CPE Installation & Commissioning Procedures 4 — Questions and Answers
Question 1: What PROFIBUS address must never be assigned to a slave device to avoid conflict with the default master address?
- 0
- 1 (Correct answer)
- 125
- 126
Correct answer: 1
Address 1 is typically reserved as the default programming device (class 2 master) address, so it should not be assigned to slave devices.
Question 2: During spur installation on a PROFIBUS PA segment, what is the maximum allowed spur length to avoid signal reflections?
- 30 m (Correct answer)
- 60 m
- 120 m
- 1 m
Correct answer: 30 m
On PROFIBUS PA segments, individual spur lengths must not exceed 30 m (in non-intrinsically safe installations) to avoid signal reflections that corrupt communications.
Question 3: What is the correct procedure when replacing a failed PROFIBUS DP slave with a unit that has a different hardware revision?
- Simply swap and power on — PROFIBUS auto-detects all changes
- Update the GSD file in the master configuration and re-download if the I/O map changed (Correct answer)
- Change the baud rate to match the new hardware
- Assign a new bus address above 100
Correct answer: Update the GSD file in the master configuration and re-download if the I/O map changed
If the hardware revision changes the module configuration or I/O layout, the master configuration must be updated with the correct GSD file and re-downloaded.
Question 4: Which commissioning step verifies that all PROFIBUS slaves are correctly identified before enabling process control?
- Running an I/O force test
- Comparing the projected slave list with the live diagnostic scan (Correct answer)
- Setting all outputs to zero
- Measuring cable impedance at each node
Correct answer: Comparing the projected slave list with the live diagnostic scan
Comparing the engineering tool's projected slave list against the live bus scan confirms every expected device is present and responding before process startup.
Question 5: What is the significance of the 'Ident_Number' field in a PROFIBUS GSD file during commissioning?
- It sets the station address
- It uniquely identifies the device type so the master can verify it is communicating with the correct device (Correct answer)
- It defines the maximum baud rate
- It specifies the number of supported modules
Correct answer: It uniquely identifies the device type so the master can verify it is communicating with the correct device
The Ident_Number is a unique manufacturer-assigned identifier; the master compares it against the slave's reported ID to confirm device type compatibility.
Question 6: In a PROFIBUS installation with an optical fiber link, which physical layer adapter must be configured at each fiber endpoint?
- RS-232 converter
- OLM (Optical Link Module) (Correct answer)
- DP/PA coupler
- Bus monitor tap
Correct answer: OLM (Optical Link Module)
An OLM (Optical Link Module) converts between the electrical RS-485 PROFIBUS signal and the optical fiber medium at each end of the fiber segment.
Question 7: What diagnostic byte value in a PROFIBUS DP slave response indicates the slave is in normal data exchange with no faults?
- 0x00 (Correct answer)
- 0xFF
- 0x08
- 0x40
Correct answer: 0x00
A diagnostic byte value of 0x00 indicates no faults are present and the slave is operating normally in data exchange mode.
CPE Installation & Commissioning Procedures 4
What PROFIBUS address must never be assigned to a slave device to avoid conflict with the default master address?