CPE Electromagnetic Compatibility (EMC) & Physical Layer 3

Question 1

What is the minimum recommended separation distance when routing Profibus cables parallel to 230 V AC power cables?

Accepted Answer

20 cm

Answer

5 cm

Answer

10 cm

Answer

50 cm

Question 2

Why are Profibus installations near variable frequency drives (VFDs) especially vulnerable to EMI problems?

Accepted Answer

VFDs generate broadband high-frequency noise during PWM switching that couples into unshielded cables

Answer

VFDs consume excessive power from the Profibus bus

Answer

VFDs interfere with the RS-485 common-mode voltage range

Answer

VFDs require a separate Profibus segment by protocol specification

Question 3

What is the electrical effect of a ground loop formed by connecting a Profibus cable shield at both ends without a potential equalization conductor?

Accepted Answer

Circulating low-frequency currents in the shield that induce noise onto the signal pair

Answer

Improved high-frequency shielding effectiveness

Answer

Faster signal rise times due to lower loop impedance

Answer

Reduced termination resistance requirement

Question 4

In a high-EMI zone, which additional protection measure beyond using shielded Profibus cable is recommended by installation guidelines?

Accepted Answer

Routing the shielded cable inside grounded metal conduit or cable trunking

Answer

Using thicker copper conductors to lower resistance

Answer

Reducing all cable lengths to under 10 m

Answer

Converting to wireless Profibus adapters at zone boundaries

Question 5

What waveform signature observed on a Profibus bus analyzer indicates missing or incorrect cable termination?

Accepted Answer

Ringing or overshoot on signal transitions

Answer

A constant DC voltage level with no transitions

Answer

Clean trapezoidal signal edges with no overshoot

Answer

Zero signal amplitude across both bus lines

Question 6

What is the function of the drain wire found alongside the braided shield in Profibus Type A cable?

Accepted Answer

It provides a convenient low-impedance connection point for the braided shield to the grounding terminal

Answer

It carries the +5V bus power supply to field devices

Answer

It carries a redundant copy of the Profibus data signal

Answer

It acts as a spare conductor for future use

Question 7

According to Profibus EMC installation guidelines, what is required when cables must pass through a wall separating two different EMC zones?

Accepted Answer

Metal cable glands providing 360° shield contact must be used to maintain shield continuity

Answer

No special measures are required at the wall penetration

Answer

A standard plastic cable gland is sufficient to seal the opening

Answer

The Profibus signal must be converted to fiber optic at every EMC zone boundary