Patent Number: 046684654
Section: summary

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention is directed to a method and apparatus for remotely monitoring with high reliability a process carried out in a hazardous environment within a containment structure. More particularly, it is directed to a method and apparatus for transmitting redundant signals from a large number of detectors through the containment structure with a minimum number of penetrations. It is particularly applicable to transmitting to the plant control room outside of the containment building reliable indications of control rod position in a nuclear reactor. 2. Prior Art There are many installations wherein the hazardous conditions under which a process is carried out require that it be enclosed in a containment structure. Under such conditions, it is desirable to be able to remotely monitor and control the process and to be able to do so with a great deal of reliability to preclude having to shutdown for lack of sufficient control, and with a minimum of pentrations through the containment structure to reduce construction costs. The latter requirement becomes particularly important in installations in which a large amount of information must be transmitted through the containment structure. Radiation and toxic chemicals are exemplary hazardous conditions which require confinement within a containment structure to protect those working with them. A nuclear reactor is an example of an installation in which hundreds of detectors and control signals of various kinds must be transmitted through the containment structure for monitoring, protection, and control functions directed from outside. Remotely monitoring the position of the control rods within the core of the nuclear reactor is a procedure which requires the transmission of a great deal of information through the containment structure. In a typical pressurized water reactor, there are several scores of drive rods which each incrementally step several neutron absorbing rods connected by a spider into and out of the reactor core. The positions of the neutron absorbing rods within the reactor core are derived from the positions of the associated drive rods; each of which is equipped with a position detector. Early rod position detectors used the change in impedance of a coil or the change in coupling between primary and secondary coils effected by the end of the drive rod as it moved through the coil to generate an analog signal indicative of rod position. The susceptability of such analog systems to variations in temperature, rod magnetization, permeability of the rod, power supply voltages and frequency, and to interference from adjacent control rods and drive mechanisms, led to the development of digital position indicating systems such as that disclosed in U.S. Pat. No. 3,846,771. This system uses a number of discrete coils spaced along the linear path traced by the end of the rod. The change in impedance of each coil in sequence as the rod advances through successive coils is used to generate discrete output signals or one output signal with discrete levels. Discrete output signals are preferred over a single signal with discrete levels because they can be more easily transmitted to remote locations and reliably decoded. Their use, however, significantly multiplies the number of signals that must be transmitted. Reliability is of critical importance in monitoring the position of control rods in the core of a nuclear reactor. It is well-known that reliability can be enhanced through redundancy. In the digital rod position indicating systems disclosed in U.S. Pat. Nos. 3,858,191 and 3,893,090, redundant sets of coils are interleaved along the path of each drive rod and the signals generated as the end of the rod passes through the coils in each set are separately transmitted through the containment building wall through separate channels to the outside where they are combined to provide an indication of rod position. All of the data generated by one set of coils in each detector is transmitted over one channel and that generated by the second set of coils in each detector is transmitted over another channel. If either channel is inoperative, the remaining channel provides the position indication for all of the rods with half the resolution of the combined indication. While such systems provide protection against a single component failure, they are highly susceptible to certain dual component failures. For instance, if one transmission channel should fail, the signals from one entire set of coils for each detector are not available. A subsequent failure in the other set of coils for any detector results in a loss of all reliable information regarding the position of the neutron absorbing rods connected to the associated drive rod. It is a primary object of the present invention to provide the capability for remotely monitoring a process carried out in a hazardous environment within a containment structure with high reliability and with a large amount of digital information transmitted using a limited number of penetrations through the containment structure. SUMMARY OF THE INVENTION This and other objects are realized by generating within the containment structure a plurality of redundant sets of detector signals representative of the value of selected process parameters, storing all of these signals within the containment structure in each of a plurality of microprocessors, serially transmitting the plurality of sets of redundant detector signals stored in each microprocessor to the outside of the containment structure over a separate serial data link, and generating separately outside the containment structure, redundant representations of the value of each of the selected parameters, each from the redundant sets of signals transmitted over one of the data links. The data link from which the redundant sets of signals used to generate each redundant representation are taken is selectable. In addition, the signal used to generate the representation is selectable as to each parameter from among the redundant signals received over the selected data link. The apparatus used to carry out the invention includes means within the containment structure for generating a plurality of redundant sets of detector signals. Interface means applies all of the redundant signals to each of a plurality of communication buses equal in number to the number of redundant sets of signals. A plurality of bus controller/serial output devices located in the containment structure are each connected to one of the communications buses, to control the interface means in applying the redundant sets of detector signals to the associated communications bus, to store these signals, and to serially output them over its own data link extending through the containment structure to the outside. Redundant receiver devices on the outside of the containment structure generate from the redundant sets of detector signals received from one of the data links, a representation of the value of the detector signal. Switching means permit selection of the data link from which each receiver receives its redundant sets of detector signals and permits individual selection as to each detector of which of the redundant signal is to be used in generating the representation of the value of that detector signal. As applied to monitoring the position of the control rods in a nuclear reactor, the detector signals are generated as multi-digit digital signals from the signals generated by the discrete coils spaced along the travel path of the rod. The redundant signals can be generated simply by reproducing the coil signals, since these components have been proven to be very dependable. Alternatively, interleaved redundant sets of coils can be used to produce the redundant detector signals. The essence of the invention is that all of the redundant signals are all transmitted over all of the redundant transmission channels with each of the receivers being able to select the individual channel from which it receives the redundant signals. With such an arrangement, failure of the same component in each of the detector to display channels is required to cause a loss of any of the transmitted information thus providing increased reliability over the earlier systems in which the redundant signals were transmitted separately over independent transmission channels .