Abstract: A method of detecting a counterflow in a pump comprises providing with detecting means for detecting variations in the discharge pressure of the pump and signal analyzing means for analyzing oscillation components contained in an output signal from the pressure detecting means, and detecting the pump's operating point to have entered a counterflow characteristic operation region when a waveform of the detection signal generated in association with the variations in the discharge pressure of the pump exhibits a predetermined spectrum distribution. Further, when it is detected that the operating point enters a counterflow characteristic operation region, the escape from that region is performed by temporally throttling the guide vane and temporally increasing the rotating speed.

Abstract: An air conditioning apparatus using a refrigerating cycle in which a scroll compressor is used to compress a refrigerant. The scroll compressor is driven by an induction motor. The speed of the induction motor is controlled by a PWM type inverter which produces an AC voltage of variable frequency. A carrier frequency higher than 10 KHz is used to effect pulse width modulation of the AC voltage of the inverter, whereby generation of uncomfortable noise is avoided. A control unit is provided to detect slip of the induction motor and to adjust the detached slip to a predetermined optimum value, thereby avoiding excessive lowering of the speed of the motor which may cause lack of lubricating oil for the compressor.

Abstract: A pump unit comprises a pump piston driven by a linear electric motor having induction and reaction members with closely adjacent flat surfaces. A reaction member can be sandwiched between two induction members. Co-operating induction and reaction members extend radially from a rod connected to the piston or to two axially spaced pistons or are grouped tangentially around it. The piston or pistons are driven synchronously and so that constant force is applied by way of a control system which includes a trajectory generator and a controller responsive to selected inputs relating to pump performance characteristics and feedback signals derived from measured current flow and piston position.

Abstract: A DC motor drive system for mechanically linking to a reciprocable pump, having safety circuits for disconnecting power from the system upon detection of excessive line voltage variations, excessive line current variations, excessive pressure demands, and electrical and mechanical faults which may occur in system operation.

Abstract: An infusion device with a disposable administration set which is inexpensive to manufacture. In the preferred embodiment of the present invention the disposable administration set has a plurality of elongated cam followers connected to a plate assembly, wherein the cam followers are displaced in a predetermined sequence and forced against a delivery tube by cam means driven by rotary drive means. The disposable administration set is injection molded as a single integral piece. The disposable administration set includes adjustment spacers disposed between the plate assembly and the cam followers which adjust the distance between them to keep the device accurate. In the preferred embodiment of the present invention the cam means are configured to provide fluid delivery at a consistent and uniform rate.

Abstract: A protection system for a rotatable element (20) which is rotatably supported by hydrodynamic bearings (22, 24) pressurized with a lubricating fluid provided from a pressure source (26 and/or 34) with the fluid being subject to a change in state from liquid to vapor when heat from the bearings during rotation of the rotatable element is absorbed by the pressurized fluid during supporting of the rotatable element in accordance with the invention includes a pressure sensor (302) in fluid communication with fluid flowing from the hydrodynamic bearings for producing a pressure signal representative of pressure of the fluid flowing from the bearings; a temperature sensor (304) in fluid communication with the fluid flowing from the hydrodynamic bearings from producing a temperature signal representative of temperature of the fluid flowing from the bearings; a prime mover (17) for driving the rotatable element with a variable rotational velocity; and a controller (400), responsive to the pressure and temperature sig

Abstract: Pumping apparatus which compresses or decompresses an actuating fluid alternately, which is in turn used to pump an artificial heart. To reduce the size of the apparatus, a diaphragm which contains a non-compressible actuating liquid is driven reciprocatingly by an electric linear motor. To prevent the occurrence of an excessive suction pressure which may be caused by the non-compressibility of the actuating fluid, at the commencement of the suction interval, the current to energize the linear motor is increased gradually and the pressure of the actuating liquid is detected. When the liquid pressure goes out of a selected safety range, the gradual increase ceases. A discharge stroke is detected from an integrated value of the motor current during the discharge interval, and when it reaches a given value, a reversal of the direction of energization of the motor is initiated.

Abstract: This invention concerns a production method and a processing apparatus for semiconductor devices, as well as an evacuating apparatus used for the processing apparatus. According to this invention, since the evacuation system of pressure-reduction processing apparatus for conducting various wafer processings during production steps of semiconductor devices is constituted only with oil-free vacuum pump, deleterious oil contaminations or carbonation products of oils produced from oils upon heating are not present in the pressure-reducing processing chamber as compared with conventional pressure-reducing processing apparatus using a vacuum oil pump as an evacuation pump and the production method of semiconductor devices using such apparatus.

