Advanced Diploma of Industrial
Module 16: Practical Shielding EMC/EMI, Noise Reduction,
Earthing & Circuit Board Layout of Electronic Systems
Module 16: Practical Shielding EMC/EMI, Noise Reduction, Earthing & Circuit Board Layout of Electronic Systems
Total Marks: 135 marks
- Supply the required answers below in blue font(not red or black).
- You must submit this assessment along with the practical component.
- Answer all the questions.
Module 16 Critical Questions:
- Question 9 & Question 17.
- These questions are mandatory to assess Module competency.
- Questions must be answered completely correctly to be assessed as competent with a score for this module.
|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.
|A1||Noise coupling or interference in a signal cable can occur in four possible ways, Common Impedance coupling, Inductive Coupling, Radiative Coupling, and Capacitive coupling.
1) Common Impedance Noise: Common Impedance Noise might occur in the circuit due to the presence of impedance (an inductive, capacitive, or reactive) in the common return path of two circuits. This may result in the error of voltage measurement depending on the value of current in the circuit and amount of impedance.
Fig. 1: Common Impedance Noise coupling
2) Inductive Coupling: These noises are produced by mutual induction between two nearby circuits. A time-varying magnetic field is produced by the noise circuit (due to flow current) causes voltage induced in the signal circuit as given by the formula.
In = 2p fBACos, where symbols have their usual meaning.
A lumped equivalent circuit can be used to explain the same where this coupling is represented by a mutual inductance placed between them.
Fig. 2: Inductive Coupling
3) Capacitive Coupling: It is caused due to disturbance due to the electric field from the noise circuit to the signal circuit. This transfer of energy due to the electric field is equivalent to a capacitance placed between them, which forms the basis of conversion of the scenario into a lumped equivalent circuit as shown in the figure.
Fig. 3: Capacitive coupling
4) Radiative Coupling:
This type of coupling occurs due to radiation from TV or Broadcast radio sources or any other communication channel.
Two ways to minimize noise coupling are:
i) By using different return paths for signals
ii) By using twisted cable in the circuit (Cao et al., 2018)
|F1||Assessor Feedback||(marks awarded)|
|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.
|A2||In differential mode coupling, coupling occurs in two lines of a closed-loop where current flows in opposite direction. However, common-mode coupling occurs in two lines in the same direction and phase.
In differential mode coupling, disturbances are weakly coupled because of conductors being placed nearby. In Common mode coupling, current can be induced due to magnetic fields.
In differential mode coupling, the current is generally larger whereas in current mode-coupling the current is very small.
In differential mode coupling, the area of the loop is very small compared to common code.
The solution of differential mode coupling is the connection of impedance series in with the high side along with a shunt capacitor across the line. However, the common-mode coupling can be solved using a common-mode choke (Chen, Chen, Chiu, & Yeh, 2015)
|F2||Assessor Feedback||(marks awarded)|
|Q3||Describe in at least 4 sentences how an electronic circuit can create an electromagnetic (EM) wave.||(4 marks)|
|A3||We know all electronic components work on electric current. A time-varying electric field generates a time-varying magnetic field and vice versa. Now, an electronic circuit has got both electric (capacitors) and magnetic (inductors) components. So, when an alternating electric current (which varies with time) is applied in an electronic circuit, it produces time-varying electric and magnetic fields. These interactions between electric and magnetic fields cause the production of an electromagnetic wave.|
|F3||Assessor Feedback||(marks awarded)|
|Q4||List any 2 primary sources of transients and spikes.||(2 marks)|
|A4||Two sources of transients and spikes are:
|F4||Assessor Feedback||(marks awarded)|
|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.||(4 marks)|
|A5||Two methods are as follows:
|F5||Assessor Feedback||(marks awarded)|
|Q6||Explain the difference between EMI and EMC.||(1 mark)|
|A6||EMI stands for Electromagnetic Interferences whereas EMC stands for Electromagnetic Compatibility. Electromagnetic interference refers to any disturbance, which is occurring in the circuit due to external sources. On the other hand, Electromagnetic Compatibility refers to devices’ ability to withstand any kind of electromagnetic interference( Cole, Linnebur, Preston, & Schofield, 2018).|
|F6||Assessor Feedback||(marks awarded)|
|Q7||A microprocessor 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 microprocessor circuit is a 100MHz receiver circuit which receives noisy signals. The receiver is sensitive at 10 times the clock frequency of the microprocessor circuit and one would have assumed that the 10th harmonic of a square wave would be significantly reduced.
