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PLC Programming Flashcards

7 cards from real EETC practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

Read the first 7 PLC Programming flashcards as text

  1. Which communication protocol is most commonly used for real-time control-level communication between a PLC and I/O modules on a DeviceNet network?

    Answer: CAN-based DeviceNet

    DeviceNet is based on the CAN (Controller Area Network) physical and data-link layers and is widely used for device-level PLC-to-I/O communication.

  2. What is the effect of placing two coils with the same address (bit) in different rungs of a ladder logic program?

    Answer: The last coil scanned determines the final state of the bit

    Duplicate output coils are a programming error; during each scan, the final coil instruction for a given address overwrites earlier ones, causing unpredictable behavior.

  3. A PLC analog input module receives a 4–20 mA signal from a pressure transmitter. What does a 4 mA signal typically represent?

    Answer: Minimum (zero) of the measurement range

    In a 4–20 mA loop, 4 mA represents the minimum (zero) of the process range, while 20 mA represents the maximum (full-scale) value.

  4. What does 'forcing' an I/O point in a PLC do?

    Answer: Overrides the program logic to fix an I/O bit at a specific state for testing

    Forcing overrides normal program control to manually set an input or output bit to a defined state, typically used during troubleshooting and commissioning.

  5. In Allen-Bradley PLC5 / SLC 500 addressing, what does the address 'N7:0' refer to?

    Answer: Integer data file 7, element 0

    In classic Allen-Bradley addressing, N designates the Integer file type, 7 is the file number, and 0 is the element (word) within that file.

  6. What is the purpose of the 'One-Shot Rising' (OSR) instruction in ladder logic?

    Answer: Produces a single true output pulse for one scan on a false-to-true rung transition

    The OSR instruction generates a one-scan true output pulse only on the rising edge (false-to-true) of its input rung condition.

  7. Which PLC operating mode allows the programmer to monitor and edit logic while the machine is running?

    Answer: Run mode with online editing

    Online editing in Run mode allows a technician to modify and download logic changes to a running PLC without stopping the controlled process.