Fieldbus with Safety Instrumented Functions (SIF)

The Fieldbus Foundation  has released an updated version of its FOUNDATION™ for Safety Instrumented Functions (SIF) technical specifications. The specifications now include support for FOUNDATION fieldbus H1 (31.25 bit/s) dual-mode devices employing powerful field diagnostics capabilities, which greatly simplifies the process of developing field instrumentation employing the SIF protocol.

FOUNDATION fieldbus, with its industry-proven distributed function blocks and open communications protocol, is an ideal platform for advancing standards-based safety instrumented functions. Its technology enables process end users to reduce both capital and operational costs significantly, and FOUNDATION for SIF has the potential to greatly improve plant and process safety through superior advanced diagnostics at both the device and network level.

The FOUNDATION for Safety Instrumented Functions protocol was approved by TÜV Anlagentechnik GmbH to meet the requirements of IEC 61508 up to, and including, Safety Integrity Level (SIL) 3. Process automation end users have clearly stated their desire for FOUNDATION for SIF technology because of its reduced footprint, reduced installed cost, and advanced diagnostics capabilities. Most of the failures related to safety systems do not happen within the logic solver, but can be traced to failures at the field device or control valve. FOUNDATION for SIF provides the most sophisticated diagnostics for safety devices and a truly digital path for safety devices.

With the dual-mode H1 device capability, instrumentation manufacturers can bring new safety products to market without having to design two entirely different devices. Developers can implement H1 devices with SIF features activated or de-activated. More importantly, this means that plants will only have to stock one type of device that can be used as either a process device or a safety device.

When SIF mode is selected, the device will behave as specified by the SIF specifications; otherwise, it will function as a normal H1 instrument. To ensure conformance to safety standards, the two modes cannot run concurrently in the same device.

The latest FOUNDATION for SIF specifications release includes a number of updates to the System Architecture, Application Model, Protocol, Function Block and Device ITK Profile specifications to make this all possible. It also includes a new application note on macro cycle calculation.

Multiple FOUNDATION for SIF pilot projects are taking place at locations around the world with different end users. These companies, along with other major end users, are encouraging the automation equipment industry to develop safety-approved products for their initial installations.