Reading and Writing TEDS with the LabVIEW PDA Module

Plug and play sensors and automatic configuration of a measurement system is made possible with the emergence of IEEE P1451.4. In order for a measurement system to properly condition, digitize, and interpret an analog sensor signal, the operating parameters of the sensors must be used to precisely configure the system and scale voltage measurements to meaningful engineering units. The proper connection and configuration of each sensor channel is a critical, but often time-consuming operation. This application note provides an overview of the IEEE P1451.4 standard and details how to create a portable solution for reading and writing digital identification and calibration data to smart sensors.

IEEE P1451.4 Standard for Smart TEDS Sensors

IEEE P1451.4 defines a relatively simple and straightforward mechanism by which an analog sensor can provide self-identification and calibration information through the use of an EEPROM embedded in the sensor itself. This information is stored in a format known as the Transducer Electronic Data Sheet (TEDS). The TEDS contains such data as sensor identification information, sensitivity, calibration parameters, location ID, and custom user data. In order to keep the TEDS structure compact but flexible enough to handle a wide range of sensors, IEEE P1451.4 provides a collection of standard TEDS formats called templates. These templates specify how to translate the TEDS bits for a particular type of sensor.

Using smart TEDS sensors saves time and makes measurement systems more reliable since there is no need to manually enter data from paper data sheets and calibration certificates. A smart TEDS sensor identifies and describes itself, so you can automatically configure the data acquisition system when you connect the sensor. This is especially beneficial if you have a high channel count with multiple sensors. The free, downloadable TEDS LabVIEW library provides capabilities of reading and writing the TEDS and therefore enables you to take advantage of smart sensors with your LabVIEW applications.

See Also:
IEEE Standard On the Way for Smart, Plug and Play Sensors

LabVIEW PDA Module

The LabVIEW PDA Module provides a portable solution to reading and writing the TEDS of smart sensors using a PDA. An add-on for LabVIEW, the PDA Module allows you to create executable files to run on a Palm or a PocketPC. By taking advantage of the easy-to-use graphical programming of LabVIEW, you can quickly create a program to read and write selected TEDS parameters of your choice. In addition, the LabVIEW PDA Module provides numeric and text inputs and displays customized for use on a PDA screen so that you can easily design a functional user interface for entering and displaying TEDS information. With your LabVIEW PDA program, you can then use a PDA any time you need to add to or modify the TEDS of the sensors.

Implementation of Your Portable TEDS Solution

The following information details how to set up a PDA and create software for interfacing with a smart TEDS sensors. This description, along with example programs that demonstrate how to read and write selected parameters of the TEDS of accelerometers and microphones, will help you successfully implement a portable TEDS solution. To set up the system, you need a Maxim/Dallas Semiconductor DS9097U-S09 Universal 1-Wire COM Port Adapter or equivalent to connect serially to the PDA. Since all communication with the smart TEDS sensor EEPROM is based on the Maxim/Dallas Semiconductor 1-Wire protocol, this adapter allows you to use the serial communication capability of the PDA to interface with the sensor. For a Palm, the Tower Technologies TT2301 iReader provides this interface. The iReader features an RJ-11 port, so you may need an additional adapter to connect the sensor.

The first task that your software must accomplish is to communicate with the EEPROM of the sensor. The LabVIEW DS2408B drivers on the Maxim/Dallas Semiconductor 1-Wire Software Development Download page are very useful, as the DS2408B is the chip used by the DS9097U adapter mentioned above to provide the actual serial port to 1-Wire interface. You can use these drivers to write your code to read and write the TEDS bitstream, or you can take advantage of the example programs to obtain code for reading a TEDS EEPROM into a Boolean array and writing a Boolean array to a TEDS EEPROM.

The next step is to code a translation of TEDS bits according to the template for the type of sensor. The white paper An Overview of IEEE 1451.4 Transducer Electronic Data Sheets (TEDS) explains the format of template files and how to interpret the Template Description Language (TDL) defined by IEEE P1451.4. To read the TEDS, you must decide what parameters you want to read, extract the corresponding bits as determined by the template from the TEDS Boolean array obtained from the EEPROM of the sensor, and convert them to the correct data type (integer, fractional number, text, etc.) as specified by the template. To write the TEDS, you must choose the parameters you want to write, convert their values into Boolean arrays according the format contained in the template, use the template to determine what bits from the TEDS bitstream should be replaced, and then substitute the new or modified parameter arrays into the TEDS Boolean array that will be written to the EEPROM of the sensor. The Read TEDS example demonstrates how to translate the TEDS for accelerometers and microphones (both old and new template versions) to obtain the Basic TEDS sensor identification information, sensitivity, calibration parameters, measurement location ID, and user data. The Write TEDS example allows you to modify the measurement location ID and user data of the accelerometer or microphone.

The final step for your software is to design the user interface. Making use of the PalmOS or PocketPC screen templates provided with the LabVIEW PDA Module eases this task by providing a framework for the size of the front panel screen, along with a run button to start your program and an exit button to close it. You can use large numeric and text controls suited to a PDA screen for entering data to be written to the TEDS. A table works well for displaying information read from the TEDS in the small space available on a PDA screen.

See Also:
An Overview of IEEE 1451.4 Transducer Electronic Data Sheets (TEDS)
LabVIEW PDA Module Examples for Reading and Writing TEDS

Conclusion

Smart TEDS sensors and the TEDS LabVIEW library save you time by allowing automatic and accurate configuration of measurement systems. A convenient, portable TEDS interfacing solution is made possible by the easy-to-use LabVIEW PDA Module, which enables you to create software to read and write the TEDS of smart sensors with PDAs.

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