Abstract: Signals from redundant sensors located throughout a pressurized water reactor (PWR) nuclear power plant are processed in four independent channel sets each of which includes a plurality of independent microcomputers which calibrate, convert to engineering units and calculate partial trip signals and engineered safeguard actuation signals from the sensor signals for use in the conventional voting logic of a plant protection system. The primary and secondary partial trip and engineered safeguard actuation functions associated with various postulated abnormal events are allocated to different independent microcomputers in the channel set for reliability. A test unit common to the channel set automatically, rapidly bypasses and tests each protection function independently while the other protection functions in the channel set remain on-line and also continually tests each microcomputer through a dummy test function performed along with the assigned protection functions.

Abstract: A terminal module provides for attaching components to terminals of a terminal frame. The terminal module utilizes an integral printed circuit board having a component assembly potted within a rectangular plastic shell with the remaining portion of the printed circuit board protruding from the shell for use as electrical terminals and for physical attachment to screw terminal strips of the termination frame. The modules are suitably of a predetermined geometric configuration, and the potted component assembly portion is contoured to fit between respective ones of stacked terminal strips.

Abstract: A self-testing contact closure test circuit and method in which invalid logic states are artificially created in order to simulate a switch malfunction, and thus to determine whether the testing circuitry correctly identifies the invalid state. The system is designed to be used with switches such as those incorporating form "C" arrangements having two pairs of contacts which under normal circumstances are in opposite states.

Abstract: Redundant trip logic microprocessors produce partial trip signals which are voted on by a pair of voters at the power interface to the actuated devices. The logic implemented by each trip logic processor is straight-forward and can be designed for each individual plant. Also included is an automatic tester and testing method which can confirm the accuracy of A/D converters, digital inputs, check the trip points of bistable, verify all the trip and voting logic, and measure the time response of each channel. The test subsystem uses a microcomputer to control the isolation of the analog field sensor signals and digital contact signals from the analog and digital inputs, control the generation and/or injection of various combinations of reference and test signals, and monitor the response of the trip logic processors and voter to the test signals.

Abstract: A method and apparatus for controlling the magnitude of an analog current through a load to be proportional to the magnitude of an input voltage. A sensing resistor is connected in series with the load. A controllable voltage is applied across the series connection of the load and sensing resistor for driving a current therethrough. A pulse width modulator receives the input voltage and a feedback voltage corresponding to the voltage drop across the sensing resistors when current is conducted thereby and produces square wave pulses each having a pulse width which is adjusted in response to a difference between the magnitudes of the input voltage and the feedback voltage.

Abstract: Apparatus and a method for use therein are disclosed for an analog signal processor, particularly one suited for use in nuclear power plant applications, which converts analog process signals to digital form and employs continuous on-line automatic calibration in order to accurately compensate for gain and bias errors occurring in its input analog circuitry.

Abstract: A power interface circuit periodically which receives test pulses to test the operation and connections thereof. Voltage and current sensors detect the result of the testing and may be used for zero-crossing detection when AC powered devices are controlled by the power interface circuit. Preferrably, asymmetrical pulses, such as those representing an ASCII character, are used as the test pulses. Three input signals are received by the power interface circuit which performs two out of the three voting on the input signals to generate a control signal for two power switches. The power switches may be connected in parallel or in series to provide additional fault tolerance.

Abstract: An adaptive digital filter is supplied with an alternating current noise signal by a separate reference line. The filter samples input signals and the signal on the reference line several times during each cycle of the noise signal. The samples of each of the input signals are then summed and optionally averaged for one cycle of the noise signal to produce filtered signals. The sampling interval for the input and reference signals is adjusted so that the sum of the reference signal samples for one cycle of the noise signal approaches zero.

Abstract: A power contact with low off current for switching a-c loads in response to a logic signal includes a rectifier bridge circuit in a series with the load and the a-c power source, a MOSFET connected across the d-c terminals of the bridge, and a series RC filter circuit in parallel with the MOSFET. A metal oxide varistor connected across the d-c side of the bridge protects the MOSFET from transients in the a-c circuit. While this power contact is capable of switching sizable a-c currents, the leakage current with the MOSFET off is less than 1/10 of a milliamp so that it can also be used to switch loads which draw very low level currents. The MOSFET is electrically isolated from the logic signal by an opto-isolator which has a unique switchable output which permits the power contact to be readily adapted for use with normally energized or normally deenergized loads.

Abstract: A redundant power supply/signal conditioner system for a resistance temperature detector includes power supply/signal conditioner modules having first and second output terminals connected to a resistance temperature detector. Diode circuits are connected across the output terminals of each of the power supply/signal conditioner modules to provide an alternate current path when the corresponding power supply/signal conditioner module is removed or is not conductive due to a failure. Each of the power supply/conditioner modules includes a constant current source for supplying a constant current which is slightly different in each of the modules. Each of the modules also includes an overvoltage protection circuit for preventing the voltage output by the constant current source from exceeding a predetermined value and a signal conditioner which outputs a signal based on the temperature detected by the resistance temperature detector.

Abstract: An analog output network provides multiple communication paths for control of an actuator in response to an input signal. The analog output network includes at least two controllers, each of which is connected to an analog output circuit and a controller selector which is connected to each of the controllers and the analog output circuits. The controller selector ensures that at least one of the analog output circuits is enabled at all times and identifies one of the controllers as an on-line controller. The analog output circuit connected to the on-line controller generates an actuation signal which passes through the actuator and the other analog output circuit. An alternate current path comprising a diode string with a voltage drop larger than the voltage drop of the actuation signal in the other analog output circuit is provided so that if an analog output circuit is removed or defective, the actuation signal from the on-line analog output circuit is still provided with a current path.

Abstract: A redundant d.c. power supply arrangement for supplying power to a load circuit, wherein the power supply arrangement is subjected to voltage transients of high frequency and magnitude which emanate from the load circuit. The arrangement includes first and second power supply branches connected in electrical parallel with the load circuit. Each power supply branch includes a d.c. voltage supply and a Zener diode connected in electrical series with the voltage supply. The Zener diodes are selected and arranged for causing at least one of the voltage supplies to deliver power to the load circuit. Each Zener diode has a reverse breakdown voltage for clamping a voltage transient emanating from the load circuit to that Zener breakdown voltage and provides a low impedance path for a resulting current surge associated with the voltage transient.

Abstract: An apparatus is provided for sensing the state of high voltage contact inputs in a process control system. Lower voltage contact closure input modules cooperate with a reference bus and reference bus regulator to reduce the voltage drop across an input module when a pair of contacts is closed, thereby reducing the energy dissipated and heat created by the input module.

Abstract: An arrangement for permitting communication among a plurality of stations on a single serial data communications bus. Each station is provided a choice between two modes of operation. All stations ordinarily operate in a normal mode, seeking access to the serial bus upon occurrence of a democratic time window. In the normal mode, each station is given an opportunity to issue a single transmission before any one station is permitted to issue a second transmission. Should any station require transmission of an urgent message, that station may seek access during an autocratic time window. Within any single round of bus arbitration, all autocratic time windows occur prior to the first democratic time window.