What is a data logger?

What is a data logger?

A data logger is an electronic instrument used to take measurements from sensors and store those measurements for future use. Some common measurements include temperature, pressure, current, velocity, strain, displacement, and other physical phenomena.

How does a data logger work?

A data logger works with sensors to convert physical phenomena and stimuli into electronic signals such as voltage or current. These electronic signals are then converted or digitized into binary data. The binary data is then easily analyzed by software and stored on a PC hard drive or on other storage media such as memory cards and CDs.

A few components that every data logger must have include:

• Hardware to digitize what you are logging, including sensors, signal conditioning, and analog-to-digital conversion hardware
• Long-term data storage, typically a PC
• Data-logging software for data acquisition, analysis, and presentation

Follow these steps when using a data logger:

• Connect sensors like thermocouples, RTDs, thermistors, strain gages, and accelerometers to the data logger
• Use your data-logging software to configure your data logger
• Configure parameters like sample rate, alarms, and start or stop conditions for your data-logging task with your data-logging software
• Run the data-logging task
• After your hardware digitizes the sensor measurements, analyze and store your data for future use

What can you do with a data logger besides just log data?

The ability to take sensor measurements and store the data for future use is, by definition, a characteristic of a data logger. However, a data-logging application rarely requires only data acquisition and storage. Inevitably, you need the ability to analyze and present the data to determine results and make decisions based on the logged data. A complete data-logging application typically requires most, if not all, of the elements illustrated below.


Acquire - This step includes your sensors and data-logger hardware as well as the conversion of physical phenomena into digital signals.

Online Analysis - This step includes any analysis you would like to do before storing the data. A common example of this is converting the voltage measurement to meaningful scientific units, such as degrees Celsius. You can complete these complex calculations and data compression before logging the data. Controlling part of a system based on current measurements -- for example, a kill switch -- is also part of online analysis. Every data-logging software application should complete the conversion from binary to voltage and the conversion from voltage to scientific units.

Log - This step refers to the storage of analyzed data including any formatting required for the data files.

Offline Analysis - This step includes any analysis you would like to do after storing the data. A common example is looking for trends in historical data or data reduction.

Displaying, Sharing, Reporting - This step includes the creation of any reports you need to make to present your data. However, note that the figure above shows you can also present data straight from online analysis. This represents the ability to monitor and view the data as you acquire and analyze it in addition to simply viewing historical data.

These data-logging system elements are discussed in additional depth in the data logger white paper, A Review of PC-Based Data Logging and Recording Techniques, available for download.

Does NI have data-logging software?

Yes.  LabVIEW SignalExpress is a non-programming, full featured data-logging package from National Instruments.  With LabVIEW SignalExpress you can easily acquire, view, analyze, and log data to to a variety of file formats.  Data logging features include alarming, triggering analog or digital lines for control, creating html reports, viewing and processing of historical data, and high-speed disc streaming to binary files.  LabVIEW SignalExpress was designed to get datalogging systems up and running within minutes.

For more advanced logging features, such as parallel processing, advanced logic, if/then statements, case structures, you can port your entire LabVIEW SignalExpress logging application into one of the LabVIEW graphical environments for full programming development.  For more information on datalogging hardware and software from National Instruments visit www.ni.com/dataloggers

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what are the differences between dataloggers and DAQ boards!
- gihan. gihan_gomah@yahoo.com - Mar 15, 2006