Automation Technician Certification
Examination Questions And Correct
Answers (Verified Answers) Plus
Rationales 2026 Q&A | Instant
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Question 1
Which of the following best defines a programmable logic controller (PLC) in an
industrial automation context?
A. A general-purpose computer used for office data processing
B. A solid-state control device that receives input signals, executes a user-
programmed logic sequence, and outputs control commands
C. A pneumatic timing relay assembly with fixed logic
D. A analog signal conditioning unit with no digital processing capability
Answer: B. A solid-state control device that receives input signals, executes a
user-programmed logic sequence, and outputs control commands. Rationale: A
PLC is specifically designed for industrial environments to perform discrete and
analog control via a stored program. Options A, C, and D describe unrelated or
outdated devices.
Question 2
In a PLC scan cycle, which step occurs immediately after the input scan?
A. Program execution
B. Output update
,C. Housekeeping
D. Communication with HMI
Answer: A. Program execution. Rationale: The standard PLC scan cycle is Input
Scan → Program Execution → Output Update → Housekeeping. The input scan
reads physical inputs, then the program executes using those values, followed by
output update.
Question 3
What is the typical voltage range for a standard 4-20 mA current loop signal?
A. 0-5 VDC
B. 1-5 VDC
C. 0-10 VDC
D. 10-50 VDC
Answer: B. 1-5 VDC. Rationale: A 4-20 mA signal is often converted to 1-5 VDC
across a 250-ohm resistor (V = I × R). The other ranges are not standard for this
loop type.
Question 4
Which type of sensor is most appropriate for detecting the presence of a clear
glass bottle on a high-speed conveyor?
A. Inductive proximity sensor
B. Capacitive proximity sensor
C. Ultrasonic retroreflective sensor
D. Photoelectric through-beam sensor
Answer: D. Photoelectric through-beam sensor. Rationale: Through-beam
photoelectric sensors provide reliable detection of transparent objects because
the receiver can detect minute changes in light intensity. Inductive sensors
detect metals only, capacitive can be affected by fill level, and ultrasonic may
have inconsistent reflection on glass.
,Question 5
A 3-phase induction motor draws 20 A at 480 V with a power factor of 0.85. What
is the approximate real power in kilowatts?
A. 8.2 kW
B. 14.1 kW
C. 16.3 kW
D. 24.5 kW
Answer: B. 14.1 kW. Rationale: Real power P = √3 × V × I × PF = 1.732 × 480 × 20
× 0.85 = 14,136 W ≈ 14.1 kW. The other options result from omitting √3 or using
incorrect PF.
Question 6
Which protocol is most commonly used for communication between a PLC and a
remote I/O chassis over Ethernet?
A. RS-232
B. Modbus RTU
C. EtherNet/IP
D. HART
Answer: C. EtherNet/IP. Rationale: EtherNet/IP is a widely adopted industrial
Ethernet protocol for PLC-to-I/O communication. RS-232 and Modbus RTU are
serial; HART is for process instruments.
Question 7
What is the purpose of a watchdog timer in a PLC system?
A. To time the duration of a motor start
B. To detect PLC program execution faults and trigger a safe state
C. To measure the cycle time of a conveyor belt
D. To count the number of products per minute
, Answer: B. To detect PLC program execution faults and trigger a safe state.
Rationale: A watchdog timer monitors the scan cycle; if the program hangs or
exceeds the set time, it forces an alarm or shutdown, preventing unsafe
operation.
Question 8
In a ladder logic rung, two normally open contacts are placed in series. This
represents which logical function?
A. OR
B. AND
C. NOT
D. XOR
Answer: B. AND. Rationale: Series contacts require both conditions to be true for
the rung to conduct, which is the AND function. OR uses parallel branches, NOT
uses normally closed, and XOR is a more complex combination.
Question 9
Which instrument is used to measure the rotational speed of a shaft without
physical contact?
A. Tachometer generator
B. Optical encoder
C. Stroboscope
D. Magnetic pickup
Answer: B. Optical encoder. Rationale: An optical encoder uses a disc with slots
and a light source to produce pulses proportional to shaft rotation, providing
non-contact speed and position feedback. A tachometer generator contacts,
stroboscope requires visual observation, magnetic pickup senses ferrous teeth
but is less common for pure speed.
