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AutoQuiz: How to Calculate Uptime for an Automation System

AutoQuiz is edited by Joel Don, ISA's social media community manager.

This automation industry quiz question comes from the ISA Certified Automation Professional (CAP) certification program. ISA CAP certification provides a non-biased, third-party, objective assessment and confirmation of an automation professional's skills. The CAP exam is focused on direction, definition, design, development/application, deployment, documentation, and support of systems, software, and equipment used in control systems, manufacturing information systems, systems integration, and operational consulting. Click this link for more information about the CAP program.

Consider the following automation system data:

  • Preventive maintenance for 1 hour every month
  • Quarterly preventive maintenance for 2 hours each quarter
  • One failure that results in 6 hours of downtime
  • One failure that results in 4 hours of downtime

What is the uptime for this automation system if it runs 24 hours a day, 365 days a year?

a) 99.66%
b) 99.77%
c) 99.86%
d) 99.89%
e) none of the above

The most important measure for production equipment support is operational availability, or “uptime.”

Automation equipment that operates for 365 days x 24 hours per day = 8,760 total possible “up” hours. This equipment gets preventive maintenance for 1 hour every month (12 hours per year), plus additional quarterly preventive maintenance of another 2 hours each quarter (8 more hours per year).

There was one failure that resulted in 6 hours of downtime and a second failure that resulted in 4 hours of downtime. Thus, total downtime for all maintenance was 12 + 8 + 6 + 4 = 30.

The correct answer is A, “99.66%.”

Reference: Nicholas Sands, P.E., CAP and Ian Verhappen, P.Eng., CAP., A Guide to the Automation Body of Knowledge. To read a brief Q&A with the authors, plus download a free 116-page excerpt from the book, click this link.

About the Editor
Joel Don is the community manager for ISA and is an independent content marketing, social media and public relations consultant. Prior to his work in marketing and PR, Joel served as an editor for regional newspapers and national magazines throughout the U.S. He earned a master's degree from the Medill School at Northwestern University with a focus on science, engineering and biomedical marketing communications, and a bachelor of science degree from UC San Diego.

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Joel Don
Joel Don
Joel Don is an independent content marketing, social media and public relations consultant. Prior to his work in marketing and PR, Joel served as an editor for regional newspapers and national magazines throughout the U.S. He earned a master's degree from the Medill School at Northwestern University with a focus on science, engineering and biomedical marketing communications, and a bachelor of science degree from UC San Diego.

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