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What Ladder Logic Symbol is Used to Identify a Discrete Output?

The post What Ladder Logic Symbol is Used to Identify a Discrete Output? first appeared on the ISA Interchange blog site.

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

Identify the symbol

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 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.

Discount Alert: ISA is offering a one-time only special for the PLC Fundamentals course at 40% off regular pricing. This special is for the pilot course offering only.


Identify the instruction symbol shown in the post image.

a) control relay coil
b) output terminal energize
c) timer coil
d) motor coil
e) none of the above


<span class="collapseomatic " id="id8577" tabindex="0" title="Click Here to Reveal the Answer“>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 is used to represent the “On” or “Off” condition for a discrete output. The “output status” is a “1” if the ladder logic evaluates as true and is a “0” if the ladder logic evaluates as false. Output terminal energize is defined as follows:  Turns a bit on or off.  Use OTE instruction in your ladder logic to turn a bit when rung condition is evaluated as true.

The correct answer is B.


Source: ISA News