Abstract: Error-free, reliable registration of a fault in a power distribution circuit is achieved by a faulted circuit indicator that measures the current in the circuit after a discrete time delay following the detection of an overcurrent condition. A fault is registered only if the measured current is less than a prescribed level, evidencing that the overcurrent has operated a protection device (such as a fuse), upstream from the faulted circuit indicator, to interrupt the circuit and clear the fault. Hence, only actual (true) faults, resulting in circuit interruption and isolation of the fault, will be indicated, thereby precluding false registrations that may otherwise occur from non-faults such as transient currents, momentary overloads, inrush currents, and the like.

Abstract: The transmission of torsional vibrations from a rotating driving shaft, at the output of an internal combustion engine, to a driven shaft, at the input of a manual transmission, are reduced or eliminated by employing a normally-engaged, oil-cooled wet clutch to interconnect the two shafts, the clutch being controlled to introduce a desired amount of slippage. Slipping the wet clutch to a relatively small extent allows the necessary torque to be transmitted, but any torque fluctuations in the driving shaft will be effectively absorbed and prevented from causing torsional vibrations in the drivetrain.

Abstract: A parameter, such as the current flowing through a conductor, is measured by initially passing an energizing magnetic flux through a hall element to produce a hall voltage proportional to the sensed parameter. To eliminate temperature, aging and non-linear effects normally associated with a hall element, the amplitude of the hall voltage is effectively ignored and only its polarity is detected and employed to control the operation of an integrator to develop a cancelling current to establish an equal, but opposite direction, cancelling flux in the hall element. With a zero net flux, the integrator will hold the cancelling current at the level required to balance out and cancel the initial energizing flux. Since the cancelling current needed to null the energizing flux will be proportional to that flux, the current may be used to produce a control voltage to represent the measured parameter.

Abstract: A horizontally moving vehicle body may b stabilized and held at a constant vertical level, as its wheels move up and down in response to disturbing forces, by utilizing the kinetic energy of the rotating wheels to create counter forces on the vehicle body in the direction opposite to the disturbing forces to counterbalance the disturbances. As a disturbing force moves a wheel downward (assume the wheel falls into a hole in the road), a vertical force is imparted toward (against) the vehicle body to effectively push the wheel downward and away from the body, the body thereby remaining at its normal level and not following the wheel. On the other hand, when a wheel moves upward (assume it rides over a bump in the road), the kinetic energy of the wheel is converted to a vertical force in the direction away from the vehicle body to lift the wheel upward and force it toward the body, as a result of which the body remains undisturbed at its normal level and will not follow the upward movement of the wheel.

Abstract: By simultaneously charging a pair of capacitors from the same low voltage level to the same high reference voltage level, the two charge time durations will be functions of and will be proportional to the capacitances of the two capacitors. A comparison of those charge time durations will thus provide an indication of the ratio of the capacitances of the two capacitors. This is achieved by including, in the measuring system, an oscillating circuit whose frequency is determined by the capacitance of one of the capacitors. A periodically-recurring rectangular wave is then developed having pulse components with pulse widths determined by the capacitance of the other capacitor, the frequency of the rectangular wave being equal to the oscillating frequency. The duty cycle of the rectangular wave is therefore proportional to and respresents the ratio of the capacitances of te capacitors.

Abstract: By simultaneously charging a pair of capacitors to the same d-c voltage and then simultaneously discharging those capacitors to the same d-c reference voltage, the two discharge time durations will be functions of and will be proportional to the capacitances of the two capacitors. A comparison of those discharge time durations will thus provide an indication of the ratio of the capacitances of the two capacitors. This is achieved by including, in the measuring system, an oscillating circuit whose frequency is determined by the capacitance of one of the capacitors. A periodically-recurring rectangular wave is then developed having pulse components with pulse widths determined by the capacitance of the other capacitor, the frequency of the rectangular wave being equal to the oscillating frequency. The duty cycle of the rectangular wave is therefore proportional to and represents the ratio of the capacitances of the capacitors.

Abstract: When a d-c bus voltage is produced by rectifying applied a-c power line voltage in a rectifier bridge (such as a phase-controlled SCR rectifier bridge), controlled by a feedback loop which compares a feedback signal representing the d-c bus voltage with a command signal representing a desired set point level and from the comparison automatically maintains the bus voltage at the set point level, unwanted a-c line voltage interruptions may have a deleterious effect on the rectifier bridge itself and on a load driven by the bus voltage. This occurs because during a power interruption (when the bus voltage drops) the command signal causes the feedback loop to impose a control on the rectifier bridge which attempts to increase the d-c bus voltage back to the magnitude represented by the command signal. When power is subsequently restored, the d-c bus voltage will suddenly increase very sharply and may destroy electrical and/or mechanical components in the system.

