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Sensors: TEDS plug & play revolution |
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The sensors ìplug & playî revolution has begun
By Brian Betts
Brian Betts is National Instruments Data Acquisition Product Manager and can be contacted at
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In the installation and setup of a data acquisition system, time is money. According to a 2003 National Instruments data acquisition user survey, almost 20% of the total cost of developing a data acquisition system is incurred during system setup. Cumbersome wiring, sensor configuration, and manual data entry from paper sensor data sheets are time consuming and can lead to user error.
A new standard for sensors, known as IEEE 1451.4, reduces the time and challenges associated with sensor configuration. The standard defines a protocol to make sensors plug-and-play, similar to the way a USB mouse is plug-and-play with a computer. IEEE 1451.4 defines a mechanism for adding self-describing behavior to sensors with an analog signal interface. This mixed-mode interface includes the traditional analog sensor signal in addition to a low-cost serial digital link to access a Transducer Electronic Data Sheet (TEDS) embedded in the sensor. To extend the benefits of Sensors Plug&Play to traditional analog sensors, Virtual TEDS files provide the same Transducer Electronic Data Sheet in file format. With a TEDS, the sensor identifies and describes itself to the data acquisition system to which it is connected.
 Configuring a data acquisition system currently entails manually entering sensor parameters, such as range and sensitivity, from a printed data sheet into software. This information is used to mathematically convert raw voltages from the sensor into scaled engineering units. A system with smart TEDS sensors can automate this process by reading sensor parameters digitally from the TEDS chip on the sensor. There is no chance of erroneous data entry.
Although other ìsmartî sensor technologies have been proposed, IEEE 1451.4 is unique because it uses the analog output of the sensor. This feature makes smart TEDS sensors compatible with legacy data acquisition systems. In addition to reducing the upgrade complexity for the user, it also makes it easier for sensor manufacturers to add plug-and-play capabilities to their products. In fact, dozens of sensor vendors, including Honeywell-Sensotec and Endevco, already offer smart TEDS sensors.
National Instruments provides hardware and software for Sensors Plug&Play. The latest version of NI measurement and control services software, NI-DAQmx 7.2, is fully compliant with Virtual and smart TEDS sensors.
 Your data acquisition system may not be designed for deployment to a single test or application. Instead, it may be routinely reconfigured to adapt to new tests or changing application requirements. For these systems, setup time is important not only initially, but every time the system is reconfigured. Sensors Plug&Play products can minimize system setup time because they do not require manual sensor configuration.
Sensors Plug&Play products can also keep track of their own calibration schedules. Because transducer electronic data sheets include information about the sensor calibration date and period, they can tell the system when it needs to be recalibrated. Upon calibration, you can update the transducer electronic data sheets with the current calibration and expiration dates.
Sensors Plug&Play products also simplify setup of high-channel-count systems. Because the sensors describe themselves to the system, you do not have to manually keep track of which sensor is connected to which channel. For example, you can connect 100 smart TEDS accelerometers in any order to 100 accelerometer input channels. Transducer electronic data sheets also provide a user-defined area. With this memory allocation, you can program information such as the physical location of the sensor. For example, you can program the TEDS on an accelerometer with the information ìfront-bearing housing, motor 1.î Regardless of which input channel it is connected to, the data acquisition system knows the physical location of the sensor.
Of course, very few of the huge installed base of sensors are smart TEDS sensors. Upgrading all existing sensors to be smart TEDS sensors is not realistic. To address this challenge, National Instruments and a consortium of worldwide sensor vendors have developed Virtual TEDS files. Virtual TEDS files extend the benefits of IEEE 1451.4 to traditional analog sensors by storing sensor TEDS information in a database file instead of on an embedded memory chip. You can access Virtual TEDS files stored on a single centralized database on the Web for millions of sensors from multiple vendors.
You can select Virtual TEDS files for a particular sensor model number or for individual part numbers with part-specific parameters. In addition to working with traditional analog sensors, Virtual TEDS files are also useful in applications where sensor-operating conditions prevent the use of any electronics in the sensor.
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