Standard for A Smart Transducer Interface for Sensors and Actuators Mixed-Mode Communication Protocols and Transducer Electronic Data Sheet (TEDS) Formats
|Publication Date:||25 March 2004|
The main objectives of this standard are to
- Enable plug-and-play at the transducer level by providing a common IEEE 1451.4 Transducer communication interface compatible with legacy transducers.
- Enable and simplify the creation of smart transducers.
- Facilitate the support of multiple networks.
- Simplify the setup and maintenance of instrumentation systems.
- Provide a bridge between the legacy instrumentation systems and the smart mixed-mode transducers.
- Enable implementation of smart transducers with minimal use of memory.
There was previously no defined common digital communication interface standard between mixed-mode transducers and network capable application processors (NCAPs). Each transducer manufacturer defined its own interface. Consequently, transducer manufacturers could not support all of the control networks for which their products might be suitable. A universally accepted mixed-mode transducer interface standard will facilitate the development of compliant smart sensors and actuators and could lead to lower development costs. This common interface allows the transducer manufacturers to support multiple control networks easily and helps to preserve the user's investment if it becomes necessary to migrate to a different network standard. In addition, this standard will make systems much easier to implement and use.
This standard simplifies the development of smart mixed-mode transducers by defining hardware and software blocks that are independent of specific control networks. The standard describes the following:
- An IEEE 1451.4 Transducer containing a Mixed-Mode Interface (MMI) and a transducer electronic data sheet (TEDS).
- The MMI, which is a master-slave, multidrop, serial connection. It requires a master device to initiate each transaction with each slave or node according to a defined digital communication protocol. The MMI may contain circuitry to detect and report a hotswap of transducers. The MMI may use either separate digital and analog connections, or two wires for power supply and timeshared analog signal and digital TEDS data. The MMI is used to access the TEDS.
- The TEDS, which is fixed and dynamic data, contained in one or more memory nodes on the MMI.
- A template, which is a software object describing the data structure of TEDS. It is implemented in the Template Description Language and resides in the Transducer Block.
- The Template Description Language, which is a scripted and tagged language providing a standard method to describe the functionality of IEEE 1451.4 Transducer.
- A Transducer Block, which is a software object describing the IEEE 1451.4 Transducer. It resides in the NCAP, which is the master device (e.g., an instrument or data acquisition system). The Transducer Block is used to access, decode, and encode TEDS using the TDL.
Furthermore, the Working Group has defined a set of TEDS templates for various transducers to facilitate the creation of sensor systems containing plug-and-play smart transducers.
The IEEE 1451.4 Transducer provides a self-describing capability, via the TEDS. The TEDS contains fields that describe the identity, type, operation, and attributes of the transducer. The IEEE 1451.4 Transducer is a sensor or actuator with one or more addressable devices, referred to as nodes, on a 2-conductor digital bus. The TEDS is required to be either physically, or virtually, associated with the IEEE 1451.4 Transducer. The resulting hardware partition encapsulates the measurement aspects inside the IEEE 1451.4 Transducer, while the application related aspects may reside either in the NCAP or in the TEDS.
The IEEE 1451.4 Transducer is a sensor or actuator with one, or more, addressable devices, which herein will be referred to as nodes, containing TEDS.
A digital communication protocol is defined for transactions on the bus. The transactions are as follows:
- Read (Read TEDS)
- Write (Write TEDS)
- Configure (Set Gain, Change Mode, Set Filter)
- Check status (Read Settings)
The IEEE 1451.4 MMI may be used for control networks and data acquisition in a variety of applications, such as portable instruments and data acquisition plug-in cards for PCs.
The Transducer Block object located in the NCAP describes the behavior of the IEEE 1451.4 Transducer. It interprets TEDS data according to the data structure defined in templates. Further processing of the data may take place both in the NCAP and in other processors in larger systems. The NCAP includes an IEEE 1451.1 object model with an IEEE 1451.4 Transducer Block.
The standard does not constrain competitive differentiation in areas of quality, feature set, and cost, and at the same time, offers the opportunity to design to a common interface, which can be used in a wide variety of applications.
This standard defines the protocol and interface that allows analog transducers to communicate digital information with an IEEE 1451 object. It also defines the format of the Transducer TEDS. The Transducer TEDS is based on the IEEE 1451.2™ TEDS. The standard does not specify the transducer design, signal conditioning, or the specific use of the TEDS.