Siemens Level 1 Exam – Latest 2025/2026 Practice
Questions with Verified Correct Answers | A
Grade.
Q1
What is the primary function of a Programmable Logic Controller (PLC) in an industrial automation
system?
A. To provide a fixed, hardwired logic sequence that cannot be altered without rewiring.
B. To accept input signals, execute logical decisions based on a stored program, and control output
devices.
C. To convert pneumatic pressure signals directly into hydraulic flow rates without electrical
intervention.
D. To function solely as a data storage device for historical process logging without real-time control.
Answer: B
Rationale: The fundamental operation of a PLC involves a continuous cycle of reading inputs (sensors),
processing these inputs according to the user-defined control program (logic), and updating outputs
(actuators). Unlike relay logic which is hardwired, the PLC's logic is defined through programming,
offering flexibility and diagnostic capabilities.
Q2
Which statement accurately distinguishes a PLC control system from a traditional relay control system?
A. Relay control systems offer greater flexibility and easier modification of control logic compared to
PLCs.
B. PLCs rely on hardwired connections for logic implementation, whereas relay systems use
programmed instructions.
C. Relay systems use hardwired physical connections for logic, while PLCs use programmed instructions
stored in memory to determine system behavior.
D. Both systems function identically, but PLCs are exclusively used for safety-critical applications while
relays are used for non-critical tasks.
Answer: C
Rationale: The key distinction lies in the implementation of logic. Traditional relay logic requires physical
wiring of relays to create specific logic functions, making changes difficult. A PLC stores logical
instructions in memory, allowing for easy modification, complex logic implementation, and diagnostics
without physical rewiring.
Q3
What is the correct sequence of operations in a standard PLC scan cycle?
A. Execute Program, Read Inputs, Update Outputs.
B. Read Inputs, Update Outputs, Execute Program.
,C. Update Outputs, Read Inputs, Execute Program.
D. Read Inputs, Execute Program, Update Outputs.
Answer: D
Rationale: The PLC operates in a cyclic scan. First, the CPU reads the status of physical inputs and stores
them in the Process-Image Input (PII) table. Second, the CPU executes the user program logic using the
data from the PII. Finally, the CPU writes the results from the Process-Image Output (PIQ) table to the
physical output modules.
Q4
What is the function of the Process-Image Input (PII) table during the PLC scan cycle?
A. It stores the final output states generated by the logic program before they are physically applied.
B. It acts as a buffer, storing a snapshot of the input module statuses at the start of the scan cycle for
consistent logic processing.
C. It serves as the permanent storage location for the user's ladder logic program and system
configuration.
D. It directly controls the voltage levels supplied to the field output devices during the output update
phase.
Answer: B
Rationale: The Process-Image Input table captures the state of all input modules at the precise moment
the scan begins. This ensures that the logic program processes a consistent set of input data throughout
the execution phase, preventing erratic behavior if a physical input changes state mid-scan.
Q5
Which functions are performed by the CPU of a PLC? (Two answers are correct)
A. Supplying 24V DC power directly to field sensors.
B. Accepting input status data from the input modules.
C. Executing the user control program logic.
D. Pneumatically actuating cylinder valves.
Answer: B, C
Rationale: The CPU is the "brain" of the PLC. Its primary responsibilities include communicating with I/O
modules to accept input data (B) and executing the stored user program to make control decisions (C).
Power supplies handle electrical power distribution, and actuators perform the physical work.
Q6
A PLC system has a user memory capacity specified as 2,400 bytes. What is the total capacity in bits?
A. 300 bits
B. 2,400 bits
C. 19,200 bits
, D. 24,000 bits
Answer: C
Rationale: Digital memory capacity calculations require unit consistency. Since 1 byte consists of 8 bits,
the calculation is
2,400 bytes×8 bits/byte=19,200 bits
. This conversion is fundamental for understanding memory allocation for data blocks and program
storage.
Q7
Which logic gate produces a "1" (TRUE) output only when ALL of its inputs are "1" (TRUE)?
A. OR Gate
B. XOR Gate
C. NAND Gate
D. AND Gate
Answer: D
Rationale: The AND gate implements logical conjunction. In a 2-input AND gate, the output is true only if
both Input A AND Input B are true. If any input is false (0), the output becomes false (0). This is
represented in ladder logic as contacts in series.
Q8
What is the primary function of an XOR (Exclusive OR) gate in digital logic?
A. Outputting a 1 when all inputs are 0.
B. Outputting a 1 when inputs are different (one is 0, the other is 1).
C. Outputting a 1 when all inputs are 1.
D. Inverting the input signal to the opposite state.
Answer: B
Rationale: The XOR gate is a digital comparator. It outputs a "1" only if its inputs differ (e.g., 0 and 1, or
1 and 0). If inputs are the same (both 0 or both 1), the output is "0". This is useful for error detection or
difference detection circuits.
Q9
In Siemens STEP 7 programming, which counter instruction increments the current count value by 1
each time the input logic transitions from 0 to 1?
A. Count Down (CTD)
B. Count Up (CTU)
C. Count Up/Down (CTUD)
D. Timer On-Delay (TON)
Questions with Verified Correct Answers | A
Grade.
