Introduction to TEDS Sensors

IEEE 1451.4 is the standard that defines the architecture and protocol for compiling and addressing non-volatile memory embedded within analog measurement sensors. Once programmed, the data stored in the memory chip can be downloaded and utilized in an automated test scenario. This digital information is called a Transducer Electronic Data Sheet (TEDS).

The ability to store information particular to the sensor provides many advantages:

• Multi-channel tests are expedited by permitting sensors to communicate their calibration value, model number, serial number, and other specifications which are then utilized by the data acquisition equipment.
• Intelligent signal conditioning equipment may interrogate sensors for their calibration data and automatically normalize their output signals.
• Paperwork and bookkeeping errors are reduced while maintaining conformance to ISO 9001:2015 certified by DQS, Inc. and QS 9000 calibration record-keeping requirements.
• Significant reduction of hardware and software setup time.
• Elimination of tracing through multiple cables to find the properties of the attached sensor.

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TEDS is non-volatile memory within a sensor that is utilized for storing information about that sensor. The manufacturer can program initial information into the TEDS chip. This can include manufacturer name, sensor type, model number, serial number, and calibration data. Memory space allocation permits the end user to add information such as location identification, latest calibration date, and other unique sensor related attributes.

The sensor operates in a mixed mode fashion (analog or digital). The information stored in the TEDS chip is downloaded when the sensor operates in digital mode. In analog mode, the sensor functions normally as a measurement device. A suitable TEDS signal conditioner or data acquisition front end is used to access the sensor memory. The digital communication occurs over the same wires ordinarily used for analog measurement signal transmission. Once the pertinent data has been transferred from the sensor, the memory circuit is switched off and the sensor resumes normal analog operation. A TEDS sensor may be used with a conventional signal conditioner however, there would be no access to the memory. A conventional sensor may also be used with a TEDS signal conditioner but there would be no TEDS functionality.

For universal applicability, the architecture of this technology is defined by the IEEE 1451.4 Smart Transducer Interface standard. By conforming to a universal standard, any TEDS sensor will be capable of being addressed by any TEDS signal conditioner, regardless of manufacturer. PCB® Group Inc. has products that comply with the standard and has provided thousands of TEDS enabled sensors and signal conditioners for installations throughout the world.

The TEDS memory circuit is built into the ICP® sensor alongside the conventional signal conditioning circuitry. A diode isolation scheme facilitates the switching between the ICP® sensor circuit and the TEDS circuit. The sensor will function as a normal measurement device and output an analog measurement signal when forward biased with a conventional positive voltage. The TEDS memory becomes accessible when the sensor is reversed biased and exposed to a negative voltage. The TEDS signal conditioner generates the reverse bias, or negative voltage pulses. These pulses interrogate the memory and the contents are then transmitted, via the same two wires, back to the signal conditioner and controlling PC. The data is then available within the application software for viewing, channel setup, printing or archiving in a spreadsheet or database format. Being quite small, the TEDS circuitry adds little to the weight of the sensor and will not degrade the sensor performance. This also permits the TEDS circuitry to be added to virtually any ICP® sensor. Excluded are only the smallest sensors where there is simply no additional space to accommodate TEDS.