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Noise Isolation

Noise Isolation. Keeping the Gremlins Out. How noise gets into your circuits. Key Characteristics of the noise source. Voltage. ‘High’ voltage. Strong electric field. Capacitive coupling. ‘High dV/dt. Capacitive coupling. Current. ‘High’ current. Strong magnetic field.

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Noise Isolation

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  1. Noise Isolation Keeping the Gremlins Out

  2. How noise gets into your circuits

  3. Key Characteristics of the noise source Voltage ‘High’ voltage Strong electric field Capacitive coupling ‘High dV/dt Capacitive coupling Current ‘High’ current Strong magnetic field Inductive coupling Frequency ‘High’ frequency Radiative coupling Radiation Distance from the victim Distance = 0 Direct contact Conductive coupling Distance > wavelength Probably Radiative Not For Us 0 < Distance < Wavelength Capacitive or Inductive

  4. Key Characteristics of the noise source Voltage Current Frequency Distance from the victim

  5. What is the most likely coupling mechanism for Fluorescent light noise Capacitive High Voltage Arc welding noise Inductive High Current Digital clock noise Capacitive High dv/dt

  6. What is the most likely coupling mechanism for Fluorescent light noise Arc welding noise Digital clock noise

  7. Conductive coupling Motor Sensor

  8. More conductive coupling +12V +5V

  9. How should I wire these up? 12V 7.5V + G + G Motor + G HC11 + G + G Sensor

  10. Which waveform must be conductively coupled? Why?

  11. Identifying characteristics of conductive coupling Metallic contact required Unaffected by people or cable movement Non-zero average value for the waveform Techniques to reduce conductive coupling Break the conductive contact Use filtering

  12. Identifying characteristics of conductive coupling Metallic contact required Unaffected by people or cable movement Techniques to reduce conductive coupling Break the conductive contact Use filtering

  13. Capacitively coupled noise Simplified circuit Coupling capacitance

  14. Physical Representation of capacitively coupled noise

  15. Equivalent circuit for capacitively coupled noise If If

  16. Reducing Capacitively coupled noise

  17. Reducing Capacitively coupled noise Shield Position the shield to intercept the noise current Connect the shield to return the noise current to the source How many connections to the shield are required?

  18. Summary of capacitive noise reduction techniques Reduce capacitive noise coupling by 1. Reducing coupling capacitance 2. Reducing circuit impedance 3. Using shielding Capacitive shielding requires 1. Proper shield location 2. Correct shield connection

  19. Summary of capacitive noise reduction techniques Reduce capacitive noise coupling by Capacitive shielding requires

  20. Isolation Why do you need it? Conductive noise Large voltage differential Provide fault isolation (Safety) Minimize leakage currents How do you get it? Magnetic coupling Optical coupling

  21. Isolation Why do you need it? How do you get it?

  22. Isolation via magnetic coupling

  23. PCB mount miniature relays

  24. Reed Relay construction

  25. Optical Isolation

  26. Create a design to connect L-298 H-Bridge 68HC11 PS2501 Opto-Isolator

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