Air temperature and humidity sensors provide a wealth of information in the form of analog output signals that are proportional to air temperature and relative humidity. These devices are commonly used along with electronic data collection systems as well as for providing input for industrial control systems.
In most cases, air temperature sensors are comprised of several devices that are specifically designed for measuring the surrounding or ambient atmospheric temperature. Among the most common types of air temperature sensors include resistive temperature devices, or RTDs, thermocouples, thermometers, infrared sensors, and silicon diodes.
Thermocouples operate when two different types of metals come into contact with one another and then contract and expand based on different rates of temperature. While they are commonly used as thermostats, they may also be utilized as air temperature sensors. This is because thermocouples have the ability to make measurements across vast temperature ranges. It is not uncommon for thermocouple air temperature and humidity sensors to be used in high-temperature environments.
Resistive temperature devices are used for measuring the decrease or increase that occurs in electrical resistance of matter as temperatures rise. This type of device is typically more accurate when used across small temperature chances. It should be noted that RTDs are not able to measure temperatures a low or as high as thermocouples are able to measure. RTDs do offer the benefit of being more stable and durable than thermocouples. Due to the fact that RTD devices are not typically affected by electrical noise, they are commonly used in industrial environments.
Other types of air temperature sensors include infrared temperature sensors. These are indirect measurement devices that do not require physical contact with the material that is to be measured. This is because they measure the thermal radiation that is produced. While infrared temperature sensors work well in environments in which temperatures can become quite hot, silicon diode sensors typically work better at the opposite extreme and are used for measuring extreme cold.
In choosing air temperature and humidity sensors, it is important to select sensors that are durable, accurate, and can provide repeatable results.