Abstract: Apparatus for measuring the concentration of a gas present in a sample chamber by ambient pressure diffusion employs a nondispersive infrared gas analysis technique. The sample chamber has the form of a tube that is closed at one end, with a source of radiation and a detector mounted side by side at the other end. The inwardly-facing surfaces of the tube are specularly reflective, whereby the optical length of the sample chamber is twice its physical length. A gas filter cell located in the optical path permits the concentration of an analyte gas to be measured accurately despite the presence in the sample chamber of an interfering gas. A small ultrasonic vibrator affixed to the wall of the sample chamber prevents unwanted particles from accumulating on the semipermeable membranes through which ambient gases diffuse into and out of the sample chamber.

Abstract: The sensitivity of a nondispersive infrared gas analyzer increases with increasing pathlength, which increases the absorption of the infrared radiation by the gas whose concentration is to be determined. The present invention includes the addition of an obstructing element that further increases the average pathlength. In one embodiment the obstructing element consists of a highly reflective elongated cylinder located with its axis collinear with the axis of the tubular chamber. In another embodiment, the sample chamber includes a converging section, the smaller end of which is joined to an elongated tubular section of uniform cross section. The improvements are applicable to both pumped and diffusion-type sample chambers.

Abstract: The sensitivity of a nondispersive infrared gas analyzer increases with increasing pathlength, which increases the absorption of the infrared radiation by the gas whose concentration is to be determined. The present invention includes the addition of an obstructing element that further increases the average pathlength. In one embodiment the obstructing element consists of a highly reflective elongated cylinder located with its axis collinear with the axis of the tubular chamber. In another embodiment, the sample chamber includes a converging section, the smaller end of which is joined to an elongated tubular section of uniform cross section. The improvements are applicable to both pumped and diffusion-type sample chambers.

Abstract: A gas sample chamber that is particularly advantageous for use with a semiconductor laser has the form of an elongated hollow tube with a specularly reflective inside surface, a semiconductor laser located at one end of the tube and a detector located at the opposite end of the tube. In one embodiment, apertures in the wall of the tube permit a gas to enter and leave the sample chamber by free diffusion. In another embodiment the gas flows into the hollow tube from a pressurized source through a port or is drawn through the tube by a suction pump. In other embodiments, the tube is partitioned into two successive sections by means of a window located within the tube. The window is transparent to radiation of two different wavelengths that coincide with the absorption bands of two different gases. The semiconductor laser is tuned to these wavelengths successively so that two gas components can be detected and measured simultaneously.

Abstract: The fire detector includes a carbon dioxide sensor and a microcomputer. When the rate of increase of the concentration of carbon dioxide at the sensor exceeds a threshold, an alarm is produced. The threshold is set at one of three possible levels by the microcomputer in response to the state of the atmosphere at the sensor as determined by the microcomputer based on several variables that are derived from the sensed concentration of carbon dioxide. The derived variables include the average concentration of carbon dioxide, the average rate of change of carbon dioxide concentration, the monotonicity of the increase or decrease of the carbon dioxide concentration and the range of concentrations sensed in each cycle of operation. The threshold setting is determined every ten seconds. In this way, the setting of the rate threshold is responsive to variations in the carbon dioxide level at the sensor that are caused by entities other than a fire, such as the presence or absence of people in a closed room.

Abstract: An instrument for determining the concentration of a particular gas that might be present in a sample has no moving parts and is extremely compact and inexpensive. A novel waveguiding structure serves both as an optical element and as the sample chamber. As an optical element, the waveguiding structure collects radiation from a blackbody source located at the entrance end of the waveguiding structure and conducts the radiation through the waveguiding structure, concentrating it on two infrared detectors mounted at the opposite end of the waveguiding structure. As a sample chamber, the waveguiding structure causes the radiation to undergo multiple reflections that result in the average path length being substantially greater than the physical length of the waveguiding structure. Each of the detectors has its own optical filter, and baffling assures that each detector responds only to radiation which has passed through its filter.

Abstract: The improved sample chamber includes an elongated hollow tube closed at one end and having specularly-reflective inwardly facing surfaces. A source of radiation and a detector of radiation are mounted side by side in the open end of the hollow tube, both facing the closed end. A plurality of filtering apertures are formed in the tube, and each aperture is covered by a sheet of a semipermeable membrane that serves to prevent airborne particles larger than a predetermined size from entering the chamber while not interfering with the free diffusion of the gas to be measured into and out of the chamber. The use of an elongated hollow tube that is closed at one end results in no loss in the efficiency with which the radiation is conducted from the source to the detector while decreasing the external length of the chamber by 50 percent.

Abstract: The proper operation of an NDIR toxic gas sensor can be checked by using a non-toxic gas that has an absorption band that overlaps the absorption band used for measuring the toxic gas. The NDIR sensor cannot distinguish which of the two gases is responsible for causing the observed absorption of radiation in the sensor. Since detectors of toxic gases typically operate at low concentration levels, the extent of overlap between the absorption band of the toxic gas and of the non-toxic gas may be relatively small, since a larger concentration of the non-toxic gas can be used with no ill effects. The method may be applied to sensors for detecting carbon monoxide or methane for example.

Abstract: A gas sample chamber for use in a gas analyzer consists of an elongated hollow tube having an inwardly-facing specularly-reflective surface that permits the tube to function also as a light pipe for conducting radiation from a source to a detector through the sample gas. A number of apertures in the wall of the elongated hollow tube permit the sample gas to enter and exit. Particles of smoke and dust of a size greater than 0.1 micron are kept out of the chamber by use of a semi-permeable membrane that spans the apertures in the hollow tube. Condensation of the sample gas components is prevented by heating the sample chamber electrically to a temperature above the dew point of the component of concern. In one embodiment, at least one detector are spaced around the periphery of the elongated hollow tube adjacent one end of it. In another embodiment, at least one detector are spaced along the length of the elongated hollow tube.

Abstract: An affordable ventilation controller comprises a low cost and very stable carbon dioxide sensor and a remote-controlled louvered suction fan equipped with an air filter. The ventilation controller operates independently of any existing heating or cooling system that might be present in a closed room. The carbon dioxide sensor measures accurately the gas concentration level in parts-per-million (ppm's) as a ventilation index. When a predetermined ventilation index is exceeded indicative of bad ventilation, a remote-controlled suction fan equipped with a louver and an air filter is activated to draw in fresh air from the outside in order to regulate the CO.sub.2 concentration and provide good ventilation. However, if an exceedingly high concentration of CO.sub.2 is sensed, the controller inhibits the control signal to the suction fan, since such a high level might indicate the presence of a fire.

Abstract: A diffusion-type gas sample chamber for use in a gas analyzer consists of an elongated hollow tube having an inwardly-facing specularly-reflective surface that permits the tube to function also as a light pipe for transmitting radiation from a source to a detector through the sample gas. A number of filtering apertures in the wall of the otherwise non-porous hollow tube permit the sample gas to enter and exit freely under ambient pressure. Particles of smoke and dust of a size greater than 0.1 micron are kept out of the chamber by use of a semi-permeable membrane that spans the apertures in the hollow tube. Condensation of the sample gas components is prevented by heating the sample chamber electrically to a temperature above the dew point of the component of concern.