Gas sensors are used in many different industrial and medical applications. Gas sensors generate a current that is proportional to the percentage of a particular gas sensed in an air sample. This current goes through a load resistor and the resulting voltage drop is measured. The LPV521 is an excellent choice for this application because the device draws only 345nA of current and operates on supply voltages down to 1.6V. Depending on the sensed gas and sensitivity of the sensor, the output current can be in the order of tens of microamperes to a few milliamperes. Gas sensor data sheets often specify a recommended load resistor value or suggest a range of load resistors from which to choose.

Oxygen sensors are used when air quality or oxygen delivered to a patient needs to be monitored. Fresh air contains 20.9% oxygen. Air samples containing less than 18% oxygen are considered dangerous. This application detects oxygen in air. Oxygen sensors are also used in industrial applications where the environment must lack oxygen. An example is when food is vacuum packed. There are two main categories: oxygen sensors that sense oxygen when oxygen is abundantly present (for example, in air or near an oxygen tank), and oxygen sensors that detect traces of oxygen in ppm.