Data loggers and data recorders are used to obtain digital signals and other types of data from various types of electrical devices such as sensors. These data logging devices are designed to store data that can be downloaded to a data storage device. The data that is gathered can be recorded and saved to a computer database for immediate and later use. Data logging is quite similar to data acquisition. Data loggers can be fitted with alarms. Signal inputs that can be used are DC/AC voltage and current, charge, frequency.
Sensors that are used to giving inputs are: strain gauges, thermocouples, LVDT's, thermistors, accelerometers, RVDT's, tachometers, relay switches, timers, encoders and counters. There are a few procedures that make up the act of data logging. The first thing you need is a measuring instrument or sensor, etc. to that can be used to gather the specific data you want to log such as temperature, humidity, weight, wind speed, pressure, flow, radiation, etc. Once you have collected the data in the instrument you need to have a type of interface to connect the measuring instruments to a computer.
You can use either analog or digital sensors depending on the type of data that you are gathering. Digital sensors let you connect them directly to a computer, but most sensors that are used in data logging are analog types that can measure fluctuations in physical characteristics at specified intervals. If you are using an analog system you will need to convert it to digital with an adaptor.
You will need a computer to store the data in and you will also need computer software to display the data to you and to enable you to see the information and use it however you need.
There are some important features that need to be taken into account during selection of data logging devices such as: the frequency of data sampling, accuracy, resolution, digital output and input channels, or differential analog input channels, etc. In differential types, the input is the difference between two signals. Digital types are used in telecommunication applications and use low level signals of on-off. Connection to the host equipment may be through: RS232 cables, radio, direct backplane interface, GPIB, TTL, Ethernet, modem, telemetry, parallel, SCSI etc.
The frequency at which analog signals are sampled and converted to digital signals is the sampling frequency. Data logging is usually performed for areas such as: meteorology, weather, aerospace, seismology, medical, marine studies, defense systems, laboratories, industries, chemical and processing plants, etc.