Transcript EMI / EMC
EMI/EMC B.T.P.MADHAV B.T.P.MADHAV 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 B.T.P.MADHAV Basic Types of EMI: These are of two types. They are a) 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 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 B.T.P.MADHAV 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 B.T.P.MADHAV B.T.P.MADHAV 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. 1. Thermal Effects 2. Non-thermal Effects. B.T.P.MADHAV 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 MILITARY STANDARDS MIL - STD - 461A TEST DESCRIPTION FREQ CE01 Power Leads 30 Hz-20 kHz CE02 Control / Signal Leads 30 Hz-20 kHz CE03 Power Leads 20 kHz-50 MHz CE04 Control / Signal Leads 20 kHz-50 MHz CE05 Inverse Filter Method 30 Hz-50 MHz CE06 Antenna Terminal 10 kHz-10 GHz CE07 N/A B.T.P.MADHAV MIL - STD - 461B/C TEST DESCRIPTION FREQ CE01 Power / Signal Leads 30 Hz-15 kHz CE02 N/A CE03 Power/Signal Leads CE04 N/A CE05 N/A CE06 Antenna Terminal 10 kHz-26 GHz CE07 Power Leads Spikes / Time Domain 15 kHz-50MHz B.T.P.MADHAV MIL - STD - 461D TEST DESCRIPTION FREQ CE101 Power Leads 30 Hz-10 kHz CE102 Power Leads 10 kHz-10 MHz CE106 Antenna Terminal 10 kHz-40GHz MIL - STD - 461E TEST DESCRIPTION FREQ CE101 Power Leads 30 Hz-10 kHz CE102 Power Leads 10 kHz-10 MHz CE106 Antenna Terminal 10 kHz-40GHz B.T.P.MADHAV MIL - STD - 461A TEST DESCRIPTION FREQ CS01 Power Leads 20 Hz-50 kHz CS02 Power Leads 50 kHz-400MHz CS03 Intermodulation 15 kHz-10 GHz CS04 Undesired Sig. Rejection 15 kHz-10 GHz CS05 Cross Modulation 15 kHz - 10 GHz CS06 Spikes, Power Leads CS07 Squelch Ckts CS08 Undesired Sig. Rejection CS09 N/A CS10 N/A 30 Hz-10 GHz B.T.P.MADHAV MIL - STD - 461B/C TEST DESCRIPTION FREQ CS01 Power Leads 30 Hz-50 kHz CS02 Power Leads 50 kHz-400 MHz CS03 Intermodulation 15 kHz-10 GHz CS04 Undesired Sig. Rejection 30 kHz-20 GHz CS05 Cross Modulation 30 kHz - 20 GHz CS06 Spikes, Power Leads CS07 Squelch Ckts CS08 N/A CS09 Structure Common Mode Current 60 Hz-100 kHz CS10 Damped Sinusoidal Transients (terminals) 10 kHz-100 MHz B.T.P.MADHAV MIL - STD - 461D TEST DESCRIPTION FREQ CS101 Power Leads 30 Hz-50 kHz CS103 Antenna Port-Intermod 15 kHz-10 GHz CS104 Antenna Port-Rej. of Undesired Sig. 30 Hz -20 GHz CS105 Antenna Port-Cross Mod. 30 Hz-20 GHz MIL - STD - 461E TEST DESCRIPTION FREQ CS101 Power Leads 30 Hz-150 kHz CS103 Antenna Port-Intermod 15 kHz-10 GHz CS104 Antenna Port-Rej. of Undesired Sig. 30 Hz -20 GHz CS105 Antenna Port-Cross Mod. 30 Hz-20 GHz B.T.P.MADHAV MIL - STD - 461A TEST DESCRIPTION FREQ RE01 Magnetic Field 30 Hz-50 kHz RE02 Electric Field 14 kHz-10 GHz RE03 Spurious & Harmonic 10 kHz-40 GHz RE04 Magnetic Field 20 Hz-15 kHz RE05 Vehicle & Eng. Equipment 150 kHz-1 GHz RE06 Overhead Powerlines 14 kHz-1 GHz RS01 Magnetic Field 30 Hz-30 kHz RS02 Magnetic Induction Powerline & Spike RS03 Electric Field 14 kHz-10 GHz RS04 Parallel Line Fields 14 kHz-30 MHz RS05 N/A B.T.P.MADHAV MIL - STD - 461B/C TEST DESCRIPTION FREQ RE01 Magnetic Field 30 Hz-50 kHz RE02 Electric Field 14 kHz-10 GHz RE03 Spurious & Harmonic 10 kHz-40 GHz RE04 N/A RE05 N/A RE06 N/A RS01 Magnetic Field, Equipment and Cables 30 Hz-50 kHz RS02 Magnetic Induction, Equipment and Cables Powerline & Spike RS03 Electric Field, Equipment and Cables 14 kHz-40 GHz RS04 N/A RS05 Electromag Pulse Field Transients B.T.P.MADHAV MIL - STD - 461D TEST DESCRIPTION FREQ RE101 Magnetic Field 30 Hz-100 kHz RE102 Electric Field 10 kHz-18 GHz RE103 Antenna Spurious & Harmonics 10 kHz-40 GHz RS101 Magnetic Field, Equipment and Cables 30 Hz-100 kHz RS103 Electric Field, Equipment and Cables 10 kHz-40 GHz RS105 Transient Electromag Field Transients CS109 Structure Current 60 Hz-100 kHz CS114 Bulk Cable Injection 10 kHz-400 MHz CS115 Bulk Cable Injection Impulse CS116 Sine Transients - Cables, and Power Leads 10 kHz-100 MHz B.T.P.MADHAV MIL - STD - 461E TEST DESCRIPTION FREQ RE101 Magnetic Field 30 Hz-100 kHz RE102 Electric Field 10 kHz-18 GHz RE103 Antenna Spurious & Harmonics 10 kHz-40 GHz RS101 Magnetic Field, Equipment and Cables 30 Hz-100 kHz RS103 Electric Field, Equipment and Cables 2 MHz-40 GHz RS105 Transient Electromag Field Transients CS109 Structure Current 60 Hz-100 kHz CS114 Bulk Cable Injection 10 kHz-200 MHz CS115 Bulk Cable Injection Impulse CS116 Sine Transients - Cables, and Power Leads 10 kHz-100 MHz B.T.P.MADHAV 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 B.T.P.MADHAV B.T.P.MADHAV 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 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 CLASSIFICATION OF EMI FILTERS 1) Low pass power line filters. 