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An Introduction to TEDS

Have you ever… stared at your accelerometer (with its arcane model number neatly etched), only to wonder about the useful information like: What’s the high or low frequency point? What’s the exact sensitivity? Or when was this last calibrated?  Without reflecting on sanity, you wish, “…if only this little guy could talk.”  Well it turns out that now they can.  Sensors with Transducer Electronic Data Sheet (TEDS) capability provide a standardized means for various types of sensors to “tell” the data acquisition system (or test personnel) their specifications on demand. At the International Modal Analysis Conference (IMAC) in Orlando this year, the Modal Shop’s Structural Test Product group manager, Mr. Marco Peres, gave a talk about the history and current status of the TEDS in the dynamic sensor industry.   While estimates of the number of TEDS accelerometers in service are approaching 200,000 units, there are many test professionals who are still learning…

The basic function of TEDS capability is to provide a standardized means of digital communication in what was formerly the “analog only” section of the measurement channel.  This is accomplished by a “reverse bias” scheme that allows a standard 2 wire ICP® accelerometer to toggle into digital communication mode when an appropriate negative supply voltage is introduced.  With forward biases the accelerometer responds for accurate analog measurements, but with reverse bias the sensor responds with a digital data stream of predetermined size and format.  Just like analyzers in the sound and vibration market have evolved to include the constant current supply for ICP operation, most modern dynamic data acquisition systems now include the minimal extra system design to handle the TEDS feature.  In addition to allowing the digital data stream, the TEDS standard (IEEE 1451.4) defines the structured, yet flexible format for handling the sensor information.  Accelerometer TEDS can report the standard information like: manufacturer, model number, serial number and calibration value (along with units)  or as detailed as defining frequency response transfer function, or as customizable as including test by test installed setup specifics such as orientation direction, component and node name.  Marco’s IMAC presentation describes a few of the common templates and the following section of the IEEE website provides an excellent primer on the next level of detail of TEDS operation.

At this point, readers of this newsletter definitely fall into two distinct camps… Either you clicked that last set of links eager to dive into the “bits and bytes” of the TEDS functionality or you are (patiently?) waiting for me to just tell you how to practically use the standard.

How to do I implement and/or simplify the use of TEDS?

The beauty of standardization and the time that has passed since balloting (originally approved in May 2004 – Happy Birthday TEDS!) is that TEDS capabilities are either standard features or available options from virtually every manufacturer.  All you need to do is ask.  If your Data Acquisition (DAQ) system includes TEDS functionality, you may select TEDS enabled sensors from any vendor and they will work “plug and play” style.  If you don’t ask, the sensor vendor will program the sensor with their choice of default template.  While it is certain to be accurate, it may not have all the information or utility that you desire.  First, check with your DAQ vendor to assure what template versions they support so that you may assess the available functionality and make an educated choice.  Once armed with the knowledge of which template you wish to use, it should be no problem getting this programmed in by any reputable accelerometer vendor.  Also be aware of one other little detail, many DAQ vendors have chosen to only handle the read portion of the TEDS process.  In this case, your DAQ will only be able to read a preprogrammed TEDS sensor and will not have the ability to update any of the user addressable fields, like calibration update.

If you wish to address the user updatable fields you may wish to pick up a simple PC compatible software utility that can address the sensors through a USB “dongle” to allow your laptop or PC to reverse the bias and decode the subsequent bit stream.  Read/write utilities are available from some accelerometer vendors and can be a big help if you plan to actively update/manage the TEDS content of your sensors.  Another available option is to ask your metrology lab or calibration service provider to update the TEDS information when you have your annual recalibration.  TEDS write features are available on some modern calibration systems.

Lastly, if you are one of the dozen or so  people in the world developing system level hardware or software for this market, there is also a TEDS developer kit which provides embeddable libraries.  This code can aid a system developer’s learning curve and shorten development times needed to provide capability standards throughout the industry.

As you can see from the varied audience we have to address with TEDS, there can be an awfully large pool of questions to answer.  Please don’t hesitate to contact your PCB field application engineer or The Modal Shop directly if we can help.

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