CPE CPE Network Topology & Cabling Standards 2 — Questions and Answers
Question 1: What is the maximum segment length for PROFIBUS DP at 12 Mbit/s using Type A cable?
- 10 m
- 100 m (Correct answer)
- 200 m
- 400 m
Correct answer: 100 m
At the maximum 12 Mbit/s baud rate, the segment length is limited to 100 meters due to signal propagation and timing constraints.
Question 2: Which PROFIBUS topology allows a star wiring arrangement while still maintaining the logical bus structure?
- Using RS-485 hubs (active star couplers)
- Using optical fiber star couplers
- Using repeaters as star points
- Both A and B are correct methods (Correct answer)
Correct answer: Both A and B are correct methods
Active RS-485 star hubs and optical fiber star couplers both allow physical star wiring while preserving the PROFIBUS logical bus behavior.
Question 3: In PROFIBUS PA cabling, what is the typical supply voltage range provided to field devices over the two-wire MBP bus?
- 5–9 V DC
- 9–32 V DC (Correct answer)
- 24–48 V DC
- 48–72 V DC
Correct answer: 9–32 V DC
PROFIBUS PA (IEC 61158-2 MBP) field devices operate from 9 V to 32 V DC supplied over the same two-wire cable used for communication.
Question 4: What is the maximum current that a single PROFIBUS PA segment power supply can deliver to bus-powered field devices?
- 100 mA
- 500 mA (Correct answer)
- 1 A
- 2 A
Correct answer: 500 mA
A standard PROFIBUS PA segment power conditioner typically limits total segment current to 500 mA to protect the bus and support intrinsic safety constraints.
Question 5: What is the maximum segment length for a PROFIBUS PA segment using standard (non-IS) installation?
- 200 m
- 500 m
- 1,900 m (Correct answer)
- 3,000 m
Correct answer: 1,900 m
A PROFIBUS PA segment in standard installation can extend up to 1,900 meters using the recommended cable type with appropriate power supply.
Question 6: In PROFIBUS DP, what is a 'spur' (stub) and what is the maximum recommended stub length at 12 Mbit/s?
- A branch cable from the trunk to a single device; maximum 0.3 m at 12 Mbit/s (Correct answer)
- A bypass cable for redundancy; maximum 1 m at 12 Mbit/s
- A shielded extension; maximum 2 m at 12 Mbit/s
- A cable shield drain wire; maximum 0.5 m at 12 Mbit/s
Correct answer: A branch cable from the trunk to a single device; maximum 0.3 m at 12 Mbit/s
A spur (stub) is a short branch off the main trunk cable; at 12 Mbit/s stubs must not exceed 0.3 m to avoid signal reflection errors.
CPE CPE Network Topology & Cabling Standards 2
What is the maximum segment length for PROFIBUS DP at 12 Mbit/s using Type A cable?