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What Is a Data Logger?
Data logging and recording is a common measurement application. In its most basic form, data logging is the measuring and recording of physical or electrical parameters over a period of time. The data can be temperature, strain, displacement, flow, pressure, voltage, current, resistance, power, and many other parameters. A wide range of products can be categorized as data loggers, from basic devices that perform a single measurement to more complex devices that offer analysis functions and integrated displays. Many applications are more involved than just acquiring and recording signals, sometimes involving a combination of online analysis, offline analysis, display, report generation, and data sharing. Moreover, applications are beginning to require the acquisition and storage of other types of data, such as recording sound and video in conjunction with the other parameters measured during an automobile crash test.
Figure 1. Data loggers can be both PC-based or stand-alone devices.
Data logging is used in a broad spectrum of applications. Chemists record data such as temperature, pH, and pressure when performing experiments in a lab. Design engineers log performance parameters such as vibration, temperature, and battery level to evaluate product designs. Civil engineers record strain and load on bridges over time to evaluate safety. Geologists use data logging to determine mineral formations when drilling for oil. Breweries log the conditions of their storage and brewing facilities to maintain quality. The list of applications for data logging goes on and on, but all of these applications have similar common requirements.
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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 onboard memory or a PC
- Data-logging software for data acquisition, analysis, and presentation
Follow these steps when using a data logger:
- Connect sensors like thermocouples, resistance temperature detectors (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.
Figure 3. Data-Logging Application Elements
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 compressions 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.
Next Steps
Selecting the Right Data Logger
Reader Comments | Submit a comment »
what are the differences between dataloggers
and DAQ boards!
- gihan. gihan_gomah@yahoo.com - Mar 15, 2006
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