The distance x should be 2.1 mm.
|F7||Assessor Feedback||(marks awarded)|
|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).||(6 marks)|
|A8||ESD or Electrostatic discharge is a phenomenon in which there is a sudden electricity flow between two charged objects whereas lightning is those ESDs, which occur naturally.
ESD is caused by the method of electrostatic induction (when a charged body is placed near an uncharged conductor, it induces an electric charge in it). Lightning is caused due to discharges occurring due to clouds.
ESD causes very high voltage spikes in the system thus causing damage and lightning can cause a voltage difference between earth and neutral wires, which should ideally be zero ( Curran et al., 2016).
|F8||Assessor Feedback||(marks awarded)|
|Q9||With diagrams/figures explain the relationship between spectrum usage and created interference.||(5 marks)|
|A9||There is a huge difference between the spectrums, which is used in day-to-day life in various devices through FM and TV broadcast, or long, medium, or short- wave radios or mobile phones and the interference created by us.
Interferences created are far different from spectrum usage. The range is usually above 9 kHz. The two given figures quite appropriately explain the difference.
Fig. 4: Spectrum usage
Fig. 5: Interferences created
|F9||Assessor Feedback||(marks awarded)|
|Q10||A diagram describes the representation of EMI.||(4 marks)|
|A10||EMI stands for Electromagnetic Interferences. Electromagnetic interferences refer to noises or disturbances caused in the circuit, which causes measurement errors. It can happen in many possible manners such as conductive interference (caused due to finite impedances in the wire), capacitive interference (caused due to electrical disturbances), inductive interferences (caused due to magnetic disturbances), and radiative interferences (caused due to radiation from various sources).
Fig. 6: Various types of interferences
|F10||Assessor Feedback||(marks awarded)|
|Q11||Provide answers for the following:
|A11||a) Earthing is the process of connecting the dead part of the wire, i.e., the part which does not carry, to the ground. On the other hand, grounding is the process of connecting the current-carrying part to the ground.
b) Basic EMC function of a ground system is to protect the electrical equipment from damage.
|F11||Assessor Feedback||(marks awarded)|
|Q12||Discuss 3 ways that grounding systems for a circuit reference can be configured.||(6 marks)|
|A12||The three configurations of grounding are single-point grounding, multi-point grounding, and hybrid grounding.
Single point grounding: As the very terminology suggests, single-point grounding involves grounding of all circuit elements at a single point, for this all the circuit elements connected to a single wire, and that wire is grounded at a point.
Fig. 7: Single point Grounding
Multi-point grounding: Unlike single-point grounding, here each circuit elements grounded separately at many points on the ground.
Fig. 8: Multi-Point Grounding
Hybrid Grounding: In this system, each circuit element is connected to the ground accompanied by a reactive element like a capacitor or inductor.
Fig. 9: Hybrid Ground
|F12||Assessor Feedback||(marks awarded)|
|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.
|A13||a) The narrow emission can be restricted as follows:
1) By using proper layout
2) By doing proper grounding
3) The clock lines should be buffered
b) The list of high-frequency broadband sources is as follows:
1) Nuclear Electromagnetic Pulse
2) Ultra Wide Band
3) HPM High Power Magnetic radio transmitter (used in military communications) and weapons
c) There are three ways of reducing the rates of clocks:
1) By putting impedance in series, We can increase the series impedance of the driver output at its harmonic frequency, for this, we must put a small ferrite impeder in series with the output.