Abstract: A variable speed pump control system and method which senses operational parameters during the first one half of the down stroke to control pump speed to maximize production. The method and equipment maintains ths fluid level of a well as low as possible while avoiding the pump-off condition. A variable speed motor drives a pump jack and a control means varies the pump speed. Means are provided for simultaneously sensing the pump speed, load on the rod, and the position of the rod in the pump stroke. These measurements are utilized to calculate the power transferred between the rod string and the beam during a portion of the downstroke. Before the pump is continuously operated, a series of measurements are made in the full barrel pumping condition to determine the power transferred between the rod and beam at various speeds. These are utilized to establish a relationship between pump speed and power during a portion of the downstroke.

Abstract: The determination as to whether an operational compressor in a multiple-screw compressor water chiller is fully loaded is made by sending a relatively long duration test pulse to the load solenoid of the compressor. If the compressor is fully loaded, no measurable change in the current drawn by the compressor motor will be measured since no slide valve movement will have occurred and no additional load will have been placed on the compressor. If, however, the compressor is not fully loaded at the time the test pulse is sent, the compressor slide valve will move to load the compressor to an extent such that a reliably measurable change in compressor motor current draw occurs.

Abstract: The operation of a variable speed electric driven pump turbine is monitored continuously during pumping to detect the operation point of the pump turbine, and to prevent it from falling into a hump characteristic region, which is recognizable on a graph of total dynamic head versus flow rate. Stalling occurs in the hump characteristic region as a result of a partial reverse flow of the water with respect to the runner. When the operation point of the pump turbine approaches the hump characteristic region, a corrective action is taken that includes increasing the output level of the electric driven pump turbine to increase its rotating speed, temporarily.

Abstract: A method and device are provided for infusing a fluid into a patient via a tubing. A peristaltic pumping apparatus is provided which applies a pumping action to the tubing. A linear variable differential transformer measures the diameter of the tubing subject to the pumping action. The diameter of the tubing is measured at various times and changes in the diameter of the tubing are utilized to adjust the pumping action on the tubing.

Abstract: Differential motor load drops are employed to indicate gas lock or pump off of an electrical submersible pump.

Abstract: A rotary compressor includes first and second compressing devices in a casing to successively carry out a parallel operation wherein first and second compressing devices are parallely driven and a single operation wherein one of first and second compressing devices is driven. A relatively high driving frequency is applied to the rotary compressor during single operation as compared to the driving frequency during parallel operation necessary to produce the same compressing capacity to enhance the EER of the rotary compressor and to extend the variable compressing capacity of the rotary compressor.

Abstract: Here is disclosed an air conditioner comprising a scroll type compressor and a brushless DC motor having a rotor provided with a permanent magnet and a stator provided with a sensor adapted to detect a relative position of said rotor and said stator. Here is additionally disclosed an air conditioner in which the rotor of the brushless DC motor comprises a permanent magnet basically made of rare earth elements inclusive of yttrium, transition metal and boron and a driving circuit for the motor includes a braking circuit adapted to excite coils of the motor to thereby reduce reverse rotation of the rotor.

Abstract: A flat resistance for a blower control unit of an automobile air conditioner, and a blower control unit using the same. The flat resistance includes: a porcelain enameled metallic substrate including a flat head portion, having an edge and one surface, and parallel terminal supporting portions projecting outwardly from the edge of the head; a resistance circuit printed on the one surface of the head portion, the resistance circuit including a plurality of resistances electrically connected in series; a temperature fuse, interposed in the resistance circuit, for being tripped to break the resistance circuit when the porcelain enameled metallic substrate becomes overheated; and terminals, printed on both the head portion and the terminal supporting portions, each terminal being connected to one end of a corresponding one of the resistances.

Abstract: To provide smooth constant flow from a pump, a chromatographic system comprises: a chromatographic column having an inlet; a pump for supplying fluid to the inlet of the chromatographic column; a power means for the pump motor; positive and negative feedback loop means for controlling said power means; means for energizing and de-energizing said positive and negative feedback control means; said negative feedback control means receiving a signal from said means for measuring flow rate and including means for comparing said signal with said corrected flow rate reference signal while said second feedback loop is energized to generate an error signal controlling said power means; and said positive feedback control means applying an acceleration voltage to said motor from a time a preset period after the initiation of a return stroke of said piston until after a timed duration.

