IEEE TRANSACTIONS ON ELECTROMAGNETIC COMPATIBILITY, VOL. 42, NO. 4, NOVEMBER 2000 405 On the Uncertainty in the Current Waveform Measurement of an ESD Generator Tae-Weon Kang, Student Member, IEEE, Yeon-Choon Chung, Member, IEEE, Sung-Ho Won, Member, IEEE, and Hyo-Tae Kim, Member, IEEE Abstract—The uncertainty in the current waveform measure- ment of an electrostatic discharge (ESD) generator is evaluated. The measurands are the current amplitude and the rise time of the output current waveform of the ESD generator. An intuitively simple model is proposed to evaluate the uncertainty in the cur- rent amplitude measurement. Type A and Type B evaluations for all contributions to the measurement uncertainty are performed to obtain the combined standard uncertainty. The evaluated ex- panded uncertainty (95.5% confidence level) of the current am- plitude and the rise time at ESD voltages of 2, 4, 6, and 8 kV are within the specification of IEC 61000-4-2. The results show that the uncertainty in the current amplitude measurement stems from the voltage reading of the measuring equipment, the difference be- tween the displayed and the actual voltages of the discharge tip of the ESD generator, and the inaccuracy of the delta time measure- ment of an oscilloscope, whereas the uncertainty in the rise time measurement mainly originates from the measuring equipment. Index Terms—Current amplitude, electrostatic discharge, IEC standard, measurement uncertainty, output current waveform, rise time. I. INTRODUCTION T HE PROBLEM of measurement uncertainty has been a subject of considerable interest to the metrological com- munity. This subject is also important in the field of electromag- netic compatibility (EMC) tests of reliability. EMC compliance tests of electrical and electronic equipments involve an ESD im- munity test whose a representative international standard is IEC 61 000-4-2 [1]. The immunity test is carried out by using an ESD generator satisfying the requirements described in the IEC stan- dard. Considerable effort has been drawn in the study of ESD current waveforms to develop discharge simulators for simpli- fying and standardizing ESD immunity tests [2]–[6]. Several researchers considered ESD fields: Wilson and Ma [7] treated ESD fields both analytically and experimentally by idealizing an ESD spark as an electrically short, time-dependent, linear source placed above an infinite, perfectly conducting ground plane, whereas Mardiguian [8], [9] reported measurements of ESD fields at many distances and polarizations. The repeata- bility of ESD current waveforms was treated by an experimental approach [6], [10]. Recently, Rhoades and Maas [11] discussed Manuscript received June 25, 1999; revised February 1, 2000. T.-W. Kang, Y.-C. Chung, and S.-H. Won are with EMC Group, Division of Electromagnetic Metrology, Korea Research Institute of Standards and Science (KRISS), Yusong, Taejon 305-600, Korea (e-mail: twkang@kriss.re.kr). H.-T. Kim is with the Department of Electrical Engineering, Pohang Univer- sity of Science and Technology (POSTECH), Pohang 790-784, Korea. Publisher Item Identifier S 0018-9375(00)10211-X. Fig. 1. Typical current waveform of an ESD generator. a new ANSI ESD standard overcoming the deficiencies of the international ESD standards. To the best of our knowledge, little effort has gone into the uncertainty analysis in the current waveform measurements of the ESD generator. In this paper, we set up the measurement system of the output current waveform of an ESD generator ac- cording to the IEC standard and evaluate the uncertainty in ac- cordance with the ISO guide to the expression of uncertainty in measurement [12], [13]. To do this, the measurand of the current amplitudes is expressed by an intuitively simple model. Type A and Type B evaluations for the uncertainty of the measur- ands are performed to obtain the combined standard uncertainty. The expanded uncertainty is obtained for the confidence level of 95.5%. A few concluding remarks summarize the paper. II. THE MEASURAND AND ITS MATHEMATICAL MODEL A typical waveform of the output current of the ESD gen- erator is shown in Fig. 1, which is taken from IEC 61 000-4-2 standard. As shown in Fig. 1, the measurands for the ESD cur- rent waveforms are current amplitudes , , and , and the rise time . Fig. 2 is the measurement system of the output current wave- form of an ESD generator. The system was set up according to the IEC standard to verify the characteristics of the ESD gener- ator. It consists of a 1.5 m 1.5 m metal target plane, a current 0018–9375/00$10.00 © 2000 IEEE