Programmable Logic Controllers – Exam 2

PROGRAMMABLE LOGIC CONTROLLERS – EXAM 2

Petruzella, 6th Edition | 50 Multiple-Choice Questions,
Answers & Expert Rationales

ISBN: 9781264163342
Study Guide: 2026 Updated Practice Edition
Examination: Advanced PLC Instructions, Timers,
Counters, Data Handling, Communications and Industrial
Applications
Total Questions: 50
Suggested Time: 60 minutes
CHAPTER 1 — PLC TIMERS AND TIMING INSTRUCTIONS
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1. What is the primary purpose of a PLC timer instruction?
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A. To measure electrical resistance
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B. To introduce a time delay into a control operation
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C. To increase input voltage
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D. To measure motor current
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✔ CORRECT ANSWER: B
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EXPERT RATIONALE: Timer instructions allow a PLC to delay an operati
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on for a specified period. They are commonly used in sequencing, mac
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hine control and process timing.
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2. What does TON represent in PLC programming?
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A. Timer Output Number
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B. Time Operation Network
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,C. Timer On-Delay
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D. Total Output Network
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✔ CORRECT ANSWER: C
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EXPERT RATIONALE: TON is an on-
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delay timer. Its timing begins when the enabling logic becomes true, an
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d its done condition becomes true after the preset time has elapsed.
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3. What happens when the enabling condition of a typical nonretenti
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ve TON instruction becomes false?
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A. The accumulated time resets
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B. The timer continues indefinitely
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C. The preset value doubles
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D. The CPU shuts down
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✔ CORRECT ANSWER: A
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EXPERT RATIONALE: A typical nonretentive on-
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delay timer resets its accumulated time and done status when its enabl
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ing condition becomes false.
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4. What does TOF represent?
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A. Timer Output Frequency
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B. Total Operating Function
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C. Time On Frequency
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D. Timer Off-Delay
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✔ CORRECT ANSWER: D
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, EXPERT RATIONALE: A TOF instruction creates an off-
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delay. Its output remains true for the specified period after the enablin
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g condition becomes false.
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5. What is the function of a retentive timer?
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A. It permanently stops the PLC
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B. It retains accumulated timing information when its enabling conditio
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n becomes false
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C. It automatically changes the PLC program
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D. It increases the timer's electrical supply
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✔ CORRECT ANSWER: B
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EXPERT RATIONALE: A retentive timer retains accumulated time when i
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ts enabling logic becomes false. A separate reset instruction is generally
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mrequired to clear the accumulated value.
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6. A timer has a preset of 10 seconds. What does the preset value rep
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resent?
A. The required timing duration
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B. The PLC scan frequency
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C. The number of input modules
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D. The motor voltage
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✔ CORRECT ANSWER: A
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EXPERT RATIONALE: The preset value defines the target timing amount
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. The actual time represented depends on the timer's configured time b
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ase or instruction implementation.
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7. What is the accumulated value (ACC) of a timer?
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