Abstract: A self-optimizing, capacity control system for a refrigeration system including a compressor, a condenser, and an evaporator, all connected in a closed refrigeration circuit is provided. The compressor includes a plurality of adjustable inlet guide vanes, a motor connected to regulate the inlet guide vanes position and an electrical speed motor connected to drive the compressor. The self-optimizing capacity control system includes a microprocessor responsive to continual measurements of a PRV signal, a compressor head signal, a motor current signal and a motor speed signal for determining both the compressor speed and the position of the inlet guide vanes to define a current operating point in an initial surge surface array stored in a random-access memory. The microprocessor will initiate a "learning" mode in which the compressor motor speed will continually be decreased incrementally and the PRV will be moved to a more open position until an operating point is found where the compressor is surging.

Abstract: By sensing the outdoor ambient temperature and the outdoor coil temperature in a heat pump when the outdoor coil is frost-free, a control system determines the split or difference that will later exist between those temperatures (the coil temperature drops as frost accumulates) when sufficient frost has built up on the outdoor coil to necessitate defrosting. When that defrost temperature split, called the Normal Defrost Value or NDV, is exceeded, defrost is initiated and the coil will be defrosted. Since the amount of frost that may have already accumulated on the coil is unknown when the control system is initially powered up (such as when power is restored after an outage), the control system calculates, from the current outdoor ambient temperature, an assumed value for the coil temperature which is likely to exist if the coil were frost-free. The first NDV determined after power up is based on the assumed coil temperature.

Abstract: To conserve energy in a large capacity refrigeration or air conditioning system, where liquid (usually water) is chilled by the system's evaporator and is then used to cool a building, the temperature setpoint of the chilled liquid leaving the evaporator may be reset upward from its desired level. Normally, if the temperature of the leaving chilled liquid falls below the setpoint by a fixed differential (such as 4.degree. F.) to a cut-out temperature, the system's compressor is shut down as a safety precaution to prevent freeze-ups. A nuisance compressor shutdown may be avoided when the setpoint is reset to a higher level (since the actual temperature of the leaving chilled liquid at that time may be at or below the desired setpoint and may be more than 4.degree. below the reset setpoint) by lowering the cut-out temperature to a fixed level substantially below the desired setpoint, such as down to 36.degree. F.

Abstract: A surge detection apparatus for use in a refrigeration system having a centrifugal compressor driven by an electric motor includes a first pressure transducer for sensing a condenser pressure and a second pressure transducer for sensing an evaporator pressure. A first bandpass digital filter responsive to the condenser pressure and the evaporator pressure is provided for generating a first signal representative of the rate of change of the pressure developed across the compressor. A current transformer is used to sense a current in the electric motor driving the compressor. A second bandpass digital filter responsive to the motor current is provided for generating a second signal representative of the rate of change of the RMS current being drawn by the compressor drive motor. A third signal representative of a differential pressure threshold and a fourth signal representative of a first motor current threshold and a second motor current threshold are provided.

Abstract: Surge protection is provided for a d-c power supply, wherein rectified a-c line voltage is filtered in an LC filter having a shunt-connected filter capacitor, by inserting a limiting resistor in series with the filter capacitor during power-up to reduce the inrush current and the voltage overshoot to acceptable values. Once the power-up period is over and d-c power is fed to a load, the limiting resistor is bypassed.

Abstract: When a series string of similar circuit components, such as capacitors, are connected across a source of d-c voltage and those circuit components do not divide the applied voltage equally because of having different leakage resistances, and consequently different leakage currents, the voltage imbalance may become so great that the maximum allowable voltage or voltage rating of at least one of the circuit components may be exceeded, resulting in damage to or the destruction of that component. To limit the voltage imbalance, thereby to protect the circuit components, each of those components is shunted by a separate voltage limiting device, such as a zener diode. The threshold or breakdown voltage of each limiting device is less than the maximum acceptable voltage of the device's companion circuit component so the voltage across that component will be limited to and will never be greater than that maximum acceptable level regardless of the differences that exist in the leakage resistances.

