ITU-T Recommendations

The time to half value of a double exponential surge, simulating a lightning impulse, is traditionally measured from a virtual zero point to the 50% amplitude decay point of the waveform, as explained in clause I.3. The time duration of electrostatic discharge (ESD) and electrical fast transient (EFT) impulses is measured as the time for which the impulse exceeds the 50% amplitude level. The time measured from virtual zero will always be longer than the time between the two waveform 50% points. Edition 3 of IEC 61000-4-5 (2014) departs from the traditional lightning surge time to half value measurement by specifying the use of the time between the two waveform 50% points for the 1.2/508/20 and 10/700 surge generator waveforms. Amendment 1 to Recommendation ITU-T K.96 introduces Appendix II, which discusses the time value changes caused by the Edition 3 approach and how other standards can be referenced to maintain the tradition measurement method.