Electrical Fast Transient（EFT）測試是一種用於評估電子設備抗 EFT 干擾能力的測試方法。EFT 是一種短時間內發生的電壓變化，通常是由於閃電、開關操作等突發事件產生的瞬間電壓峰值。EFT 測試可以確保設備能夠在 EFT 干擾下正常運行，並且不會對其他設備造成干擾。
在進行 EFT 測試時，測試人員會使用 EFT 發生器來模擬 EFT 干擾，並將這個干擾信號傳遞到待測設備上。待測設備會在 EFT 干擾下進行操作，而測試人員會監測設備是否能夠正常運行。
在 EFT 測試過程中，測試人員會使用不同的測試參數，例如 EFT 發生器的峰值電壓、脈衝寬度、重複頻率等。這些參數通常是由相關的 EMC 標準和規定所指定的。
通過 EFT 測試，可以確定設備能夠承受 EFT 干擾的強度和頻率範圍，以及設備在受到 EFT 干擾時是否能夠正常運行。這些測試可以幫助設計人員和製造商確保其產品符合相關的 EMC 標準和規定。
總之，EFT 測試是一種用於評估電子設備抗 EFT 干擾能力的測試方法，通過模擬 EFT 干擾信號來確定設備能夠承受 EFT 干擾的強度和頻率範圍，以及設備在受到 EFT 干擾時是否能夠正常運行，以確保設備符合相關的 EMC 標準和規定。
Establishes a common and reproducible reference for evaluating the immunity of electrical and electronic equipment when subjected to electrical fast transient/bursts on supply, signal, control and earth ports. The test method documented in IEC 61000-4-4 describes a consistent method to assess the immunity of an equipment or system against a defined phenomenon.
The standard defines:
-test voltage waveform
-range of test levels
-test equipment
-verification procedures of test equipment
-test set-up
-test procedure
The standard gives specifications for laboratory and post-installation tests.
Electrical Fast Transients (EFT) are caused anytime a gaseous discharge occurs (a spark in air or other gas), the most common being the opening of a switch through which current is flowing. As the switch is opened, arcing occurs between the contacts; first at a low voltage and high frequency while contacts are close together, and later at a higher voltage and lower frequency as the contacts become separated. Coupling of the EFT into electronic products occurs when power cables handling high currents are run in close proximity to power, data, and/or I/O cables.
Electronic products are tested for EFT immunity to insure their continued reliable operation if subjected to realistic levels of fast transients. The European Union’s EMC Directive mandates EFT testing for virtually all electrical and electronic products as a condition for obtaining the CE Mark before shipping to a member state of the European Union.
Generic Immunity, Product and Product Family Standards require that EFT tests be performed in accordance with Basic EMC Standards: IEC 801-4, IEC 61000-4-4 or EN 61000-4-4. Thermo KeyTek’s Application Note, “EMC Standards Overview,” provides an overview of European Standards for electromagnetic compatibility, describes how the Standards relate to one another, and lists sources for procuring copyrighted documents.
1 IEC 801-4, IEC 61000-4-4, and EN 61000-4-4 are essentially the same for test voltages and levels.
The Basic EMC Standards for EFT define methods of generating consistently reproducible fast transients for test purposes. They specify generator and coupler/decoupler design and performance in an attempt to produce correlation results between test sites. The Basic EMC Standard specifies how to perform EFT testing, the Generic, Product and Product Family Standards specify the test levels and pass/fail performance criteria.
Capacitive Coupling via 33nF capacitors is the required coupling method to AC or DC power mains. These coupling capacitors are included as part of a Coupler/ Decoupler (C/D) in commercially available EFT simulators. The design of the decoupling portion of the C/D, which prevents the EFT burst from traveling back onto the power mains, is also specified in IEC 61000-4-4.
A Capacitive Coupling Clamp is used to couple EFT bursts onto data, I/O, and telecommunications lines. Construction of the clamp is shown in Figure 5 of IEC 61000-4-4; however, considerable differences exist in commercially available clamps. Some clamps use higher quality materials and some designs allow for the use of an optional safety interlocked cover.
IEC 61000-4-4 requires that the simulator output be verified periodically. A 50 ohm load and attenuator rated for high voltage is required and the measurement must be made using an oscilloscope with at least 400MHz bandwidth.
One problem noted with IEC 61000-4-4 is that simulator designs can be quite different and although each has a 50 ohm source impedance and provides the specified pulse into a 50 ohm termination, some simulators provide significantly more or less energy than others into loads that are not 50 ohms – the AC power input of most electronic products is something other than 50 ohms. To deal with the problems, changes to the standard were proposed to require waveforms be verified into a 1000 ohm load. Unfortunately, these changes were not accepted; however, this and other proposed improvements to IEC 61000-4-4 will be included in a forthcoming Annex.
For EFT tests, the Generic Immunity Standards and Household Appliances Product Family Standard require that products operate as intended after the test. No degradation or loss of function is allowed below a performance level specified by the manufacturer. During the test, degradation is allowed, but not a change in the actual operating status or data storage. Refer to the tables located in the Generic, Product and Product Family Standards for specific Performance Criteria. The product cannot become unsafe under any conditions.
