Abstract: A system for controlling a track propelled excavator that has an allowable 360 degree swing arc including: (a), a positioning controller for all five (propel, swing, boom, arm,and bucket) motions: (b), positioning of small members that represent the large deck, boom, arm, and bracket by a flow of fluid in series with each large member's actuator--eliminating a need for transmitting each digging member's angular position back to the controller; (c), a handle with tooth type edge that represents the large bucket, for scraping along templates for guiding desired earth contours; (d), guide plates and positioning switches for acheiving accurate and safe placement of the bucket during swing and digging motions; (e), a mobile armrest that allows ease of operator's small scale motions when guiding large scale digging: (f), and, an assembly for pulling the small bucket/handle through a series of desired small scale positions to achieve automatic trench digging.

Abstract: A teaching aid computer, requiring no electrical or spring power, designed for elementary and middle school students, that when properly set and manipulated, provides real number solutions to equations involving multiple degree, as well as single degree unknowns. Parallel, interconnecting balancing beams are marked so as to provide adjustable positions for weights, whose resultant torques represent equation constants and coefficients of each degree of the unknown quantity. Further, by positioning and clamping movable axes beams, students can see and feel the results of adding or subtracting a few, or a series of numbers. Also, sliding beams, as well as sliding weights captively located in channels of each beam, with no required extra loose weights, allow simple decimal settings and answers to equations involving multiplication, and division.

Abstract: A protective relay for providing an infinitely variable family of curves for use in ground-fault protection. In one embodiment, the protective relay includes a saturable reactor across the output terminals thereof. The saturable reactor impedance varies in accord with the load or fault current such that a trip characteristic based on the zero sequence current and the load or fault current is obtained. The trip characteristic is selected by a potentiometer that limits the amount of dc current to the saturable reactor. Once established by setting the potentiometer, the trip characteristic defines the amount of 3I.sub.O neutral current, as a function of three-phase current, necessary to operate the protective relay. Varying the potentiometer setting provides the infinite family of curves.

Abstract: Protective relay apparatus which performs a segregated phase current comparison of a three-phase protected line section, with a single relay at each end thereof for making the phase current comparison. The single relay includes a rectifier arrangement which provides a signal responsive to the largest phase current of a predetermined polarity, at any instant. In response to a fault detection, it successively phase compares the signals from its rectifier with the signals of the corresponding phases from the rectifier in the relay at the other line end.