A data logger, is an electronic instrument that records measurements at set intervals over a period of time. Depending on the particular data logger, measurements can include: air temperature, relative humidity, AC/DC current and voltage, differential pressure, time-of-use (lights, motors, etc.), light intensity, water temperature, water level, dissolved oxygen, soil moisture, rainfall, wind speed and direction, leaf wetness, pulse signals, room occupancy, plug load, and many more.
Data loggers are typically compact, battery-powered devices equipped with an internal microprocessor, data storage, and one or more sensors. They can be deployed indoors, outdoors, and underwater, and can record data for up to months at a time, unattended. A data logger may be a single-unit, stand-alone device with internal sensors, which fits in the palm of a hand, or it may be a multi-channel data collection instrument equipped with one or more external sensors.