Standard for a Smart Transducer Interface for Sensors and Actuators - Transducer to Microprocessor Communicatio Protocols and Transducer Electronic Data Sheet (TEDS) Formats
|Publication Date:||16 September 1997|
The main objectives of this standard are to:
• Enable plug and play at the transducer (sensor or actuator) level by providing a common communication interface for transducers.
• Enable and simplify the creation of networked smart transducers.
• Facilitate the support of multiple networks.
The existing fragmented sensor market is seeking ways to build low-cost, networked smart sensors. Many sensor network or weldbus implementations are currently available, each with its own strengths and weaknesses for a specific application class. Interfacing transducers to all these control networks and supporting the wide variety of protocols represents a significant and costly effort to transducer manufacturers. A universally- accepted transducer interface standard would not only allow for the development of smart sensors and actuators, it could also lead to lower development costs. Therefore, the objective of this project is not to propose another control network, but to develop a smart transducer interface standard that will isolate the choice of transducers from the choice of networks. This would relieve the burden from the manufacturer of supporting a cross product of sensors versus networks, and would help to preserve the user"s investment if it becomes necessary to migrate to a different network standard.
There is currently no defined common digital communication interface standard between transducers and network capable application processors (NCAPs). Each transducer manufacturer builds its own interface. Consequently, transducer manufacturers cannot afford to support all of the control networks for which their products may be suited. It was concluded at a series of five transducer interface workshops held between 1994 and 1995 that a common transducer communication interface standard be proposed. This common interface would allow the transducer manufacturers to more easily support multiple control networks.
This standard will simplify the development of networked transducers by defining hardware and software blocks that do not depend on specific control networks. This project has developed a standard hardware interface to connect a smart transducer interface module (STIM) to an NCAP. While the project does not include specifications for signal conditioning or data conversion, it does provide a mechanism for specifying the combination of transducer, signal conditioning, and signal conversion to the rest of the system. This mechanism is the transducer electronic data sheet (TEDS). The working group has defined a TEDS which supports a wide variety of transducers as well as a digital interface to access the TEDS, read sensors, and set actuators. This allows transducer manufacturers competitive differentiation in areas of quality, feature set and cost, and at the same time affords the opportunity to design to a common interface which can be used in a wide variety of applications.
The TEDS, which provides for self-identifying transducers, is at the core of this effort. The TEDS contains fields that fully describe the type, operation, and attributes of one or more transducers. By requiring that the TEDS be physically associated with the transducer, the resulting hardware partition encapsulates the measurement aspects in a STIM on one side of the digital interface, and the application related aspects on the NCAP on the other side. In addition to control networks, STIMs can be used with microprocessors in a variety of applications such as portable instruments and data acquisition cards.
Data output by the STIM may be in integer, single precision real, or double precision real formats. The data is passed to the NCAP and from the NCAP to the rest of the system. Further processing of this data may take place both in the NCAP and in other processors in the larger system. Throughout this standard it is assumed, but not required, that all processing will be performed on data in a single- or double-precision real format.
All fields in the TEDS are specified based on the assumption that, unless specifically stated to the contrary, all data will be converted to single- or double-precision real before any processing is performed.
This standard provides areas that are "open to industry." It should be noted that any use of these areas compromises the "plug and play" potential of NCAPs and STIMs.
The IEEE 1451.2 transducer to microprocessor interface is compatible with the P1451.11 information model standard. The two parts form a standard interface for networked smart sensors and actuators.
This standard defines a digital interface for connecting transducers to microprocessors. It describes a TEDS and its data formats. It defines an electrical interface, read and write logic functions to access the TEDS, and a wide variety of transducers. This standard does not specify signal conditioning, signal conversion, or how the TEDS data is used in applications.