An InstrumentChoice data logger is a device that records changes in physical conditions over time. They are often used to track historical data, such as temperature readings, humidity, cloud cover, etc. They can either be single, battery-powered units or include multiple channels for data logging.

Most internal memory storage data loggers are stand-by units that run on batteries or AC. They are designed to allow for continuous recording over a specified period, and then recorded data can be retrieved over a subsequent period. Stand-by units can run on either battery power or AC power. Internal memory storage units that run on batteries will need an external power source, or they must be plugged into a power outlet.

instrumentchoice-data-loggerAll externally-mounted data loggers, however, must have a continuously-read/write (CDR) input device to enable it to communicate with the computer programs that provide its sensor and control functions. Most externally-mounted instruments use a combination of servo-measurement commands and digital output pin connectors (DOPs) to communicate with the computer. Some servo-measurement commands send a low-resolution voltage signal that is not sensitive enough to trigger a false alarm. In contrast, other types of command may do just that by triggering an alarm when a certain output level is reached. Digital output pin connectors allow a user to attach a meter to an external data logger that measures absolute humidity and temperature. Absolute humidity meters (also known as humidity alarms or hygrometers) are used to indicate the moisture content in the air using a hygrometer and a digital display.

A single InstrumentChoice data logger can record either one or more input events over a designated time interval. Each input event can be separated into a variety of different categories, including humidity, temperature, barometric pressure, and lighting. Most data loggers can also be configured to record a particular time range over a specified period, which allows for the observation of long-term trend data. A stand-alone data logger is a useful tool for the monitoring of processes and systems because it has its own power supply, which eliminates the need for an extra power source. It also has a minimum and maximum recording time to eliminate instances where data are lost due to human error.

There are several types of data loggers. Stand-alone environmental condition measuring instrument collects data at regular intervals and stores them in a hard drive or tape drive. Some stand-alone instruments require an external power source, which makes them unsuitable for use in locations where power is not available at all times, and they are often relatively expensive. Time and temperature recording instrumentation records data during specific periods and then stores the data in a computer database. Relative humidity (Rhum) measurement is commonly included in these types of instruments. In a related but separate application, a humidity thermometer records the indoor and outdoor air temperature and humidity during specific periods, which may be coupled with other measures, such as humidity alarms.