2) By putting the capacitor in parallel, This method is generally undesirable as it increases the capacitive load on the driver so its effect can rather make the emission worse instead of improving it.
3) By using a low-performance buffer.
d) Level of a constant can be decreased by the Spread Spectra Clock Generation technique. In this particular technique, the frequency of the clock modulated at 0.5-2%. The waveform selected in this technique is basically is known as even spectra spreading. This technique helps in providing wider spectral energy. By using it, the Bandwidth falls from constant 120kHz to 10-20 Db. Patented by Lexmark 1996.
|F13||Assessor Feedback||(marks awarded)|
|Q14||Why is it difficult or almost impossible to shield against magnetic fields at low frequencies (at least 4 points required)?||(4 marks)|
|F10||Assessor Feedback||(marks awarded)|
|Q15||Generally, analog circuits are not as susceptible to transient upset as digital ones but may be more susceptible to the demodulation of RF energy. Describe at least 4 points on how to restrict the operating bandwidth to the minimum acceptable level to reduce the level of interfering signal.||(4 marks)|
|A15||The four ways of restricting operating bandwidth to the minimum acceptable level are as follows:
|F15||Assessor Feedback||(marks awarded)|
|Q16||List any 3 advantages and 1 disadvantage of surface mount devices (SMDs). (3 marks + 1 mark)||(4 marks)|
|A16||Advantages: Some of the advantages of SMDs are:
1) Reduced component size, which enables it to fit in fewer boards.
2) These are more reliable and less prone to failures, so it can withstand any kind of vibration or shake.
3) Lower costs.
Disadvantage: One of the major disadvantages of SMD is that its solder joints are small in size, which reduces its reliability (Halligan, 2107).
|F16||Assessor Feedback||(marks awarded)|
|Q17||List and briefly describe the 4 basic types of Surge Protection devices (SPDs).||(8 marks)|
|A17||Four types of surge protector devices are described as follows:
Type 1-surge protectors act as the first layer of protection against lightning or other sources. It is of outdoor use.
Type 2-surge protectors, which are also known as, branch surge panels protect branch circuits or entrance service entrance from various kinds of surges. It is mainly for industrial, residential, or commercial use.
Type 3-surge protectors or power strips electronic household appliances (like TV, PC, etc.) from low-level surges, which could damage these devices. Therefore, they are the last line of household defense.
Type 4-surge protectors also known as surge protection modules offer a bit different type of protection than Type 3. These can protect industrial applications as well as commercial and industrial equipment cabinets.
|F17||Assessor Feedback||(marks awarded)|
|Q18||List the principles used in PCB shielding.||(4 marks)|
|A18||Principles for PCB shielding are as follows:
Outer enclosures in partitioning houses are not required to be always shielded. Partitioning into the dirty and clean box is also effective. It can be easily done with onboard shielding (Huang & Dai, 2017)
|F18||Assessor Feedback||(marks awarded)|
|Q19||Briefly describe any 4 applications for different types of screened cables.||(8 marks)|
|A19||Types of screened cables are as follows:
|F19||Assessor Feedback||(marks awarded)|
|Q20||What are the 2 main principles of cable routing?||(2 marks)|
|A20||Two main principles of cable routing are as follows:
|F20||Assessor Feedback||(marks awarded)|
|Q21||List any 2 advantages of using screened connectors.||(2 marks)|
|A21||Two advantages of using screened connectors are as follows:
|F21||Assessor Feedback||(marks awarded)|
|Q22||List any 3 filter thumb rules for various available conditions for unwanted signals?||(3 marks)|