Abstract: A control system for an AC motor driven cyclic load, such as a beam pumping unit, includes a flywheel, transducer, tachometer, outside set point source, controller, and variable frequency power supply. The flywheel is rotatably connected between the motor and the cyclic load for receiving and storing rotational kinetic energy from the motor and the load during portions of a cycle of the cyclic load when there is excess energy and returning the stored rotational kinetic energy to drive the cyclic load during portions of a cycle when there is an energy demand by the cyclic load. The transducer generates a transducer signal which is a function of the cycle speed. The tachometer means generates a tachometer signal which is a function of the speed of rotation of the motor's rotor. The outside set point source generates an outside set point signal representative of a desired set point cycle speed of the cyclic load.

Abstract: A powered respirator comprises a motor-driven fan unit drawing air through an upstream filter for delivery to a facepiece. Operation of the fan motor is controlled in response to a differential pressure sensor tapped in across the fan unit so as to reduce the fan throughput in response to an increase in the pressure differential and to increase the fan throughput in response to a decrease in the pressure differential, and thereby match the delivery of air to the breathing demand of the wearer. The diaphragm or other pressure-responsive member of the sensor is isolated from unfiltered air and can therefore provide no leakage path for contaminants to the facepiece. In an alternative embodiment the positions of the fan and filter are reversed so that the fan is upstream of the filter, and similarly controlled in response to the differential pressure across the fan.

Abstract: A refrigerating circuit apparatus comprises a variable capacity compressor for compressing refrigerant, an inverter circuit for supplying a variable output frequency to the compressor, a memory for storing data representing at least two different control modes including a first mode wherein the output frequency of the inverter circuit is changed at one frequency changing rate until the difference between the actual pressure value of refrigerant flowing into the compressor and a set value is minimum and a second mode wherein the output frequency of the inverter circuit is changed at a different frequency changing rate until the difference between the actual pressure value of refrigerant flowing into the compressor and the set value is minimum, a select switch for selecting either first or second mode stored in the memory and a control circuit for varying the output frequency of the inverter circuit based on the selected mode to control the rotation speed of the compressor.

Abstract: A motor-driven fuel pump comprising a pumping unit, a brushless electric motor for driving the pumping unit, a control circuit for controlling power supply to the brushless motor and a pump casing for encasing the pumping unit, the brushless motor and the control circuit. The control circuit comprises a current limiting circuit which inhibits flow to the brushless motor of a current above an amperage which is higher than an amperage of a normal operating current and lower than an amperage of a current which would flow at starting of the brushless motor without the current limiting circuit.

Abstract: A system for detecting an occlusion in a fluid line is disclosed which can detect occlusions in the upstream or container side of a disposable cassette containing a fluid pump therein. The cassette includes a piston-type pump with inlet and outlet valves, and is for installation onto and use with a main pump unit including motors for driving the pump and valves contained in each cassette. The system utilizes control circuitry to monitor the intake stroke of the pump in the cassette, to detect an upstream occlusion in the fluid line leading to the pump, and to provide an alarm in the event of a container-side occlusion.

Abstract: A pump comprising at least a pump body having a chamber (110) communication with an inlet duct (130) and an outlet duct (140) via respective inlet and outlet valves (136, 146), a piston (120) moveable in sealed manner within said chamber, a cyclical actuator (400) of the rotary cam type for co-operating with said piston to cause it to slide, and a motor (500) for driving the cam in an unchanging predetermined direction while injecting volumes greater than the cylinder capacity of the pump, wherein the pump includes control means (404, 220, 600) adapted, on detecting that a required volume has been injected, to determine the position occupied by the rotary cam and to return the piston to the initial position of its delivery stroke prior to injecting a following volume by reversing the direction of rotation of the motor during reinitialization of the piston whenever the rotary cam is positioned on its delivery slope on such detection, and in contrast reinitializing the piston without reversing the direction of

Abstract: A method for minimizing the production of sand in submersible-pump well applications is disclosed, in which control of fluid production rates is used to maintain a low rate of change of formation pressure. Simulation of well drawdown conditions in advance of startup allow the prediction of well performance and the selection of a drawdown profile to be implemented in control systems.

