Abstract: A method and apparatus for generating an adjustable concentration of a selected gas within a carrier gas flow including a gas generator which is responsive to a drive signal. A gas analyzer detects the selected gas concentration within the carrier gas flow from the gas generator and provides a signal proportional to the measured concentration to a comparator. A gas concentration selector provides a second signal to the comparator, the signal being proportional to a desired concentration of the selected gas. In response to these signals, the comparator adjusts the drive signal to correct the gas generator output for the difference between the signals and to thereby substantially adjust the concentration of the selected gas within the carrier gas flow to the desired concentration. The method and apparatus automatically corrects for drift or other inaccuracies associated with the generation of the selected gas.

Abstract: A device for measuring the concentration of a radiation-absorbing agent in a gas mixture features circuitry for automatically calibrating the device according to a reference gas mixture. An error detector compares the transmittivity of the reference gas mixture, as determined by a photometer, to a reference current determined by Beer's Law. The error signal thus generated is provided to a sample and hold circuit which includes a digital counting circuit and a digital-to-analog converter. The output of the sample and hold circuit causes the drive current supplied to the radiation source of the photometer to be adjusted to automatically calibrate the device.