May 20, 2021
With the new SIL 3 output drivers, Pepperl+Fuchs has closed the last gap in its portfolio of SIL 3-certified isolated barriers. Intrinsically safe SIL 3 components are now available for all signal types—digital and analog, for control signals to the actuators and for measurement signals from the field, as devices for DIN rail mounting and as isolating components for termination boards. For practical applications, this means that the previously necessary workaround with redundant SIL 2 components is no longer necessary for SIL 3 applications: positioners, electric valves or HART IP converters in intrinsically safe SIL 3 applications can now be connected directly to the control system with a single safety barrier.
This considerably reduces the effort required for numerous SIL 3-relevant applications, such as the control of turbo generators and compressors or the operation of burners, where field devices in the hazardous area must be controlled with analog signals. Due to the lack of suitable SIL 3 isolated barriers for the transmission of signals between the control system and the field devices, the signal circuits previously had to be set up using redundant SIL 2 devices—in compliance with the relevant normative requirements. Today, the use of an interface module suitable for SIL 3 is sufficient for this purpose. If, for example, a long proof time is to be achieved, it even makes sense to use SIL 3 isolated barriers in SIL 2 applications.
SIL 3 Applications: What Users Have to Pay Attention to
SIL 3 is not just SIL 3: users must pay attention to a number of specifics when using SIL 3-compliant components. SIL 3 interface modules must fit into the overall “signal circuit” system with its characteristic values. According to IEC 61508, these modules must not exceed a certain probability of failure on demand (PFD). The PFD plays a central role in the low demand mode (low demand rate of the safety function) typically found in process automation.
SIL is function-oriented, which means that an SIL level is assigned to a safety-related function, which comprises various function groups. In a signal circuit, so-called fault budgets are assigned to these function groups. Typically, 40 % for the sensors, 25 % for the actuators and 15 % for the control system. The signal paths between the field device and the controller or vice versa should each account for 10 %.
When selecting an isolation barrier suitable for a SIL 3 application, it is always worth taking a look at the safety manual to see to what extent its PFD values fit into the overall system. Users should ensure that the typical values are not exceeded, if possible, for modules that are certified as SIL 3 suitable. Otherwise, other devices in the loop must compensate for this with better values. In case of uncertainties, Pepperl+Fuchs’ functional safety experts are available to provide competent advice on how to set up applications in compliance with SIL and standards.
The Quick Check: 10 Good Reasons for Pepperl+Fuchs as a Partner for Functional Safety
Pepperl+Fuchs offers a portfolio of SIL 2 and SIL 3 rated devices that is unique in its scope, making an unmatched range of modules for SIL applications available to customers around the world. More than 10 million installed SIL components worldwide demonstrate the decades of expertise in functional safety and the high quality level of our SIL products.
1. 45 Years of Experience in Functional Safety – Pepperl+Fuchs is a contributor in functional safety with decades of experience in the development of safety-related devices (initially still based on the standards of the time DIN4788, VDE0116, VDE0660-209, DIN19250, EN954, today current according to IEC61508-SIL and EN ISO 13849-PL)
2. FSM Certificate – Beyond the requirements of user standard 61511, Pepperl+Fuchs is one of the few companies certified for Functional Safety Management.
3. More than 750 Functional Safety Devices – The portfolio of functional safety components is the largest in the market in terms of diversity and scope. As far as SIL 3 isolated barriers are concerned, Pepperl+Fuchs is the only supplier with a complete range.
4. Expertise in SIL and Machinery Directive – In plants, both standards of functional safety are always required, sometimes even for one function such as safe shutdown. Pepperl+Fuchs offers everything from a single source.
5. Use of Various Testing Organizations – Pepperl+Fuchs offers SIL components that are certified by many different organizations to ensure an objective assessment.
6. Voluntary External Assessments – Many devices, for which an in-house assessment would actually suffice, are tested by an external assessment.
7. Conservative Product Assessment – We actually base our consideration on the 10 % defect percentage generally accepted for interface devices in a loop.
8. Safety Manuals and Functional Safety Compendium – Safety manuals provide information on the application of the respective device, which is required at various stages of the product life cycle. They are available at any time and at no extra charge to our customers.
9. Certified Safety Professionals – At Pepperl+Fuchs, functional safety is in the hands of certified safety specialists and functional safety engineers.
10. Partnerships with Safety Control Manufacturers – Pepperl+Fuchs works with all leading control system manufacturers, who also offer safety controls.
- – The first output drivers ever available for intrinsically safe applications
- – The new isolators are HART-transparent, so they can also be used to perform partial stroke tests.
- – Complete portfolio of SIL 3 isolators for all signal types
- – DI: Switching amplifiers
- – DO: Valve control and relay modules
- – AI: Transmitter power supplies, repeaters
- – AO: Output drivers
- – Isolating barriers available in all signal types for K-System (DIN rail mounting) and H-System (termination boards)