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B.T.P.MADHAV Lecturer, Dept.of ECE KL UNIVERSITY

EMI/EMC. B.T.P.MADHAV Lecturer, Dept.of ECE KL UNIVERSITY. CHAPTER-I. EMI ENVIRONMENT. EMI / EMC • EMI is defined as the undesirable signal which causes unsatisfactory operation of a circuit or device.

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B.T.P.MADHAV Lecturer, Dept.of ECE KL UNIVERSITY

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  1. EMI/EMC B.T.P.MADHAVLecturer, Dept.of ECEKL UNIVERSITY B.T.P.MADHAV

  2. CHAPTER-I EMI ENVIRONMENT B.T.P.MADHAV

  3. EMI / EMC • EMI is defined as the undesirable signal which causes unsatisfactory operation of a circuit or device. • EMC is defined as the ability of electronic and communication equipment to be able to operate satisfactorily in the presence of interference and not be a source of interference to nearby equipment. • EMS Electromagnetic susceptibility (EMS) is the capability of a device to respond to EMI. B.T.P.MADHAV

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  5. Basic Types of EMI: • These are of two types. They are • Intra-EMI: • EMI is said to be intra-EMI if the functional characteristics of one module within an electronic equipment or system is disturbed due to EMI from another module. • b) Inter-EMI: • EMI is said to be inter-EMI if the functional characteristics of • one equipment is disturbed due to EMI generated by another • equipment. B.T.P.MADHAV

  6. EMI SOURCES These are divided mainly into two types. I. Natural and II. Man-made I. Natural EMI sources are again of the following types: Terrestrial and Extra-Terrestrial. Terrestrial Sources These are atmospheric thunderstorms, lightning discharges and precipitation static. Extra-Terrestrial Sources These are sun-disturbed & quiet, cosmic noise and radio stars. B.T.P.MADHAV

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  8. The common effects of EMI (i) Annoying Effects Very often, momentary and random disturbances in radio and television reception occur. (ii) Disturbing Effects Unwanted reset and change of status in settings in computers and digital equipment is noticed due to EMI. The malfunctioning of computer key boards are noticed. (iii) Catastrophic Situations The burning of electronic components, loss of data, change of threshold settings, improper or unwanted operations and sometimes biological hazards occur very often. B.T.P.MADHAV

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  11. BIOLOGICAL EFFECTS OF EMI / EMR • EM waves, light, heat, x-ray and gamma rays are all different forms of electromagnetic radiation. • However, they differ in their wavelength. These radiations have hazardous effects on men and material. • The effects can be divided into two categories. • Thermal Effects • 2. Non-thermal Effects. B.T.P.MADHAV

  12. EMC STANDARDS These are of two types a) Military Standards These include emission and susceptibility standards. Emission standards specify emission limits in voltage or current, power or field strengths in specified frequency ranges. Susceptibility standards specify conducted spike or radiated field parameters. b) Civilian Standards The civilian EMC standards are applicable for equipments used for commercial, industrial and domestic applications. The emission standards are specified to protect the broadcast services from interference. These also take into account the physiological interference effects experienced by human beings. B.T.P.MADHAV

  13. MILITARY STANDARDS B.T.P.MADHAV

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  23. ADVANTAGES OF EMC STANDARDS The advantages are: 1. Compatibility, reliability and maintainability are increased. 2. Design safety margin is provided. 3. The equipment operates in EMI scenario satisfactorily. 4. Product life is increased. 5. Higher profits are possible. B.T.P.MADHAV

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  25. CHAPTER-II EMI CONTROL TECHNIQUES B.T.P.MADHAV

  26. METHODS TO ELIMINATE EMI OR DESIGN METHODS FOR EMC The effective methods to eliminate EMI are 1. Shielding 2. Grounding 3. Bonding 4. Filtering 5. Isolation 6. Separation and orientation 7. Circuit impedance level control 8. Cable design 9. Cancellation techniques in frequency or time domain 10. Proper selection of cables, passive components 11. Antenna polarization control 12. Balancing B.T.P.MADHAV

