We are often asked why a portable gas monitor sensor fails--especially when the instrument has hardly been used. This issue seems to be a source of endless frustration for those who aren't intimately familiar with gas detection technology.
How Sensors Work
The first thing we need to understand is how gas sensors work. Generally, most sensors used in a portable gas detector are electrochemical sensors. In other words, the sensors are small containers of electrolyte liquid (an electrically conducting solution).
The sensors also contain electrodes that are submersed in the electrolyte solution. The electrodes are a highly conductive precious metal like copper or zinc.
When the sensor is exposed to its targeted hazardous gas, combustible gas, or unsafe oxygen level, a certain electrochemical reaction is produced by the interaction of the electrodes and the electrolytes. The gas monitor translates this into a percent or ppm concentration and displays it on the LCD display.
Why They Fail
Because the electrodes (the metals) are constantly immersed in the electrolyte solution, they are continually dissolving or degrading. This happens whether the instrument is in use or not. While it is true that a sensor will degrade faster with regular exposure to its target gas, it is unavoidable that degradation occurs even when not in use. So sensors fail for the same reason they work - the presence of electrochemical reactions.
There are also times that a sensor will leak its electrolyte solution. This is more common in oxygen sensors, but can happen in the others as well. When this happens the sensor will fail rather quickly. Such a failure can sometimes damage the gas monitor's circuit board too--though this is rare.
Finally, sensors can also fail because they are "poisoned." A sensor can be poisoned when it is exposed to a super high concentration of its target gas. For example, if you expose a combustible sensors to the butane in a butane lighter, you can kill the sensor.
The take away here is that failing sensors do not mean your monitor is cheap. As of yet, there simply is no affordable technology available that can do what electrochemical sensors can do. In fact, great strides have been made in the quality of these sensors over the years. This is why warranty coverage keeps getting longer and longer - a definite win for the consumer.