A "smart sensor" is a transducer (or actuator) that provides functions beyond what is necessary to generate a correct representation of a sensed or controlled quantity (e.g., temperature, pressure, strain, flow, pH, etc.). The "smart sensor" functionality will typically simplify the integration of the transducer into applications in a networked environment. For example, a measurement from a temperature transducer requires the network controller to make a voltage-to-temperature conversion to represent the data in either degrees fahrenheit or degrees celcius. An intelligent temperature transducer (smart sensor) has a built-in transducer electronic data sheet (TEDS) to make the measurement conversion and provide the data in units of temperature to the network controller. To do this, the smart sensor module also contains the digital interface to provide a communication channel between the network control and the smart sensor.

There are two main components of a functional smart sensor:
1) a transducer interface module (TIM) and
2) a network capable application processor (NCAP)

TIM

A TIM is a module that contains the interface, signal conditioning, Analog-to-Digital and/or Digital-to-Analog conversion and in many cases, it also contains the transducer. A TIM can range in complexity from a single sensor or actuator to a module containing many transducers including both sensors and actuators.

NCAP

An NCAP is the hardware and software that provides the gateway function between the TIMs and the user network or host processor (the transducer channel). The IEEE 1451 standard defines the communications interface between an NCAP or host processor and one or more TIMs. Three types of transducers are recognized by the IEEE 1451 standard; sensors, event sensors and actuators.

A transducer channel is considered 'smart' because of three features:

— It is described by a machine-readable, Transducer Electronic Data Sheet (TEDS).

— The control and data associated with the transducer channel are digital.

— Triggering, status, and control are provided to support the proper functioning of the transducer channel.

An NCAP or a host processor, controls a TIM by means of a dedicated digital interface medium. The NCAP mediates between the TIM and a higher-level digital network. The NCAP may also provide local intelligence.

Smart Sensor Plug and Play

The IEEE 1451 standard provides for TIMs that can be plugged into a system and be used without having to add special drivers, profiles or make any other changes to the system. This is referred to as “plug and play” operation. The primary features that enable plug and play operation are the TEDS and the basic command set. A TIM may be added to or removed from an active transducer interface media with no more than a momentary impact on the data being transferred over the bus. “Hot Swap” is the term used to refer to this feature.

Next topic: What is the IEEE 1451 standard?