Abstract: A device and method for determining pulses in a modulated signal is disclosed. The modulated signal is processed and converted into a quantized analog type of digital data stream. The data stream is evaluated over time by considering preceeding and subsequent values in the data stream to generate a filtered wave form. By using extreme values in the filtered wave form pulse detection is accurately determined regardless of whether the modulated signal has complicating features, such as dicrotic notch, or high noise levels, or both.

Abstract: The present invention relates to an oximeter for monitoring oxygen saturation of arterial blood. Light of two wavelengths is transmitted through a specimen. Detectors measure the attenuation of light through the specimen to produce two modulating data streams. The data streams are thereafter processed, evaluated, and compared to determine oxygen saturation. A novel method to process, evaluate and compare the two data streams is disclosed.

Abstract: A device for measuring the concentration of a radiation-absorbing agent in a gas mixture features circuitry for automatically calibrating the device according to a reference gas mixture. An error detector compares the transmittivity of the reference gas mixture, as determined by a photometer, to a reference current determined by Beer's Law. The error signal thus generated is provided to a sample and hold circuit which includes a digital counting circuit and a digital-to-analog converter. The output of the sample and hold circuit causes the drive current supplied to the radiation source of the photometer to be adjusted to automatically calibrate the device.