The earliest form of recording data involved manually taking measurements, recording them to a written log, and plotting them on graph paper. In the late 19th century, this process was automated with the use of strip chart recorders that mechanically recorded measurements onto paper. Strip chart recorders were a great leap over manual recording but still had drawbacks.
Today, the more popular method of recording data is with a data logger (or paperless chart recorder). Data loggers are stand-alone box instruments that measure signals, convert them to digital data, and store the data internally. Many data loggers include built-in displays and the ability to transfer the data to a PC for offline analysis, permanent storage, or report generation.
With the evolution of PC performance, new PC-based measurement devices have emerged. PC-based data loggers offer more than just the basic PC connectivity of traditional stand-alone data loggers. With a PC-based data logger, the PC is part of the system, so the data logger can take advantage of the ever-increasing performance of the PC processor, hard drive, display, and I/O bus.
With a traditional stand-alone data logger, you must first record the data and then manually transfer it to a PC before you can import it into a spreadsheet program or other tool to graph and visualize the data.
Because a PC-based data logger is always connected to the PC, live measurements are displayed on the PC monitor in real time and you can see results instantly. You can use programming environments, such as NI LabVIEW, to build custom user interfaces for controlling your measurement device and displaying the results. Creating a user interface with LabVIEW is as simple as dragging and dropping controls and graphs on the user interface.
Data analysis with a traditional stand-alone data logger is typically performed offline only after the data has been transferred to the PC.
Using a PC-based data logger, you can take advantage of multicore processors and increasingly available RAM in the PC to perform signal processing and analysis on your data as you acquire it. LabVIEW includes many common math and signal processing functions that use configuration wizards and make it easy to add analysis to your measurements.
With a traditional stand-alone data logger, you are generally limited to hardware and software functionality defined by the vendor. These functions are good for accomplishing general-purpose tasks, but they may not help you meet your unique application requirements. For example, you may want to log data only under certain conditions or generate custom alarms that aren't built into the data logger.
PC-based data loggers are software-defined instruments. This means the functionality of the device is defined by the software, and you can customize the software to meet your specific application needs. Using LabVIEW, you can easily build functionality for custom alarms, logging conditions, report generation, and signal analysis. You can log data to virtually any file format for importing into other tools and sharing data with others.
Data storage is an important component of a data logger. You can log only as much data as you can store in your data logger. Traditional stand-alone data loggers are limited by the amount of memory built into the device.
Because the PC is actually a part of a PC-based data logger, you are limited only by the amount of hard drive space on the PC. Today, it's not uncommon to find a PC hard drive with terabyte capacity that provides ample space for your current measurements as well as permanent storage space.
For applications that require long-term monitoring over days or weeks, you may have difficulty continually checking results. Remote monitoring is useful because you can see results from a remote location. Using a PC-based data logger, you can take advantage of the PC's network connectivity to transmit results over a network for remote viewing. With LabVIEW, you can create custom alarm conditions that send e-mails or even design a Web service that you can visualize over a Web-based application.
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