2) Low pass telephone line filters. 3) High pass data line filters. 4) Band pass communication filters. 5) 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 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 B.T.P.MADHAV 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 EFFECT OF IMPROPER GROUNDING Lightning stroke current from radio tower i Radio equipment cabinet Side flash because of long load grounding lead equipment cabinet VL L di/dt B.T.P.MADHAV 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 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 B.T.P.MADHAV 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 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 Ground loop Signal wire Circuit-I Ground wire Circuit-II 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 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. There are two categories of transient suppression devices are there 1) Gas discharge tubes. 2) Semiconductor devices. The nature and shape of the transient interference signal waves change during propagation through transmission lines. B.T.P.MADHAV Gas – Tube surge suppressors L Fuse Gas tube supply Surge current Load G 1. 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 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 1. 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. ADVANTAGES. 1) Low cost 2) High transient energy absorption DISADVANTAGES 1) Low average power dissipation. 2) Progressive degradation with repetitive surges APPLICATIONS 1) Due to high peak current, they used at equipment power input stage. 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 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 B.T.P.MADHAV TYPICAL SYSTEMS IN ELECTRONIC EQUIPMENT 1) Transmitters. 2) Receivers 3) Antennas 4) Power supplies 5) Motors 6) Control devices 7) Digital circuits 8) Computers 9) Integrated circuits B.T.P.MADHAV 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 Receivers : - RF Amplifier Mixer IF Amplifier Demodulat or 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 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 INDUCTORS An inductor or a reactor is a passive electrical component that can store energy in a magnetic field created by the electric current passing through it. An inductor is usually constructed as a coil of conducting material, typically copper wire, wrapped around a core either of air or of ferromagnetic material. Guide lines for inductors :Core losses ---- -----Causes Energy losses 1)Eddy currents ------- Amount of energy loss increases with the area inside the loop of current. 2)Hysteresis ---------- Materials with low coercivity have narrow hysteresis loops and so low hysteresis losses. 3)Non-linearity -------- E.g.... Intermodulation. B.T.P.MADHAV When an inductor is inserted in series in a noise producing Circuit , its impedance increases with frequency. The lower frequency signals are permitted to pass due to the low impedance. However, the higher frequency noise elements are attenuated and prevented from proceeding through the circuit. when general-purpose inductors are used, signal wave forms may become distorted, and satisfactory impedance may not be obtained at noise frequencies B.T.P.MADHAV Capacitors : Capacitors are used for charge storage, timing, filtering, blocking, control of rise and fall times and to provide low impedance paths for high frequency signals. Different Types of Capacitors are -----1.Electrolytic Capacitors 2.Paper Capacitors 3.Mica and Ceramic Capacitors 4.Polystyrene Capacitors 5.Feed – through Capacitors Impedance of the Capacitor is Z C RS jwl B.T.P.MADHAV Rp (1 jwRp C ) When a bypass capacitor is connected from the signal to ground, the capacitor impedance decreases as the frequency increases. Since noise is a high frequency phenomenon, and the impedance is minute at high frequencies, the capacitor will channel the noise directly to ground, eliminating it from the circuit. At lower desired frequencies the capacitor appears as an open circuit and the desired frequencies are allowed to pass the filter. B.T.P.MADHAV Resistors :Incoming noise is converted to heat and dissipated in the resistor. But note that a fixed resistor does produce thermal noise of its own. Resistors are grouped into 1) wire-wound 2) Film type 3) Composition-carbon & mixed Wire-wound Low noise Composition Noise is