Abstract: An optical absorption gas sensor for detecting an analyte gas comprises a gas sample receiving chamber, at least one light emitting diode (LED) and a photodiode or other photosensor. A plurality of light pulses are generated by passing pulses of current through the at least one LED. The current through the at least one LED is measured a plurality of times during each pulse and taken into account when generating a compensated output signal. The transfer ratio between LED current and photodiode output signal is calculated a plurality of times during each pulse. An ADC measures the LED and photodiode currents alternately. The LED pulses are generated by inductor discharge flyback and the period of time for which current is supplied to the inductor prior to each pulse is selected so that the photodiode output current is at an optimal region within the input range of the ADC. At least the temperature of the at least one LED is measured and taken into account when generating the compensated output signal.

Abstract: An optical absorption gas sensor has an LED light source and a photodiode light detector, a temperature measuring device for measuring the LED temperature and a temperature measuring device for measuring the photodiode temperature. The sensor is calibrated by measuring the response of photodiode current at zero analyte gas concentration and at a reference analyte gas concentration. From these measurement, calibration data taking into account the effect of photodiode temperature on the sensitivity of the photodiode and, independently, the effect of changes in the spectrum of light output by the LED on the light detected by the photodiode with LED temperature can be obtained. Calibration data is written to memory in the gas sensor and in operation of the gas sensor, the output is compensated for both LED and photodiode temperature. The LED and photodiode can therefore be relatively far apart and operate at significantly different temperatures allowing greater freedom of optical pathway design.

Abstract: An optical absorption gas sensor includes a radiation source, detector and radiation guide which has a rectangular cross section and curves around a side of the cross section. Locating elements locate a support element relative to the radiation guide to align the radiation source and detector with the guide. Radiation from the reference radiation source may be transmitted through a transparent measurement radiation source. Radiation from a reference radiation source may be directed around the measurement reference source. A light emitting diode may generate radiation which is detected by a photodiode and the photodiode may be driven to generate radiation having a different emission spectrum detectable using the light emitting diode, in another operating mode. Two or more abutting L-shaped radiation guide portions may form the radiation guide.

Abstract: An optical absorption gas sensor has an LED light source and a photodiode light detector, a temperature measuring device for measuring the LED temperature and a temperature measuring device for measuring the photodiode temperature. The sensor is calibrated by measuring the response of photodiode current at zero analyte gas concentration and at a reference analyte gas concentration. From these measurement, calibration data taking into account the effect of photodiode temperature on the sensitivity of the photodiode and, independently, the effect of changes in the spectrum of light output by the LED on the light detected by the photodiode with LED temperature can be obtained. Calibration data is written to memory in the gas sensor and in operation of the gas sensor, the output is compensated for both LED and photodiode temperature. The LED and photodiode can therefore be relatively far apart and operate at significantly different temperatures allowing greater freedom of optical pathway design.

Abstract: An optical absorption gas sensor includes a radiation source, detector and a radiation guide. The radiation source and detector are close together and in thermal communication. The radiation guide has a rectangular cross section and curves in a first sense, around an axis parallel to the major dimension of the rectangular cross section, and then in a second opposite sense, and again in the first sense. A relatively long path for radiation is provided in a compact device, without the attenuation of radiation which would occur if the radiation guide did not have a rectangular cross section and curved only around an axis parallel to the major dimension of the rectangular cross section. A reference measurement can be obtained by mounting a reference radiation source behind a translucent measurement radiation source and directing radiation from the reference radiation source through the measurement radiation source.