Monitoring circuit for reactor safety systems

Claim 1

In a nuclear reactor which includes first and second reactor safety channels coupled to the reactor, each of the first and second reactor safety channels being responsive to the same reactor parameter to develop first and second measurement signals respectively, with each of the first and second measurement signals having a magnitude which is a function of the reactor parameter being measured, a safety circuit for continuously monitoring the first and second reactor safety channels, comprising: first and second log amplifiers coupled to said first and second safety channels respectively, said first and second log amplifiers being responsive to said first and second measurement signals to develop first and second log measurement signals proportional to the log of said first and second measurement signals respectively, a summing circuit to which said log amplifiers are coupled developing a ratio signal being the subtraction of one of said log measurement signals from the other of said log measurement signals, an offset voltage circuit coupled to one of said first and second log amplifiers for applying a reference dc voltage thereto so that with the absolute values of said log measurements equal said ratio signal has a desired nonzero value, and a comparator circuit coupled to said summing circuit and responsive to said ratio signal to develop an alarm signal with the magnitude of said ratio signal being outside of a predetermined range of magnitudes.