Functional Safety in Hazardous Areas with Ex i Isolators and Ex Remote I/O

Functional safety has been an important aspect for many years in process automation systems. Interest in this subject has been increasing ever since the expiration of DIN 19250 and DIN 19251 in July 2004 and their replacement by IEC 61508 "Functional safety of electrical / electronic / programmable electronic safety – related systems" and IEC 61511 "Functional safety – Safety instrumented systems for the process industry sector".In safety circuits in equipment designed for operation in Zone 0 or Zone 1 hazardous areas, intrinsic safety Ex i type of protection according to EN 50020 or IEC 60079-11 is often used, in particular due to its maintainability and ease of testing.

Conventional designs of these safety circuits use Ex i isolators that create intrinsically safe circuits from the non-intrinsically safe signals of the automation system and also galvanically isolate the field and control room signals from each other. The IS pac Ex i Isolator product range manufactured by the R. STAHL Schaltgeräte GmbH has been classified according to IEC/EN 61508 for just these types of applications. Almost all devices meet or exceed the SIL 2 requirements. Loop-powered devices such as isolating repeaters or binary outputs even meet SIL 3 requirements. The IS pac isolators can therefore be used in installations and systems with safety-related circuits. Thanks to the high quality and technology standard of the R. STAHL Schaltgeräte GmbH, both in production and in development, it was not necessary to implement any modifications or variations of the IS pac devices to accomplish this. This affords major advantages for the user in that the same device variant can be used in both standard applications and safety applications.

Nowadays, many new installations are equipped with field bus technology. Even though there is already a foundation for fail-safe bus systems such as Profisafe, their use in safety circuits has been limited due to a lack of availability of appropriate field devices with bus capabilities. This is where the R. STAHL Schaltgeräte GmbH comes in with its innovative and proven intrinsically safe Remote I/O System I.S.1. The I.S.1 system meets the requirements of SIL 1, which is a completely adequate safety level for at least 30% of all safety applications in the opinion of many users. In the SIL analysis, the Remote I/O System I.S.1 was examined in its entirety. As a result, SIL classification was extended to the intrinsically safe Profibus DP according to the RS485-I.S. PNO standard as well as to the necessary field bus isolator. The user then benefits from the major advantage of the ability to build, operate and, during operation, test safety chains in hazardous areas using conventional SIL-classified field devices using the Profibus DP.

With these solutions, the R. STAHL Schaltgeräte GmbH allows the user to select any field device desired to design safety-related circuits in hazardous areas. Conventional approaches wired through Ex i isolators as well as the "modern" version using an intrinsically safe field bus and remote I/O technology can now be implemented.

Additional information on the products and the SIL test reports important for project planning are available on the Internet on the R. STAHL home page www.stahl.de or the product pages www.ispac.info or www.is1easy.com.