When in vitro met functional safety

a) monitoring the position of mechanical safety devices;

b) monitoring of the monitoring devices;

c) plausibility testing (e.g. monitoring the function of redundant electronic systems);

d) self-testing of measurement systems.

The flow chart of figure 1 indicating the different approaches based on the IEC 61010 standards series and the functional safety approach.

Figure 1 – Risk reduction using a combination of techniques

Risk ranking

The use of EN IEC 62061 and EN ISO 13849 opens a major can of worms for teams more familiar with the design of in vitro devices. The two standards address the functional safety of machinery and more specially control systems.

SILs being defined based on a top-level hazard identification, this then defines the subsequent rigor at system, hardware and software levels. PLs define the ability of safety-related parts of control systems to perform a safety function under foreseeable conditions are allocated one of five performance levels.

Figure 2 indicating the SILs and PLs based on the level of risk

Figure 2 SIL and PL requirements based on risk

As with all functional safety standards, both bring a variety of key considerations in scope:

• Systematic failures
• Common cause failures
• Diagnostic coverage
• Failure rates
• Built in self-test

There is no real meat on the bones in annex J of IEC 61010-2-101, but this is also the case in the PEMS section of IEC 60601, but as functional safety is such a large subject area it would not be practical to cover the topic in detail in an in vitro device standard. Annex J is also informative so introducing the state of art topic and encouraging the reader to delve deeper.

Taking the subject further

If you are interested in the subject of functional safety, then a detailed understanding of EN IEC 62061 or EN ISO 13849 would be required, but many embedded engineers who attend our training courses are already au fait with the subject, and this is important particularly in identify requirements for programmable devices such as microcontrollers. Most safety relevant microcontrollers on the market these days are accompanied by a safety manual that helps shed light on the quality of e.g. diagnostic coverage or built in self-test. This helps in the decision-making process when selecting the device.

By Alastair Walker, Consultant & Owner