Abstract: A system for controlling the throughput of a metering pump, the pump including a pumping member (8) driven by a transmission member (4) for converting rotary motion of a reversible drive motor (1) into reciprocating motion of the pumping member, the system comprising means for adjusting the amplitude of the reciprocating motion and means for adjusting the period of said motion.

Abstract: In connection with a protective circuit for an electrically driven liquid or water vacuum cleaner it is proposed to utilize the abrupt rise of the vacuum, which is encountered when a blocking element interrupts the connection between the receptacle for the liquid and the motor/blower area. The vacuum rise is detected by a diaphragm-type vacuum governor and used for triggering a lockable flip-flop which then interrupts the current supply of the drive motor. The locked condition can be released only by disconnecting the unit from the mains.

Abstract: To provide smooth constant flow from a pump, a chromatographic system comprises: a chromatographic column having an inlet; a pump for supplying fluid to the inlet of the chromatographic column; a power means for the pump motor; positive and negative feedback loop means for controlling said power means; means for energizing and said positive and negative feedback control means; said negative feedback control means receiving a signal from said means for measuring flow rate and including means for comparing said signal with said corrected flow rate reference signal while said second feedback loop is energized to generate an error signal controlling said power means; and said positive feedback control means applying an acceleration voltage to said motor from a time a preset period after the initiation of a return stroke of said piston until after a timed duration.

Abstract: A variable capacity refrigeration system includes a control scheme having three interrelated closed loops. The system includes a refrigeration system controller and at least one variable speed, electronically commutated DC motor driving a compressor. In the first closed loop, the controller supplies a speed command signal to a motor drive which governs the speed of the motor driven compressor. The speed of the compressor varies the system's capacity to condition the temperature of a comfort zone. A temperature sensor in the zone provides a temperature feedback signal to the controller to complete the first closed loop. In the second closed loop, the speed command signal from the controller is varied in response to a speed feedback signal received from a compressor drive which includes both the motor and the motor drive. The third closed loop is between the motor drive and the motor.

Abstract: Method of setting the output of a circulating pump installed in a hot water heating system and drivable by a variable rpm electromotor, including driving water by the pump from a water heater through a piping system to consumer devices situated in various locations served by the heating system, returning the water to the water heater by way of a return pipe, sensing the flow velocity of the water by a measuring device installed in the piping system, obtaining from the measuring device an electric voltage proportionate to the flow velocity, applying the voltage to a regulator which regulates the electromotor of the pump, generating output voltage values by the regulator, at least in lower voltage ranges, which are, up to 60% of a maximum voltage, higher than those voltage values which correspond to a characteristic curve of the circulating pump, and steplessly varying the rpm of the electromotor as a function of the output voltage of the regulator.

Abstract: In a method and device for the application of foamed or non-foamed flowable substances upon a substrate, where the quantity of the substance to be applied in function of the surface units to be coated is preselected, the flow rate of the material dispenser to the applicator is controlled by a control element and the quality of application is insured by measurements of the application pressure.

Abstract: An electric fan comprises a rotary shaft supported on a mounting base plate. The rotary shaft is extended through a cylindrical stator and on a tip of the rotary shaft, the bottom of a cup-shaped rotor yoke as well as an impeller are secured. The stator is enclosed in the rotor yoke, on whose inner wall an anisotropic rotor magnet magnetized in the reverse polarity alternately in its circumferential direction is secured. The stator and the rotor form a DC brushless motor, whereby the impeller is rotated through the rotation of the rotor and the rotary shaft. In the proximity of the rotor magnet, there is provided a hall integrated circuit (IC), through which a rotating position of the rotor may be detected. On the basis of the rotating position signal from the hall IC, a microcomputer controls the current flowing period in such a manner that the current flowing through the stator coil will partly overlap between each phase.

Abstract: A metering fuel pump adapted for feeding fuel containing vapor or air to an engine that includes a housing assembly. The metering fuel pump further includes a motor section encased inside the housing assembly for providing the required rotary motion to a two-stage pump section. The speed of the motor section is controlled by a motor controller section that provides a voltage regulated flow of fuel. The two-stage pump section imparts pressure to the fuel and encloses a cyclonic vapor separator section.

