More than just another safety bus

Users can now depend on AS-Interface Safety at Work for all their safety requirements on site, from the simplest networking system available for low level field devices.

"The AS-interface is popular because it's by far the simplest networking system for low level field devices, with huge advantages over conventional parallel wiring and higher-level fieldbus systems", says Ken Davies, Managing Director of Functional Safety Engineering, Siemens technical partner for safety and one of the UK's leading experts in AS-Interface technology.

He continues: "But it's when you add safety related components such as emergency stops, position switches and light barriers (up to Category 4 in compliance with EN954-1), that the AS-Interface network really comes into its own".

The success of AS-Interface should come as no surprise because it is so much more than just another safety bus.

Transferring safety related and standard data together along yellow AS-Interface cable, with a "worst case" response time of 40ms, AS-Interface sets new standards in safety related fieldbuses.

Even with this added functionality AS-Interface remains incredibly simple to install, with no loss in either performance or usability.

But that does not mean that AS-interface must replace your current bus, as Davies explains: "AS-Interface is an ideal partner for new or existing higher-level bus systems, and we have gateways available which can provide straightforward data transfer between AS-Interface and fieldbuses such as Interbus and CAN etc".

He adds: "The launch of the much-awaited Profibus safety at work concept, also provides direct transfer of safety data between networks and devices at a higher level, allowing engineers to design a totally integrated safety solution".

The components for safety at work, in compliance with EN50295 and IEC62026-2, are fully compatible with all other AS-Interface components, so existing installations and applications can be expanded to include the safety relevant functions.

A conventional AS-Interface network comprises controller, master/gateway, power supply and yellow AS-Interface cables along with various slaves.

The only additional components required for safety related applications are a safety monitor and safety slaves.

When the safety related network is powered up for the first time, the safety monitor identifies each slave by a unique code table.

Then each time the monitor calls a slave, it checks that the code corresponds to the one it has already stored.

Any deviation or violation of monitoring times, results in a safe shutdown at the safety monitor (via dual channel hard wired safety outputs).

This information is communicated to both the master and PLC, without either of them having an active role.

The information can easily be evaluated for diagnostic purposes if required using the plant or system control.

For monitors with two dual channel enabled circuits, the two-hand operator controls, door interlocks and stop Category 1 operating modes can be configured using a PC.

Here, the simple "drag and drop" method defines the parameters for the operating modes, as well as additional functions such as contactor control, restart inhibit, local acknowledgment and safety switch.

The safety monitor configuration can also be saved to document the system or downloaded into additional monitors.

AS-Interface Safety at Work is certified to Category 4 in accordance with EN954-1 by the BIA and TUV (German inspectorate).

Because all the responsible parties were involved from the initial concept and maintained close contact throughout development, users have the peace of mind that they can depend on AS-Interface Safety at Work for all of their safety requirements on site.

Depending on the particular requirements, it is available with one or two dual channel enabled circuits.

There are also integrated slaves for safety at work, eg emergency stop pushbuttons, position switches, light curtains and light arrays with an integrated AS-Interface.

These components can be directly connected to the yellow AS-Interface cable without the need for an additional module.

Since the launch of AS-interface safety at work, many hundreds of projects have been successfully implemented ranging from airport baggauge handling through to welding machines for the automotive industry.

Engineers within the UK have enthusiastically received the principle of AS-interface safety at work and there has been a dramatic increase in the interest for standard AS-Interface as a direct result of this.

Davies concludes by saying; "With the latest introduction of AS-interface V.3, along with AS-interface safety at work, it really does have a complete offering for the customer at sensor and actuator level".

"And because of our expert knowledge in this area, we can provide total AS-Interface safety solutions from initial concept right through to validation".

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