Electromagnetic Compatibility (EMC) & Physical Layer Flashcards

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

Answer: 20 cm

Profibus installation guidelines specify a minimum separation of 20 cm from 230 V AC power cables to reduce capacitive and inductive coupling that causes noise on the bus.

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

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

VFD PWM switching creates high-frequency voltage transients that radiate and conduct onto nearby cables, causing bit errors on Profibus networks unless proper shielding and separation are maintained.

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

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

A double-ended shield connection creates a current loop; differences in ground potential drive low-frequency currents that generate magnetic fields coupling noise onto the differential signal pair.

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

Answer: Routing the shielded cable inside grounded metal conduit or cable trunking

Grounded metal conduit or trunking provides an additional Faraday-cage-like electromagnetic shield around the Profibus cable, necessary when shielded cable alone is insufficient in extreme EMI environments.

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

Answer: Ringing or overshoot on signal transitions

Reflected signals from unterminated cable ends superimpose on the original waveform, producing ringing or overshoot that is clearly visible on the rising and falling edges when analyzed with a bus tester.

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

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

The drain wire runs in continuous contact with the braided shield and allows the shield to be terminated easily to a screw-type grounding terminal without disturbing the braid structure.

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

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

Metal cable glands with full 360° shield contact are mandatory at EMC zone boundaries to ensure the cable shielding is uninterrupted and effective as the cable transitions between environments.