4. THEORETICAL: EMISSION AND SUSCEPTIBILITY. pressure sensor, i.e, via printed-circuit board tracks, internal wiring which acts as an

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1 4. THEORETICAL: EMISSION AND SUSCEPTIBILITY There are many ways for the electromagnetic-interference to be coupled to the pressure sensor, i.e, via printed-circuit board tracks, internal wiring which acts as an antenna and another way of coupling is due to the vehicle wiring harness which behaves as an antenna and allows the interference into the electronic-system. The coupling process is dependent on the frequency of the electromagnetic-interference. The wire harness and the electronic-system will not act as efficient antennas for frequencies 20 MHz, due to their huge dimensions. The short conducting wires, communication bus, PCB Tracks, wire-harness behaves as a reasonably efficient antenna beyond 1GHz, hence the investigation is carried out beyond 1GHz. The analysis is performed for Radiated-emission and radiated-susceptibility. Conducted-emission and conducted-susceptibility. The vehicle wire harness attenuates high frequencies above 200 MHz, since its length is very long. hence no longer acts as a good antenna. But the length of PCB tracks are small comparable to the quarter wavelength value, hence the electromagneticinterference could be coupled directly into the electronic-system Radiated emission and radiated susceptibility: Basically, the radiation are categorized as radiated emission and radiated susceptibility[62-71]. The radiations caused due to itself is termed as radiated emissions and the radiations caused due to its environment is called radiated susceptibility. The two U-Channels form frame or the chassis of the vehicle, which is the backbone of vehicles, over which the entire assembling of engine, body and all 26

2 accessories are assembled. All conductors, wire harness, air hoses etc, run through these U-Channels. Taking single U-channel into consideration for various cases, analysis is performed. Data communication (C A ) conductor, voltage (C B ) supply conductor and the layout of the printed-circuit board are considered for investigation Specifications of conductors: To determine Resistance, parasitic inductance and parasitic capacitance components, these are the main causes for cross-talk interference. C A = Cross-sectional area of 0.5 mm 2, Insulation of 0.7mm thick and ε r =3.8. C B = Cross-sectional area of 6.0 mm 2, Insulation of 0.76mm thick and ε r =3.8. Ground is a hot rolled U-shaped steel as the ground structure of dimensions 300mm length, 93mm breath and width of 8.3mm Investigation for different layouts: Layout 1: Figure 4.1 shows, a single conductor layout: C A 5mm apart from both vertical and the horizontal ground plane. Figure 4.1: Layout of a single conductor. Layout 2: Figure 4.2 shows, two Conductor s layout: C A and C B close to the ground and close to each other. 27

3 Figure 4.2: Layout of two conductors close together. Layout 3: Figure 4.3 shows, two Conductor s layout: C A and C B close to each other and both conductors are 5mm apart from vertical and horizontal the ground plane. Figure 4.3: Layout of two conductors close to each other and away from chassi. Layout 4: Figure 4.4 shows, two Conductor s layout: C A close to the ground and C B 5mm apart from the vertical and horizontal ground plane. Figure 4.4: Layout of two conductors apart(5mm). Layout 5: Figure 4.5 shows, two Conductor s layout: C A and C B placed 6mm apart and C A, 5mm apart from the vertical and horizontal ground plane. Figure 4.5: Layout of two conductors apart and away from chassi Resistance analysis: For low frequencies, / (4.1) And For High Frequencies, / (4.2) 28

4 Inductance analysis: Self and mutual conductance for two conductors carrying Currents I k (C A ) and I J (C B ) respectively, are measured using relations (4.3),(4.4). And, (4.3), (4.4) Electromagnetic-interference due to parasitic capacitance is given equation(4.5). (4.5) Flux density is constant, therefore the above equation(4.5) approximates to (4.6) Capacitance analysis: or (4.7) Self and Mutual capacitance for two conductors carrying voltages V 1 and V 2 respectively, are measured using relation (4.7) and (4.8). (4.8) Electromagnetic-interference due to parasitic capacitance is given as (4.9) Since resistance is negligible, so the equation (4.8) is approximated as 2 V/m (4.10) 29

5 Using the above relations (4.3) through (4.10), the total electromagnetic-interference for various layout cases are analyzed and tabulated in Table 4.1. Table 4.1: Radiations due to various layouts. Case L P /M P µh C P /C M pf R P Ω/m V NL V NC V NT V/m KV/m KV/m x x x x x RE-Differential-mode(DMC) current: The DMC[3][6] are generally equal in its magnitude, but they are absolutely opposite in the direction, the DMC and common-mode(cmc)[62][63] current are proficient to create noteworthy radiated-emission. I 2 = -I 1, I 1 = I D, I 2 = -I D (4.11) And, / (4.12) From the equation (4.12) it is clear that the utmost radiated field shows a discrepancy with the square of its frequency(f) followed by loop-area(ls) and current(i D )level, thus to curtail the radiation we required to moderate the current(i D ) level and loop-area. The radiation due to conductor carrying current of 10mA is plotted, as shown in Figure 4.6 for various frequencies. 30

6 RE-Common-mode(CMC) current: The common-mode(cmc) currents[67][68] are generally equal in magnitude, but they are in same the direction, the differential-mode(dmc) current and common-mode (CMC)current are proficient to create noteworthy radiated-emission, thus model as dipole. I 2 = I 1, I 1 = I C, I 2 = I C (4.13) Thus,, / (4.14) Figure 4.6: Radiated emission of electric field intensity due to conductor carrying (I J = 10mA). Hence from the equation(4.14) ) it is clear that the utmost radiated field shows a discrepancy with frequency(f) followed by length(l) and current(i D )level, refer Figure 31

