Electromagnetic Compatibility (EMC) & Physical Layer Flashcards
7 cards from real CPE practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Electromagnetic Compatibility (EMC) & Physical Layer flashcards as text
What is the correct passive Profibus bus termination network configuration?
Answer: 390 Ω pull-up to +5V, 220 Ω across A-B, 390 Ω pull-down to GND
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.
What is the consequence of operating a Profibus segment with no active bus termination at one or both ends?
Answer: Signal reflections cause intermittent data corruption
Without termination, signal energy is reflected from unterminated cable ends, creating superimposed waveforms that cause bit errors and intermittent communication faults.
What measurements does a Profibus bus analyzer perform to assess physical layer signal quality?
Answer: Signal voltage levels, noise margin, timing jitter, and reflection waveforms
A Profibus bus analyzer captures and analyzes signal voltage, noise margin, jitter, and reflection signatures to give a complete picture of physical layer health.
What is the primary purpose of a potential equalization bonding conductor in a Profibus installation?
Answer: To equalize ground potentials between cabinets and reduce common-mode interference currents
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.
What physical characteristic of Profibus Type A cable primarily limits the maximum achievable baud rate to 12 Mbit/s?
Answer: Capacitance per unit length and resulting signal propagation delay
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.
What is the maximum number of devices (stations) allowed on a single Profibus DP segment before a repeater is required?
Answer: 32
Profibus DP allows a maximum of 32 stations per segment (including masters and repeaters), limited by the cumulative electrical load of RS-485 transceiver unit loads on the bus.
What common-mode voltage range must Profibus RS-485 transceivers tolerate without data corruption?
Answer: ±7 V
The RS-485 specification requires transceivers to operate correctly with common-mode voltages between -7 V and +12 V, accommodating the ground potential differences typical in industrial systems.