AS-Interface
AS-i 5 in the starting blocks
The ASi-3 standard is now reaching its limits in some applications - time for a 'new edition' of communication via flat cable. As ASi-5, this also makes IO-Link network-compatible, among other things.
The AS-Interface system (ASi) is a simple and cost-effective wiring technology for sensors and actuators. It allows power supply and data communication via a single flat cable using piercing technology. With more than 300 member companies, ASi is a globally widespread standard with almost 40 million end devices in realized applications. Based on a bidirectional data exchange with 4 bits, ASi also enables secure and analog data transmission.
Today's ASi system communicates according to the master-slave principle and always consists of a master and several connected participants as well as a power supply. ASi is frequently used in logistics applications in particular. ASi allows subsections to be integrated easily, flexibly and independently of location. In mechanical engineering applications, the uniform installation standard and simple integration into all common control systems are particularly advantageous.
However, today's control systems are very powerful, meaning that the ASi-3 standard is now reaching its limits in some applications. In addition to the 4-bit process data per slave, the cycle time of 10 ms with 62 participants is also a limitation. Previously, ASi offered 1 bit per module as diagnostic feedback. Although Pepperl+Fuchs offers a patented channel-related diagnostic display on the module itself, ASi-3 cannot integrate this into the controller. Further development was necessary.
ASi-5 and Industry 4.0
With ASi-5, more data can be transmitted, more devices can be connected and precise diagnostics can be achieved. In detail, this means that with time and frequency multiplexing, ASi-5 can transmit 32 bytes of process data per slave in just one cycle. ASi-5 transmits 16 digital inputs and 16 digital outputs with a reduced number of 24 slaves in just 1.2 ms. ASi-5 is also designed to be strictly deterministic in terms of time. In an application with more than 24 participants, dedicated inputs and outputs can nevertheless be prioritized to 1.2 ms.
These new properties make it possible to implement applications that require a very short response time or a large amount of data. If a large number of IOs are concentrated in an application, they can be efficiently collected in one place. ASi-5 allows continuous monitoring of the transmission quality as well as fast and detailed diagnostics.
Addressing the ASi-5 participants has also become more modern: Using a smartphone app together with the ASi-5 addresser, addresses or parameters of ASi-5 devices can be set very easily; double addressing is ruled out. The entire line can also be viewed and the device can be used as a diagnostic tool.
The IO-Link integration
IO-Link has shown high growth rates in recent years and is used millions of times a year in new installations, as the notary statistics of the IO-Link community show. The technology is available worldwide and is manufacturer-, fieldbus- and network-independent. The use of existing point-to-point connections and standard 3-wire cabling provides an inexpensive, downward-compatible interface for binary, analog and complex sensors and actuators.
The ASi system overview schematically shows the simple and topology-free wiring in the control cabinet and in the field.
© Pepperl+FuchsIn addition to status information, this allows additional diagnostic data to be transmitted and the parameters of end devices to be adjusted during operation. IO-Link also enables the collection of many IOs in a small space via so-called IO sensor hubs, as is often the case with valve islands or in mechanical engineering. IO-Link devices and standard IOs can be connected to the IO-Link masters from Pepperl+Fuchs in mixed operation. The multi-protocol function makes integration into the fieldbus level flexible. After application-specific parameterization, IO-Link end devices can be connected like standard components.
However, despite all its strengths, IO-Link as point-to-point communication lacked direct network capability. This can be achieved by integrating the IO-Link master function into fieldbus or ASi modules.
When connecting standard sensors and intelligent IO-Link sensors directly to fieldbus modules, it is usually necessary to assign one IP address per eight ports - with the associated effort for integration into the controller. With ASi-3, around 1000 IOs can already be transferred via just one IP address; ASi-5 extends this significantly. System expansions can be carried out in the defined data format without an additional IP address.
ASi modules also offer advantages over fieldbus modules in terms of granularity and costs: Generally provided with only four ports, they are less expensive and can be installed close to the devices, which also simplifies cabling for decentralized IOs. ASi can be used as a gateway protocol independently of the controller.
In future, ASi-5 technology will enable the integration of IO-Link with a full 32-byte channel width, overcoming the previous limitations of ASi-3. This makes IO-Link with all the advantages of AS-Interface immediately network-compatible. This end-to-end digitalization from the sensor to the cloud is the basis for Industry 4.0 and IoT concepts.
ASi-3 remains available
ASi-5 does not simply replace ASi-3. ASi-5 can run in parallel on the same flat cable and bring advantages when a lot of data, an IO-Link connection or extremely short cycle times are required. The ASi-3 product range will be further developed and will continue to exist in parallel. Granular solutions for two, four or eight standard IOs will continue to be implemented most cost-effectively with ASi-3.
Even though ASi-5 runs on the same flat cable, it is a completely new technology. The next step is qualification for industrial use. The system will be industrially 'hardened' and products will be developed in parallel. The ASi-5 specification will be available to all ASi members for in-house developments from the end of 2019. The transition from ASi-3 to ASi-5 can be compared to the system change from Profibus to Profinet. This has taken more than ten years to date - and although the growth trend of Profinet is very strong, there are still many Profibus installations. ASi has the advantage in this comparison that communication is possible on the same flat cable, so there is no need to make a hard choice between ASi-3 and ASi-5. Consequently, a very long coexistence can be assumed. Where ASi-3 is technically sufficient, the cost advantages of ASi-3 will outweigh the disadvantages; where the greater performance of ASi-5 is required for the application, there will soon be a good supplementary option.
ASi-5 allows the market standards IO-Link, AS-Interface and Ethernet to be combined. The user has the flexibility to collect individual sensor signals via an ASi-3 ultra-compact module, to make IO-Link end devices network-compatible via an ASi-5 module with IO-Link master and to connect several safe IOs in combination with standard IOs simply via an interface module. In addition, the separate diagnostic channel provides a transparent image of the entire system and, thanks to IO-Link, allows 'transparency' right down to sensor level.
The combination with Ethernet fieldbus modules with multi-protocol and integrated IO-Link master rounds off the solution options for applications. Thanks to the multi-protocol, these solutions are independent of the controller and facilitate the standardization of Industry 4.0 concepts.
Author:
Dr. Konrad Kern is Head of Product Management at Pepperl+Fuchs in Mannheim.
The joint project
The ASi-5 technology was developed in a joint project involving a total of seven companies. This process was officially completed in November 2018. The technology should be available to all AS-i members for the start of development at the end of 2019 and is currently undergoing industrial hardening and testing. Series availability of the new ASi-5 chip in mass production is planned for mid-2019. This means that the market launch of seriously tested products and the integration of IO-Link into the ASi-5 system will still take some time, and the market is being prepared. However, customer-specific projects can already be tackled now. The multi-protocol capability in the control level will also be an important feature for ASi-5 in order to facilitate standardization.
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