ISA Interchange

Welcome to the official blog of the International Society of Automation (ISA).

All Posts

AutoQuiz: What is the Impact of a Loss of Power in a Flow Control Mechanism?

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

Today's automation industry quiz question comes from the ISA Certified Control Systems Technician (CCST) program. Certified Control System Technicians calibrate, document, troubleshoot, and repair/replace instrumentation for systems that measure and control level, temperature, pressure, flow, and other process variables. Click this link for information about the CCST program. This question is from the Level III study guide, Domain 2, Loop checking. Level III represents a professional who has a 13-year total of education, training, and/or experience.

 

loss-of-power-flow-control-mechanism-valves-fic-900

In the post graphic (highlighted), a loss of power to FIC 900 will result in the:

a) level in C-101 to increase
b) level in C-101 to decrease
c) output of TDT 920 to increase
d) output of TDT 920 to decrease
e) none of the above

 

A loss of power to FIC 900, which is a flow controlling mechanism and opens and closes the valve, causes the valve to automatically close-Fail-Closed (FC). Symbols for failure modes are on the line between the valve symbol and the actuator symbol. The arrow pointing down, as it does here, indicates FC.

If the arrow had pointed up, that would indicate Fail-Open.

Therefore, with the valve closed, hot oil quits flowing through the line. The purpose of this flow is to transfer heat from the oil to the contents of the process vessel C-101.

TDT 920 measures the difference in the temperature of the hot oil flow before and after it contacts and transfers heat to the contents of C-101. Since there is no flow, the difference in temperatures of the two pipe sections move toward the same (ambient) temperature. Thus the difference in temperatures, and therefore TDT 920 output, decreases.

The correct answer is D.

 

Joel Don
Joel Don
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.

Related Posts

Companies Ramp Up Production of N95 Masks in Response to COVID-19

COVID-19 has exponentially increased the need for N95 disposable masks in hospitals and medical facilitie...
Kara Phelps Apr 3, 2020 5:15:00 AM

Newsweek Vantage Report on Cyber Risks to Critical Infrastructure: ISA's the Expert Partner

Newsweek Vantage recently published an independent report on cyber risks to critical infrastructure—and t...
Kara Phelps Mar 24, 2020 3:11:27 PM

Auto Manufacturers Could Build Ventilators: The Power of Standards in a Global Crisis

As COVID-19 shutters manufacturing plants in North America and around the world, GM, Ford, and Tesla are ...
Kara Phelps Mar 19, 2020 1:49:27 PM