Abstract: A method for simultaneously measuring one or more properties (e.g. temperature, concentration of NOx and ammonia, etc) in an exhaust gas mixture. Signals from one or more sensors that are cross-sensitive to one or more gases can be combined. A decoupling observer algorithm can be applied, such that these cross-sensitivities are decoupled. The sensors simultaneously obtain an estimate of one or more gases in the diesel exhaust. A decoupling observer algorithm can be structured and arranged to be operable among a plurality of positions corresponding to several internal configurations.

Abstract: A method for simultaneously measuring one or more properties (e.g. temperature, concentration of NOx and ammonia, etc) in an exhaust gas mixture. Signals from one or more sensors that are cross-sensitive to one or more gases can be combined. A decoupling observer algorithm can be applied, such that these cross-sensitivities are decoupled. The sensors simultaneously obtain an estimate of one or more gases in the diesel exhaust. A decoupling observer algorithm can be structured and arranged to be operable among a plurality of positions corresponding to several internal configurations.

Abstract: When a laser beam interacts with a workpiece to be welded by the beam, a plume of optical radiation is generated. An apparatus and method is disclosed in which radiation from the plume is received back through a beam delivery path comprising optical elements (L1,L2) having chromatic aberration. This alters the focus of different spectral bands of the plume radiation and a discriminating aperture is formed by a face of an optical fibre (3). After passing through the fibre, the plume radiation is separated from any laser radiation and the respective powers of the different spectral bands are measured (5). By subtraction, an error signal is obtained which is used to control the focus of the laser beam.