Abstract: An interferometric fluid sensing system is provided.

Abstract: This disclosure relates to hollow fibre waveguide spectroscopic gas cells built using connectors and the method for making them. The connectors are used to construct gas cell end pieces which allow gas and light to enter the hollow fibre waveguide simultaneously thus creating a gas cell. The connectors comprise a window which intersects or is in close proximity to a junction of bores within the connector, the bores transmitting gas through the connector to or from the hollow fibre waveguide. Connectors may also be used to connect two sections of fibre together in order to produce longer gas cells which enhance the signal-to-noise ratio of spectroscopic measurements. The window, which is at least partially transparent at the wavelength of the light used for spectroscopic purposes, is affixed so as to maintain a gas tight seal for the gas cell.

Abstract: This invention generally relates to a method of controlling emission wavelength of a light emitting device, and a system for wavelength control of a light emitting device, for example for wavelength stabilisation of a laser diode. One method of controlling emission wavelength of a light emitting device comprises: determining an indication of series resistance of the device, the series resistance comprising ohmic resistance of the device; providing a current through the device to maintain light emission of the device; measuring a forward voltage of the device during said light emission, the forward voltage being across an impedance comprising impedance of an active region of the device and the series resistance; determining an indicator of active region voltage on the basis of the measured forward voltage and the determined indicator of series resistance; and controlling a temperature of the device on the basis of the determined indicator of active region voltage.

Abstract: A gas analyzer and a corresponding method is provided to measure the concentration of formaldehyde within enclosed environments such as within buildings comprising an ultraviolet light source, a sample chamber, a detector. The detector measures the intensity of light received by photosensors within a measurement range of wavelengths, and at least one reference range of wavelengths. Advantageously, the concentration of formaldehyde is determined taking into account fluctuations in the intensity of light emitted by the light source, and in the presence of any interferents such as nitrogen dioxide.

Abstract: A gas analyser is provided to measure the concentration of formaldehyde within enclosed environments such as within buildings comprising an ultraviolet light source, a sample chamber, a detector. The detector measures the intensity of light received by photosensors within a measurement range of wavelengths, and at least one reference range of wavelengths. Advantageously, the concentration of formaldehyde is determined taking into account fluctuations in the intensity of light emitted by the light source, and in the presence of any interferents such as nitrogen dioxide. A method of measuring the concentration of formaldehyde in enclosed environments is also presented.

Abstract: An optical absorption gas sensor comprising a body having an internal wall which defines a chamber, at least one aperture in the body through which a gas sample can enter the chamber, a light source, at least one reflector, a detector assembly which extends into the chamber and has a first side and an opposite second side, a detector which measures light which is incident at least a range of angles on at least a part of a first surface of the detector assembly on the first side of the detector assembly, wherein the light source is located within the chamber on the second side of the detector assembly, the whole being configured such that light from the light source passes through the gas sample and is reflected around the detector assembly, by the at least one reflector, onto the detector.

Abstract: An optical absorption gas sensor comprising a body having an internal wall which defines a chamber, at least one aperture in the body through which a gas sample can enter the chamber, a light source, at least one reflector, a detector assembly which extends into the chamber and has a first side and an opposite second side, a detector which measures light which is incident at at least a range of angles on at least a part of a first surface of the detector assembly on the first side of the detector assembly, wherein the light source is located within the chamber on the second side of the detector assembly, the whole being configured such that light from the light source passes through the gas sample and is reflected around the detector assembly, by the at least one reflector, onto the detector.

Abstract: A method for determining the safety of a gas mixture containing first and second flammable components together with non-flammable components, comprises using an optical detector to make at least two measurements influenced by the concentration in the gas mixture of the first and second flammable components. The percentage lower explosion limit of the gas mixture is calculated by a method based on the combination of the measurements. The method leads to acceptably accurate results, despite the presence of other flammable component(s) in the gas mixture.

Abstract: A method and apparatus for determining the safety of a gas mixture containing flammable components such as methane together with ethane or other hydrocarbon, together with a diluent gas. The method includes the filtered infrared spectroscopy of the gas mixture in a gas cell using a filter. The peak transmission wavelength and bandwidth of the filter are so chosen to provide an output, when an infrared light source having a flat wavelength distribution is used, indicative of the % LEL of the gas mixture, within a predetermined tolerance. The filter may be a gas correlation filter containing a mixture of methane and ethane, together with a diluent gas.

Abstract: A method for determining the safety of a gas mixture containing first and second flammable components together with non-flammable components, comprises using an optical detector to make at least two measurements influenced by the concentration in the gas mixture of the first and second flammable components. The percentage lower explosion limit of the gas mixture is calculated by a method based on the combination of the measurements. The method leads to acceptably accurate results, despite the presence of other flammable component(s) in the gas mixture.

Abstract: The method detects the presence of poly-chlorinated biphenyls on a surface, by the use of UV fluorescence spectroscopy in the back-emitting mode. The apparatus comprises a source of UV radiation. Exposure means are provided for conveying UV radiation from the source to the surface. Collecting means collect radiation back-emitted from the surface. A filter filters the collected radiation, and a spectrometer analyses the filtered collected radiation. The filter allows radiation having a wavelength within the range of from 320 nm to 360 nm to pass to the spectrometer.

Abstract: A method and apparatus are described for determining the safety of a gas mixture containing flammable components such as methane together with ethane or other hydrocarbon, together with a diluent gas. The method comprises the filtered infrared spectroscopy of the gas mixture in a gas cell (10) using a filter (16). The peak transmission wavelength (&lgr;max) and bandwidth of the filter (16) are so chosen to provide an output, when an infrared light source (42) having a flat wavelength distribution is used, indicative of the %LEL of the gas mixture, within a predetermined tolerance. The filter may be a gas correlation filter containing a mixture of methane and ethane, together with a diluent gas.