| 摘要 |
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.
|
