Photoacoustic sensor with baseline and span correction

摘要

A photoacoustic detector wherein a detector response transfer function can be measured at various times under predetermined conditions during the life of the detector. One or more of the time related transfer functions each can, when acquired, be compared to the stored initial transfer function established at initial manufacture and calibration of the detector. Span and baseline correction values can be determined. These values can be used to compensate detected output values during normal operation. Time related transfer functions can be compared to each other as well as to the stored initial transfer function.

主权项

1. A photoacostic detector comprising:
a sensing chamber; control circuits coupled to the sensing chamber, the control circuits include a pre-stored representation of a detector transfer function indicative of detector performance wherein the detector transfer function is measured by varying a source of radiant energy injected into the sensing chamber between multiple intensity values while sensing and measuring a photoacoustic output wherein the pre-stored representation of the detector transfer function is compared to a current transfer function, and, which includes circuitry to determine at least one compensation value; circuitry to combine at least one compensation value with at least one current indicator of gas concentration; at least one acoustic transducer carried adjacent to the chamber where the control circuits are coupled to the transducer, where the control circuits receive a first electrical signal from the transducer and including processing circuits, which, over a predetermined time interval, process the first electrical signal from the transducer to increase the signal-to-noise ratio thereof; a second acoustic transducer carried adjacent to the chamber and where the processing circuits process a second electrical signal, from the second acoustic transducer and confirmation circuitry to determine that first and second ambient-noise corrected signals, obtained from the first and second electrical signals, exhibit a constant amplitude ratio and a fixed phase relationship, and which responsive thereto, generates an indicium indicative thereof.