CPE Electromagnetic Compatibility (EMC) & Physical Layer 2

Question 1

What is the correct passive Profibus bus termination network configuration?

Accepted Answer

390 Ω pull-up to +5V, 220 Ω across A-B, 390 Ω pull-down to GND

Answer

The Profibus termination network uses a 390 Ω resistor to +5V, a 220 Ω resistor across the differential pair, and a 390 Ω resistor to GND, providing impedance matching and idle-state line bias simultaneously.

Question 2

What is the consequence of operating a Profibus segment with no active bus termination at one or both ends?

Accepted Answer

Signal reflections cause intermittent data corruption

Answer

Without termination, signal energy is reflected from unterminated cable ends, creating superimposed waveforms that cause bit errors and intermittent communication faults.

Question 3

What measurements does a Profibus bus analyzer perform to assess physical layer signal quality?

Accepted Answer

Signal voltage levels, noise margin, timing jitter, and reflection waveforms

Answer

A Profibus bus analyzer captures and analyzes signal voltage, noise margin, jitter, and reflection signatures to give a complete picture of physical layer health.

Question 4

What is the primary purpose of a potential equalization bonding conductor in a Profibus installation?

Accepted Answer

To equalize ground potentials between cabinets and reduce common-mode interference currents

Answer

The potential equalization conductor minimizes the ground potential difference between interconnected cabinets, reducing common-mode currents that would otherwise flow through the cable shield and cause interference.

Question 5

What physical characteristic of Profibus Type A cable primarily limits the maximum achievable baud rate to 12 Mbit/s?

Accepted Answer

Capacitance per unit length and resulting signal propagation delay

Answer

The distributed capacitance (≤30 pF/m) combined with cable length creates an RC time constant that limits signal rise times, capping the practical baud rate at 12 Mbit/s.

(CPE) Certified Profibus Engineer Practice Test

(CPE) Certified Profibus Engineer Practice Test

CPE Electromagnetic Compatibility (EMC) & Physical Layer 2