CPE Troubleshooting & Maintenance Techniques 3

Question 1

A PROFIBUS DP network operates at 1.5 Mbit/s. The maximum allowable cable length per segment at this baud rate is approximately:

Accepted Answer

400 m

Answer

At 1.5 Mbit/s, the maximum segment length is approximately 400 m according to PROFIBUS specifications due to signal propagation and attenuation constraints.

Question 2

What is the purpose of the 'Freeze' mode command in PROFIBUS DP troubleshooting?

Accepted Answer

Lock input values from multiple slaves at a single point in time

Answer

The Freeze command causes all slaves in a defined group to simultaneously latch their current input data, enabling synchronized diagnostics or process snapshots.

Question 3

During a PROFIBUS segment audit, you measure a resistance of 220 Ω between the two bus lines (A and B) with the network powered off. What does this indicate?

Accepted Answer

Correct termination with two 110 Ω terminators in parallel

Answer

Two 110 Ω termination resistors (one at each end) appear as 55 Ω in parallel — a reading of 220 Ω between A and B lines confirms two properly installed terminators.

Question 4

A PROFIBUS PA segment has 8 field devices consuming an average of 15 mA each. The segment coupler provides 400 mA. What is the remaining current budget?

Accepted Answer

280 mA

Answer

8 devices × 15 mA = 120 mA consumed; 400 mA − 120 mA = 280 mA remaining, which can accommodate additional field devices.

Question 5

Which PROFIBUS DP error condition is indicated when the 'Watchdog_Active' bit in Station_Status_2 is set to 1?

Accepted Answer

The slave's watchdog timer is enabled and actively monitoring the master

Answer

When Watchdog_Active is set in Station_Status_2, it means the slave has enabled its watchdog timer and is actively monitoring for periodic data exchange with the master.

(CPE) Certified Profibus Engineer Practice Test

(CPE) Certified Profibus Engineer Practice Test

CPE Troubleshooting & Maintenance Techniques 3