CPE Installation & Commissioning Procedures 5 — Questions and Answers
Question 1: When commissioning a PROFIBUS DP network at 1.5 Mbit/s, what is the maximum permitted segment length using Type A cable?
- 100 m
- 200 m
- 400 m (Correct answer)
- 1000 m
Correct answer: 400 m
At 1.5 Mbit/s with Type A cable, the maximum segment length is 200 m; at 500 kbit/s it is 400 m — at 1.5 Mbit/s the answer is 200 m.
Question 2: What is the purpose of setting the 'Min_Slave_Intervall' parameter in a PROFIBUS DP master configuration?
- To limit how often a slave can send diagnostics
- To define the minimum time between two consecutive accesses to the same slave (Correct answer)
- To set the watchdog timer for the slave
- To control the token rotation time
Correct answer: To define the minimum time between two consecutive accesses to the same slave
Min_Slave_Intervall defines the minimum time gap between consecutive polling cycles for a single slave, ensuring the slave has enough processing time.
Question 3: During a PROFIBUS PA commissioning in a hazardous area, what parameter must be verified to ensure intrinsic safety compliance?
- Maximum trunk voltage below the entity parameters (Vmax, Imax, Ci, Li) (Correct answer)
- Bus address is above 100
- Baud rate is set to 31.25 kbit/s
- All spurs are shorter than 1 m
Correct answer: Maximum trunk voltage below the entity parameters (Vmax, Imax, Ci, Li)
Intrinsic safety requires that the field device entity parameters (Vmax, Imax, Ci, Li) are not exceeded by the segment power supply, as verified against the barrier/coupler specifications.
Question 4: A PROFIBUS master reports 'No_Data_Exch' for a specific slave address. After checking power and cabling, what is the next diagnostic step?
- Increase the watchdog timeout to maximum
- Verify the slave's bus address DIP switches or software address setting matches the master configuration (Correct answer)
- Replace the master hardware
- Lower the baud rate to 9.6 kbit/s
Correct answer: Verify the slave's bus address DIP switches or software address setting matches the master configuration
Address mismatches between the slave hardware setting and master configuration are a frequent cause of No_Data_Exch; verifying the address is the logical next step after physical checks.
Question 5: What is the role of the PROFIBUS DP Class 2 master during commissioning compared to the Class 1 master?
- Class 2 handles real-time I/O; Class 1 handles diagnostics only
- Class 2 provides acyclic services for parameterization and diagnostics while Class 1 runs cyclic I/O (Correct answer)
- Class 2 is the backup master when Class 1 fails
- Class 2 assigns bus addresses automatically
Correct answer: Class 2 provides acyclic services for parameterization and diagnostics while Class 1 runs cyclic I/O
The Class 2 master (e.g., a handheld configurator) provides acyclic access for device parameterization and extended diagnostics, while the Class 1 master handles cyclic process I/O.
Question 6: When commissioning a PROFIBUS segment, what does a static voltage of approximately 0.5 V between lines A and B (no traffic) indicate?
- Normal idle state with correct termination
- Missing or faulty bus termination resistors (Correct answer)
- Short circuit between conductors
- Correct differential voltage during data transmission
Correct answer: Missing or faulty bus termination resistors
Correct idle-state termination should produce approximately 3.7–5.0 V between A and B; a reading of ~0.5 V suggests missing or incorrectly installed termination resistors.
Question 7: What is the maximum number of PROFIBUS DP slave stations permitted on a single logical network (all segments combined)?
- 32
- 64
- 122 (Correct answer)
- 126
Correct answer: 122
PROFIBUS DP allows up to 122 slave addresses (addresses 1–126, with some reserved for masters and broadcast), giving a practical maximum of 122 slaves per network.
CPE Installation & Commissioning Procedures 5
When commissioning a PROFIBUS DP network at 1.5 Mbit/s, what is the maximum permitted segment length using Type A cable?