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

This 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 more information about the CCST program.

In a PLC program, the continuous sequence of steps or “operating cycle” performed by a PLC processor is known as:

a) updating
b) polling
c) scanning
d) rectifying
e) none of the above

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Answer A is not the correct choice. Updating is a general term used for making updates to a software element value, program, or file.

Answer B, polling, is a method for sequentially observing each channel of a network or device in order to determine if it is ready to receive data or for requesting computer action..

Answer D, rectifying, refers to the conversion of alternating current to a relatively steady or pulsating direct current. There is most likely a rectifier circuit in the power supply that powers the PLC or PLC I/O.

The correct answer is C, scanning. The time it takes for the PLC to complete its scanning of all program steps in one “operating cycle” is called the “scan time.”

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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