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A measurement and control system for employment with a plurality of significantly spaced process access locations wherein a single cable extends in a loop by these access locations, and both ends of the cable are terminated at a central controller. The cable consists of a solid, conductive, outer ho

A measurement and control system for employment with a plurality of significantly spaced process access locations wherein a single cable extends in a loop by these access locations, and both ends of the cable are terminated at a central controller. The cable consists of a solid, conductive, outer housing and four spaced conductors within the housing, the housing being otherwise filled with a dielectric material. Data units are positioned at each access location, and each data unit is configured to supply and receive, or one of the other, discrete data by being coupled to the cable, two of the conductors of the cable furnishing power for the data unit, and the other two providing communications. Certain of the data units employ transducers to measure a single physical state. Outputs from these transducers, in analog form, are serialized, converted to digital data, cross-compared to determine off scaled readings, and the good readings averaged. The average readings, together with other measurements at that process location, are polled by the central controller which polls each data unit around the loop on the order of once each 30 seconds.

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A process measurement and control system comprising: an electrically conductive cable comprising an outer positioned conductive solid cover, first and second pairs of spaced electrical conductors positioned within said cover, and a solid dielectric material being positioned within said cover and fil

A process measurement and control system comprising: an electrically conductive cable comprising an outer positioned conductive solid cover, first and second pairs of spaced electrical conductors positioned within said cover, and a solid dielectric material being positioned within said cover and filling space between said conductors and said cover, said cable extending in a loop commencing at a selected location, passing adjacent to a plurality of spaced process access locations and terminating at said selected location; a source of alternating current power being applied to said first pair of conductors of said cable; a control terminal located at said selected location and comprising: signal generating means for generating recurring sets of address signals, one unique address signal in a set for each of said process access locations, coupling means for connecting said address signals to said second pair of conductors, and discrete periods between succeeding address signals defining a time domain communications channel for an address, first selective coupling means synchronous with said signal generating means for effecting a discrete coupling circuit with said second pair of conductors of said cable for each ordered discrete time space and communications channel, signal application means coupled to said first selective coupling means for providing through said first selective coupling means and on said second pair of conductors of said cable at least one directive signal in at least one time domain communications channel, and signal indication means for indicating at least one process condition coupled through said first selective coupling means from said second pair of conductors; a plurality of first communications terminals, at least one of said first communications terminals being positioned adjacent to a said process access location, and comprising: power conversion means connected to said first pair of conductors of said cable for providing direct current biasing voltages generally for a said first communications terminal, first selective switching means coupled to said second pair of conductors of said cable and responsive to a said unique address signal for effecting coupling with said second pair of conductors for a said discrete period and thereby with a selected said communications channel, a plurality of digital storage elements, each being connected through said first selective switching means to said second conductors, a plurality of signal terminals, a plurality of transducer assemblies each of which is responsive to a physical state for providing as an output an analog signal, and wherein at least four of said transducer assemblies are positioned to sense a single physical state, and an analog output from each of said transducers is connected to one of said signal terminals, second selective switching means for sequentially providing signal coupling with each of said plurality of signal terminals, first analog-to-digital conversion means coupled to said second selective switching means for providing, sequentially, digital representations of discrete signals on a plurality of different said signal terminals, and first signal means responsive to sequential signals from said first analog-to-digital conversion means for coupling to a discrete one of said storage elements a digital signal which is a function of a signal on at least one of said signal terminals, and wherein said first signal means includes: comparator means responsive to digital representations of said analog outputs of said at least four transducer assemblies for comparing each said last-named outputs with at least one selected signal and providing, as compared outputs, only outputs which are within a selected range of said selected signal, and averaging means responsive to said compared outputs for providing a digital representation of the averaged said compared outputs to one of said storage elements; a plurality of second communications terminals positioned adjacent to other of said spaced said process access locations than those to which said first communications terminal are adjacent, and comprising: power conversion means connected to said first pair of conductors of said cable for providing direct current bias voltage generally for said second communications terminal, third selective switching means coupled to said second pair of conductors of said cable and responsive to unique said address signal for effecting coupling with said second pair of conductors for a discrete period and thereby with a selected said communications channel, a plurality of second digital storage elements, each last-named storage element being selectively coupled through said third switching means to said second conductors, a plurality of second signal terminals, fourth selective switching means for sequentially providing a signal coupling with each of said plurality of second signal terminals, and second signal means including digital-to-analog conversion means responsive to a digital signal stored in one of said digital storage elements for providing a signal through said fourth selective switching means to one of said second signal terminals, which last-named signal is a selected function of a digital signal stored in one of said digital storage elements.