Improved diffuser diagnostic for in-situ flue gas measurement device

A process gas analysis system (100) is provided. The system includes a probe (104) insertable into a source of process gas and having a distal end (108) and a chamber proximate the distal end. A gas sensor (122) is mounted within the chamber and is configured to provide an electrical indication relative to a species of gas. A diffuser (110) is mounted proximate the distal end (108) of the probe (104) and is configured to allow gas diffusion into the chamber. A source of calibration gas is operably coupled to the probe (104) and is configured to supply calibration gas, having a known, concentration of the gas species. Electronics (106) are coupled to the sensor (122) and configured to store a pre-calibration process gas concentration and to measure an amount of time (sensor return time) for the sensor response to return to the pre-calibration process gas concentration. The electronics (106) are configured to compare a measured sensor return time with a known-good sensor return time to provide an indication relative to the diffuser (110).