Abstract: A safety helmet having a rigid outer shell, a shock absorbing layer inside of the outer shell, and a shield layer fabricated from a strong and lightweight material positioned between the outer shell and the shock absorbing layer. The shield layer is preferably free to move relative to the outer shell in a direction toward the shock absorbing layer.

Abstract: A capacity control system for a refrigeration system including a compressor, a condensor, 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 capacity control system includes a microprocessor responsive to continual measurements of a PRV signal, a compressor head signal and a suction flow signal for calculating a current operating point. The microprocessor determines whether the operating point is sufficiently away from a surge surface. The microprocessor will cause the operating point to move to a new operating point of a lower compressor speed and a more open PRV position if the operating point is sufficiently away from surge.

Abstract: A control system for a rotary helical screw compressor of the variable speed type includes a variable speed motor driving the compressor for varying the compressor capacity and a slide valve member which is adjusted optimally for varying the volume of gas trapped in the working chamber prior to discharge as a function of the pressure ratio across the compressor. There is also provided a control system for a rotary helical screw compressor of the fixed speed type which include a first slide valve member for varying the compressor capacity through modulating the volume of gas trapped in the working chamber prior to compression and a second slide valve member for adjusting optimally the volume of gas trapped in the working chamber prior to discharge as a function of the pressure ratio across the compressor.

Abstract: An inverter-motor combination is regulated in accordance with this invention to minimize deterioration of the power factor as the inverter is reduced from 100% load. This is accomplished by sensing the motor current and providing a control signal to regulate the inverter output frequency in accordance with a first function, representing virtually linear decrease in frequency as the load is reduced from 100% to substantially 70% of full load. A constant voltage stage is connected to regulate the d-c bus controller to provide a modified control signal for regulating the d-c bus level according to a second function, maintaining the d-c bus voltage at virtually 100% while the load is reduced to 70%. Thus the d-c bridge is not phased back and the power factor of the complete system is not degraded over this described operating range.

Abstract: The control system disclosed herein regulates a centrifugal compressor which has inlet guide vanes adjustable to vary the compressor capacity. A variable speed motor is connected to drive the compressor, and variation of this motor speed provides another input for regulating the compressor capacity. A control system achieves optimum energy efficiency, while avoiding surge, by the manner in which the motor speed and the inlet guide vane positions are regulated. To do this, a control signal must be derived to indicate the compressor head value. This signal is achieved by providing two signals, one related to the absolute condenser pressure, and the second related to the absolute evaporator pressure. The control system operates on these two signals to provide a third signal which is a function of a ratio, in which the numerator is the difference between the condenser and evaporator pressures, and the denominator is the evaporator pressure. Alternative measurement and processing techniques are described.

Abstract: An evaporator inlet water temperature control system for controlling the inlet water temperature of an evaporator utilized in an inverter driven centrifugal chiller. The system creates the proper chilled water set point at the evaporator outlet needed to maintain the inlet water at its set point for greater efficiency of operation. Control is accomplished by generating an electrical error signal which is a function of an inlet water set point voltage and the actual inlet water temperature. A logic signal is produced as a function of the error signal detected by the circuit and establishes a dead zone band representing a range in which the error signal is acceptable. Output of the control system is passed to the capacity control circuit of an inverter driven centrifugal compressor chiller.

Abstract: A cooling system having an electric drive motor utilizes a portion of the sub-cooled liquid which would otherwise be passed from the condenser through an expansion device to the evaporator to cool the motor. The rotor cooling passage which extends longitudinally through the outer portion of the rotor has its outermost surface (that is, the surface farthest removed from the center of the motor) shaped in an arc having the same center as the center of the rotor. This ensures even distribution of the cooling liquid under the high centrifugal forces developed during motor operation. The stator has a passage from its outside surface inwardly to the longitudinal cooling portion of the stator. The inwardly extending passage includes an orifice, sufficiently large to prevent contamination problems but of an appropriate size to ensure good throttling and thus provide good heat transfer. The cross-sectional areas of the cooling passages are sized to minimize the velocity of the generated vapor.

Abstract: The control system of the invention regulates a centrifugal compressor having inlet guide vanes adjustable as one means for varying the compressor capacity. A variable speed motor is connected to drive the compressor, and provides another means for regulating the compressor capacity. The control system regulates the motor speed alone over one portion of the load variation curve, and regulates the motor speed jointly with the inlet guide vane opening over another portion of the load variation curve, to achieve the most energy-efficient operating condition while avoiding the surge condition. This optimum control path is realized by utilizing a signal which is a measure of the compressor head value. Compressor surge or instability is avoided by deriving a critical Mach number (speed indication) for any given operating condition, as a function of the compressor head and vane position, and preventing the motor speed from going below that Mach number under the specific operating conditions.