Abstract: Highly reliable and consistent starting is achieved by first initializing the rotor position, namely establishing the rotor in a known starting position. This is accomplished by gating on two pairs of SCRs in sequence and supplying current pulses through the gated SCRs to the stator of the motor to rotate the rotor to a first position and then to a second position, the rotor coming to a complete stop in each of those positions. The rotor aligns itself with the magnetic field created by the stator in each position and any ambiguity in the rotor position is eliminated. Thereafter, the inverter is operated asynchronously in a second mode with predetermined pairs of the inverter SCRs being sequentially gated into conduction at an increasing frequency to current pulse energize the motor to effect step-by-step rotation of the rotor at a faster and faster rate, the motor current being reduced to zero at the termination of each energizing pulse to force commutate the conducting pair of SCRs.

Abstract: The current outdoor ambient temperature and outdoor coil temperature in a heat pump are sensed when the heat pump's outdoor coil is clean and frost-free, and from those current temperatures the split or difference that will later exist between the temperatures, when sufficient frost has built up on the outdoor coil to necessitate defrosting, may be determined. When that defrost temperature split, called the Defrost Value or DV, is reached, defrost is initiated and the frost that has accumulated on the coil is melted. Before defrost occurs, however, changing weather conditions (namely, changing outdoor temperature and/or changing outdoor relative humidity) may effectively invalidate the previously determined defrost temperature split or DV, and a frost condition may be reached at a substantially different temperature split, either greater or smaller than that previously calculated.

Abstract: The condition of a rechargeable battery, which is employed as a backup d-c power supply for a load in the event of an emergency and is normally charged by a d-c charging voltage through a series-connected protective fuse, is monitored by momentarily reducing the charging voltage and effectively sensing or measuring the voltage across the series-connected fuse and battery during the momentary reduction, while not affecting the load. If the battery is connected and is functioning properly and if the fuse is connected and is continuous, the sensed voltage will exceed a predetermined desired threshold level, and this normal condition may be visually and/or audibly indicated. On the other hand, if the battery is disconnected, or if the battery voltage is abnormally low, or if the fuse is absent or is open, then the sensed voltage will fall below the desired threshold level, signifying a trouble condition. When such a condition is detected, a trouble indicator provides an appropriate visual and/or audible signal.

Abstract: A variable speed fan drive, operated in response to the sensed coolant temperature in an internal combustion engine for a vehicle, blows a controlled amount of air through the engine's radiator to maintain the coolant temperature in a desired narrow operating range. The air pulled in by the fan also cools the refrigerant flowing through the condenser of the vehicle's air conditioning system, the condenser being positioned in front of the coolant radiator. If insufficient condenser cooling occurs, even though the coolant may be adequately cooled, the refrigerant temperature rises and causes the compressor discharge pressure in the air conditioning system to increase. That pressure is monitored or sensed and if it exceeds a predetermined maximum allowable level the normal operation of the control system is overriden and the fan is driven at its maximum speed to maximize the air blown through the condenser and radiator, thereby decreasing the refrigerant temperature and thus the discharge pressure.

Abstract: The power dissipated, in a trigger circuit for gating on a semiconductor switch, is minimized by employing a constant current source to provide the gate trigger current. This assures adequate triggering regardless of supply voltage variations or switch intrinsic control voltage requirements. Power is saved by supplying only the current required to drive the semiconductor switch on, thereby preventing overdrive. With constant d-c gate current, the precise amount of power needed to turn on and close the switch is provided while wasting relatively little energy due to gate intrinsic voltage variations of the switch or to input line voltage variations.

Abstract: An improved torque measurement circuit and method for an internal combustion engine of the four cylinder, two-cycle type includes synchronous detection circuits and circuits to account for inertia forces due to the mass of the pistons and connecting rods. The synchronous detection circuits multiply a signal directly proportional to torque variations with sine wave and cosine wave signals to produce a synchronous detection signal. A summing circuit is provided to combine the synchronous detection signal with a signal proportional to the square of the angular velocity of the crankshaft of the engine to produce a resultant output signal directly proportional to average torque and independent of speed.

Abstract: When additional heat exchangers, such as oil coolers and turbocharged air coolers, are mounted in front of or within the normal coolant heat exchanger or radiator of an internal combustion engine, a variable speed fan drive may be employed to blow air through all of the heat exchangers to cool the various fluids flowing through those heat exchangers. Since the different fluids usually have different desired operating temperature ranges for optimum engine performance, controlling the variable speed fan drive only in response to the temperature of the engine coolant can result in overheating of at least one of the other fluids. This is avoided by temperature sensing the different fluids and effectively determining which one of them has the highest relative temperature in its operating range. The fan drive is then controlled in response to the sensed temperature of that particular fluid. In this way, all of the fluids will be maintained within their desired operating temperature ranges.