This post was authored by Joel Don, ISA's social media community manager.

This automation industry quiz question comes from ISA’s technical training course, PLC Fundamentals for the Technical Professional (TC40). This course focuses on the role the programmable logic controller plays in the design of a control system and how proper selection, installation and maintenance can reduce operating costs and improve performance. It provides the technical expertise necessary to install, perform routine programming and maintenance and apply proper troubleshooting and configuration techniques.

Identify the instruction symbol shown in the post image.

a) normally open
b) examine input open
c) examine input closed
d) normally closed
e) none of the above

Click Here to Reveal the Answer

Here’s the answer to the quiz question from ISA’s technical training course, PLC Fundamentals for the Technical Professional (TC40).

The symbol represents a logically true condition for a discrete input. When power is present at the addressed terminal the instruction becomes logically true. When power is not present at the address terminal the instruction becomes logically false. Examine Input (or If) Closed is defined as follows: Examines a bit for an On condition. 

Use the XIC instruction in ladder logic to determine if a bit is ON.  0 = False.  1 = True.

The correct answer is C.



About the Author
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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