CPE Installation & Commissioning Procedures 3

Question 1

Which PROFIBUS DP baud rate requires the use of cable Type A to achieve the full specified segment length?

Accepted Answer

12 Mbit/s

Answer

At 12 Mbit/s, only Type A cable (shielded, 135–165 Ω, low capacitance) can reliably cover the specified 100 m maximum segment length.

Question 2

When connecting a PROFIBUS PA device to a DP/PA coupler, what is the typical trunk line impedance used?

Accepted Answer

100 Ω (IEC 61158-2 Type A)

Answer

PROFIBUS PA uses IEC 61158-2 Type A cable with 100 Ω balanced impedance for the trunk and spur connections.

Question 3

What is the recommended action when a PROFIBUS repeater is added to extend a segment beyond the maximum node count?

Accepted Answer

Terminate each segment independently at both ends

Answer

Each segment separated by a repeater must be independently terminated at both physical ends to prevent signal reflections.

Question 4

During PROFIBUS installation, what does a 'Retry_Error' counter incrementing on the master indicate?

Accepted Answer

The master is retransmitting requests due to no or corrupt responses

Answer

An incrementing Retry_Error counter means the master is not receiving valid responses and is retransmitting, indicating communication failures on the bus.

Question 5

What is the effect of setting a slave's watchdog timeout too short during commissioning?

Accepted Answer

The slave frequently enters safe state unnecessarily during normal communication delays

Answer

A watchdog timeout set shorter than the maximum master cycle time will cause the slave to enter safe state during normal operation, triggering unnecessary safety shutdowns.

(CPE) Certified Profibus Engineer Practice Test

(CPE) Certified Profibus Engineer Practice Test

CPE Installation & Commissioning Procedures 3