Reference no: EM132340856

Practical Shielding EMC/EMI, Noise Reduction, Earthing & Circuit Board Layout of Electronic Systems Written Assessment -

Q1. Interference is present in a signal cable between a PLC and a temperature sensor which is running next to a power cable in the tray.

a) List and briefly describe the different types of noise coupling paths possible.

b) List any 2 ways of minimizing the coupling issues?

Q2. The fundamental to an understanding of EMC are the concepts of differential mode, common mode and antenna mode radiated field coupling.

List any 5 differences between differential mode and common mode coupling.

Q3. Describe in at least 4 sentences how an electronic circuit can create an electromagnetic (EM) wave.

Q4. List any 2 primary sources of transients and spikes.

Q5. Describe 2 methods to prevent CM (common mode) to DM (differential mode) conversion in circuits that carry high-frequency signals (such as wideband data or video) or which could be susceptible to RF.

Q6. Explain the difference between EMI and EMC.

Q7. A micro-processor circuit with a clock frequency of 10MHz has been mounted in a metal enclosure. There are, however, some concerns about emissions leaking from the enclosure with the screws screw separation distance x. Close to the micro-processor circuit is a 100MHz receiver circuit which receives noisy signals. The receiver is sensitive at 10 times the clock frequency of the micro-processor circuit and one would have assumed that the 10th harmonic of a square wave would be significantly reduced.

a) You first suspect that (as the other people thought) some RF might be leaking from the lid. You open the lid but the noise at the receiver does not increase a lot. In fact, taking the lid away does not make a big difference. Discuss what might be the problem and if it is possible to emit at 100MHz. Also recommend what the distance x between the screws should be.

b) You are still confronted with a heat problem and need to make holes in the box for forced air cooling. What is the maximum whole size allowable if the people using the receiver inform you that 20dB attenuation should be enough?

c) If the hole size in 5.2 is not adequate for cooling, what can be implemented to increase the hole size without compromising the 20dB attenuation.

Q8. Although lightning and ESD are both pulsed noise, they differ in their treatment and threats. Describe why they are two distinct threats (list at least 3 differences).

Q9. With diagrams/figures explain the relationship between spectrum usage and created interference.

Note - This question is mandatory. It should be answered and students are expected to get this question completely right to be assessed as competent with a score for this module.

Q10. With a diagram describe the representation of EMI.

Q11. Provide answers for the following:

a) What is the difference between Earthing and Grounding in the context of EMC?

b) What is the primary EMC function of a ground system?

Q12. Discuss 3 ways that grounding systems for a circuit reference can be configured.

Q13. The major source of radiation in digital circuits is the processor clock(s) and its harmonics. All the energy in these signals is accumulated at a few specific frequencies, with the result that the clock signal levels are 10 to 20 dB higher than the rest of the digital circuit radiation.

a) Since the commercial radiated emissions standards do not distinguish between narrowband and broadband how can you reduce the narrowband emissions?

b) List the high frequency broadband sources.

c) If circuit constraints allow, list the methods that can be used to slow down clock rates in order to minimize harmonic generation.

d) How can we decrease the level, measured in a constant 120 kHz bandwidth falls, by between 10 to 20 dB without any extra effort made in layouts and without slowing the clock rise times?

Q14. Why is it difficult or almost impossible to shield against magnetic fields at low frequencies (at least 4 points required)?

Q15. Generally, analog circuits are not as susceptible to transient upset as digital ones, but may be more susceptible to demodulation of RF energy. Describe at least 4 points on how to restrict the operating bandwidth to the minimum acceptable level in order to reduce the level of interfering signal.

Q16. List any 3 advantages and 1 disadvantage of surface mount devices (SMDs).

Q17 List and briefly describe the 4 basic types of Surge Protection devices (SPDs).

Note - This question is mandatory. It should be answered and students are expected to get this question completely right to be assessed as competent with a score for this module.

Q18. List the principles used in PCB shielding.

Q19. Briefly describe any 4 applications for different type of screened cables.

Q20. What are 2 main principles of cable routing?

Q21. List any 2 advantages of using screened connectors.

Q22. List any 3 filter thumb rules for various available conditions for unwanted signals?

Q23. In at least 5 points describe how does the performance of any filter depend on the impedance seen at its terminal?

Q24. Describe any 2 differences between differential and common mode coupling from PCB's.

Q25. Explain in about 4 sentences what the first and foremost step in PCB layout is?

Q26. Commercial surge protection identifies three distinct zones with differing surge exposure categories. List and briefly describe these categories.

Q27. Describe the principle of using transmission lines on PCB's.