An electrical circuit which separate the signal current using input filters has been developed for a wide range neutron flux monitoring system. In general, a wide range neutron flux monitoring system is for measuring signals from a single neutron detector using a pulse counting method and a Campbell method simultaneously. Therefore, it is difficult to design a suitable signal processing circuit for both measurements. The developed system employs two filters different in their characteristics and placed in parallel at the input stage of the preamplifiers. The filters separate the detector signals into two frequency ranges which are then amplified. It becomes possible by processing the signals into a pulse system and a Campbell system with the individual amplifiers in this way to enlarge the impedance of the first stage amplifier in the Campbell system without being influenced by the pulse counting unit which requires a low input impedance. Thus, the signal-to-noise characteristic can be improved, and a more accurate measurement can be obtained. As a result, the system including a neutron detector has been developed and tested in an experimental reactor. The obtained overlap between the pulse system and the Campbell system was 2.3 decades, on the basis of a 0.8% maximum measurement error.
