Abstract: An arrangement for ensuring the stability of the set point for a gas analyzer is disclosed. The set point control circuit utilizes an amplifier which is alternately switched between a reference voltage and a sensor signal to provide a signal to a processor representing the reference signal and the sensor signal. The processor compares the two signals and adjusts the heater associated with the sensor to provide a stable set point for the gas analyzer. The arrangement eliminates the need for precision resistors within the set point control circuit and therefore significantly reduces the cost of the circuitry.

Abstract: A non-dispersive infrared gas analyzer is disclosed that accurately measures the concentration levels of a plurality of gases within a gas mixture. The analyzer includes first and second sample cells and is utilized advantageously for the measurement of NO.sub.x and hydrocarbon gas present in the exhaust of an automobile engine. The gas mixture of the exhaust is chilled before entering the first sample cell to remove a substantial amount of the water vapor from that sample cell to facilitate measurement of the NO.sub.x gas. The second sample cell receives the gas mixtue in an unchilled state to allow for accurate measurement of the hydrocarbon gas. The analyzer includes processors which are utilized to further correct the NO.sub.x measurement and which also interact with each other to provide an output data stream that is representative of the concentration levels of the gases that are being analyzed.

Abstract: This invention relates generally to the sensing of phenomena using heat sensitive devices. More particularly, the invention relates to an improved method and system wherein the ratio of the dissipation coefficients of a pair of electrically heated matched temperature sensitive devices is detected, which method and system are insensitive to variation in ambient temperature.

Abstract: Automatic zeroing apparatus zeroes an infrared gas analyzer automatically upon the occurrence of preselected conditions to indicate zero in the absence of absorption of infrared radiation by a gas mixture being analyzed. The gas analyzer has a sample cell for containing a gas mixture to be analyzed. Infrared radiation directed through the sample cell is detected at a preselected wavelength to produce a detection signal. A signal processor outputs a signal systematically related to the difference between the detection signal and a reference signal. For zeroing the sample cell is filled with gas substantially nonabsorbent of infrared radiation at the respective characteristic wavelength. A comparator produces an error signal when the output signal differs from zero. A gain control automatically controls the signal level of the detection signal to reduce the output signal substantially to zero with the nonabsorbent gas filling the sample cell.

Abstract: An adaptor assembly is described for sampling gas in an airway tube attached to a patient. The adaptor assembly employs a filter arrangement in a subassembly which extends transversely of the axis of the patient's airway and maximizes the ratio of the effective filter area to the dead volume added by the adaptor assembly to the sampling system.

Abstract: Pulse modulated infrared energy is directed through a sample cell containing a gas mixture. The gas mixture may include a selected one of a plurality of gases. Each gas exhibits a characteristic absorption in the infrared wavelengths. A detector responsive to infrared energy at a preselected wavelength develops an AC signal having an amplitude proportional to the infrared energy passing through the sample cell at the preselected wavelength and having a frequency corresponding to the preselected pulse modulation frequency. The preselected wavelength is common to the absorption characteristic of each of said gases. The AC signal is processed to develop a DC signal having an amplitude determined from the AC signal. The DC signal is applied to an amplifier having a variable gain feedback which provides a plurality of gain steps. Each gain step is associated with a different one of the gases a single surrogate gas may be used to calibrate each gain step.

Abstract: An infrared gas analyzer is described wherein infrared energy is directed through a sample cell from a source at one end thereof. A detector at the opposite end of the sample tube monitors infrared energy of at least one pre-selected wavelength in order to produce a signal representative of the infrared energy passing through the sample cell. The analyzer is of modular construction including a disposable sample cell, an infrared source housing, a detector housing and printed circuit boards mounting signal processing components for the analyzer. A mounting base is adapted for receiving the sample tube, housings and printed circuit boards in operating alignment and interconnection with each other, detents positively securing the components in place.

Abstract: A method and apparatus are described for determining the partial pressure of carbon dioxide in the arterial blood of a patient. The method and apparatus are particularly useful where the patient is under anesthesia. Carbon dioxide concentration is measured at the end tidal of the patient's exhaled breath. Nitrous oxide concentration is also measured so that the measured values of the carbon dioxide concentration may be corrected in accordance with the measured value of the nitrous oxide concentration. Particular wavelengths of detection are described, together with other apparatus parameters to provide a high level of accuracy.

Abstract: An infrared gas analyzer is described wherein infrared energy is directed from a suitable source through a sample cell, the infrared energy being interrupted at a predetermined frequency. Infrared energy of a preselected wavelength causes a detector for each monitored gas to produce a signal proportional to the infrared energy passing through the sample cell and having a frequency corresponding to the predetermined frequency. Each preselected wavelength corresponds to the characteristic absorption wavelength of a preselected gas. A signal processor for the analyzer includes a preamplifier adapted to compensate for temperature variations in the detector while an output amplifier is adapted to compensate for temperature variations in the sample cell in order to provide a more accurate output signal.

Abstract: A non-dispersive infrared gas analyzer is described. Infrared energy is directed through a sample cell, and is interrupted at a predetermined frequency. The infrared energy at at least one preselected wavelength is detected to produce an AC signal having an amplitude proportional to the infrared energy passing through said sample cell and having a frequency corresponding to the predetermined frequency. The preselected wavelength corresponds to the characteristic absorption wavelength of a preselected gas. This AC signal is processed to produce a DC signal having an amplitude proportional to the concentration of the preselected gas in the mixture being analyzed. The signal processor includes an output amplifier, a voltage biasing network including a summing junction connected to the input of the amplifier, and a first variable control manually adjustable to bring the current at the summing junction to zero in the presence of a non-absorbing gas in the sample cell.