New Interface Standard Simplifies Integration of Sensors and Actuators

It just got easier to assemble smart sensors and actuators—digital devices that function much like eyes, ears and hands—into control networks that monitor and adjust manufacturing processes.

That's the key benefit of a new standard developed by representatives of the National Institute of Standards and Technology and more than 25 companies. Recently adopted by the Institute of Electrical and Electronics Engineers, the standard, IEEE-1451.2, is designed to simplify the now complex task of interfacing "smart" transducers—combinations of digital sensors and actuators—into the more than 50 different types of proprietary networks deployed throughout industry.

The network-independent, digital interface provides a common bridge for reading sensors, setting actuators and accessing key identifying and historical information on the devices. "This provides the opportunity for achieving `plug and play' interoperability over a local area network or the Internet," says Jim Moore, director of corporate technology at Moore Products, a maker of sensors and measurement and control systems. "Now we have what is roughly equivalent to the standardized pin connectors that enable computers and printers to work together without regard for who made them."

Functionally separating transducers from the peculiarities of network protocols should translate into larger markets for the estimated 3,000 sensor and actuator manufacturers in the United States, says Kang Lee, head of NIST's sensor integration group and chairman of the IEEE TC-9 Committee that developed the standard.

"It has been too costly," Lee explains, "for many transducer manufacturers to customize their interfaces to satisfy requirements that are peculiar to each network." As a result, manufacturers have tended to specialize in application areas, each favoring one or, at most, a small subset of the multitude of control-network alternatives.

Moreover, the diversity of network protocols has impeded the spread of intelligence to the sensor and actuator nodes of control systems, notes Stan Woods, project manager at Hewlett-Packard Laboratories, research arm of the California-based maker of measurement, computing and communication products. "Use of smart transducers in manufacturing systems has not been proportional to the growing opportunities for improving measurement and control," says Woods, leader of the TC-9 working group that wrote the standard.

Chief elements of IEEE 1451.2 are a network capable application processor, 10-wire, transducer- (and network-) independent interface, a set of communication protocols, and a transducer electronic data sheet, or TEDS. The TEDS, according to Lee of NIST, is the "core" of the standard, providing a common format for capturing and conveying key information on each device in a network. Data sheets contain information such as manufacturer name, date code, serial number, limits of use, uncertainty, warm-up time, sampling rate and date of last calibration.

"The TEDS enables device-level intelligence and self-identification of devices," Lee says. "This simplifies installation, integration and maintenance."

There are several options for implementing the standard. Transducer firms can make stand-alone "smart transducer interface modules" for sale to users, systems integrators and manufacturers of computers, programmable logic controllers, and test and measurement equipment. Another option is for transducer manufacturers to buy network capable application processors from control network vendors and to integrate these standard-compliant microprocessors into their smart devices.

The new standard's ultimate impact on the development, application and integration of smart transducers will depend on its rate of adoption in industry. Both Woods and Moore are hopeful of widespread acceptance. Because it is network independent, IEEE 1451.2 does not broach controversial areas that have impeded standardization efforts in other areas of sensor networking technology. They also credit NIST's involvement with helping to ensure impartiality during the standard's development.

"NIST helped to make the process non-political and fair for everyone involved," Woods says. "It convened workshops that permitted companies to raise key issues, and NIST's technical work helped to keep the focus on technology."

A non-regulatory agency of the Commerce Department's Technology Administration, NIST promotes U.S. economic growth by working with industry to develop and apply technology, measurements and standards.