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Study of the Fitting Method in the Sensitivity Calibration of a HEMP Measuring System

This paper presents the study of the fitting method for the sensitivity calibration data of a time-domain high-altitude electromagnetic pulse (HEMP) measuring system combined with the engineering practice. Due to the simple and practical requirements in engineering applications, this paper discussed and compared three different fitting methods and two different fitting models typically used in the HEMP measuring system: conversion coefficient averaging method, least square method, and relative least square method with direct proportion model and linear model. Uncertainty is used as the judgment of fitting performance in this paper. Both type A and type B uncertainties are analyzed. The statistical method is used in the analysis of type A uncertainty. Results of 50 different measuring systems with a different fitting method are observed and compared. And the standard deviation is used to represent the relative standard uncertainty of fitting. The GUM method with an ideal linear assumption of the sensitivity is used and the strict expressions of uncertainties are deduced in the analysis of type B uncertainty. The results show that the relative least square method is more suitable than the least square method in the fitting of HEMP measuring system calibration. The averaging method with direct proportion model is preferable considering the convenience and efficiency in practice. And the relative least square method with both the direct proportion model and linear model can be considered as well. The least square method with the linear model is not recommended in the application of time-domain HEMP measuring systems.