Solid Metal Oxide Technology for Gas Detectors
Solid state metal oxide sensors are made of a metal oxide (usually tin oxide) that responds to the presence of a gas by varying its resistance; the measuring head measures the change in resistance and converts it to concentration.
The advantages of solid state metal oxide sensors are that they have a very long lifetime, typically 10 years. They can detect a very wide range of gases, even gases that electrochemical types and paper tape machines cannot detect. Because they are fairly inexpensive, they are often used for detection at the "source point" and respond quickly to leaks and allow continuous detection. They have no moving parts to cause mechanical failure.
Whilst solid metal oxide sensors are capable of detecting a wide range of gases with high sensitivity, they have poor selectivity and therefore have a significantly higher chance of 'false alarms' than other technologies. In addition, when they are not exposed to the detected gas for a period of time, solid metal oxide sensors oxidise and go to 'sleep', meaning they do not react to real gas leaks. Furthermore, solid metal oxide sensors provide a non-linear output and are therefore much more difficult and time consuming to calibrate than electrochemical sensors with a linear output.
