Campbell Scientific Inc.'s (CSI) 109 temperature sensor can be used to measure the temperature of air, soil, and water. This type of temperature sensor has a wide range of applications and can be used in harsh environments. It consists of a thermistor encapsulated in epoxy resin. Its outer layer is wrapped in an aluminum shell, allowing the sensor to be buried in soil or completely submerged in water. Its maximum working depth is 15m (or 21psi).

When used to measure air temperature, the probe is usually placed inside a 41303-5A radiation shield to prevent sunlight from shining on the sensor and ensure the accuracy of the measurement data. This type of sensor can be applied to all models of data collectors produced by CSI. Among them, the CR200 series data collector has a dedicated instruction for the 109 temperature sensor. In addition, the 109 temperature sensor can also be connected to the wireless sensor measurement network through the CWS900 series wireless sensor interface, achieving digital wireless transmission of measurement data.