Abstract: A magnetic wind oxygen sensing device provides a local magnetic field defined by magnetic pole pieces, and employs a plurality of thermal elements in a bridge in the local magnetic field to measure oxygen concentration in a surrounding gas mixture, creating a magnetic wind and determining the thermal effects induced in sensing elements as a result of the wind. A pair of sensing elements are positioned such that one lies upstream and one downstream of each wind generator, and both are substantially in thermal equilibrium with adjacent gas so they are unaffected by changes in thermal capacity of background gas components. When oxygen is present, the two sensing elements are passively cooled below, and heated above the temperature set by a local heater, respectively. In the absence of oxygen, the sensors reside at the same temperature, so they are self zero-ing, and this zero point does not shift when background gases with differing thermal characteristics are present.

Abstract: A zirconium oxide shell forms a chamber of fixed volume, and a controller monitors voltage across the shell indicative of difference between inside and outside oxygen levels, applying a signal to pump oxygen. Pumping is effected to empty the chamber, to develop an internal reference, for example by comparison to ambient air, for calibration, and thereafter to substantially continuously null the difference, i.e., to track the oxygen level of a sample environment. Integrated pump current yields a measure of the oxygen added to or removed from the chamber. A suitable material for forming the sensor is a mixture of about 91% zirconium oxide and 9% yttrium oxide, which is formed to shape as a paste or slurry and sintered at about 1400° C., and then platinum coated, for example by a CVD process, to form porous electrodes on each surface. The controller may apply a sequence of current pulses, and check the Nernst cell output indicative of &Dgr;P across the wall, until &Dgr;P=0.

Abstract: Apparatus for measuring the combustion characteristics of a gaseous fuel. Wobbe index and calorific value are measured with a fast response time by maintaining a stoichiometric mixture in a mixer supplied with the gaseous fuel at a constant pressure together with ambient air. The pressure of ambient air is controlled by measuring the residual oxygen from combustion of the mix and employing variations in that measured value to control the ambient air supplied to the mixer. The control signal for the ambient air is proportional to the Wobbe index. A separate measurement of the oxygen in the stoichiometric mix provides a signal proportional to the calorific fuel value.

Abstract: A zero compensation circuit particularly is used in an oxygen sensing apparatus and method employing a sensing cell including two pairs thermistors and a source of an inhomogenous magnetic field. One thermistor of each pair is electrically heated and is positioned inside the magnetic field, and the second thermistor of each pair is positioned adjacent to the respective first thermistor of each pair, substantially outside the magnetic field. When oxygen is present in the sensing cell, the thermistors inside the magnetic field generate a gas flow in the direction of the adjacent thermistors of each pair positioned outside the magnetic field, thus tending to reduce the temperature of the thermistors inside the field and increase the temperature of the thermistors outside the field.

Abstract: Apparatus for measuring concentration of a paramagnetic gas in a gas mixture includes first and second magnet pole pieces positioned adjacent each other with a selected gap therebetween, for generating an inhomogeneous magnetic field. The pole pieces have a selected sectional shape, and a gap-facing surface with a selected configuration, that provide an elongated region of maximum magnetic field intensity in the gap. Electrically heated magnetic wind generating thermistors are positioned in the gap. Electrically heated magnetic wind sensing thermistors are positioned adjacent to the magnetic wind generating thermistors, proximate to the elongated region of maximum magnetic field intensity, such that a heated region associated with the wind generating and wind sensing thermistors is substantially encompassed by the elongated region of maximum magnetic field intensity.

Abstract: Oxygen sensing apparatus and methods utilize a sensing cell including two pairs of electrically heated thermistors and a source of an inhomogeneous magnetic field. One thermistor of each pair is positioned inside the magnetic field, and the second thermistor of each pair is positioned adjacent to the respective first thermistor of each pair, substantially outside the magnetic field. When oxygen is present in the sensing cell, the thermistors inside the magnetic field generate a gas flow in the direction of the adjacent thermistors of each pair positioned outside the magnetic field, thus tending to reduce the temperature of the thermistors inside the field and increase the temperature of the thermistors outside the field. The thermistors are connected in a measuring bridge circuit including elements for maintaining the temperature of the thermistors at a substantially constant level, thereby providing a signal that can be used to compensate for changes in the thermal characteristics of the background gases.

Abstract: A selective infra-red detector is used to determine the amount of a selected gas present in a gas sample. A beam of infra-red energy is passed through a gas sample and into the selective infra-red detector. An outer annular portion of the beam is reflected from a paraboloidal mirror onto a first focal point, while an inner annular portion of the beam passes through a chamber containing a fluid which will absorb the spectral wavelengths of the selected gas and is reflected by a spherical mirror onto a second focal point. Separate infra-red energy detectors are positioned near the first and second focal points to measure the infra-red energy. The difference or ratio between the infra-red energy measured by each infra-red energy detector is a measure of the amount of selected gas present in the gas sample.