Abstract: A method of testing live AC circuits for neutral-ground, neutral-isolated ground, and isolated ground-ground faults, involves measuring impedances of circuit portions, including hot-neutral, neutral-ground, neutral-ground and isolated ground loops. In general either a test current generating a driving voltage is used, or in the case of hot-neutral, a load current generating a load voltage, and the voltage without current are use to measure voltage drop. These voltages are proportionate to the impedances of the circuits, which are expressed as ratios indicating the presence of faults. The method is reliable, despite much variation in circuit characteristics, including oversized neutral, shared neutral same phase, shared neutral opposed phase, supply line impedance, and high impedance grounds, it is easily able to detect faults across conductors and shared neutral loads.

Abstract: A method of testing live AC circuits for neutral-ground, neutral-isolated ground, and isolated ground-ground faults, involves measuring impedances of circuit portions, including hot-neutral, neutral-ground, neutral-ground and isolated ground loops. In general either a test current generating a driving voltage is used, or in the case of hot-neutral, a load current generating a load voltage, and the voltage without current are use to measure voltage drop. These voltages are proportionate to the impedances of the circuits, which are expressed as ratios indicating the presence of faults. The method is reliable, despite much variation in circuit characteristics, including oversized neutral, shared neutral same phase, shared neutral opposed phase, supply line impedance, and high impedance grounds, it is easily able to detect faults across conductors and shared neutral loads.

Abstract: A continuous mechanical ventilator system includes a ventilator known in the art, with a pneumatic circuit connectable to the patient and operating in the normal manner. A bag and bag valve are interposed within the pneumatic connection such that when the value is closed, the patient is on full assisted breathing from the ventilator. When the bag valve is opened, gas from the ventilator passes into the bag from which it may be drawn freely by the patient in an unassisted manner. Electronic controls provide means for varying the proportion of breaths to be assisted by the ventilator to the breaths from the bag which, of course, are unassisted. The exhalation valve normally provided, is normally operatively connected to the ventilator in the usual way, when the device is in the assisted mode. However, during the unassisted mode, the exhalation valve is isolated from the rest of the circuit so that no pressure pulses be fed to the exhalation valve during this time.