Data Loggers:
The Next Generation

Data loggers aren't what they used to be–they're better. With the integration of more intelligence and improved communications, the distinction between today's data loggers and other PC-based data acquisition equipment is becoming blurred. Bruce Fuller, Fluke Corp.

There was a time when data acquisition (DA) was conducted by an engineer who took readings with clipboard and pen in hand from countless gauges and panel meters. Translation and analysis of data required weeks, and the results could be riddled with errors caused by manual manipulation of the data.

Nearly 20 years ago, a handful of manufacturers introduced the first commercially available portable data loggers. These devices vastly improved previous methods of data collection but were large and cumbersome and had poor user interfaces.

Photo 1. Like many companies, Dofasco Steel uses LAN-capable data acquisition systems to monitor production, replace paper-bound chart recorder systems, and distribute data throughout the facility.

The size of data loggers was dictated by the large signal conditioning cards, which plugged into the back of most data loggers. The cards provided 12-20 fixed channels of a dedicated input (e.g., RTDs, thermocouples, or DC), which often prevented you from using the full channel count of the data logger. At the time, one solution was to purchase DC-only input cards and additional external signal conditioning from other vendors. This, however, raised the overall cost of the DA system and further complicated the setup for various tests.

Operators of early data loggers required in-depth training to understand the cryptic and time-consuming front-panel programming. Interfacing early data loggers with computers consisted of little more than downloading the stored data, and analysis was left entirely to the user. The final data were made available on grocery tape-style printers or basic ASCII files. And postprocessing of data was a time-consuming task that required a staff with specialized training.

Data collection has become easier and more intuitive with such design improvements as smart control of signal conditioning and channel assignment. A few data loggers on the market (e.g., the Fluke 2600 family) now have programmable signal conditioning for individual channels. This feature saves you time and money when, for example, a channel assigned as a high-voltage AC input channel must be changed to a low-level DC input channel. With the new technology, you accomplish the changeover by pushing a button on the front panel—a major improvement over dedicated signal conditioning cards and external signal conditioners.

Screen 1. Data loggers now have supporting PC software that allows seamless data transfer to analysis programs using Dynamic Data Exchange.

The smart data loggers of today also have improved communications. Onboard RF modems based on interference-resistant technology previously available only to the U.S. military allow portable data loggers to be seamlessly linked using noise-immune, encrypted radio transmission formats. Off-the-shelf wireless data loggers can provide stand-alone data logging or act as remote front ends in real-time data collection systems for short-term troubleshooting or permanent monitoring. Data from RF-based data loggers can be viewed in real time at locations up to 1/2 mile away on a PC.

Although the RS-232 and IEEE 488 communication standards will continue as common interfaces for data loggers, there is a growing trend toward Ethernet communications in DA equipment (see Photo 1). This option lets you access data over existing company LANs, providing real-time information to all interested users on the network. Power companies, steel manufacturers, biomedical research firms, and automobile manufacturers are taking advantage of this communication option, which is being supported by many major DA equipment manufacturers.

PC Cards (or PCMCIA cards) have also added convenience and efficiency to smart data loggers. The cards not only extend the memory of data loggers from 256 KB to more than 4 MB but also allow storage of multiple setup files, which can be recalled and loaded into the data logger as different tests arise. PC Cards provide an effective way of transporting data from the field to a computer for analysis.

Software for data loggers provides rapid and user-friendly examination and presentation of data. Although simple setup routines, data management, and communication configuration have been standard in software for years, today's software supports modems, seamless interfaces with advanced trending programs (see Screen 1), and Dynamic Data Exchange with third party monitoring and control programs.

For troubleshooting and performance analysis, manufacturers are developing portable data loggers that have embedded analysis and trending programs and present results graphically on color displays. These data loggers will have options for embedded application programs that support specialized measurement needs, such as vibration analysis or validation of sterilization procedures, and will provide multichannel, real-time information in the field.

As data loggers develop and offer more flexibility to users, the traditional definitions for DA equipment will become blurred. Smart data loggers will carry full-feature sets of computer front ends and hybrid electronic chart recorders. These data loggers will provide an intuitive interface and a variety of communication options that will increase the ease with which data analysis is performed.

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