Patent Number: 041707540
Section: summary

CROSS REFERENCE TO RELATED APPLICATION This application is related to the co-filed, co-pending application Ser. No. 622,918, filed Oct. 16, 1978 entitled "A Flexible Position Probe Assembly", now U.S. Pat. No. 4,052,686 which is assigned to the assignee of the present invention. This application is directed to the mechanical components and design which, when assembled, form an elongated flexible probe. BACKGROUND OF THE INVENTION A major requirement for a versatile and stable position probe assembly exists in the nuclear reactor field where knowledge of the precise position of control rods affecting the position of nuclear fuel rods is essential. The critical requirements for control rod position indicators for use in nuclear reactor facilities extend to both the mechanical design as well as to the electrical readout. Typically, the probe assemblies required for monitoring control rod position can vary in length from two to twelve feet, thus requiring substantial overhead clearance for installation. In many facility designs the overhead clearance required to accommodate conventional rigid control rod position probe assembly does not exist. Efforts to date to design a suitable sectionalized or flexible position probe assembly capable of being installed and removed from a reactor facility having a clearance less than the overall length of the probe have not proven to be totally reliable over an extended period of time. In addition to the mechanical deficiencies of prior art position probe assemblies, the analog manifestation of the position indication developed by these probe assemblies have not proven satisfactory due to the adverse effects of temperature changes, line voltage and frequency variations, noise pick-up, and, interference from ambient magnetic fields. There is disclosed herein with reference to the accompanying drawings a unique probe design capable of flexing in two planes for ease of installation in facilities with limited overhead clearance, and developing a phase encoded electrical indication of the position of a magnetically permeable material, and signal processing circuitry for converting said phase encoded signal to a direct digital indication of the position of the magnetically permeable material. SUMMARY OF THE INVENTION A flat flexible elongated strip is inserted through slots machined in the tubular passages of each of a plurality of tubular spools, on each of which is wound primary and secondary windings to form a core section. The length of the flexible strip and the number of core sections, wherein each core section may measure 1/2 inch in length, positioned on the flexible band is a function of the required operational length of the probe assembly. The core sections are maintained in adjacent contacting relationship by a spring element at one end of the probe assembly. The spring element permits flexing of the probe assembly in either of two opposite directions defining a plane perpendicular to the surfaces of the flexible strip corresponding to the width of the flat flexible strip. The flat flexible strip effectively divides the tubular passages of each of the core sections in half, such that the alignment of adjacent core sections in contacting relationship about the flexible strip forms two longitudinal internal probe passages which are electrically isolated. Lead wires from the primary windings of the respective core sections extend through one of the internal passages to an external electrical terminal, while lead wires from the secondary windings of the respective core sections extend through the second internal probe passage to an external electrical terminal. The isolation of the primary and secondary leads within the longitudinal passages eliminates electrical interference, and further the routing of the electrical leads via the internal probe passages isolates electrical leads from adverse ambient conditions. Typically, the movement of a predetermined magnetically permeable element or object, such as a control rod in a nuclear reactor installation, or a magnetically permeable liquid, such as a liquid metal, is monitored indirectly as a function of the coupling and decoupling of one or more of the plurality of differential transformer core sections comprising the position probe assembly. Since the successive coupling or decoupling of adjacent differential transformer core sections in response to movement of the magnetically permeable material, follows the dimensional length of each core section, the accuracy of position indication is directly related to the length dimension of the core section. For instance, if the length of each core section is 1/2 inch, the resolution and accuracy of the position probe assembly will be approximately .+-.1/2 inch of the actual position of the predetermined element. The output signal developed at the secondary windings of the plurality of differential transformer core sections form a phase encoded digital signal in Gray code, which is not a function of analog signal strength. This output signal format is inherently independent of line voltage and frequency variations, as well as variations in nuclear reactor operating temperatures. A Gray code pattern, instead of the more common binary code, is desirable for two reasons: 1. A conventional binary code changes more than one bit as the code progresses, thus leading to large errors when the timing of the bits is not perfect; the unique characteristic of the Gray code is that only one bit changes as the code progresses, and therefore erroneous timing of a bit only produces a single increment error, which in the case of a core section length of 1/2 inch would correspond to a 1/2 inch increment error. 2. The Gray code requires only one secondary coil per primary and core section, while the binary code would require multiple secondaries for each core section. Signal processing circuitry converts the Gray code phase encoded digital output signals from the position probe assembly into a binary coded decimal format for numerical display of the position of the monitored magnetically permeable material.