# exida explains Blog

## Back to Basics 06 – IEC 61508

In the following series of blogs, we'll go back to basics and run down everything you need to know to get started in functional safety. We'll start with some more general terms and descriptions and make our way to more advanced material.

IEC 61508: 2010 International Performance-Based Standard

The

## Back to Basics 18 – Route 1H

Route 1H 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.

Route 1H  is…

## 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

## 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…

## 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…

## 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…

## Back to Basics 23 – Stiction

What is 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…

## Obtaining My CFSE/CFSP Certification: Why Bother?

It’s an interesting question and one I asked myself.  For any engineer and/or professional working in the controls business or process industries where safety-related equipment is required, it is essential (per IEC61511-1 Clause 5.2.2: Organization and Resources) to prove competency to carry out any safety-lifecycle activities.  So what does…

## The Dos and Don’t of SIS Application Programming

It’s interesting that the majority of the time when people talk about functional safety, they are usually thinking about hardware: what sensors to use, which logic solver, what actuator, solenoid or valve to select; what voting architecture, etc.  What often gets overlooked, initially, is the application program.

Essentially, when…

• by Dr. William Goble, CFSE
• Thursday, September 27, 2018
• Certification

## The New Technology in Logic Solvers

I heard about a “safety certified” PLC in the late 1980s at an ISA SP84 standard committee meeting. The “logic solver” (as they later called it) was the focus of attention in the field of functional safety back then. Many engineers even said, “My system is safe because I…