  27. Filtering : These are used to filter out conducted EMI. The filtering effectiveness is expressed by Insertion loss (IL). It is defined as B.T.P.MADHAV

  28. CLASSIFICATION OF EMI FILTERS • Low pass power line filters. • Low pass telephone line filters. • High pass data line filters. • Band pass communication filters. • Band reject filters. • lumped element low-pass filters(capacitive and inductive filters). • L-section filters • π-section filters • T-section filters • High pass filters • Band pass filters • Band reject filters B.T.P.MADHAV

  29. Shielding : • The main objective of shielding is to restrict radiations to a specified region to prevent it from entering into susceptible devices. • The quality of shielding is expressed in the form of shielding effectiveness of the material. • The shielding of materials can be solids, screens and braids. They can be in the form of boxes, partitions, cables and connector shields. B.T.P.MADHAV

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  31. Grounding : • Grounding provides a conducting path between electronic devices and ground. • The ground is nothing but some reference point. It is a circuit concept. • The ideal ground is characterized by zero potential and impedance. GROUNDING is a technique that provides a low resistance path between electrical or electronic equipment and the earth or common reference low impedance plane to bypass fault current or EMI signal. B.T.P.MADHAV

  32. EFFECT OF IMPROPER GROUNDING Lightning stroke current from radio tower Side flash because of long load grounding lead i Radio equipment cabinet equipment cabinet VL L di/dt B.T.P.MADHAV

  33. The types of grounding techniques are a) Floating Ground : It isolates circuits from a common ground plane. It may be hazardous some times. The ground plane is in the form of wire or a conductive rod. b) Single – point Grounding : It reduces the effects of facility ground currents. This is used to control EMP energy. c) The multiple point grounding : It reduces ground lead lengths. B.T.P.MADHAV

  34. Bonding : • It provides a low-impedance path between two conducting surfaces. It is a part of grounding and represents its physical implementation. • It creates homogeneous structure for current flow and suppresses the creation of potentials between two metallic parts. • Bonding is useful to protect against the effects of shocks, protect circuits from current return paths. • They reduce potential difference between the devices and carry large faulty currents. • The bonding is of two types. • Direct bonding is made by metal-to-metal between the connected elements. • Indirect bonding is made by contact using conductive jumpers. B.T.P.MADHAV

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  36. ISOLATION TRANSFORMERS • The isolation transformers are used to suppress the common-mode and differential mode interferences. • CM is the unwanted electrical p.d b/w any current carrying conductor and the reference ground. • DM is the unwanted p.d b/w any two current carrying conductors. • Transformers are used to isolate ground current loops. B.T.P.MADHAV

  37. Vc = ( Vpg + Vng )/2 Vd = (Vpg - Vng )/2 • The shield facing the primary side is connected to the primary neutral to suppress DM interference. • The shield facing the secondary side is connected to the reference ground to suppress CM interference. B.T.P.MADHAV

  38. Ground loop Signal wire Circuit-I Circuit-II Ground wire Ground loop VG1 VG2 To obtain noise immunity, the ground loop must be broken. This can be done using transformers, optical couplers etc. Flux Circuit-I Circuit-II Ground loop B.T.P.MADHAV

  39. Transient suppressing devices • Electrical surges are short duration transient waves of current, voltage, or power on low voltage power supply lines i.e (<1000v rms ) • Such transients produce EMI in the practical operation of equipment. • The energy delivered by a surge to a receptor is W =∫ V(t).i(t) dt • The transient that travels along well protected power supply lines and due to • this input stages of the receptors may damage. Transient and surge suppressing devices • There are two categories of transient suppression devices are there • Gas discharge tubes. • Semiconductor devices. • The nature and shape of the transient interference signal waves change during propagation through transmission lines. B.T.P.MADHAV

  40. Gas – Tube surge suppressors Fuse L Gas tube Surge current supply Load G The gas discharge tube can handle very large transient currents ( >10KA), when the tube is connected between the line and the ground. 2. When the transient EMI voltage in line exceeds the striking voltage of the tube, an arc discharge occurs and the ionized gas produces a low impedance from line to ground to shunt surge current. B.T.P.MADHAV

