Intrinsic safety interface
specialists MTL are taking the lead in functional safety
components by introducing key modules from its MTL4000
and MTL5000 IS isolator range along with the MTL4840 HART®
multiplexers, each certified by a third party to the new
international standard IEC61508 for functional safety.
The standard allows system designers and users to unify
their approach to safety issues by providing internationally
accepted and recognised guidelines for safety systems
design.
Safety Instrumented Systems (SIS) are not a new concept
and it has long been the practice to fit protective systems
to industrial process plant where there is a potential
threat to life or the environment should something go
wrong. What is new is that IEC61508 provides guidelines
to achieving an adequate Safety Integrity Level (SIL)
for systems, sub-systems and components. The new MTL4000-SR,
MTL5000-SR and MTL4840 HART®-SR products come with
certified reliability data, thus the safety system designer
no longer has the uncertainty of having to use uncertified
devices. Interfaces available in the new SR- Isolator
Series cover Digital Input (DI), Digital Output (DO) and
Analogue Input (AI) functions.
Of particular importance to HART® users is the certification
for the MTL4840 HART® interface system. A common method
of exploiting the HART® protocol is to multiplex the
digital data stream from field devices onto the primary
analogue field wiring, and then demultiplex the signals
and present them to a maintenance software package for
monitoring and diagnostics. When calculating the SIL for
such systems the multiplexer is seen as an intrusion in
the loop and negatively impacts on the SIL. By incorporating
a multiplexer that has been assessed as a safety related
sub-system, users can exploit the many benefits of HART®
without compromising the SIL of the loops involved.
The benefits to users of specifying sub-systems or components
assessed for use in a Safety Instrumented System are significant;
a more scientific, numeric approach to specifying and
designing safety systems is possible; the nature of the
risk can be quantified and a protective system appropriate
to that risk can be designed. Because the protective system
is assessed against a widely accepted standard, its suitability
can be clearly demonstrated to all. Under- or over-specifying
of protective systems is less likely and, in many cases,
a less expensive solution may be shown to provide adequate
protection.
In parallel with the release of these new products, MTL
has produced a free Application Note, AN9025 ‘An
introduction to functional safety and IEC61508’,
explaining the principles of IEC61508 along with worked
examples of solving practical issues associated with the
new standard. This is available via www.mtl-inst.com or
direct from your local MTL office. |
