Patent Number: 039792552
Section: summary

BACKGROUND OF THE INVENTION This invention relates to a method of operating a system in which an excursion in some variable parameter necessitates immediate responsive action. More specifically, this invention may be applied to monitor parameters of a nuclear reactor in order to respond to safety related excursions. PRIOR ART In many machines and industrial processes, safety requires that an excursion in some vital plant variable (e.g., nuclear reactor power) greater than a preset amount cause automatic trip (rapid shutdown) of the process. "Excursion" is defined, for the purpose of this application as a change in the increasing or decreasing direction from the present value of the variable, at any rate of change. In addition, normal startup or shutdown of many machines and industrial processes requires the capability to suspend the trip function by manual action or by automatic surveillance equipment in order that the excursion tripping mechanism not trip the machine or process when the variable is legitimately increasing or decreasing. Automatic trips with automatically computed setpoints according to plant conditions have been developed and commercially used. The prior art has been unable, however, until the present invention, to calculate a continually variable excursion setpoint from present and past values of the variable which was responsive both to excursions of short duration and to excursions of long duration that take many minutes or even hours to develop. It has been well known in the art to initiate a variable setpoint excursion trip of very short duration by utilizing a high pass filter which would pass very rapidly changing signals. Such an apparatus and method was unable, however, to detect an excursion which was long in developing but which was equally as important to detect as the short excursions. Another prior art device utilizd a circuit which incorporated an operational amplifier integrator circuit to calculate the variable setpoint. This prior art device, however, had the defect that the voltage across the capacitors in the feedback loop of the operational amplifier would drift thereby causing the setpoint to change thus rendering the equipment unsuitable for accurate detection of a lengthy excursion. SUMMARY OF THE INVENTION This invention discloses a method for operating a nuclear reactor or any machine or process where it is of importance for safety reasons to terminate operation when a given parameter deviates from a variable operating value by more than a given amount regardless of the rate at which the deviation occurs. A variable setpoint is continually generated from the past history of the operating parameter. The setpoint is generated by adding to the current value of operating parameter a predetermined excursion margin whenever this causes the variable setpoint to decrease. Thus, the setpoint will follow the operating parameter in a downward direction. If, however, the operating parameter remains constant or increases the setpoint is not permitted to change unless independently permitted to do so. Such permission is uspplied only when it has been determined that such an increase is legitimate. When such permission is supplied, the setpoint can only increase to within the excursion margin of the operating parameter. The system is caused to trip when the setpoint is exceeded regardless of how long it has taken for the operating parameter to climb to the point where it has a value higher than the setpoint. The same technique may be applied in a similar manner to excursions in the negative direction.