  41. Applications • Because of high current handling capability gas tube surges suppressors are used in AC power distribution lines and in telecom lines as lightning and other high energy surge or transient arrestors. • Drawbacks • It’s response time is slow and it can’t be used for fast rise time surges. • The tube remains in the conducting state even after the surge is removed. Semiconductor Transient suppressors Semiconductor transient suppression device maintain a constant voltage at a desired level across a device by offering variable resistance when transient voltages are present. B.T.P.MADHAV

  42. METAL OXIDE VARISTORS • Metal oxide varistors in which metal oxide semiconductors are used to exhibit voltage dependent resistance. Fuse L supply Load G • When connected between line and common point , these devices present very high resistance at normal operating voltage levels. • when high voltage spikes appear in the AC or DC line the terminal voltage exceeds the switch on voltage and the resistance decreases rapidly.

  43. ADVANTAGES. • Low cost • High transient energy absorption • DISADVANTAGES • Low average power dissipation. • Progressive degradation with repetitive surges • APPLICATIONS • 1) Due to high peak current, they used at equipment power input stage.

  44. Component selection The selection of components can be classified into three categories: A) Components that affect the RELIABILITY and FUNCTIONALITY .These Components are marked as RELIABILITY CRITICAL components or components that MODERATELY affect RELIABILITY. B) Components that affect the EMI PERFORMANCE are marked as EMI CRITICAL and EMI MODERATE. C) Components that affect the AUDIO PERFORMANCE, e.g. Signal to Noise Ratio are marked as AUDIO CRITICAL and AUDIO MODERATE. B.T.P.MADHAV

  45. Signal control Shielding uses conductive material to wrap up the EMI completely to ground. In this way, electromagnetic energy is kept inside the system. It also gets harder for an external signal to cause EMI into the system. It is useful to both conducting EMI and radiated EMI. Generally this is an expensive way to protect the sensitive part of the system, and it takes space. It works well for higher frequencies. For clock frequencies or edge rates lower than 100 MHz, EMI is coupled from the clock signal onto the shield and the shield itself does the radiating. In this case, shielding has very little effect. Good decoupling and careful layout can reduce conducting EMI better than shielding, in most cases. Bypassing or "decoupling" capacitors on each active device (connected across the power supply or ground, as close to the device as possible) help to guide the clock or any other high-frequency signal component directly to ground instead of interfering other signals. B.T.P.MADHAV

  46. CHAPTER-III EMC DESIGN GUIDELINES AND CHOICE OF PASSIVE COMPONENTS FOR EMC B.T.P.MADHAV

  47. TYPICAL SYSTEMS IN ELECTRONIC EQUIPMENT • Transmitters. • Receivers • Antennas • Power supplies • Motors • Control devices • Digital circuits • Computers • Integrated circuits B.T.P.MADHAV

  48. Transmitters:- • The physical design of the transmitter should be so as to achieve input-output isolation. • Thus high power stages are physically removed from low level signal stages. • Interstage shielding will help to achieve isolation where physical isolation is not feasible due to space constraint. • Grounding measures should be applied considering multipoint grounding. Lumped or distributed constant filters should be used at required source of interference. • The undesired RF paths should be decoupled by the use of bypass capacitors and series inductors. B.T.P.MADHAV

  49. Receivers : - RF Amplifier Mixer IF Amplifier Demodulator AF Amplifier Local Oscillator • RF Must be low noise amplifier. • Use AGC circuits to maintain Constant output • By maintaining the perfect Isolation Between blocks. • By maintaining the high of RF amplifier, sensitivity is also high. • Selectivity is to be High. • Fidelity ---- Ability of the receiver to reproduce all frequencies. B.T.P.MADHAV

  50. Objective :- • To study the behavior of passive components such as resistors, capacitors, inductors and transformers at various frequencies. • To know the factor affecting the choice of components for high frequency applications • Passive components, such as resistors, capacitors, and inductors, are powerful tools for reducing externally induced interference when used properly. B.T.P.MADHAV

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