Conducted Immunity IEC 61000-4-6 Presentation is about conducted immunity in general, and IEC 61000-4-6 in particular. Differences between edition 1.1 and 2.2 will be mentioned.

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. 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. Scope as stated covers 9kHz to 80MHz. However, under section 5 “Test Levels” the first sentence states no tests are required from 9kHz to 150kHz.

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. CDN limitations prevents testing much above 230MHz with small CDNs. Large CDNS have a lower cutoff due to internal circuit resonances.

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. Efficiency of most practical antennas not good at 30 MHz. Near/Far field boundary comes into play.

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. If testing at 3v, you start off with 0.5 dB measurement uncertainty!!

Equipment RF Generator Signal generator Amplifier Attenuator Specific requirements regarding harmonics. The standard treats all of these as the RF Generator.

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 Mention 150 to 50 ohm adapters since they are required for the level setting procedure. Also, shorting 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. Reasons for the open circuit spec? Could not find an answer to that. Models real world??? The level adjustment is due to: 6dB (1/2) for the conversion between open circuit and terminated levels. 9.5dB (1/3) for the voltage divider effect of the 150-50 ohm converters. Total = 1/6, or 15.5dB

CDN setup for calibration. EUT side is on the left CDN setup for calibration. EUT side is on the left. Cable at top is from amplifier, going through 6dB attenuator. Attenuator needed for impedance matching, since input of CDN will look more like 250 ohms instead of 50. Cable at left goes to 50 ohm measuring device, usually a spec-an. Attenuator is also used here, both for impedance matching and for reducing the level to protect the measurement set. 150-50 ohm adapters and shorting adapters are on both sides.

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. Change in edition 2.0 was that only one CDN would be terminated while testing.

Typical test setup from the standard Typical test setup from the standard. Please note the distances specified. One CDN is used to inject signal, one CDN is used to terminate the setup. Any additional CDNs are simply used to decouple the signal from the AE.

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) Edition 2.0 removed the statement that modulation must remain on during the test. Minimum dwell time reduced.

Evaluation of results. Normal performance. Temporary loss of function, which ceases after disturbance ceases without intervention. Temporary loss of function, requires intervention. 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) Bullet 1: Formerly, every connected CDN was terminated, now only one is terminated, the others are left connected (for decoupling) but not terminated. Bullet 2: “Swept” no longer mentioned under test generator, section 6.1. However, it is still mentioned in section 8 although the sweep rate (decades/second) no longer mentioned.If swept instead of stepped, how fast? Has anyone actually done a frequency swept test?

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. Bullet 3: This is good for systems that can’t easily measure forward power with modulation on. Bullet 5: Step in the right direction, but several problems. This is great for in situ testing.

Changes to this drawing include the termination at CDN-M2 (middle) Changes to this drawing include the termination at CDN-M2 (middle). When not injecting this port, this is the only one that will be terminated while testing other ports. Also added is the CDN-M2 on the AE device. It will remain terminated in an effort to maintain 150 ohm source impedance while using the EM clamp.

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. Bullet 1: Especially true with large number of CDNs – cost becomes a factor. Also, shipping damage possible from heavy internal ferrites being shaken loose and damaged. Bullet 2: Possibly to get correlation with similar test levels of radiated immunity.

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.

No distance specified, only the 30cm cable distance requirement is mentioned. Part of the return path is the GRP. If only one CDN is required, return path would be almost exclusively the ground plane, and distance will affect that. Suggest laying the EUT on its side and testing conventionally if possible.