Q1
What is the primary function of a Programmable Logic Controller (PLC) in an industrial automation
system?
A. To provide a fixed, hardwired logic sequence that cannot be altered without rewiring.
B. To accept input signals, execute logical decisions based on a stored program, and control output
devices.
C. To convert pneumatic pressure signals directly into hydraulic flow rates without electrical
intervention.
D. To function solely as a data storage device for historical process logging without real-time control.
Answer: B
Rationale: The fundamental operation of a PLC involves a continuous cycle of reading inputs (sensors),
processing these inputs according to the user-defined control program (logic), and updating outputs
(actuators). Unlike relay logic which is hardwired, the PLC's logic is defined through programming,
offering flexibility and diagnostic capabilities.
Q2
Which statement accurately distinguishes a PLC control system from a traditional relay control system?
A. Relay control systems offer greater flexibility and easier modification of control logic compared to
PLCs.
B. PLCs rely on hardwired connections for logic implementation, whereas relay systems use
programmed instructions.
C. Relay systems use hardwired physical connections for logic, while PLCs use programmed instructions
stored in memory to determine system behavior.
D. Both systems function identically, but PLCs are exclusively used for safety-critical applications while
relays are used for non-critical tasks.
Answer: C
Rationale: The key distinction lies in the implementation of logic. Traditional relay logic requires physical
wiring of relays to create specific logic functions, making changes difficult. A PLC stores logical
instructions in memory, allowing for easy modification, complex logic implementation, and diagnostics
without physical rewiring.
Q3
What is the correct sequence of operations in a standard PLC scan cycle?
A. Execute Program, Read Inputs, Update Outputs.
B. Read Inputs, Update Outputs, Execute Program.
,C. Update Outputs, Read Inputs, Execute Program.
D. Read Inputs, Execute Program, Update Outputs.
Answer: D
Rationale: The PLC operates in a cyclic scan. First, the CPU reads the status of physical inputs and stores
them in the Process-Image Input (PII) table. Second, the CPU executes the user program logic using the
data from the PII. Finally, the CPU writes the results from the Process-Image Output (PIQ) table to the
physical output modules.
Q4
What is the function of the Process-Image Input (PII) table during the PLC scan cycle?
A. It stores the final output states generated by the logic program before they are physically applied.
B. It acts as a buffer, storing a snapshot of the input module statuses at the start of the scan cycle for
consistent logic processing.
C. It serves as the permanent storage location for the user's ladder logic program and system
configuration.
D. It directly controls the voltage levels supplied to the field output devices during the output update
phase.
Answer: B
Rationale: The Process-Image Input table captures the state of all input modules at the precise moment
the scan begins. This ensures that the logic program processes a consistent set of input data throughout
the execution phase, preventing erratic behavior if a physical input changes state mid-scan.
Q5
Which functions are performed by the CPU of a PLC? (Two answers are correct)
A. Supplying 24V DC power directly to field sensors.
B. Accepting input status data from the input modules.
C. Executing the user control program logic.
D. Pneumatically actuating cylinder valves.
Answer: B, C
Rationale: The CPU is the "brain" of the PLC. Its primary responsibilities include communicating with I/O
modules to accept input data (B) and executing the stored user program to make control decisions (C).
Power supplies handle electrical power distribution, and actuators perform the physical work.
Q6
A PLC system has a user memory capacity specified as 2,400 bytes. What is the total capacity in bits?
A. 300 bits
B. 2,400 bits
C. 19,200 bits
, D. 24,000 bits
Answer: C
Rationale: Digital memory capacity calculations require unit consistency. Since 1 byte consists of 8 bits,
the calculation is
2,400 bytes×8 bits/byte=19,200 bits
. This conversion is fundamental for understanding memory allocation for data blocks and program
storage.
Q7
Which logic gate produces a "1" (TRUE) output only when ALL of its inputs are "1" (TRUE)?
A. OR Gate
B. XOR Gate
C. NAND Gate
D. AND Gate
Answer: D
Rationale: The AND gate implements logical conjunction. In a 2-input AND gate, the output is true only if
both Input A AND Input B are true. If any input is false (0), the output becomes false (0). This is
represented in ladder logic as contacts in series.
Q8
What is the primary function of an XOR (Exclusive OR) gate in digital logic?
A. Outputting a 1 when all inputs are 0.
B. Outputting a 1 when inputs are different (one is 0, the other is 1).
C. Outputting a 1 when all inputs are 1.
D. Inverting the input signal to the opposite state.
Answer: B
Rationale: The XOR gate is a digital comparator. It outputs a "1" only if its inputs differ (e.g., 0 and 1, or
1 and 0). If inputs are the same (both 0 or both 1), the output is "0". This is useful for error detection or
difference detection circuits.
Q9
In Siemens STEP 7 programming, which counter instruction increments the current count value by 1
each time the input logic transitions from 0 to 1?
A. Count Down (CTD)
B. Count Up (CTU)
C. Count Up/Down (CTUD)
D. Timer On-Delay (TON)
