EETC PLC Programming 4

Question 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?

Accepted Answer

CAN-based DeviceNet

Answer

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.

Question 2

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

Accepted Answer

The last coil scanned determines the final state of the bit

Answer

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

Question 3

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

Accepted Answer

Minimum (zero) of the measurement range

Answer

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.

Question 4

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

Accepted Answer

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

Answer

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

Question 5

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

Accepted Answer

Integer data file 7, element 0

Answer

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.

(EETC) Electrical Technician Certification Practice Test

(EETC) Electrical Technician Certification Practice Test

EETC PLC Programming 4