Induced-charge errors in charge-transfer measurement: Calculations for sparks and additional brush-discharge geometries

We recently reported calculations of the influence of induced-charge errors on brush discharge charge-transfer measurement for electrostatic hazard assessment. We concluded, tentatively, that, provided concave charged systems were avoided, the use of a correction factor of ×2 to ×2.5 when interpreting charge-transfer measurements made with fast, unshielded probes would avoid the underestimation of hazards at a 60 nC threshold level. However, our calculations applied directly only to brush discharges with a restricted range of geometries and consequently, it was not certain that the factors were necessarily sufficient in all circumstances. This paper presents numerical calculations that extend our results to a wider variety of geometries and include sparks as well as brush discharges. For brush discharges, the results reinforce the conclusions of the original work. For sparks they suggest that a similar worst-case correction factor (×2.2) is applicable.