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 closed
b) normally open
c) examine input closed
d) examine input open
e) none of the above
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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 false condition for a discrete input. When power is present at the addressed terminal the instruction becomes logically false. When power is not present at the address terminal the instruction becomes logically true. Examine Input (or If) Open is defined as follows: Examines a bit for an off condition. Use an XIO instruction in ladder logic to determine if a bit is off. 1 = True. 0 = False.
The correct answer is D.
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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.