Sensing element and sensor
The sensing element is the part that directly responds to the quantity of interest. A complete sensor assembly may include mechanical protection, wiring and preliminary conditioning around that element.
Transducer
A transducer converts one form of physical quantity or energy into another usable form. In measurement discussions the word is broad; many sensors are transducers, but not every transducer is a complete industrial transmitter.
Transmitter
An industrial transmitter accepts a sensor input and produces a standardized output. It may perform amplification, linearization, temperature compensation, damping, diagnostics and digital communication.
Range and span
The lower range value (LRV) and upper range value (URV) define the configured endpoints. Span is URV minus LRV. A 0–10 bar transmitter has a 10 bar span; a −10 to +10 bar range has a 20 bar span.
Smart instruments
Smart devices can expose configuration and diagnostic data in addition to the primary process value. HART, for example, provides bidirectional digital communication between intelligent field instruments and host systems while commonly coexisting with a 4–20 mA signal.