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Articles and Technical Papers

Repairing the Weak Link in Data Acquisition and Control

A-B Journal (September 1997)

Modem communications is now recognized as a critical component of the data acquisition and control function as a result of the development efforts that have continually improved the technology's reliability and integrity. The required technologies-particularly Frequency Hopping Spread Spectrum (no site license required) for wireless data transmission and Frequency Shift Key (FSK) for data transmission by wire - are now in common usage, addressing the most difficult industrial environments while providing high levels of data communications reliability and integrity.

Data-Linc Group manufactures the world's broadest line of high-performance, custom configured, industrial-grade modems. The company recognizes that the ability to offer a complete line of wireless, dial-up, leased line, fiber optic and wire modems (as well as multiplexers, date switches and other peripherals) would prove instrumental in providing turnkey data communications solutions even for the most complex and diverse DCS and SCADA applications.

To avoid the potential for finger pointing in the event of installation or operational problems, Data-Linc provides a breadth of data communications capability in order to reduce the number of vendors responsible for resolving possible system problems. Of additional benefit to Rockwell Automation customers, this broad data communications capability is supplemented by an in-depth knowledge of, for example, Allen-Bradley PLCs, RTUs, Power Monitor II, and other equipment with respect to compatibility, interoperability, and connectivity. Data-Linc even publishes a document entitled "Interfacing Data-Linc Modems with Allen-Bradley Equipment" as an aid to the local A-B offices and distributors.

The recently launched Rockwell Automation Encompass program is designed to formalize relationships with companies able to provide value-added capabilities to Rockwell Automation's own product line and to thereby better serve the needs of its customers. Because Rockwell Automation operates worldwide, Encompass Program Participants must address the specific requirements of a diverse and broadly based market. Individual country requirements and unique specifications, including global approval processes, impose an additional burden upon manufacturers to comply with the myriad regulations of the international marketplace.

Serving the Customer

Rockwell Automation devotes considerable time and expense to ensure an exceptional level of data reliability in its PLCs, RTUs, drives, and other equipment. Data-Linc, in turn, concentrates its own R&D on the other critical component of the data acquisition and control task - the transmission of data between stand-alone devices.

Not long ago, data communications were typically regarded as the "weak link" in an installation, often requiring the services of consulting engineers expert at designing against potential adverse conditions that might result in compromised data. Electromagnetic interference, noise, surge, and shifting ground plane problems were commonly encountered when transmitting data by wire. Wireless data communications could be plagued with its own variety of interference problems such as noise, contention, and multi-path fading, as well as the time and expense required to obtain a site license.

Dramatic advances in data communications technology have eliminated virtually all of the prior deficiencies in support of industrial automation applications and have thereby led to the rapidly increasing use of modems to address requirements previously prohibitively expensive or even impossible. The decades of effort dedicated to the optimization and enhancement of Carrier Modulation (CM) technologies, particularly with FSK and Frequency Hopping Spread Spectrum capabilities, has enabled Data-Linc to meet the ever-increasing performance, features, and specifications defined by current automation industry requirements.

Performance Challenges

Companies specializing in modem communications today are expected to support higher baud rates, longer range, more rapid turnaround delays/response times and severe environmental operating conditions (i.e., temperature, shock, vibration, etc.). In addition, products designed for the American market may be unsuitable for other countries. For example, license-free radio modems can operate in the 902-928 MHz band in North America, which is a prohibited band in many parts of the world. In Europe, the permissible band is 2.4-2.4835 GHz. Unfortunately, the higher band does not support the 90-mile range capability that 900 MHz communications can deliver. Finally, wireless data communications in Europe is restricted to a radiated power rating of no more than one-tenth watt, further limiting the distance capability.

The industrial market often imposes severe operating conditions on equipment expected to function in difficult environments. This fact, of course, further challenges equipment manufacturers to meet the conditions encountered in the field.

Data-Linc continues to extend and enhance its technology and products to keep pace with the need for equipment capable of operating in the harshest of applications. For example, the Data-Linc License Free Radio Modems are used by the Pico American Dream and Budweiser Hydroplane Racing Teams, the top two point total winners for the 1996 season, to transmit engine performance and other data from the hydroplane cockpit to the crew personnel in the pits. It would obviously be a rare occurrence that shock or vibration environments in an industrial automation application could prove to be worse. Data-Linc wireless and wire modems have also been designed to withstand high EMI (electromagnetic interference), environments as well as severe temperatures - even the Data-Linc dial-up/leased line modem will support an operating temperature range of -40°C to +85°C. As one final example, the Data-Linc Radio Modem is designed to provide dual protection against loss of communications, relying not only upon spread spectrum technology for interference immunity but also utilizing the frequency hopping technique to accomplish interference avoidance.

In summary, suffice it to say that the industrial automation market imposes its own particular challenges for data communications equipment manufacturers. A continuing commitment toward keeping abreast of the ever increasing performance demands of the industry, as well as service and support, will always be an on-going challenge.


The ultimate in compatibility, interoperability and connectivity with Rockwell Automation Equipment, combined with the required features, benefits, and specifications for any specific application defines the bottom line in serving the customer. By custom factory configuring the modems, multiplexers, cables, and other data communications equipment for each application, Data-Linc offers a service to its customers, at no additional charge, intended to provide a "no-brainer" installation.

Supplying equipment with LEDs and other "remote diagnostics" enables Data-Linc to quickly trouble-shoot problems that might otherwise have required a trip to the site. Finally, the careful selection of technologies serves to insure the end user against potential operational problems. The total elimination of possible problems during installation, start-up, and operations will never be realized. Nevertheless, a relentless focus on optimizing ease of installation and trouble-free operation will obviously best serve the customer's needs.

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