What is a transducer and how are sensors different?

The terms sensor and transducer are frequently used interchangeably, however, there are differences. Going strictly by definition, a transducer is a device that translates primarily nonelectrical quantities into electric signals [1]. Instrument engineers limit the definition to a device used for measurement purposes. In this context, transducers can be used for measuring mechanical, thermal acoustic, optical and electrical quantities.

The basic input block to any sensor is a transducer (often called the sensing element) but the sensor can include far more circuitry to make it useful and easier to interface in an end application. This has led to the terms sensor and sensor system as broader extensions of the sensing element. The terms sensor or sensing node are also commonly used but transducer/transducing node is rarely used even though IEEE standards documents use this terminology.

Many standards organization provide their own definitions for sensors and transducers including American National Standards Institute (ANSI), Instrument Society of America (ISA), the Institute of Electrical and Electronic Engineers (IEEE) (IEEE 1451), and others. In fact, in 1975 ANSI declared that the term transducer was preferred to sensor [2]. However, the producing and using industries almost completely ignored this, so today sensor is used far more commonly than transducer.

A transducer can also convert an electrical signal into a physical quantity to make an actuator. When this occurs, a transducer is not a sensor. For example, a piezoelectric transducer can be used for actuation and/or sensing purposes. A loudspeaker is also a transducer that convert electrical signals into motion. Its counterpart, the microphone, is a type of pressure sensor/transducer.

1. “Section 8: Transducers and Sensors,” Standard Handbook of Electronic Engineering,5^th Edition, Donald Christiansen and Charles K. Alexander, McGraw-Hill, 2005.
2. “Introduction to Sensors,” https://www.nap.edu/read/4782/chapter/4#10.