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Standard for Smart Transducers
It is time to update this breakthrough transducer interface standard to incorporate lessons learned and to accelerate its adoption into general use.
Imagine buying a "shrink-wrapped" transducer that can simply be plugged in and used immediately without having to refer to a paper data sheet or think about configuration. Now imagine being able to quickly replace that transducer, or using that same transducer on a different piece of equipment without any configuration changes. The data for that transducer are always automatically labeled with the correct physical units, range, and uncertainty, and of course you always have the current calibration and manufacturer-specific application information readily at hand because it resides within the transducer itself.
These examples are just some of the benefits envisioned with devices called smart sensors, smart actuators, or, collectively, smart transducers. "Smart sensors," the most common reference, have been discussed since the 1980s but are still not widely available. While the rest of this article deals with smart sensors, the principles and benefits apply equally to smart actuators.
When approved in September 1997, IEEE 1451.2 was truly a groundbreaking standard. It defined terms and established several basic principles for smart sensors and for communicating to sensors. Since its adoption, IEEE 1451.2 has received praise for its technical accomplishments, but has not yet enjoyed wide use. The Institute of Electrical and Electronics Engineers (IEEE) requires IEEE standards to be reviewed every five years. We will review IEEE 1452.2-1997 in 2002.
This article will describe the important new principles established by IEEE 1451.2, discuss the most frequently requested changes to the standard, and propose several enhancements that will facilitate its wider use. These enhancements center on a simplification of the standard and the use of an off-the-shelf physical layer such as RS-232 or RS-485, while maintaining the benefits of the Transducer Electronic Data Sheet (TEDS).
Some of the requested changes are based on comments received during the Sensors conference at Sensors Expo Spring 2001 in Chicago. The sensor community is invited to refine this proposal and encouraged to participate in a workshop at the Sensors conference in Philadelphia in October 2001 (www.sensorsexpo.com/philadelphia). The purpose of this article is to propose changes to IEEE 1451.2-1997 that can help make the standard attractive to a much wider audience.
Benefits Provided by the IEEE 1451.2 Standard
The IEEE 1451.2-1997 working group visualized benefits for several categories of users: sensor manufacturers, application software programmers, system integrators, and end users.
Sensor Manufacturers. Sensor manufacturers gain a standard way to specify the device operation and calibration, a standard physical interface between the sensor and the communications device, and the ability to use standardized off-the-shelf components to build smart sensors.
Application Software Programmers. Application software programmers gain a standard model for device control and data, as well as a standard data structure for implementing self-configuration.
System Integrators. System integrators gain self-documenting hardware and software that can be used in turn to create self-documenting systems of sensors that are easy to build, maintain, and use. An additional benefit is that they can use sensors from different manufacturers interchangeably.
End Users. End users gain a consistent model for and access to a wide variety of sensors and actuators, allowing them to think about application measurements and not about the system interfacing and configuration. The end users gain improved efficiency and less downtime, resulting in reduced total system life-cycle costs.
Technical features summarized in the following sections enable these benefits.
What Is a Smart Sensor?
To realize these benefits, the IEEE 1451.2 working group had to translate them into a system architecture and define the features of that architecture. Among other things, this required addressing the issue of just what a smart sensor is. Figure 1 shows a general architecture for one concept of a smart sensor. This architecture consists of seven major elements:
* Transducer. A device converting energy from one domain into another. The device may be either a sensor or an actuator.
* Signal conditioning. Circuitry that prepares the …