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Entries tagged with: Back To Basics

Back to Basics 12 –  What is IEC 61508 Certification?

Back to Basics 12 –  What is IEC 61508 Certification?

IEC 61508 Certification is a Third-Party Validation against the standard’s requirements, comprising of:

  • Detailed Analysis of engineering processes to determine Systematic Capability and Cybersecurity Strength 
  • Detailed Analysis of hardware design / design margins resulting in Random Failure Rate in all failure modes
  • Analysis/Testing to show safe, correct operation and Cybersecurity Susceptibility

To achieve an…

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Back to Basics 13 - How Do I Start IEC 61508 Certification?

Back to Basics 13 - How Do I Start IEC 61508 Certification?

Do you want to know more about IEC 61508 certification, but you’re not sure if you are ready to jump in? Don’t worry, we will make this process as painless as possible.

Here is what to expect:

  1. Introduce Scope
  2. Kickoff Meeting
  3. Perform FMEDA on Product
  4. Creation of…

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Back to Basics 14 - Systematic Capability

Back to Basics 14 - Systematic Capability

Systematic Capability is achieved when the equipment used to implement any safety function achieves two goals: the design process has used procedures intended to prevent systematic design errors (fault avoidance) and the design has systematic design control mechanisms such as a diagnostic for incorrect software execution (fault control).  The rigor…

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Back to Basics 15 - Architectural Constraints

Back to Basics 15 - Architectural Constraints

Architectural constraints are limitations that are imposed on the hardware selected to implement a safety-instrumented function, regardless of the performance calculated for a subsystem. Architectural constraints are specified (in) according to the required of the subsystem, type of components used, and of the subsystem’s components. (Type A components are simple devices…

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Back to Basics 16 - PFDavg

Back to Basics 16 - PFDavg

PFDavg (the average Probability of Failure on Demand) is the probability that a system will fail dangerously, and not be able to perform its safety function when required. PFDavg can be determined as an average probability or maximum probability over a time period. IEC 61508 and IEC…

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Back to Basics 17 - PFH (Probability of Failure on Demand per Hour)

Back to Basics 17 - PFH (Probability of Failure on Demand per Hour)

PFH (The Probability of Failure on Demand per Hour)  is the probability that a system will fail dangerously, and not be able to perform its safety function when required. PFH can be determined as a probability or maximum probability over a time period of an hour. IEC…

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Back to Basics 19 – Route 2H

Back to Basics 19 – Route 2H

Route 2H is one of two Architectural constraints options made available in the standards IEC 61508-2 and IEC 61511. Route 1H . Both Route 1H and Route 2H are limitations that impose the hardware selected to implement a safety-instrumented function, regardless of the performance calculated for a subsystem. 

What exactly is Route 2H

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Back to Basics 20 – Safe Failure Fraction, SFF

Back to Basics 20 – Safe Failure Fraction, SFF

Safe Failure Fraction (SFF) is defined as the ratio of the average rate of safe failures plus dangerous detected failures of the subsystem to the total average failure rate of the subsystem. It is defined for a single channel (no redundancy, 1oo1).

It is a measurement of the likelihood of…

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Back to Basics 21 – The B10 Method

Back to Basics 21 – The B10 Method

The B10 method uses cycle test data to predict failure rates. 

A cycle test is done on a set of products (>20) until 10% of the units under test fail. The number of cycles until failure is called the B10 point.

The B10 number of cycles is converted to a…

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Back to Basics 22 – Cycle Testing

Back to Basics 22 – Cycle Testing

A cycle test is done on a set of products (>20) until 10% of the units under test fail. 

The number of cycles is converted to a time period by knowing the cycles per hour in any particular application. 

A failure rate is calculated by dividing the 10% failure…

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Back to Basics 23 – Stiction

Back to Basics 23 – Stiction

What is Stiction? 

stiction

Stiction is the resistance to the start of motion usually measured as the difference between the external force being applied in order to overcome the static friction and the force to maintain movement between the two contacting or working surfaces.

It can…

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