CPE Troubleshooting & Maintenance Techniques 2

Question 1

When troubleshooting a PROFIBUS DP network where some slaves intermittently lose communication, what is the FIRST diagnostic step?

Accepted Answer

Check the bus termination at both ends of the segment

Answer

Improper or missing bus termination is one of the most common causes of intermittent communication failures on PROFIBUS DP.

Question 2

A PROFIBUS segment shows high noise on the bus signal. Which tool is most appropriate for diagnosing this condition?

Accepted Answer

A PROFIBUS oscilloscope or bus analyzer

Answer

A PROFIBUS-specific oscilloscope or bus analyzer captures and displays actual bus waveforms, allowing engineers to identify noise, signal distortion, and timing issues.

Question 3

What does a 'Station Failure' diagnostic message typically indicate in a PROFIBUS DP master's diagnostics buffer?

Accepted Answer

A slave device is no longer responding within the defined watchdog timeout

Answer

A Station Failure message is generated when the DP master cannot establish communication with a configured slave within the watchdog timeout period.

Question 4

During PROFIBUS PA maintenance, a field device shows a NAMUR NE 107 status of 'Maintenance Required.' What action should be taken?

Accepted Answer

Schedule preventive maintenance without stopping the process

Answer

NAMUR NE 107 'Maintenance Required' indicates the device is still functional but needs attention soon, allowing planned maintenance without emergency shutdown.

Question 5

A PROFIBUS DP slave is configured with a watchdog time of 100 ms. The master's minimum cycle time is 80 ms. What is the expected behavior?

Accepted Answer

The network will operate normally with adequate margin

Answer

With the master cycling every 80 ms and a 100 ms watchdog, normal operation provides a 20 ms margin, which is generally sufficient for reliable communication.

(CPE) Certified Profibus Engineer Practice Test

(CPE) Certified Profibus Engineer Practice Test

CPE Troubleshooting & Maintenance Techniques 2