Functional principle of Metal-oxide(MOX) gas sensor elements
The functionality of a MOX gas sensor is based on the conductivity-change of the gas-sensitive MOX semi-conductor layer/s at gas exposure, which can be externally measured and analysed.
A specific MOX gas-sensitive layer reacts to oxidizing gases with increasing of the layer resistance and to reducing gases with decreasing of the layer resistance.
Depending on the type of gas/es and the sensor type a specific MOX gas sensor reacts in a concentration range from a few ppb up to the %-range.
By use of various MOX semi-conductor materials for the gas-sensitive layers different gases and gas mixtures can be detected. The sensitivities of MOX gas sensors can be improved by use of specific catalysts in these layers.
Sensor types differ according to
- sensor design (dimensions, case etc.),
- sensitivities to specific gases,
- cross sensitivities,
- response time.
The gas-sensitive layer(s) of the MOX gas sensor are heated by an integrated Platinum heater. The resistance of the integrated Platinum heater has a defined temperature coefficient, thereby the control of the operating temperature of the sensor is possible. This makes a targeted influencing of the sensitivity of the MOX gas sensor to specific gases and a compensation of ambient temperature variations possible.
Calculation of the Platinum heater resistance at 0°C
(RH0… resistance Platinum heater [Ω] at 0°C, Rt… resistance Platinum heater [Ω] at ambient temperature t [°C], t… ambient temperature [°C], constants / coefficients: A = 3,9083·10-3 °C-1, B = -5,775·10-7 °C-2)
Calculation of the operating/heater temperature (Platinum heater)
(tH… temperature Platinum heater [°C], RH0… resistance Platinum heater [Ω] at 0°C, UH… voltage at Platinum heater [V], IH… current at Platinum heater at UH [A], constants / coefficients: A = 3,9083·10-3 °C-1, B = -5,775·10-7 °C-2)