What is data logging? As science and technology have developed, so the need for data collection and analysis has grown. This is fulfilled, at least in part, by dedicated, microprocessor-driven data loggers.
The modern data logger is typically a hand-held battery-operated device with a large memory, powered by the latest microprocessor technology and capable of acquiring, processing, storing and analyzing electrical signals at high speed from a wide range of sensors - at regular intervals or in response to an event such as a threshold being crossed or a switch being activated.
The sensors may communicate with the logger through a cable or wireless link and may sense temperature, humidity, pressure, flow, wind speed, current, voltage, resistance and a host of other physical parameters that are important in monitoring and controlling processes or conducting research.
Data stored by stand-alone data loggers is typically downloaded into a computer for more detailed analysis and reporting, though some data loggers have sophisticated on-board processing and analysis capability and can carry out some control functions such as activating an alarm or a switch.
The advantage of using a dedicated portable data logger compared to, say, a PC, is that the logger hardware and software are specifically designed for stand-alone data logging applications. This means that it is easy to connect and set up sensors and the logging system is more rugged and less power hungry, making it capable of running on batteries for longer periods of time, often in hostile environments.
The advent of wireless communication and networking means that it is possible to interrogate a logger remotely which can be extremely useful for unattended or remote applications.
source: http://www.grant.co.uk/Data+Acquisition/What+is+data+logging/