Abstract: An apparatus and method for detecting gas concentration using an infrared absorption gas detector. Noise due to vibration is substantially reduced by integrating the voltage produced by the gas detector with an integrator having an adjustable time constant. The time constant is adjusted to a long value during times when the gas concentration is remaining relatively constant. When the gas concentration is changing substantially, the time constant is adjusted to a relatively short value to allow the output of the integrator to better follow the changes.