|A22||Three filter thumb rules are as follows:
|F22||Assessor Feedback||(marks awarded)|
|Q23||In at least 5 points describe how does the performance of any filter depends on the impedance seen at its terminal?||(5 marks)|
|A23||The five points are as follows:
|F23||Assessor Feedback||(marks awarded)|
|Q24||Describe any 2 differences between differential and common mode coupling from PCB’s.||(4 marks)|
|A24||The differences between DM and CM coupling from PCBs are as follows:|
|F24||Assessor Feedback||(marks awarded)|
|Q25||Explain in about 4 sentences what the first and foremost step in PCB layout is||(4 marks)|
|A25||The first and foremost step in the PCB layout is the consideration of the PCB design. Component orientation plays a major role in designing a PCB layout properly. For Example, while setting resistors and LEDs in a PCB it should always be facing the same direction. This would make the PCB layout easy to install and manufacture as well. Thus, considering how to place the components is one of the major tasks before manufacturing a PCB board.|
|F25||Assessor Feedback||(marks awarded)|
|Q26||Commercial surge protection identifies three distinct zones with differing surge exposure categories. List and briefly describe these categories||(6 marks)|
|A26||Fig. 10: Three surge protection categories
The three surge protection categories with distinct zones are as follows:
|F26||Assessor Feedback||(marks awarded)|
|Q27||Describe the principle of using transmission lines on PCB’s.||(3 marks)|
|A27||Circuit Design exposed to a variety of occasions is termed as Transmission line. It is one of many elements. It emphasizes Signal Integrity analysis. This is the reason why many analysts built on this basis. The transmission line is considered suitable for electrical power or Electrical Signal Transmission in between two or more terminals.|
|F27||Assessor Feedback||(marks awarded)|
END OF ASSESSMENT
Cao, Y. S., Wang, Y., Wu, S., Yang, Z., & Fan, J. (2018, July). PCB Edge Shielding Effectiveness Evaluation and Design Guidelines. In the 2018 IEEE Symposium on Electromagnetic Compatibility, Signal Integrity, and Power Integrity (EMC, SI & PI) (pp. 269-274). IEEE.
Chen, H. W., Chen, Y. J., Chiu, M. Y., & Yeh, D. C. (2015). U.S. Patent No. 9,196,586. Washington, DC: U.S. Patent and Trademark Office.
Cole, M., Linnebur, P. D., Preston, D. A., & Schofield, K. (2018). U.S. Patent Application No. 16/052,106.
Curran, B., Fotheringham, G., Tschoban, C., Ndip, I., & Lang, K. D. (2016). On the Modeling, Characterization, and Analysis of the Current Distribution in PCB Transmission Lines With Surface Finishes. IEEE Transactions on Microwave Theory and Techniques, 64(8), 2511-2518.
Fang, J., Chen, Y., Zou, S., Liu, X., Hu, Z., Quan, W., … & Ding, M. (2016). Low-frequency magnetic field suppression in an atomic spin co-magnetometer with a large electron magnetic field. Journal of Physics B: Atomic, Molecular and Optical Physics, 49(6), 065006.
Halligan, M. (2017). High-Density Signal Interface Electromagnetic Radiation Prediction for Electromagnetic Compatibility Evaluation (No. SAND2017-12071). Sandia National Lab. (SNL-NM), Albuquerque, NM (United States).
Huang, M., & Dai, J. (2017, October). PCB layout modification to change the noise transfer path. In Electromagnetic Compatibility (EMC-Beijing), 2017 IEEE 5th International Symposium on (pp. 1-3). IEEE.
Kukreja, B., Xu, Z., Leftik, A., & Srinivasan, A. (2017). U.S. Patent No. 9,733,983. Washington, DC: U.S. Patent and Trademark Office.
Li, L. E., & Marzetta, T. (2015). U.S. Patent No. 9,124,475. Washington, DC: U.S. Patent and Trademark Office.
Novelen, R. M. (2017). U.S. Patent No. 9,725,991. Washington, DC: U.S. Patent and Trademark Office.