Abstract: An optical communication system (11) includes a plurality of nodes (16,17,18,19), each node connected in a first optical communication path (22) and a second optical communication path (23) extending parallel to the first optical communication path. The first optical communication path (22) is joined to each node by a first receiver (30) and first transmitter (31), while the second optical communication path (23) is joined to each node by a second receiver (32) and second transmitter (33). One of the nodes comprises a control unit node (19) having a control unit (37) associated therewith. The other nodes of the communication system comprise data unit nodes, each having a data unit (36) associated therewith. The communication system (11) normally operates with the control unit (37) in an open mode of operation in which data is not transferred across the node. Thus, in normal operation, the communication system (11) operates in an open ring configuration.

Abstract: An electromagnetic well logging tool for imaging the electrical characteristics of a borehole. A tool inserted into the borehole includes the appropriate mechanical apparatus to align a plurality of transmission lines adjacent to the borehole wall without requiring direct electrical contact. Electrical circuitry applies a step or impulse voltage on one end and samples the reflections at the same end of each transmission line, where the reflections indicate the magnitude of any changes of dielectric constant of the material of the borehole wall. The transmission lines are preferably angled relative to the center line of the borehole for a complete mapping of the circumference. The tool is moved at a desired speed through the portion of the borehole where measurement is desired. The sampling rate of the reflections depends on the desired speed of the tool and the desired resolution of the measurements.

Abstract: In an induction logger, a method for nulling the output signal from a pair of series-coupled receiver coils by altering the magnetic flux distribution within the coils by use of one or more magnetic equalization bodies. The shape and aspect ratio of the equalization body are chosen to minimize temperature dependence of the initial permeability. Alternatively, a highly conductive equalization body may be used.