9.1 Ammonia Sensor

If the sensor stops working correctly, the current implementation may not detect it. If the sensor fails short, the system should detect the fault as a very high level of ammonia, but if the sensor fails as high impedance (High-Z), the system will not currently detect this fault. It may be possible to detect a High-Z fault by looking for abnormally high ratios of sensor resistance at runtime or if the measured voltage at the output is very low. In the case of a short-circuit failure, the failure will be detected as a very high ammonia level, which should trigger the alarm.

Another fault that could occur is a failure of the heating system. If the sensor is not heated, the gas response is not known. Monitor the current flow through the heater and/or the package temperature to verify the sensor is heated.

Finally, the environmental conditions around the sensor should be monitored. The data from the manufacturer shows considerable changes in response depending on humidity and temperature. These changes should be monitored and corrected for in the application.