Data Loggers and Data Recorders Information
Data loggers and data recorders acquire digital data from sensors and other signals. Typically the device is used in situ or in the field, and stores data over a period of time.
The term data logger is primarily used to describe a device that stores data for subsequent download to a host PC. Data recorder is a broader term used to describe any device that records sensor or signal inputs. Either device may also include real-time features such as monitors and alarms. They can be hand-held, modular, stand alone, rack mounted, DIN rail mounted, or printed circuit board devices. The following chart describes how each form factor has unique capabilities and functionality.
|Hand-held devices have a user interface and display. The device may be programmed for a set time interval, to accept a specific sensor or signal input, or may display results before interfacing with a host PC. These devices may be limited by available storage capacity and capabilities.||
Image Credit: DATAQ Instruments
|Printed circuit boards mount directly in to a black plane or mother board. These devices allow you to transform an industrial PC, laptop or other host into a data logger.||
Image Credit: National Instruments
|Modules, or black boxes, are preferred when taking measurement for an extended period of time or when taking measurements in extreme environments. Most modular devices are exclusively used to acquire data for subsequent downloads to a host PC.||
Image Credit: Linseis Inc.
|Devices that mount on a standard DIN rail occupy very little space and are easy to set-up. The most common DIN rail is 35mm. Sensor and signal terminals are easily accessed. A host is usually required for interfacing, acquiring, and analyzing the stored data.||
Image Credit: Newport Electronics, Inc.
|Rack mounted devices are designed for mounting in standard sized enclosures. The most common size is a 19” telecommunications rack. They are easily mounted and may have a rear access panel for wiring the device.||
Image Credit: Pacific Sensor Technologies
|Stand-alone devices are benchtop or floor-standing units with a full casing or cabinet and an integral interface. In many cases stand-alone devices do not require a host to analyze or display data.||
Image Credit: Dewetron, Inc.
The functionality of a data logger or data recorder crosses the functionality of a chart recorder. Both devices are used to acquire data while the latter implies that data is represented in a plot, graph, or other visualization of data versus time. With the use of a host computer, the same functionality can be achieved by almost all data loggers and data recorders. They may even interface with a printer when a hardcopy is desired. More detailed information specific to chart recorders is available in GlobalSpec's Chart Recorders Selection Guide.
The user interface (UI) is the front end of the device that allows users to program, configure, or conduct other human-machine interactions. The interface can be simple or even nonexistent such that you plug in a sensor and turn it on. It may also be an advanced UI, such as a touch screen interface or graphical display and keyboard, which allows users to define complex actions, such as time-delayed data capture, mathematical computations, or alarm and control functions.
The computer interface is used for downloading, transferring, or acquiring data. It is important to select a device that is capable of interfacing or transferring data to a compatible host. Host connection choices include direct backplane interface, RS232, RS422, RS485, USB, IEEE 1394, GPIB, SCSI, TTL, parallel, Ethernet, modem, and radio, telemetry, or other wireless interfaces.
Memory is an important specification as it determines the amount of data that can be stored. Most devices are characterized by bytes, a unit of digital information typically representing 8 bits, and available memory may range from several kilobytes (kB) to several gigabytes (GB). Devices may also specify memory by number of data points. Data points cannot be converted to bytes as it is not a standard value and depends on the resolution and the type of data being captured.
Image Credit: Zbavitje.com
Resolution refers to the degree of fineness of the digital word representing the analog value. A ten-bit number contains 210, or 1024, increments. A 0-10V signal could therefore be resolved into approximately 0.01V increments. A 12-bit representation would be in 212 (4096) increments, or divisions of 0.0024V for the same signal. Each additional bit doubles the resolution, and one bit is required for the polarity (sign) of a number.
Sampling frequency can be an important specification when dealing with rapid fluctuations. Data loggers and recorders take time elapsed measurements and the sampling frequency defines the time needed to take a measurement. Sampling frequency is characterized by hertz (Hz) which is the number of values recorded per second.
Data Loggers and data recorders are data acquisition instruments and share many of the same performance characteristics as other types of data acquisition instruments. Physical parameters are captured, converted to a digital format and stored or transmitted to a host. Temperature, vibration, shock, and other environmental parameters are some of the most common measurements acquired by loggers and recorders. These devices can also accept a wide variety of other types of signal and sensor inputs. They may even supply excitation to an active sensor or device. More information about performance specifications relative to all data acquisition devices is available in GlobalSpec's Data Acquisition Selection Guide.
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