Machine safety and functional safety: Which type?
What did you say? There’s potentially more than one type or level of Functional Safety on any one machine?
Absolutely! Let me explain.
First of all let’s look at the definition of functional safety. Functional Safety is the part of the overall safety of a system or piece of equipment that depends on the system or equipment operating correctly in response to its inputs, including the safe management of likely operator errors, hardware failures, and environmental changes.
Drilling into this definition you can find major components of a machine control system like a safety PLC, safety drive, safety network, safe I/O and safety programmable relay, to mention a few. These components make up a control system. If you’re an automation or component supplier or a design engineer you may well be very interested in the product level of functional safety. This means that these products contain hardware, software, environmental factors, component failure rates and overall lifecycle issues (again, to mention a few) that must collectively and individually operate correctly when performing safety related functions. These requirements are spelled out in what I call product design standards like IEC 62508 and IEC 61800 to mention a few. Organizations like TUV, UL, FM, CSA, etc. are all NRTL’s (Nationally Recognized Testing Laboratories) and they fully evaluate, test, list and certify these products to the required design standards to perform safety related functions.
Also, having drilled into this definition you will find applications of safety rated components (above) and possibly standard components. These components will have been designed into a machine control system by an OEM, systems integrator and sometimes an end user to perform safety related functions. This is the overall system level of functional safety. It’s been my experience that the system level of functional safety is what Certified Functional Safety Engineers or Professionals (CFSE or CFSP) deal with. Each safety related circuit is designed and built to meet certain machine safety application standards like IEC 62061, ISO 13849-1 and ISO 10218-1, to mention a few. Already practiced in Europe and beginning to be practiced in the US is the validation of product and system level designs to perform the safety related functions.
In my opinion, the requirement of both the product level and the system level of functional safety is for the system or equipment to be operating correctly in response to its inputs, including the safe management of likely operator errors, hardware failures and environmental changes (as described in the definition).
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