Conducted Immunity IEC 61000 -4 -6 What

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. n n Scope: Immunity requirements of electrical and electronic equipment to electromagnetic disturbances coming from intended radio-frequency transmitters in the frequency range of 9 k. Hz 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 80 MHz instead of 30 MHz (emissions breakpoint)? Efficiency of antenna at low frequencies more critical in immunity. Range up to 80 MHz easily accomplished by CDNs. Radiated Emissions easily performed at farther distances, while radiated immunity power requirements prohibit testing farther than 3 m.

Test Levels: Specified as open-circuit voltage (emf) n n n 120 d. Bu. V or 1 V. 130 d. Bu. V or 3 V. (note: 3 V = 129. 5 d. Bu. V) 140 d. Bu. V or 10 V X – open level 80% amplitude modulated with 1 k. Hz 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. 1 m above ground reference plane. Interconnecting cables 30 to 50 mm above GRP. CDNs 0. 1 to 0. 3 m 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 150 k. Hz to 80 MHz 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 10 cm distance from ground plane as there is for standard orientation.