The detection of hydrogen using catalytic flammable gas sensors

The response to hydrogen (0.1 – 2.0% in air) of flammable gas sensors consisting of pellistors coated with supported palladium has been investigated. An optimum diffusion-limited response of 15 – 30 mV/(% H2), depending on reactor geometry, was obtained with pellistors operated at ≈200 °C under atmospheric pressure. Both ambient and generated water reduced catalytic activity and response, particularly at low temperature. Activity was also greatly reduced by overheating of the pellistor. The influence of these factors on recommended operating procedures is considered.