Examination Questions And Correct
Answers (Verified Answers) Plus
Rationales 2026 Q&A | Instant
Download Pdf
Question 1
Which of the following best defines a programmable logic controller (PLC) in an
industrial automation context?
A. A general-purpose computer used for office data processing
B. A solid-state control device that receives input signals, executes a user-
programmed logic sequence, and outputs control commands
C. A pneumatic timing relay assembly with fixed logic
D. A analog signal conditioning unit with no digital processing capability
Answer: B. A solid-state control device that receives input signals, executes a
user-programmed logic sequence, and outputs control commands. Rationale: A
PLC is specifically designed for industrial environments to perform discrete and
analog control via a stored program. Options A, C, and D describe unrelated or
outdated devices.
Question 2
In a PLC scan cycle, which step occurs immediately after the input scan?
A. Program execution
B. Output update
,C. Housekeeping
D. Communication with HMI
Answer: A. Program execution. Rationale: The standard PLC scan cycle is Input
Scan → Program Execution → Output Update → Housekeeping. The input scan
reads physical inputs, then the program executes using those values, followed by
output update.
Question 3
What is the typical voltage range for a standard 4-20 mA current loop signal?
A. 0-5 VDC
B. 1-5 VDC
C. 0-10 VDC
D. 10-50 VDC
Answer: B. 1-5 VDC. Rationale: A 4-20 mA signal is often converted to 1-5 VDC
across a 250-ohm resistor (V = I × R). The other ranges are not standard for this
loop type.
Question 4
Which type of sensor is most appropriate for detecting the presence of a clear
glass bottle on a high-speed conveyor?
A. Inductive proximity sensor
B. Capacitive proximity sensor
C. Ultrasonic retroreflective sensor
D. Photoelectric through-beam sensor
Answer: D. Photoelectric through-beam sensor. Rationale: Through-beam
photoelectric sensors provide reliable detection of transparent objects because
the receiver can detect minute changes in light intensity. Inductive sensors
detect metals only, capacitive can be affected by fill level, and ultrasonic may
have inconsistent reflection on glass.
,Question 5
A 3-phase induction motor draws 20 A at 480 V with a power factor of 0.85. What
is the approximate real power in kilowatts?
A. 8.2 kW
B. 14.1 kW
C. 16.3 kW
D. 24.5 kW
Answer: B. 14.1 kW. Rationale: Real power P = √3 × V × I × PF = 1.732 × 480 × 20
× 0.85 = 14,136 W ≈ 14.1 kW. The other options result from omitting √3 or using
incorrect PF.
Question 6
Which protocol is most commonly used for communication between a PLC and a
remote I/O chassis over Ethernet?
A. RS-232
B. Modbus RTU
C. EtherNet/IP
D. HART
Answer: C. EtherNet/IP. Rationale: EtherNet/IP is a widely adopted industrial
Ethernet protocol for PLC-to-I/O communication. RS-232 and Modbus RTU are
serial; HART is for process instruments.
Question 7
What is the purpose of a watchdog timer in a PLC system?
A. To time the duration of a motor start
B. To detect PLC program execution faults and trigger a safe state
C. To measure the cycle time of a conveyor belt
D. To count the number of products per minute
, Answer: B. To detect PLC program execution faults and trigger a safe state.
Rationale: A watchdog timer monitors the scan cycle; if the program hangs or
exceeds the set time, it forces an alarm or shutdown, preventing unsafe
operation.
Question 8
In a ladder logic rung, two normally open contacts are placed in series. This
represents which logical function?
A. OR
B. AND
C. NOT
D. XOR
Answer: B. AND. Rationale: Series contacts require both conditions to be true for
the rung to conduct, which is the AND function. OR uses parallel branches, NOT
uses normally closed, and XOR is a more complex combination.
Question 9
Which instrument is used to measure the rotational speed of a shaft without
physical contact?
A. Tachometer generator
B. Optical encoder
C. Stroboscope
D. Magnetic pickup
Answer: B. Optical encoder. Rationale: An optical encoder uses a disc with slots
and a light source to produce pulses proportional to shaft rotation, providing
non-contact speed and position feedback. A tachometer generator contacts,
stroboscope requires visual observation, magnetic pickup senses ferrous teeth
but is less common for pure speed.