7 4.6. Thus to curtail the radiation we required to moderate the current(i D ) level and length(l) Radiated susceptibility: The pressure sensor underneath an investigation is placed in a TEM cell, to afford an accurate and consistent field, the wires have been separated by a distance of S, the load-resistance R S and R L are to be found at, x=0 and x=l correspondingly. We boast to find out the V S and V L for a specified incident electric-field E i. The electric-field is being transverse [65] and so forth of the magnetic-field is normal Conducted emission and conducted susceptibility: Fundamentally, the Electromagnetic interference are due to conduction. Generally are categorized as conducted emission and conducted susceptibility. The printed circuit board of FM Stereo is considered for conducted analysis Investigation of the printed-circuit board: The conducted Electromagnetic-interference is generated from power supplies as shown in Figure 4.8, due to switching of semi-conductor devices. Electromagneticinterference, generally caused by Differential-mode(DMN) noise along with commonmode(cmn) noise, whereas Differential-mode(DMN) noise is due to the coupling of, where L is parasitic inductance and Common-mode(CMN) noise is as a result of the coupling, where C is parasitic capacitance. For the PCB shown in Figure 4.9 and Figure 4.10 the differential-mode parasitic inductance is calculated using Partial Element Equivalent Circuit (PEEC) matrix. The sample dimensions of PCB traces are as shown in the Figure

Figure 4.8: Power circuit of FM stereo. Figure 4.9: Printed-circuit-board of FM stereo. LL P = 45.9-4.6-3.4-1.3-0.4-0.4-2.6-0.3 1.0 16.3 1.0 2.3 0.9 0.6 0.

8 Figure 4.8: Power circuit of FM stereo. Figure 4.9: Printed-circuit-board of FM stereo. LL P = nh ; 3.9 mω (4.15) 33

9 Figure 4.10: Metallic trace of PCB, FM stereo. Figure 4.11: Dimension of PCB traces of FM stereo. The Common-mode capacitance is calculated as (4.16) 34

10 1 / (4.17). (4.18) Line Impedance Stabilization Network: Three different types of LISN are V-LISN for un-symmetric emissions (line-toground), Delta-LISN symmetric emissions (line-to-line) and T-LISN Asymmetric (midpoint line-to-line). The FM stereo board is refered for our analysis as shown in Figure The Purpose of Line Impedance Stabilization Network is to isolate the power mains, noise isolation and coupling devices. The LISN equivalent of FM stereo board is shown in Figure 4.13 and the Simplified LISN of FM stereo is shown in Figure The FCC [62] limits over 450 KHz to 30 MHz and that of Comité-International- Spécial-des-Perturbations-Radio-électriques (French: Special-International-Committee on Radio-Interference (CISPR) 22 limits 150-KHz to 30-MHz the LISN layouts are same but the component value differs. LL P = nh ; 3.9 mω (4.19) 35

11 Figure 4.12: Equivalent circuit diagram of FM stereo. Figure 4.13: LISN equivalent of FM stereo. Figure 4.14: Simplified LISN of FM stereo. 36

12 The entire current is the sum or else the difference of common-mode(cmc) and differential-mode(dmc) currents. I T = I C ± I D (4.20) And, Coupling coefficient k is = 1 (4.21) Thus, the drop due to differential-mode currents is given by And Where, And (4.22) (4.23) (4.24) (4.25) are Differential-mode impedance and Common-mode impedance. Hence, And Also, And 2V C = V P + V N (4.26) 2V D = V P - V N (4.27) I C = V P + V N / 2*50Ω (4.28) I D = V P - V N / 2*50Ω (4.29) 37

1. Z=58850 1 2. Z=38850 3. Z=18850 4. Z=8850 2 3 4 Figure 4.

KHz) 16: Conducted emission differential-mode current and

13 1. Z= Z= Z= Z= Figure 4.15: Conducted emission common-mode current and impedance (>150 KHz) 1. Z= Z= Z= Z= Figure 4.16: Conducted emission differential-mode current and impedance (>150 KHz). 38

14 Conducted susceptibility: The frequency range is 150 KHz to KHz, the detected audio level from the handset shall not exceed 55dB subjected to common-mode 3V on the cord. The Pressure sensor under test is influenced with Modulated Tone of (1 KHz, 80% AM) EMI signal [67] [68], the common-mode voltage between phase and ground is measured. The Figure 4.15 shows the variation of radiations with respect to common-mode current. Figure 4.15 shows the variation of radiations with respect to differential-mode current. The chart 4.1 gives information of radiation due to various layout. 1 V NT 2 V NC 3 V NP Chart 4.1: Electromagnetic-interference due to 5 different layout Chapter Summary: Based on the outcome obtained we can conclude that, as the frequency increases the radiations are increased, to assess and limit the radiations, the major requisite is to design an antenna and Low-pass-filter(LPF), as per our requirements. 39

Understanding and Optimizing Electromagnetic Compatibility in Switchmode Power Supplies

Understanding and Optimizing Electromagnetic Compatibility in Switchmode Power Supplies 1 Definitions EMI = Electro Magnetic Interference EMC = Electro Magnetic Compatibility (No EMI) Three Components