Smart sensors -

Smart sensors

Media attention generally falls on the latest gee-whiz processor advances and forecasts of their potential uses and market sizes. But the trend of older technologies coming down in price and thus creating new markets for themselves is sometimes more exciting. As prices fall, new uses for old components emerge. One example of this trend is the increasing use of so-called smart sensors, which have on-board processing.

Being analog components, most sensors are prone to nonlinearities. They also exhibit offset and gain errors and typically have limited dynamic range and high impedance at the outputs, which make them susceptible to electrical noise. As a result, ordinary (dumb?) sensors typically require dedicated external circuitry to perform signal conditioning, error compensation, and filtering. If lots of data are generated in spurts, buffering may also be required.

Smart sensors, unlike their dumb brethren, integrate the sensor with the required buffering and conditioning circuitry in a single enclosure. Circuitry on-board the smart sensor usually consists of data converters, a processor and firmware, and some form of nonvolatile memory. Being processor-based devices, such sensors can be custom programmed to satisfy specific system requirements and later reprogrammed as needed.

A smart sensor can be easily added to a piece of embedded hardware as, say, a single chip or a daughtercard via a digital interface. Or, as is increasingly common in the field of remote data sensing, a wireless-equipped smart sensor can perform local processing of the raw data and then ship the processed data up to a base station at regular intervals.

The benefits are tremendous. Vendor-supplied firmware on-board a smart sensor can automate the removal of nonlinearities and offset and gain errors from raw sensor readings, thus eliminating the need for custom post-processing at the main processor. The calibration data on a smart sensor can also be stored locally, in nonvolatile memory, so that the module as a whole can be moved and reused without recalibration.

On-board data processing and local storage also make possible new capabilities at the sensor's location, such as the ability to take action without intervention by the host processor. For example, a smart sensor could issue a quick early warning when measured parameters are approaching critical limits or changing at an abnormal rate. A sensor could even send a maintenance alert to the main system controller calling for replacement of itself.

As you read this month's features on sensors of various sorts, remember that even components as seemingly mundane as these can be made significantly more interesting with a little firmware. As the price of computing power drops, new uses for that power continue to emerge.

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