Abstract: The angular deflection or tilt angle from vertical is determined by an inclinometer wherein a weight is offset and hung from a rotatable shaft to which a needle pointer is affixed. When the inclinometer is oriented such that the shaft is vertically aligned, the gravitational force on the weight is in a direction parallel to the shaft's axis and no torque results. When so oriented, a magnetic spring system holds the shaft in a reference position and the needle points to the center of a graduated scale, thereby indicating a zero tilt angle. If the inclinometer, and consequently the shaft, are tilted in a tilt plane, defined by the shaft and the center of the scale, the weight exerts a torque on the shaft and causes pivoting of the needle away from the center of the scale to indicate the direction of tilt and the magnitude of the tilt angle.

Abstract: By providing a circular, dished agricultural disc with peripheral V-shaped notches and intervening ovate-shaped openings, the disc may be operated at relatively high speeds while still achieving vigorous cutting, stirring and mixing of the soil. At the same time, excessive throwing of soil is avoided, thereby preventing soil accumulation into high ridges with wide furrows inbetween.

Abstract: By providing a circular, dished agricultural disc with peripheral W-shaped notches, a small tooth being formed at the center of each notch, the disc may be operated at relatively high speeds while still achieving vigorous cutting, stirring and mixing of the soil. At the same time, excessive throwing of soil is avoided, thereby preventing soil accumulation into high ridges with wide intervening furrows.

Abstract: Thermostat control of separate heating and cooling apparatus is achieved with a system that requires only a two-conductor connection between the thermostat and the apparatus. A pair of oppositely-poled diodes is employed at each end of one of the conductors of the connection so that when the control system is established, by a selector switch, in the heating mode the half cycles of one polarity of an AC voltage effect the operation of the heating apparatus, whereas when the system is switched to the cooling mode the opposite polarity half cycles cause operation of the cooling apparatus. The invention is especially advantageous when a central air-conditioning system is added to a building where only a two-wire cable connects the thermostat to the existing heating system. Rewiring of the thermostat cable is unnecessary.

Abstract: The phases of a three-phase AC power supply are applied to a three-phase load, such as a motor, by respective ones of three triacs. Three alternating voltages, phase-displaced by 120.degree., appear across the triacs. When each alternating voltage is in its half cycles of one polarity, for example when the main terminal T.sub.2 is negative relative to the main terminal T.sub.1 of the triac to which the voltage is applied, the triac conducts continuously. During the half cycles of the opposite polarity, however, the conduction angle or time of each triac is varied in response to a control effect. In this way, the magnitude of the phase voltages applied to the load are varied to control the operation of the load, such as to vary the speed of the motor. No neutral point exists for the load currents so a triac, during the negative excursion of its main terminal T.sub.2, cannot conduct unless the terminals T.sub.2 of the other two triacs are in a positive excursion and have been triggered into conduction.

Abstract: Constant condenser pressure is maintained in a refrigeration system by modulating the speed of at least one fan motor of an air-cooled condenser coil in response to the temperature of the refrigerant in the condenser coil, the speed varying directly with temperature. Motor speed variations are achieved by controlling the conduction time of a triac which couples the fan motor to a source of alternating voltage. The triac is triggered into conduction at a phase angle, following the beginning of each half cycle of the alternating voltage, determined by the charging rate of a timing capacitor which charges through a photosensitive transistor optically coupled to an LED. Variation of the refrigerant temperature in the condenser coil changes the light emission of the LED and this in turn varies the charging current translated to the capacitor. The greater the temperature, the greater the charging current and the faster the triac conducts following the start of each half cycle.

Abstract: The load currents, supplied by a three-phase AC power source to a three-phase load, are established and maintained at a preset desired level by sensing those currents and producing a feedback voltage which is compared with a reference potential. Anytime the load currents differ from the desired level the comparison produces a difference or error signal which causes an adjustment of the amplitudes of the three load currents such that they automatically return to the desired level, thereby regulating the current flow to the load. At start-up, the feedback arrangement is also effective in preventing instant current build-up to avoid sudden power surges. When the load is a three-phase motor, limiting the current flow facilitates a soft start with the motor gradually accelerating to full operating speed. Two overload protection circuits shut the system down in response to different overload or overcurrent conditions.

Abstract: The phase sequence of a three-phase AC power supply is detected and information representing that sequence is stored in a memory device, such as a flip-flop. Since the power supply, once it is energized, may require a few seconds to stabilize (such as may be the case when the power source is a diesel generator), the information fed to the memory device is likely to change during the stabilizing period. At the end of that period, however, the stored information represents the true phase sequence of the AC power supply, and at that time the information is read out and used to actuate switching apparatus to interconnect the three-phase AC power supply to the three terminals of a phase-sensitive load (such as a three-phase AC motor) in the manner necessary to provide the load with a desired phase rotation sequence.

