors and Actuators: Transducer to Microprocessor Communication Protocols and Teds Formats
Book (Inst of Elect & Electronic)
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Overview of Industrial Process Automation