Abstract: A control rod drop monitoring method and apparatus for use in a nuclear reactor including dedicated timers and displays to measure and display the drop time for each control rod when a reactor system trip occurs. The timers and displays may be made from CMOS technology, and may have millisecond resolution, if desired. The timers are initiated upon receipt of one or more reactor trip signals and are halted at the closure of switches for detecting the fully inserted or other preselected position of the control rods in the reactor core. The monitor system is designed for continuous operation. Reactor trip signals and limit switch signals are fed to latch circuits following a trip event or limit switch activation and are unaffected by subsequent changes in the state of the limit switches or trip signals. A manual reset is required to clear rod drop times. Also, a test mode is provided wherein all of the timers can be started and stopped, thereby providing a functional test of 100% of the monitor circuitry.

Abstract: The present invention relates to a signal selector which selects a signal for control of various operating parameters in a process facility. The system includes a display and first and second sensors each providing a signal representative of a single controlled parameter. The first signal is preferred as a control signal for the parameter. A switch is arranged on the display for manually selecting between the first and second signals or for selecting an automatic selection mode. The system further includes an arrangement for determining if the first signal is unacceptable including comparing the first and second signals to one another and to a first pre-selected threshold value and either by comparing the first signal to a second threshold value or performing a second comparison of the two signals. The system automatically switches to the second signal when the first signal is unacceptable when the switch is in the automatic selection mode.