ARTICLE: THE IMPORTANCE OF IEEE 1451T
In an ideal world, decisions about field devices, field
networks, and application software can all be made independently based on
the application requirements. The IEEE 1451 family defines standard
interfaces where there are none, and how all combine to accomplish this
vision. These are standards designed for network-based data acquisition
and control which essentially extends the domain of data acquisition
problems that can be solved to the entire Internet.
The objective of the 1451 family of standards is to make it easy to create solutions using existing networking technologies, standardized connections to smart devices, and a common software architecture. The standards allow application software, field network, and transducer decisions to be made independently. You get the flexibility to choose the products and vendors that are most appropriate to your application.
Regardless of whether your application requires only one measurement point or requires a large system with far-flung points, solutions using 1451 are easy to construct, and eliminate tedious steps prone to human error.
Without 1451, automation systems today are difficult and costly. You are often limited to the restricted offerings of a single vendor. Integration costs are high. Heterogeneous systems are even more difficult. And limited transducer intelligence requires centralized architectures that are difficult to install, difficult to modify, and difficult to maintain.
The Process Connection
At the process connection level, 1451 provides standard ways of creating totally self-describing measurement and control devices. This allows you to choose best-in-class products from your preferred vendors — true plug&play. Imagine plugging on a new sensor and having it announce its availability … with information like its serial number, calibration factors, and accuracy specifications. During installation location information can also be loaded so that you can turn on a totally self-describing system.
A new P1451.4 standard being proposed defines a standard interface that uses the connecting wires for analog signals or, upon command, for digital communications. These, for example, are interchangeable smart accelerometers and microphones made by PCB and B&K. You no longer need to keep track of calibration sheets and correctly enter that data into your application, and you dramatically reduce the effort to "wring out the system" - making sure that the application is talking to the intended devices at the proper locations.
Many devices convert to digital right at the sensor, the IEEE 1451.2 standard defines the Transducer Electronic Data Sheet and electronic interface for these. This creates an ideal modular architecture. All of the products we are demonstrating support this standard interface with a low-cost PIC microcontroller or a single integrated circuit chip. Now if you're a sensor manufacturer, 1451.2 opens up markets to you because you can simply embed the module for your favourite field network and everything else occurs automatically and transparently.
With 1451, you are not only free to choose vendors and devices you want, but you are free to choose the network that is most appropriate for your application.
In the traditional centralized approach, the application code must know specific information about the end devices: addresses, registers, variables, units, etc. This makes it difficult to add or exchange end devices. This conventional, but dated, approach requires highly skilled programmers. Moreover, such systems don't scale easily and create a multitude of opportunities to break the application.
These are costly limitations that can be overcome with the P1451.1 software architecture that moves some of this intelligence to each of the devices. The P1451.1 approach enables the benefits of objected-oriented technology. It creates flexible, natural software modules that allow engineers to think at the level of real-world systems, not at the level of programming language. Object-oriented systems are built by assembly, and produce systems that are much easier to adapt to new demands.
The reuse of existing, proven components not only shortens development time, it also leads to more robust, error-free systems. Object technology makes open systems possible. This breakthrough could have the same liberating effect in software configuration as open systems had on hardware. Separating your device specifics from your application software is key to making flexible systems that can be assembled, reassembled, or modified quickly.
Hewlett-Packard's adoption of IEEE 1451
The IEEE 1451 standards give you the flexibility to choose the software, the field networks, and the transducer devices that are most appropriate to your application. The Transducer Electronic Datasheet is key part of this true plug&play architecture. And the software architecture, taking advantage of object technology, pub/sub communications, and intelligence in the sensors, makes this happen. Hewlett-Packard has been a major participant in the development of these standards and use them to implement and architecture for distributed measurement and control that provides these benefits:
HP's Distributed Measurement and Control Operation bets that Ethernet will prevail over all other field buses in industrial applications, for all the reasons described above, and have developed a line of embedded Web servers that are complete Ethernet solution modules. More information about these products can be found at http://www.hpie.com/.
This article was supplied by Hewlett Packard.