|The HS-440 hydrogen sensor.|
AppliedSensor’s HSS-440 hydrogen gas detection module is incorporated in the BMW Hydrogen 7, being built by BMW in a limited series and deployed to selected users in the US and other countries. The BMW Hydrogen 7 features a dual-mode drive system fueled either by a 19.5-gallon gasoline tank or a 17.6-pound liquid hydrogen tank. (Earlier post.)
The AppliedSensor HSS-440 module incorporates high-performance sensing based on advancements in Field Effect (FE) technology designed specifically for fuel cell and hydrogen-powered vehicles. The modules are mounted in the car cabin, under the hood and in the trunk area to detect hydrogen gas leaks at levels below the established lower explosion limit of four percent in-air.
The FE sensor technology is based on the field effect generated by gases in metal oxide semiconductor field-effect transistor (MOSFET) devices with catalytic metals. The charging of the gate contact by the gas molecules results in a voltage change in the sensor signal. The choice of operation temperature, gate metal, and structure of the gate metal determine the selectivity of the gas response.
FE sensors respond to gases like hydrogen, ammonia, amines, ethanol, acetone, hydrocarbons, CO, and NO2. The sensitivity of the sensors is normally high for low concentrations of the gases, while it becomes saturated for high concentrations of the gases.
The HSS-440 incorporates a field-effect transistor with a catalytic metal gate stack as the gas-sensing layer. Hydrogen molecules interact with the gate thereby changing characteristics of the transistor. The sensor is fed by a constant current source and gives a voltage output proportional to the logarithm of the hydrogen concentration in the ambient.
The HSS-440 has no cross-sensitivity detection towards HC, H2S, N2, CO, CO2, NOx, or H2O.