Abstract: A metal diaphragm impulse pump with no valves is disclosed. The pump may be used in an angular velocity sensor utilizing the Coriolis effect on a fluid jet. A magnetic core is mounted within an anvil and a drive coil is wound around the core. The drive coil may be driven sinusoidally and the diaphragm, which is mounted on the anvil responds with a vibratory motion in like manner. Sensing poles are provided in quadrature with the drive coils and may be used to sense the vibratory motion and thereby control the fluid flow.

Abstract: An apparatus for transferring a small amount of fluid has at least one series of vibration pump units each having a fluid transfer pipe designed to perform a respirating action by the operation of a vibrator which vibrates in response to application of a high-frequency voltage. The fluid transfer pipes are connected in series via fluid diodes which serve to enable the fluid to flow only in one direction, while resisting reversing of the fluid, so that the fluid is transferred in one direction through the successive fluid transfer pipes. In order to minimize the pulsation of the fluid pressure at the downstream end of the apparatus, the vibrators of the pump unit are excited with predetermined phase differentials. Additional fluid diode is connected to the outlet end of the most downstream pump unit.

Abstract: Velocity control of two plungers provided in a pulsationless duplex plunger pump is effected by detecting pressure of a resultant discharge from the two plungers and positions of the plungers, and correcting sequentially a velocity instruction of the each plunger, based on pressure corresponding to the detected position of the each plunger so that the sum of velocities of the two plungers will be constant.

Abstract: A liquid flow system comprising a bidirectional liquid pump, a bidirectional electric motor coupled to drive the pump, and a liquid flow line having the pump connected therein. The system further comprises a motor control circuit connected to power the motor in either the forward or the reverse direction. The control circuit includes a switch for connecting the motor windings to the power lines, the switch being operable to instantly reverse the power connections when the motor is operating in the forward direction and thereby powering the motor-pump to an instant stop and then immediately powering the motor in the reverse direction. The pump thereby instantly reverses the liquid flow in the flow line and abruptly terminates the flow. To quickly start the flow again in the forward direction later on, a priming loop is connected to the pressure side of the pump, so that the pump is able quickly to develop pump pressure.

Abstract: A pump control apparatus including a variable speed pump controllable in response to a pump drive signal, a signal generator generating a commanded flowrate signal indicating desired flowrate of the pump, a flowrate sensor providing a sensed flowrate signal indicating sensed flowrate of the pump, and an integrator connected to the sensor and generator to receive and integrate the commanded flowrate signal and the sensed flowrate signal and to provide the pump drive signal based on the difference in integrated values of the signals so as to achieve desired commanded volume over time.

Abstract: An electromagnetic linear motor having a variable length stroke and providing a substantially large force in both its power stroke and return stroke includes concentric inner and outer magnetic circuits arranged coaxially for movement relative to one another in a rectilinear path with reciprocating motion in response to the interaction of magnetic fields produced by the inner and outer magnetic circuits, respectively. The length of the stroke and the rate of reciprocation are directly proportional to the magnitude of the voltage used to excite primary and secondary coils which generate the respective magnetic fields and the rate at which the polarity of the voltage applied to the secondary coil is changed between negative and positive polarities.

Abstract: An airflow control system generates a compensating output which is combined with the normal damper control output in a damper operating device when a pole change motor driving a blower changes speed so that the damper is changed to compensate for the change in blower speed to avoid a large change in airflow. This overcomes the delay in the normal integrating damper control which produced unwanted fluctuation in airflow when the motor speed was changed.

Abstract: A refrigeration compressor system using a reciprocating compressor with continuously variable capacity. The speed of the compressor can be varied substantially continuously over predefined range of speeds. A controller for the compressor monitors one or more physical parameters indicative of the temperature of the application being refrigerated, such as the temperature itself and/or the pressure in the compressor's refrigerant suction line. Using a predefined algorithm, the controller adjusts the speed of said compressor so as to keep said monitored parameter within a predefined target range. In a preferred embodiment, the compressor is an open direct drive compressor. The compressor's motor has a substantially continuous range of useable operating speeds which varies by a ratio of more than two to one.

Abstract: This invention relates generally to the sensing of phenomena using heat sensitive devices. More particularly, the invention relates to an improved method and system wherein the ratio of the dissipation coefficients of a pair of electrically heated matched temperature sensitive devices is detected, which method and system are insensitive to variation in ambient temperature.

