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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: Whats the high or lowfrequency point? Whats the exact sensitivity? Or when was this last calibrated?

Without reflecting on sanity, you wish, if only this little guy could talk. Well it turnsout 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 theInternational Modal Analysis Conference (IMAC) in Orlando this year, the Modal ShopsStructural Test Product group manager, Mr. Marco Peres, gave a talk about the historyand current status of the TEDS in the dynamic sensor industry. While estimates of thenumber 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 ICPaccelerometer to toggle into digital communication mode when an appropriate negativesupply voltage is introduced. With forward biases the accelerometer responds for accurate

analog measurements, but with reverse bias the sensor responds with a digital data streamof predetermined size and format. Just like analyzers in the sound and vibration markethave evolved to include the constant current supply for ICP operation, most modern dynamicdata 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 frequencyresponse transfer function, or as customizable as including test by test installed setupspecifics such as orientation direction, component and node name. Marcos IMACpresentation describes a few of the common templates and the following section of the IEEEwebsite provides an excellent primer on the next level of detail ofTEDS operation.

At this point, readers of this newsletter definitely fall into two distinct camps Either youclicked 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 (originallyapproved in May 2004 Happy Birthday TEDS!) is that TEDS capabilities are either standardfeatures or available options from virtually every manufacturer. All you need to do is ask. Ifyour Data Acquisition (DAQ) system includes TEDS functionality, you may select TEDSenabled sensors from any vendor and they will work plug and play style. If you dont ask,

the sensor vendor will program the sensor with their choice of default template. While it iscertain 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 theknowledge of which template you wish to use, it should be no problem getting thisprogrammed in by any reputable accelerometer vendor. Also be aware of one other littledetail, 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 nothave 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 PCcompatible 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/writeutilities 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 askyour metrology lab or calibration service provider to update the TEDS information when you

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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 levelhardware or software for this market, there is also a TEDS developer kit which providesembeddable libraries. This code can aid a system developers learning curve and shortendevelopment 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 anawfully large pool of questions to answer. Please dont hesitate to contact your PCB fieldapplication engineer or The Modal Shop directly if we can help.

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