Upgrading Your System for Virtual TEDS

Overview

IEEE 1451.4 is an emerging standard for adding Plug & Play capabilities to analog transducers. The underlying mechanism for plug and play identification is the standardization of a Transducer Electronic Data Sheet (TEDS). A TEDS contains the critical information needed by an instrument or measurement system to identify, characterize, interface, and properly use the signal from an analog sensor.

The TEDS is deployed for a sensor in one of two ways. First, the TEDS can reside in embedded memory, typically an EEPROM, within the analog transducer, as defined in the IEEE 1451.4 standard. Second, a Virtual TEDS can exist as a separate file, downloadable from the internet. This concept of Virtual TEDS extends the benefits of the standardized TEDS to legacy sensors and applications where the embedded memory or EEPROM is not available.

Figure 1: Smart TEDS Sensor with Embedded TEDS EEPROM

IEEE 1451.4 defines a relatively simple, straightforward mechanism for adding smart, plug and play capabilities to traditional analog sensors. Without adding any new hardware to the system, these plug and play sensors can bring real, immediate benefits in ease of use and productivity to any measurement and automation system that uses sensors. Additionally, IEEE 1451.4 defines a standard framework for sensor description, embodied specifically in the TEDS, that can scale from today's traditional analog sensors to tomorrow's smart networked sensors.

Extension of the Standard for Virtual TEDS

National Instruments and sensor vendors worldwide have recognized the implicit benefit of the TEDS concept, which provides a standardized description language for sensors. The TEDS data structure can describe any analog sensor, regardless of whether or not the TEDS is physically located on an EEPROM embedded in the sensor.

A Virtual TEDS file is stored on a local computer or a web-accessible database instead of on an EEPROM. This enables the huge installed base of legacy, analog sensors to realize the benefits of TEDS without being retrofitted with an embedded EEPROM. Virtual TEDS are also valuable in applications where sensor operating conditions prevent the use of any electronics, such as EEPROMs, in the sensor.
National Instruments and leading sensor vendors have collaborated to provide Virtual TEDS, which allows users to download FREE to their local PC or server, a TEDS binary file via the internet at ni.com/sensors. These TEDS give traditional analog sensors (without the memory chip) the plug and play capability of electronic data sheets, based on the IEEE 1451.4 standard.

Simply enter the manufacturer model or serial number to access the extensive database of leading sensor vendors' electronic information. Virtual TEDS provide each sensor's specific scaling and calibration information packaged in the IEEE 1451.4 binary format. The Virtual TEDS file is downloaded via a standard browser.

Information is available from global sensor vendors including:

Endevco	Futek	Honeywell Sensotec
Kistler	Lion Precision	LEM
Macro Sensors	RDP Electronics	Sensorex
Transducer Techniques	Watlow	Wilcoxon

In order to cover such a broad range while also keeping memory usage to a minimum, IEEE 1451.4 TEDS files utilize the concept of templates that define the specific properties for different sensor types. Every IEEE 1451.4 TEDS has a standardized structure, with templates outlining how the data sheet is formed for a large number of different sensors.
National Instruments NI-DAQmx measurement services and NI LabVIEW graphical development software have been upgraded to leverage TEDS technology by supporting Sensors Plug&Play. NI-DAQmx 7.2 and higher fully supports IEEE 1451.4 compliant Virtual and smart TEDS sensors. TEDS reader functionality is built into Measurement & Automation Explorer (MAX), the DAQ Assistant, and the TEDS library for LabVIEW. Because of this functionality, you can automatically acquire sensor and TEDS related information from one or more Virtual or smart TEDS sensors with the click of a mouse.

Once the Virtual TEDS file has been created or downloaded from ni.com/sensors to the local network, open MAX to configure the Virtual TEDS file and associate it with a physical channel.



A TEDS "NI-DAQmx Task" can then be configured to include gain, timing, and triggering information. Configuration data from the TEDS file will automatically be included and those settings will be disabled to indicate they have been updated by the software. With the configuration automatically completed in MAX, creating applications in LabVIEW is greatly simplified. The DAQmx Task containing the TEDS data eliminates the need to include timing and channel configuration programming.
While MAX provides a way to interactively scan and load smart TEDS sensors into computer memory, NI-DAQmx functions in LabVIEW provide the means to programmatically read, write, and reprogram TEDS data. The functions available in LabVIEW also provide for the TEDS data stream to be retrieved as a bit stream. The ability to reprogram TEDS from LabVIEW is useful for updating calibration information or to digitally store user-defined information including the physical location of the sensor.
With the release of DAQmx 7.2, the polymorphic nature of the NI-DAQmx VIs have been updated to include a TEDS option. The DAQmx Create Task VI now allows the user to select a TEDS sensor for their analog input sensor.


While the NI-DAQmx TEDS subpalette provides the basic calls needed to programmatically configure a measurement and automation system, the separate TEDS subpalette provides additional tools for TEDS manipulation and Virtual TEDS creation. Once the bit stream from the smart TEDS sensor is read into LabVIEW, the user has the ability to perform a wide variety of TEDS specific operations, such as get specific properties, parse the bit stream, and create a new TEDS.


Using NI-DAQmx and the TEDS Library for LabVIEW functions, you can easily create an application to allow the user to enter TEDS information of a specific sensor and convert the TEDS information to a 1451.4 binary file based on the appropriate template. IEEE 1451.4 defines the TEDS structure to be very compact yet flexible and extensible enough to handle a wide range of sensor types and requirements. The TEDS information is divided into several key sections. The first portion of the TEDS, the Basic TEDS, contains the required sensor identification information, including manufacturer, model number, and serial number of the sensor.

The Basic TEDS may be followed by an IEEE standard TEDS that contains the specific ‘data sheet’ information for the sensors – typically the data needed to properly configure the electrical interface and convert the measurement data into engineering units. Typical TEDS parameters include measurement range, electrical output range, sensitivity, power requirements, and calibration data. The standard TEDS section describes everything needed to make a measurement using the sensors.

Finally, the last portion of the TEDS is available for users to store custom data and information. This is a very useful feature for storing sensor location (coded as an ID), additional maintenance information, or other custom information.

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