Abstract: A heat pump system comprising a compressor, two heat exchangers, and an expansion device. The expansion device defines two, spaced apart flow passages. A first piston is located in a first flow passage for metering refrigerant flow therethrough at a first flow rate, and a second piston is located in the second flow passage for metering refrigerant flow therethrough at a second flow rate less than the first flow rate. The expansion device includes a valve having a first position, closing the second flow passage to direct refrigerant through the first flow passage, and a second position, closing the first flow passage to direct refrigerant through the second flow passage.

Abstract: A fluid temperature measuring device, which includes a resistance temperature detector (RTD), is disclosed for measuring the temperature of a fluid flowing through one of several heat exchange conduits which empty into a channel of a heat exchanger of a refrigeration system. The device is simple, inexpensive, reliable, easy to replace, and may be used with a microprocessor control system for the refrigeration system.

Abstract: A feedback control system for a pulsed direct current (DC) arc welding system is disclosed wherein the duty cycle of current pulses supplied by a power supply is controlled in response to resistance sensed at the arc gap of the system. The circuit comprises a voltage sensor, a high-low regulator, and a pulse width signal generator. The voltage sensor senses the voltage drop across the arc gap. This voltage is directly proportional to the resistance at the arc gap. The high-low regulator responds to the sensed voltage to generate an output signal when the voltage drop across the arc gap exceeds a high limit or is below a low limit. This output signal alters the control signal from the pulse width signal generator which controls the arc welding system power supply.

Abstract: A control system for a pulsed DC arc welding system power supply is disclosed. The control system operates to automatically adjust the pulse width of the current pulses supplied at the arc gap by the power supply to control the power flow to the work pieces at the arc gap. An example of such a control system for a conventional pulsed DC arc welding system power supply comprises a variable resistance device connected in parallel with a normally closed time delay switch. This system is electrically connected in an impulsar control circuit of the power supply. The control system automatically changes the resistance within the conventional impulsar control circuit to provide an adjustment within the control circuit to alter the impulsar output signal which controls the pulse width of the current pulses supplied by the power supply.

Abstract: A method and control system for operating a vapor compression refrigeration system to prevent oil pump cavitation during startup of the refrigeration system is disclosed. The control system includes a temperature or pressure sensor located in the evaporator of the refrigeration system, a microprocessor, and an inlet guide vane control mechanism. During startup, the pressure of the gaseous refrigerant or the temperature of the liquid refrigerant in the evaporator of the refrigeration system, or compressor suction line pressure, is measured and an electrical signal corresponding to the measured pressure or temperature is processed by the microprocessor to determine the actual rate of pulldown of refrigerant pressure in the evaporator. The microprocessor compares the actual pulldown rate to a pulldown rate which has been predetermined to prevent compressor oil pump cavitation.

Abstract: A system for protecting a three-phase motor is disclosed. The system includes a signal conditioning circuit which senses the magnitude of current flowing through each motor phase and generates a single-line, three-phase voltage output signal having each of its phases corresponding to a single motor current phase. This three-phase voltage output signal is efficiently utilized by a microcomputer system to detect motor current overload and motor current imbalance. The microcomputer system instructs a motor controller to shut down the motor in response to a motor current overload or motor current imbalance.

Abstract: An electrical resistance element for a variable resistance device, such as a thick film resistance element, and a method of making the element and a device utilizing the element, such as a potentiometer, is described. The resistance element comprises a single resistance material for use as a resistance path for a contact wiper in a variable resistance device and has a selected series of generally transverse cuts made in at least one section of the resistance material of the element. The cut section(s) provides an increased current path length through the element whereby the total resistance of the element is increased. Also, the cut section(s) provides the resistance element with a resistance function which can be adjusted to vary over a wide range of resistance values depending on the length, width, and number of the cuts.