Abstract: A fuel system for an internal combustion engine wherein the fuel pressure is maintained within a desired predetermined range. An electric fuel pump supplies fuel at a pressure proportional to the electric power applied to the pump. Control circuitry compares a voltage signal corresponding to the fuel pressure within a predetermined voltage range corresponding to a predetermined fuel pressure range. When the voltage signal is below the predetermined voltage range, the electric power applied to the electric pump is increased; when the voltage signal is above the predetermined voltage range, the electric power applied to the electric pump is decreased. The control circuit may further increase or decrease the electric power at a predetermined rate.

Abstract: An air compressor pressure adjustment device designed such that any values between two set points are determined and used as first and second standard values. When the air pressure in the reservoir decreases to the first standard value the air compressor is driven at a low speed. When the air pressure increases in the reservoir and reaches an upper limit set point the compressor is turned off. When this air pressure decreases to less than the lower limit set point, the air compressor is started once more.

Abstract: In a pumping-up generator/motor system comprising an induction generator/motor, at least one cyclo-converter connected to the secondary winding of the induction generator motor for controlling the rotational speed of the generator/motor in the motor mode and for maintaining the output frequency thereof in the generator mode at a constant level, the center of the speed range of the generator/motor in the generator mode is set near the synchronous speed thereof and a plurality of converter units constituting each cyclo-converter are connected in parallel in the generator mode, and in series in the motor mode thereby allowing the capacity of the cyclo-converter to be made smaller.

Abstract: An air conditioner having a heat exchange cycle which includes at least a compressor motor that is driven by an inverting apparatus at a variable speed, an indoor heat exchanger and an outdoor heat exchanger is provided.

Abstract: To provide smooth constant flow from a pump a feedback system comprises: a power means for the pump motor; positive and negative feedback loop means for controlling said power means; means for alternately energizing and de-energizing said positive and negative feedback control means; said negative feedback control means receiving a signal from said means for measuring flow rate and including means for comparing said signal with said corrected flow rate reference signal while said second feedback loop is energized to generate an error signal controlling said power means; and said positive feedback control means applying an acceleration voltage to said motor from a time a preset period after the initiation of a return stroke of said piston until after a timed duration.

Abstract: A motor-driven compressor used as a compressor or high-pressure gas generator for a refrigerating cycle, in which the output torque of the electric motor for driving the compressor is controlled so as to make the output torque agree with the load torque required for performing compression in any revolutional angular position of the driving main shaft to thereby reduce revolutional torsional vibrations caused by disagreement between the load torque and the output torque.

Abstract: A control process for a rotary pump which is immersed in a fluid produced by a well involves the use of a rotary pump driven by a variable speed motor and comprises the steps of acting upon the rotational speed of the motor according to a pressure difference which exists between the pressure of the fluid measured in the proximity of the pump and the production pressure of the well. The production pressure P of the well being given by the formula:P=P.sub.G -Q/I.sub.pwherein P.sub.G is equal to the pressure of the unused deposit; that is, the pressure of the fluid deposit when the fluid deposit is at rest and there is no production of the well, Q equals the pump flow rate according to the motor rotation speed and I.sub.p is equal to the well productivity indication.

Abstract: A peristaltic pump controller which provides control of a positive displacement pump as either an uncalibrated or calibrated flowmeter, or a calibrated dispenser. A calibration constant is calculated, after the pump is primed, to determine the amount of volume output produced by an increment of angular rotation of the pump. The constant is determined during a calibration operation where an arbitrary calibration volume is metered. The controller has a low flow and high flow mode where the low flow mode provides a higher resolution for dispensing. The flow mode of operation is determined by the value of the calibration constant and is automatically set when the constant is calculated. During a dispensing operation, the controller will meter fluid to within a predetermined amount of the final volume dependent upon the speed of the pump motor and then dribble in the remaining amount of a batch for precision.

Abstract: A refrigeration compressor system using a reciprocating compressor with continuously variable capacity. The speed of the compressor can be varied substantially continuously over predefined range of speeds. A controller for the compressor monitors one or more physical parameters indicative of the temperature of the application being refrigerated, such as the temperature itself and/or the pressure in the compressor's refrigerant suction line. Using a predefined algorithm, the controller adjusts the speed of said compressor so as to keep said monitored parameter within a predefined target range. In a preferred embodiment, the compressor is an open direct drive compressor. The compressor's motor has a substantially continuous range of useable operating speeds which varies by a ratio of more than two to one.