Conducted Immunity IEC 61000-4-6

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Conducted ImmunityIEC 61000-4-6
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What exactly does conducted immunity mean?

• It is a test to determine overall immunity to
  radiated fields, but the test is performed with
  signals injected onto cables, ie conducted
  into the EUT.
• If the EUT is small relative to the wavelength,
  the interfering signal will not significantly
  excite the EUT itself, but the connected cables
  will act as antennae and can become resonant. The
  signal will then conduct into the EUT through the
  ports.

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Why not radiate?

• Creating fields this low in frequency require a
  large antenna and amplifier.
• At the practical EUT-antenna distances involved,
  will be operating in the near field.
  Predictability of coupling to the EUT is poor.

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Advantages (over radiated test)

• Requires significantly less amplifier.
• Does not require anechoic chamber.
• Typical test setups cost less.
• More repeatable.
• Testing ports individually aids in mitigation.
  Which port is susceptible??

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Disadvantages

• With many ports, can be more time consuming.
• Multiple ports require multiple CDNS.
• Can only approximate real world situations (all
  cables exposed).

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IEC 61000-4-6

• Testing and measurement techniques Immunity to
  conducted disturbances induced by radio-frequency
  fields.
• Scope Immunity requirements of electrical and
  electronic equipment to electromagnetic
  disturbances coming from intended radio-frequency
  transmitters in the frequency range of 9kHz to 80
  MHz. Equipment not having at least one
  conducting cable is excluded.
• Object Establish a common reference for
  evaluating the functional immunity of equipment
  when subjected to conducted disturbances.

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Frequency Breakpoint, Radiated vs Conducted

• Basic standard is 80 MHz.
• Some product family standards extend this to 230
  MHz.
• Limitations of CDNs with regards to impedance and
  decoupling requirements.

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Why 80MHz instead of 30MHz (emissions breakpoint)?

• Efficiency of antenna at low frequencies more
  critical in immunity.
• Range up to 80MHz easily accomplished by CDNs.
• Radiated Emissions easily performed at farther
  distances, while radiated immunity power
  requirements prohibit testing farther than 3m.

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Test Levels

• Specified as open-circuit voltage (emf)
• 120dBuV or 1V.
• 130dBuV or 3V. (note 3V 129.5dBuV)
• 140dBuV or 10V
• X open level
• 80 amplitude modulated with 1kHz modulation
  frequency.

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Equipment

• RF Generator
• Signal generator
• Amplifier
• Attenuator
• Specific requirements regarding harmonics.

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Coupling and decoupling device(s).

• CDN (preferred)
• Specific requirement for impedance (nominal 150
  ohm).
• Clamp injection devices
• Impedance and decoupling established at the AE
  device.
• EM Clamp
• Bulk Current Injection (BCI) probe.
• Direct injection devices
• 150 to 50 ohm adapters

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Level Setting (calibration) procedure

• Actual voltage level is half the test
  specification.
• In 150 ohm system, measured level is 1/6 the test
  specification. In a 50 ohm system, the measured
  level is ½.

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Test setup

• EUT 0.1m above ground reference plane.
• Interconnecting cables 30 to 50mm above GRP.
• CDNs 0.1 to 0.3m from the projection of the EUT
  onto the reference plane.
• Rules for selecting the injection method. (see
  7.1.1) CDNs are preferred.
• Only two CDNs required. One has the signal
  injected, the other is terminated, providing a
  150 ohm impedance.
• Selection of which port to terminate. (See 7.2)
  Pick the port with the lowest circuit impedance.
• If clamp injection is used, must adhere to
  sections 7.3 or 7.4. Emphasis is on maintaining
  a 150 ohm circuit impedance. If not, procedure in
  7.4 is used.

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Test Procedure

• Swept from 150kHz to 80MHz
• Dwell time with AM carrier at each frequency long
  enough for EUT to be exercised and respond, but
  no less than 0.5 seconds.
• Provisions for frequency switching transients.
  Level may be reduced during frequency steps. (new)

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Evaluation of results.

1. Normal performance.
2. Temporary loss of function, which ceases after
   disturbance ceases without intervention.
3. Temporary loss of function, requires
   intervention.
4. Loss of function which is not recoverable.

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Test report.

• Includes all information necessary to reproduce
  test.
• Description of EUT exercising method.
• Performance level specified by manufacturer.
• Observed effects of disturbance.
• Rationale for pass/fail.

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Changes from edition 1.1 to 2.2

• Only two 150 ohm connections The source CDN, and
  one terminated CDN.
• 1 step size, dwell time long enough for EUT to
  be exercised and respond, but no less than 0.5
  seconds.
• CDNs are now preferred in the text of the
  standard. (6.2)
• Impedance requirements for 80 to 230 MHz now
  specified, with more tolerance. (B.1)

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Changes, contd

• The modulation check (6.4) no longer specifies
  that an RF oscilloscope must be used.
• The output level can be determined either by
  measuring the power from the amp output, or by
  the signal generator output as long as the
  stability of the system can be guaranteed. (6.4)
  This was not mentioned in ed 1.1.
• Ed 1.1 stated that the modulation must remain
  switched on. (6.4) This requirement has been
  removed.
• Several drawings changed, to reflect more
  attention given to maintaining AE impedance.
• Annex F, Test setup for large EUTs.

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Comments, Observations

• Verify CDNs in-house if possible.
• Why open-circuit voltage spec?
• Current formula in 7.4 is it correct, or will
  the EUT be overtested? This seems to conflict
  with 6.2.2. By the equation, the EUT could be
  overtested.
• Overtesting depends on whether the susceptible
  circuit is capacitively or inductively coupled.

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Comments, Observations, contd

• No specific requirements to check linearity or
  gain compression, only a mention of checking
  modulation envelope. (see 6.4) 61000-4-3
  calibrates to 1.8 times the level.
• Harmonics should be checked at 1.8 times the test
  level (peak modulation envelope).
• When testing to 7.4, The modified test voltage
  level shall be recorded in the test report. How
  do you determine the test voltage from the
  current, when the circuit impedance is unknown?
  Assume 150 ohms?

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Problems with Annex F, Test setup for large EUTs.

• Two ground planes, separated by a protective
  earth conductor. Resonance?
• EUT relationship to the ground plane not defined
  adequately. No mention of 10cm distance from
  ground plane as there is for standard
  orientation.

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