Automation Canada - Machine Safety - 10

ISO 13849: WHY IMPLEMENTING A
REDUNDANT CONTACTOR IS A WISE INVESTMENT
This white paper outlines the basic safety principles and importance
of the B10d value and the benefits of using redundant safety-rated
contactors according to the ISO 13849 safety standard.
SAFETY CHALLENGES IN THE INDUSTRY
The study of safety function failure in the industry has proven that
contact welding is a common problem. Opening a circuit creates an arc
each time it's opened. Combined with high short circuit currents or high
loads, in some situations the conducting metal can reach its melting
point and the two contacts can stick together. The contactor or switch
will then never open.
The use of redundant contacts might seem extreme, but without
redundancy the machine will never stop. Contactors are an affordable
device. Implementing a second redundant contactor is a wise
investment that could prevent a catastrophic event.
ABOUT THE ISO 13849 SAFETY STANDARD
The ISO 13849 - Safety of Machinery Package provides the safety
requirements and guidance on the design and integration of safety
related parts of control systems. It specifies the characteristics to identify
the performance level required for carrying out safety functions and
should be applied, regardless of the technology and energy used.
ISO 13849-1 covers general principles for design, and provides safety
requirements and guidance on the principles of design and integration
of safety-related parts of control systems.
ISO 13849-2 focuses on validation. It specifies the procedures that
should be followed for validating by analysis or tests, the safety
functions of the system, and the category and performance level
achieved.
In Part 1, the design of the safety system is based on the risk
CANADIAN AUTOMATION
assessment of the process. This risk assessment identifies the safety
functions required to mitigate risk and the performance level these
functions need to meet to adequately mitigate the identified risks. The
performance level of a function is determined by the architectural
characteristics of the safety function (classified according to categories),
the Mean Time to Dangerous Failure (MTTFd) of the components and
system, and the average diagnostic coverage implemented in the
system. The principle is that not only should the control system be able
to perform the safety function to a level that will mitigate the identified
risk, but also do so in the presence of a failure.
APPLICATIONS UNDER THE ISO 13849 SAFETY STANDARD
Many machine manufacturing facilities use automated processes with
loads that are in motion. These moving parts always require a risk
analysis to determine the appropriate measures to protect workers from
hazards. Aſter this analysis is conducted, it's necessary to assess the
type of protection that's needed and determine the level of
performance required for the application. The level of danger, the
probability, the frequency and the possibility of avoidance will be
decisive in the choice of the required circuit.
Ideally, machine designers should use fixed guards or lock out/tag
out (LOTO) strategies to ensure safety. However, there are certain
situations where LOTO can't always be applied effectively, especially
when interventions are frequent and repetitive.
When a machine requires human intervention to remove a jam
condition or load the product, a strategy involving a monitored
removable guard or a light curtain must be adopted. In addition,
everything must be connected and monitored by a safety control
circuit.
VOLUME 4, ISSUE 2
10
https://na.noark-electric.com/
Automation Canada - Machine Safety

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