Patent Number: 047117575
Section: claims

1. Position indicating device for producing an indication of the position of a displaceable structure, said device comprising: a position representing member mounted for movement in response to displacement of the structure, said member being movable along a defined path from a starting point such that the distance to which said member extends from the starting point corresponds to the position of the structure;  a plurality of sensing elements spaced apart along the defined path such that each said element is associated with a respective location along the defined path, each said element being operative to respond to the presence of said member when said member extends from the starting point to the respective location associated with that said element;  means operatively coupling said elements into respective pairs of elements, said means having, for each pair of elements, an output producing a signal only when a single element of its respective pair is responding to the presence of said member, said elements of each said pair being spatially separated from one another by at least one said element of a different said pair;  a plurality of signal producing members each operative for producing a signal representing a predetermined logic state in response to a predetermined input signal, the number of said signal producing members being smaller than the number of said sensing elements; and  circuit means operatively connecting said outputs to said signal producing members for causing a signal at each said output to produce a predetermined input signal at a corresponding signal producing member and for causing a predetermined input signal to be produced at at least one said signal producing member whenever a signal is present at either one of at least two of said outputs. 2. A device as defined in claim 1 wherein said at least two outputs producing a predetermined input signal at said at least one signal producing member are associated with respective element pairs which are physically spaced apart along the defined path such that a signal is produced at only one of said at least two outputs at any time. 3. A device as defined in claim 2 wherein each said sensing element is an annular coil and said position representing member is of a material which varies the effective impedance of each said coil when said member extends to the location associated with that said coil. 4. A device as defined in claim 3 wherein said circuit means comprise a plurality of impedance elements each connected between one said output and one said signal producing member. 5. A device as defined in claim 4 wherein the number of said impedance elements is greater than the number of said signal producing devices. 6. A device as defined in claim 5 wherein each said impedance element is a resistor. 7. A device as defined in claim 1 further comprising at least one reference element corresponding in structure to each said sensing element and disposed at a location removed from the defined path, and wherein said means operatively coupling said elements couple said reference element to a respective one of said sensing elements. 8. A device as claimed in claim 1 in combination with a nuclear reactor having at least one operating element and a movably mounted drive rod supporting said operating element, wherein said movably mounted drive rod and said operating element constitute said displaceable structure. 9. A device as defined in claim 1 wherein said circuit means connect at least a first one of said signal producing members to at least two of said outputs and connect at least a second one of said signal producing members to only one of said outputs.