The automated test station allows up to eight toxic gas sensors to be characterized at once. The sensor chamber has been designed to allow test substrates to be quickly loaded and unloaded. A Labview™ interface is used to monitor the response of the sensors, and to control test conditions, including gas concentrations, gas flow rates, relative humidity and test sensor temperature.

Three test gases, CO, CH4 and NH3 are used in varying concentrations and diluted with a fourth cylinder of dry air, to test the sensitivity and selectivity of the sensor. Gas mass flow rates are controlled with Sierra's Side-Trak MFCs, which are powered by the Flo-Box multi-channel electronics — see schematic . The dry air line is split and controlled with two MFCs — one line entering the main gas stream, and the other through a water bath, adding water vapor to that stream.

Water temperature in the bath is controlled using an Omega setpoint controller, coupled with a two-liter heating mantle. Relative humidity is varied during the test by controlling the bubbler temperature and the ratio of dry to humid air. Gas concentrations are also varied during the test to determine the lowest detection limits of the sensor. To prevent backflow contamination check-valves are placed in each line, upstream of the sensor chamber. A side stream of dry air is also used to purge flammable or toxic gases before changing gas cylinders or system components.

The Side-Trak MFCs and the Flo-Box electronics were specified and calibrated as a system to simplify installation and ensure system accuracy. The instruments ease of integration, fast-response and accuracy has helped CeraMem test engineers reduce test cycle length and improve the quality of test data.