Abstract: Complete protection of a three-phase submersible pump motor, such as the type used downhole in an oil well, is obtained with a solid state digital logic control system that monitors each of the three phase currents and shuts the pump motor down if any of those phase currents indicates either an underload or overload condition. Time delays are introduced before shutdown to avoid undesired nuisance shutdowns otherwise caused by transient or momentary conditions. When the pump motor is de-energized in response to an underload condition, it is automatically restarted after a predetermined time delay. All of the delay functions are precisely determined by division of the power line frequency. Downhole pressure and temperature are also sensed and if they become excessive the motor is automatically de-energized to prevent overheating. The presence of an auxiliary physical condition, such as filling up a retaining tank, also causes the pump motor to be turned off.

Abstract: Overload protection of a three-phase submersible pump motor, such as the type used downhole in an oil well, is obtained with a solid state digital logic control system that monitors each of the three phase currents and shuts the pump motor down if any of those phase currents indicates an overload condition. A time delay is introduced before shutdown to avoid undesired nuisance shutdowns otherwise caused by transient or momentary conditions. The shutdown time delay is variable and is inversely proportional to the amount of overload in order that greater overloads result in faster shutdowns.

Abstract: The ground and neutral terminals of a three-wire grounded AC power source for electrical apparatus, such as the control system of a motor operated hospital bed, are both normally connected to earth ground. The integrity or continuity of the ground connection is constantly monitored by applying, between the neutral and ground terminals, sharp narrow pulses periodically recurring at a relatively low pulse repetition frequency. When the resistance in the neutral/ground circuit is less than a predetermined threshold level, the pulsing causes an LED photo coupler to flash and this in turn produces a control signal for maintaining the electrical apparatus coupled to the AC power source. When the resistance between the neutral and ground terminals exceeds the threshold level, the AC power supplied to the apparatus is interrupted.

Abstract: By actuating a momentary contact switch, an energizing circuit applies an AC voltage directly to one of the two field windings of a two-phase reversible AC induction motor to drive that motor in one of its two directions. As the motor begins to rotate, the shifted phase voltage appearing at the other field winding has a relatively high magnitude and this is employed to energize a neon photo coupler which then completes a holding or latching circuit for maintaining the motor energized so that it continues to rotate. If the motor stalls or if its rotation is purposely stopped, which may be caused by a limit-of-travel switch actuated by apparatus driven by the motor, the magnitude of the shifted phase voltage decreases and the neon photo coupler de-energizes, thereby disabling the holding circuit. By actuating another momentary contact switch, motor rotation in the opposite direction occurs and another holding circuit effects continued motor rotation until the motor stalls or is purposely stopped.

Abstract: The phase sequence of the phase currents supplied by a three-phase AC power supply to a phase-sensitive load (such as a three-phase AC motor) is monitored by developing three phase-displaced, rectangular shaped logic signals, respectively representing the three phase currents, and applying these logic signals to respective ones of the J, C and K inputs of a J-K flip-flop. When the load is correctly connected to the power supply, the phase relationship of the three logic signals will be appropriate to trigger the flip-flop to its set operating state. Any other sequence actuates the flip-flop to its reset state which, in turn, disconnects the load from the power supply.

Abstract: A rotating annular piston is hydraulically actuated to engage a rotating friction device, such as a clutch or brake, by introducing fluid pressure to an apply chamber for the piston. Disengagement is subsequently effected by exhausting fluid from the chamber, after which a centrifugal pressure head release valve in a wall of the chamber releases any residual entrapped fluid from the chamber in order to prevent undesired false actuation of the rotating piston that may otherwise occur due to centrifugal force acting on the residual fluid. The valve comprises a metallic ball subject to centrifugal force tending to move it radially outward from the piston axis but held in a tapered or conical seat of an exhaust port, thereby blocking the port, by fluid pressure supplied to the apply chamber. In the absence of that fluid pressure, however, the centrifugal force exerted on the ball unseats it and opens the port.

Abstract: Cross-contamination of the patients using the same bathtub in a health-care institution is precluded by lining the tub, before it is filled with water, with a disposable sheet of biologically-clean, flexible plastic film, thereby establishing a physical barrier to prevent any contact (and consequently a transmission path for bacteria) between the bathtub and patient and between the tub and water. Openings are made along the liner's edges in order to hang the liner onto a series of hooks affixed to the three walls surrounding the tub, the hooks being appropriately shaped so that they can be used by the installer to pierce or puncture the liner to make the openings. The liner is merely draped over the front of the tub. Installation is expedited and made easier by providing a series of markers, such as printed rings, along the edges of the liner to designate the areas that should be pierced to achieve proper positioning and centering of the liner within the bathtub.

Abstract: A series of air-cooled, vertical condensing tubes extend upwardly from a horizontal header to which refrigerant vapor is supplied. The vapor flows upwardly from the header through the condensing tubes and forms, on the tubes' internal surfaces, condensate which then flows downwardly into the header and eventually through the header's outlet. With this arrangement, the customary top header is not needed.