Download “conducted immunity” mean?

Conducted
Immunity
IEC 61000-4-6
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.
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.
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??”
Disadvantages
With many ports, can be more time consuming.
Multiple ports require multiple CDNS.
Can only approximate real world situations (all
cables exposed).
IEC 61000-4-6
Testing and measurement techniques – Immunity to
conducted disturbances induced by radio-frequency
fields.
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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.
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.
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.
Test Levels:
Specified as open-circuit voltage (emf)
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120dBuV or 1V.
130dBuV or 3V. (note: 3V = 129.5dBuV)
140dBuV or 10V
X – open level
80% amplitude modulated with 1kHz modulation
frequency.
Equipment
RF Generator
– Signal generator
– Amplifier
– Attenuator
– Specific requirements regarding harmonics.
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
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.
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.
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)
Evaluation of results.
A. Normal performance.
B. Temporary loss of function, which ceases
after disturbance ceases without
intervention.
C. Temporary loss of function, requires
intervention.
D. Loss of function which is not recoverable.
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.
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)
Changes, cont’d
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.
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.
Comments, Observations, cont’d
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?
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.