Qinetiq Limited

Eigd Limited

John Graham Crowder

Timothy Ashley

Stanley D Smith

Volker P Manheim

An infrared light emitting diode arrangement comprising an infrared light emitting diode which emits positive luminescence when forward biased and emits negative luminescence when reverse biased. The diode is driven by an alternating forward and reverse bias input so that the difference in output power between the positive luminescence and the negative luminescence of the light emitting diode is stabilised with respect to temperature. The infrared light emitting diode arrangement has particular application as a source in gas sensors and reduces or eliminates temperature control requirements for infrared light emitting diode sources.

Infrared light emitting diodes

An infrared absorption gas detector uses the amount of IR radiation of a particular wavelength to indicate the presence of a particular component or gas. A monitoring head for such a detector includes a source (8) of IR radiation, dual IR detector elements (17, 18), an optical path which extends between the source and the elements and which includes a gas sample volume, and selectively transmitting spectral filters (20, 21) immediately in front of the detector elements (17, 18) to filter the radiation impinging on them. The optical path also includes a concave mirror (9) to provide a converging beam of radiation concentrated onto both elements of the detector. The location of the gas sample volume, the separation of the two detector elements (17, 18) of the detector, and the mirror are arranged so that IR radiation emitted by the source and impinging upon each of the detector elements follows a substantially common path through the gas sample volume. The monitoring head operates, in effect, as a single beam in both space and time while having no moving parts.

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Edinburgh, United Kingdom

John Graham Crowder