## 2 Previous Research  
There have been studies regarding the digitalization of EISs [10; 11; 12]. [PERSON] et al. [10] proposed methods for processing pulse signals and the mean square value output of a fission chamber (FC) in the digital-signal-processing unit. [PERSON] et al. [11] aimed to digitalize the Intermediate Range (IR). However, the main topic of these studies was the validation of an algorithm for digital processing of an EIS using simulations, and they did not experiment on the basis of actual detector signals. [PERSON] et al. [12] demonstrated the performance of the digital wide-range neutron power measurement channel, including pulse signal processing, using a research reactor. However, the feasibility of achieving the required high-speed response in an EIS using digital circuits has not been discussed. It is essential to validate the safety functions required for an EIS to be used in commercial power reactors. Therefore, we believe that the verification conducted in this study will be beneficial for advancing the digitalization of EISs.  
Figure 1 shows the traditional EIS configuration for PWRs. An EIS has three different ranges, i.e., source range (SR), IR, and power range (PR), to monitor a wide measurement range spanning 12 digits from reactor shutdown and startup to normal operation [13]. The IR and PR process the signal output from the compensated ion chamber (CIC) or uncompensated ion chamber (UIC) by using a logarithmic amplifier or summing amplifier, whereas the SR processes the pulse signal output from the proportional counter (PC) by using several analog modules, i.e., a preamplifier, pulse amplifier, pulse shaper, and logarithmic amplifier. Using many analog modules increases O&M costs and has the potential to limit the continuity of production. Thus, digitalization will greatly benefit the SR in terms of reducing modules and continuing production for plant operation. Another advantage of digitalizing the SR is to improve its maintainability because the number of SR maintenance tests is higher than that for other ranges, e.g., the V-I characteristics test, plateau characteristics test, and DCT. The purpose of the DCT is to set a discrimination level that can distinguish pulse signals derived from neutrons from other signals. The discrimination level may vary due to environmental factors such as noise and the degradation of the detector. Typically, a graph of discrimination characteristics is created by plotting pulse counts at various discrimination levels to determine the appropriate threshold. In a traditional EIS, the pulse shaper includes a discrimination function and generates a rectangular pulse when the original pulse signal exceeds the discrimination level. The scaler-timer then counts the number of rectangular pulses within a specified period to create the graph. However, this traditional method requires multiple changes in discrimination levels and pulse counts to compensate for the loss of pulse height information. To address this issue, we explored an alternative method with digital techniques, which incorporates a peak hold function to capture the maximum pulse height of each original pulse and a software function to create a discrimination characteristics graph directly using the acquired pulse height information.