AutoQuiz: What Ladder Logic Symbol Represents a Logically True Condition for a Discrete PLC Input?

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

Today’s automation industry quiz question comes from ISA’s new course, PLC Fundamentals for the Technical Professional. The next class starts Nov. 9. This course focuses on the role the programmable logic controller plays in the design of a control system and how proper selection, installation and AutoQuiz20151023maintenance 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.

Registration Alert: ISA is offering a one-time only special for the PLC Fundamentals course at 40% off regular pricing if you register by Monday, Oct. 26. This special is for the pilot course offering only.

 

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 today’s quiz from the instructor for ISA’s November course offering, PLC Fundamentals for the Technical Professional.

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.

 

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