more. Film type Noise is in Between wire-wound and composition. Series Resistors Also among the most important and cheapest of protective elements. Properly selected according to resistance and power dissipation, they can replace more costly elements, with comparable results. B.T.P.MADHAV TRANSFORMERS Used for voltage and current transformation or level shifting, impedance matching, power transfer and Isolation process This allows noise coupling through the transformer. This coupling can be eliminated by providing an electrostatic or Faraday shield Conductors : conductors exhibits intrinsic or internal inductance due to thermal magnetic flux an ac resistance due to skin effect. Conductors exhibit external inductance giving rise to external magnetic flux. The external inductance of conductor with diameter ‘d’ located at distance ‘h’ above ground plane is L = 0.2 ln (4h/d) H/m Wiring Guidelines :For the purpose of wiring & signal connection the signals can be divided into 1. Digital & Low current, filtered & regulated power signals. 2. Analog and video signals. 3. High current switching signals 4. AC and unfiltered dc main signals. B.T.P.MADHAV 1. Wires of different types are not be bundled together. 2. Wire bundles of different types of signals should be physically separated from each other. 3. Minimum separation is to be 6-8cm. 4. The area of current loops on PCBs and board interconnections should be minimum. 5. Maximum loop area should be 4cm2. 6. Divide larger loops with smaller loops. 7. Loops and wires should cross at right angles to each other 8. Distance between twisted pairs should be atleast 1.5 times the twist length. 9. Multiple ckts with common return should be twisted as group. 10. Wires between units should follow the most direct route. B.T.P.MADHAV CHAPTER-4 OPEN AREA TEST SITES B.T.P.MADHAV DEPT.OF ECE KL UNIVERSITY OPEN AREA TEST SITES The measurements of radiated emissions and radiated susceptibility of apparatus , equipment constitute two basic electromagnetic interference and electromagnetic compatibility measurements. The purpose of radiation susceptibility testing is to determine the degradation in equipment performance caused by externally coupled electro magnetic energy. OPEN AREA TEST SITE MEASUREMENTS Open site measurement is most direct and universally accepted standard approach for measuring radiated emissions from an equipment or the radiation susceptibility of a component or equipment MEASUREMENT OF RE • EUT is switched on •The receiver is scanned over the specific frequency range • It measures electromagnetic emissions from the EUT • It determine the compliance of these data with the stipulated specifications. EUT Power line filter Power source calibrated receiver/ field strength meter Power source MEASUREMENT OF RS • EUT is placed in an electromagnetic field created with the help of suitable radiating antenna. •The intensity of the electromagnetic field is varied by varying the power delivered to the antenna by the transmitter amplifier • performance of EUT are then observed under different levels of electromagnetic field intensity. EUT Power line filter Power source Transmitter Power line filter Power source Test Antennas A convenient approach to illuminate an equipment under test with known field strengths is to used exact half wave length a long dipoles at fixed frequencies. This arrangement is superior when compared to connecting a test antenna to a signal source using co-axial cable that might distort the field pattern. Antenna Type Frequency, MHz Rod antenna 1 - 30 Loop antenna 1 – 30 Biconical antenna 30 – 220 Dipole antenna 30 - 1000 Log periodic antenna 200 -1000 Conical log spiral 200 – 10000 Wave guide horn Above 1000 Measurement Precautions 1) Electro magnetic environment According to American national standards describes that is conducted and radiated ambient radio noise and signal levels measured at the test site with the EUT deenergized, be at least 6 db below the allowable limit of the applicable specification or standard. 2) Electro magnetic scatters One method fro avoiding interference from underground scatters is to use a metallic ground plain to eliminate stror reflections from under ground sources such as buried metallic objects. 3) Power and cable connections The power needs used to energize the EUT, receiver and transmitter should also pass through filters to eliminate the conducted interferences carried by power lines. B.T.P.MADHAV B.T.P.MADHAV B.T.P.MADHAV B.T.P.MADHAV B.T.P.MADHAV