Passivated thick film catalytic type H2 sensor operating at low temperature

Thick film catalytic sensors operable at a temperature of 120 °C have been developed to measure hydrogen concentration (HC) in 0–10% (v/v) range. The sensors consists of a glass encapsulated Pt-heater coated with a catalytic thick film and a compensating element without the active film. An rf sputtered PTFE thin film on active element has been found to improve resistance of the sensors to poisoning due to hexamethyldisilazane (HMDS) and iodine etc. During operation, temperature of compensating element is held constant at 120 °C to offset the effect of ambient temperature variations. A simple circuit for control of sensor temperature and measurement of its response is described. The sensors showed linear response up to 10% (v/v) of hydrogen in ∼40 standard cm3/min air flow with response and recovery times of ∼30 and 50 s, respectively. The sensors were found to have a stable response when operated continuously for a period of 1 year.