What is a smart sensor?
One of the biggest advances in automation has been the development and spread of smart sensors. But what exactly is a "smart" sensor? Experts from six sensor manufacturers define this term. A good working "smart sensor" definition comes from Tom Griffiths, product manager, Honeywell Industrial Measurement and Control.
One of the biggest advances in automation has been the development and spread of smart sensors. But what exactly is a "smart" sensor? Experts from six sensor manufacturers define this term.
A good working "smart sensor" definition comes from Tom Griffiths, product manager, Honeywell Industrial Measurement and Control. Smart sensors, he says, are "sensors and instrument packages that are microprocessor driven and include features such as communication capability and on-board diagnostics that provide information to a monitoring system and/or operator to increase operational efficiency and reduce maintenance costs."
No failure to communicate
"The benefit of the smart sensor," says Bill Black, controllers product manager at GE Fanuc Automation, "is the wealth of information that can be gathered from the process to reduce downtime and improve quality." David Edeal, Temposonics product manager, MTS Sensors, expands on that: "The basic premise of distributed intelligence," he says, is that " complete knowledge of a system, subsystem, or component's state at the right place and time enables the ability to make 'optimal' process control decisions."
Adds John Keating, product marketing manager for the Checker machine vision unit at Cognex, "For a [machine vision] sensor to really be 'smart,' it should not require the user to understand machine vision."
Under IEEE 1451, a sensor is divided into two parts: a Smart Transducer Interface Module (STIM) contains the sensing element, the appropriate signal-conditioning circuits, and A/D converter, plus a Transducer Electronic Data Sheet (TEDS), a memory chip that identifies the type of sensor, its make and model, its calibration information, its scale factor, and more. The STIM connects to a network-capable application processor (NCAP), which provides an interface to a communications network. (Illustration courtesy of Kang Lee, National Institute of Standards and Technology)
A smart sensor must communicate. "At the most basic level, an 'intelligent' sensor has the ability to communicate information beyond the basic feedback signals that are derived from its application." says Edeal. This can be a HART signal superimposed on a standard 4-20 mA process output, a bus system, or wireless arrangement. A growing factor in this area is IEEE 1451, a family of smart transducer interface standards intended to give plug-and-play functionality to sensors from different makers. (For more on this subject, see this article online at www.controleng.com )
Smart sensors can self-monitor for any aspect of their operation, including "photo eye dirty, out of tolerance, or failed switch," says GE Fanuc's Black. Add to this, says Helge Hornis, intelligent systems manager, Pepperl+Fuchs, "coil monitoring functions, target out of range, or target too close." It may also compensate for changes in operating conditions. "A 'smart' sensor," says Dan Armentrout, strategic creative director, Omron Electronics LLC, "must monitor itself and its surroundings and then make a decision to compensate for the changes automatically or alert someone for needed attention."
Many smart sensors can be re-ranged in the field, offering "settable parameters that allow users to substitute several 'standard' sensors," says Hornis. "For example, typically sensors are ordered to be normally open (NO) or normally closed (NC). An intelligent sensor can be configured to be either one of these kinds."
Intelligent sensors have numerous advantages. As the cost of embedded computing power continues to decrease, "smart" devices will be used in more applications. Internal diagnostics alone can recover the investment quickly by helping avoid costly downtime.
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