All sensors have a finite life, indicated by operating/service life, cycling life, continuous rating, intermittent rating, storage life, or expiration date. Several factors may affect a sensor’s life: its type, design, material, frequency and duration of use, concentration levels to be measured, manufacturing process, maintenance efforts, application, storage, and environmental conditions (e.g.,temperature,humidity).
Sensors that consume internal materials during the sensing process (e.g., certain glucose or oxygen sensors) can be used only once or just a few times. Some gas sensors (e.g., Biosystems’ CO and H S sensors), although nonconsumptive, only have a 2–4 year life limit due to the factors such as evaporation (drying out), leakage, and catalyst contamination. Oxygen sensors used in automobile engines that were built prior to 1995 have a lifespan of 50,000 miles, while newer designs (1996 and later) only need to be replaced every 100,000 miles. A sulfur dioxide sensor exposed to 5 ppm 2 (parts per million) concentration continuously may last 10,000 hours or over a year;
If the concentration is lower than 5 ppm, a longer life will result. Most mechanical sensors have a long lifespan under normal operating conditions. For example, FlexiForce’s load sensors have a life of one million load cycles at loads of under 50 lb (cycling life). Many temperature sensors have a service life of over 10 years.
Aging also affects some sensors’ accuracy and cause sensors to slowly lose sensitivity over time. For instance, certain types of temperature sensors decrease their sensitivities by 0.1°C each year. Most chemical and biosensors’ accuracy depends on their ages. In addition, rough handling of a sensor could also shorten its useful life. A sensor that is repeatedly installed and removed will have a shorter life than a sensor that is installed and left in place. The best way to extend sensors’ lives is to store them properly, regularly test and verify their accuracy, and recalibrate them whenever necessary. More advanced sensors today are equipped with sensor life monitoring systems to remind the users when these sensors need to be replaced. Sensors should be replaced when they can no longer be calibrated or zeroed easily.