Abstract: A combined optical and capacitive absolute positioning encoding system uses a plurality of metallized strips deposited onto a glass scale substrate. A movable transceiver is positioned adjacent to the scale. The transceiver generates interrogating electrical an optical signals which interact with the scale. The movable transceiver also carries with it receiver mechanisms for receiving the signals after interaction with the scale. Signal processing electronics are provided to determine the relative positions of the scale and transceiver by comparing the transmitted, interrogating signals with the received signals. The system is able to determine the relative positions of the scale and transceiver even if power to the system is interrupted, or if the scale and transceiver are moved relative to one another very rapidly.

Abstract: An apparatus and method for monitoring the expansion and contraction of the thoracic cavity during respiration is disclosed. A constant current carrier is passed through the thorax of a patient using a pair of ECG leads. The resulting amplitude modulated voltage signal is synchronously detected using a reference signal which is phase-locked to the amplitude modulated voltage signal. A phase locked loop (PLL) having a tri-state phase comparator and a voltage controlled oscillator (VCO) is used to generate the reference signal. A dead zone compensation circuit is coupled to the VCO to provide a trickle current that causes the tri-state phase comparator to be biased out of its null state.