Abstract: A portable electronic unit, such as a defibrillator, includes an autotest system for automatically self-testing various electrical components within the unit during quiescent periods. The autotest system includes an autotest routine that performs an extensive array of rigorous yet time-consuming tests that are impractical to perform during normal modes of operation of the unit. A real-time clock can be set to initiate the autotest routine at a time when the unit is unlikely to be used for its normal mode of operation. The autotest system provides a strip chart printout of the results of the various self-tests performed on the unit, and provides messages on a visual display of any error conditions. If the autotest system detects a needs service malfunction, the operator must acknowledge the error with an input to the unit before the unit will enter into its normal mode of operation.

Abstract: The bias point of an electro-optic modulator, such as an Mach-Zender modulator, is automatically controlled. A pilot signal, preferably two pilot tones at different frequencies, is applied to the modulator. The output of the modulator then contains various components resulting from the pilot signal. An error signal is generated, preferably coherently, based on one of these components, termed the pilot component, which preferably is located at the difference frequency of the two pilot tones. A bias signal which controls the bias point of the modulator is adjusted based on the error signal. The coherent generation of the error signal facilitates feedback loops based on phase and/or amplitude control and also supports locking the electro-optic modulator to a bias point with a preselected slope (either negatively or positively sloping).

Abstract: A battery selecting and charging system forms part of a portable electronic device, preferably a portable medical device. When the device is powered up, a selecting circuit selects one of two rechargeable batteries to power the device until it is depleted, and then automatically switches to the other battery. When the second battery is depleted, both batteries are selected to power the device. When the device is powered down, a battery charging circuit, having both a high and low charge section, provides a high charge to the battery having the greatest terminal voltage. Thereafter, the high charge is applied to the other battery, the low charge is applied to the first battery, and then the low charge is applied to the second battery. The battery charging circuit monitors the terminal voltage to prevent any damage to the batteries or the device.

Abstract: A portable electronic unit, such as a defibrillator, includes an autotest system for automatically self-testing various electrical components within the unit during quiescent periods. The autotest system includes an autotest routine that performs an extensive array of rigorous yet time-consuming tests that are impractical to perform during normal modes of operation of the unit. A real-time clock can be set to initiate the autotest routine at a time when the unit is unlikely to be used for its normal mode of operation. The autotest system provides a strip chart printout of the results of the various self-tests performed on the unit, and provides messages on a visual display of any error conditions. If the autotest system detects a needs service malfunction, the operator must acknowledge the error with an input to the unit before the unit will enter into its normal mode of operation.

Abstract: Respiratory therapy apparatus is provided with setting elements such as knobs for inputting set values for various parameters. A digital display is provided for showing measured values of operational variables. The set point for each parameter is displayed on the display apparatus along with the measured values only when the knob or setting element for the particular parameter is engaged by the operator's hand.

Abstract: An ultrasonic flowmeter which measures gas velocity including a pair of ultrasonic transducers oppositely located around a conduit at a predetermined angle to the flow direction. Each transducer alternates between acting as a transmitter and a detector of ultrasonic frequencies, thus as one transducer transmits, the other receives. A measurement is made of the time of flight of the ultrasonic signal between the transmitter transducer and the receiver transducer and a microcomputer calculates the velocity of the gas by a known mathematical relationship utilizing the difference between the time of flight of the ultrasonic signals traveling upstream and those traveling downstream. The time of flight is determined by the phase shift or difference in phase angle between the signal at the transmitter transducer and the signal detected by the receiver transducer. To prevent ambiguity arising when the phase angle difference exceeds 360.degree.