[:en][vc_row][vc_column][vc_column_text]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 61508 and IEC 61511 use PFH as the system metric upon which the SIL is defined. Each SIL rating has an associated PFH which increases an order of magnitude for each increase in SIL rating.

The PFH is based on the dangerous failure rate, and automatic diagnostics.

If Automatic Diagnostics are effective:

If Automatic Diagnostics are NOT effective:

Here you are assume your automatic diagnostics will not find the failure before a demand.

PFH calculation is an extremely important part of safety engineering in high and continuous demand applications as it is probably the most difficult of the three barriers to meet if realistic assumptions are made and if realistic failure rates are used (like failure rates from www.SILSafeData.com).

Fun facts:

• PFH is defined for high or continuous demand mode of operation (for low demand mode see PFDavg)
• Target levels for PFH are defined in IEC 61508 for each of the 4 levels of SIL
• It’s one of the 3 design barriers that must be met for certification

[/vc_column_text][/vc_column][/vc_row][:zh][vc_row][vc_column][vc_column_text]No! They are not Inherently Safe!

A collaborative robot is intended to work “collaboratively” with a person. i.e. share a common workspace. It is force and speed limited by design to minimize any potential hazard. Collaborative robots fit the application where the task cannot be easily or cost effectively automated. They are easy to deploy, program and repurpose. Collaborative robots are new to everyone including the standards agencies.

A hazard and risk assessment is required that assesses the robot and the environment that it is deployed in. Just as any other robot, things such as collisions, speed, type of end effector and worksite need to be evaluated. Collaborative robots have their own sorts of collisions and hazards. They may not be as severe, but they still exist.

This all comes down to risk and the amount of risk that you are willing to accept! The diagram below shows the high-level steps for doing a Hazard and Risk Assessment. When following the steps, if you assess the risk and find it to be acceptable (your companies acceptable risk norms) then you are done. No need to add any risk reduction.

The next best approach is to determine if protective measures other than a Safety Function can reduce the risk to an acceptable level. If not, then you must assign a SIL and implement a safety function that will provide the required risk reduction.

exida can effectively train your team to perform machine hazard and risk assessments to identify all possible hazards and estimate the risk for each hazard. Specifically, exida coaches you through the process of evaluating the risk, developing and implementing risk reduction options. exida can also educate your team in multiple approaches to SIL target selection. These are just some of the things exida does to ensure you are on the right path![/vc_column_text][/vc_column][/vc_row] [:]