This section provides an overview of AS-Interface and what it can do for you. It will appeal mostly to 'novices' or those having little or no knowledge of AS-Interface.
General
Question:I’ve heard about AS-Interface Version 3. What can you tell me about that?
Version 3 Specification was announced in late 2004.
It enhances the Version 2 specification by extending functionality to cover better serial communications,extended IO counts, improved configuration and parameterisation, synchronised output switching and a number of other developments aimed at specific market sectors. With Version 3, vendors will be able to create devices for specialist applications, opening up new opportunities for AS-i throughout industry. None of the features of Version 2.1 are impacted negatively and all aspects of Version 3 are fully backwards compatible with Version 2.1.
At time of writing (May 2006) Version 3 devices are beginning to appear - some of them quite startling in their use of innovation (for example, read this). The Version 3 Specification is available free of charge to members.
Question:Is AS-Interface truly open?
Yes, you can buy compatible products from over 100 companies so your choice of supplier is not restricted. Interoperability is guaranteed by conformance testing. International Standards to which AS-Interface complies include IEC62026 and EN50295. The AS-Interface specification is available free of charge to all members and no license fees are required to use AS-Interface devices. The only exception to this is the Safety at Work profile, which requires anyone integrating the Safety at Work profile to pay a fee to cover the considerable upfront development costs incurred by the Safety Consortium. For vendors wishing to manufacture and sell safety slaves, a small license fee is required, to cover administration costs and a fixed number of licenses. A list of nearly 300 corporate patents covering AS-i technology was recently passed over to AS-International to underpin license-free openness. This list can be scrutinised, although a fee is involved.
Safety
Question:Another common belief is that with bus-based systems it is impossible to achieve the fault tolerance
Category 3 and 4 systems must be designed such that a single fault in a safety related part does not lead to the loss of the safety function. Common mode faults must be taken into account if the probability of a fault occurring is high. The individual fault must be detected during or before the next demand on the safety function. The traditional way of achieving this is to use duplicated wiring because conventional wiring is generally not continually tested. Also certain types of failure, such as a short circuit between adjacent cores, may actually appear as a correctly functioning safety device unless a functional safety check is also carried out. With AS-Interface Safety at Work, the wiring between the Safety Monitor and the safety slaves is continually monitored at up to 620 times per second. This means that any fault in the cabling (open circuits, short circuits, short circuits to ground etc.) is immediately detected. On detection the system is switched off in the appropriate manner for the stop category. System restart is inhibited until the fault is cleared and the fault indicated either by means of LED's on the front of the safety monitor or via a HMI device where fitted. With this method of fault detection, control and indication exceeds the requirements of EN 954-1.
Question:Some safety experts argue that it is preferable to separate safety and control. Is the single cable
The comment applies predominantly to event-driven safety networking solutions, where you have to ensure that the safety event is occurring within a time frame that is consistent with the safety function. Ensuring that the safety event has priority is critical and separating the safety function is a common solution. AS-Interface Safety at Work is not event driven, so we can eliminate the need for two networks. The advanced diagnostics capability of AS-Interface also means we can eliminate a second possible point of concern with single cable solutions, by the good diagnostics interaction between system and user.
Question:What applications has AS-Interface Safety at Work been used in?
Just about every possible safety application, including robotics, conveyor systems, handling systems, airport carousels and lots more. Recently an Expert Alliance member worked with the HSE on a commercial fun ride at a UK theme park. AS-Interface Safety at Work was used because of its integrity and its ability to utilise both safe and non-safe data!
Question:What approvals/certification have been given to AS-I Safety at Work technology?
It has been tested by the TUV and found to fully meet the requirements for safety categories up to and including Category 4 of EN 954-1.
AS-Interface Safety at Work has also been tested against IEC61508 'Functional safety of electrical (electronic)/ programmable electronic safety related systems' and achieved certification for use in systems up to and including SIL3. Copies of the relevant Certificates can be provided on request.