When talking aerospace sensors, ‘analogue’ or ‘digital’ become hardly necessary, being simply a matter of approach to operation, and that it is the underlying physical principles that are all-important.
Classification of sensors. In discussing sensing devices one has to decide whether to classify them according to the physical property they utilize (like piezoelectric, photovoltaic, etc.) or based on the function they perform (including measurement of length, temperature, etc.). Within the former case you can present a reasonably integrated take a look at the sensing process, however it is a bit disconcerting when one desires to compare the merits of, say, 2 kinds of Multi Axis Force Sensor, if one must examine separate sections on resistive, thermoelectric and semiconductor devices to make the comparison.
Alternatively, to attempt to differentiate devices by function often is commonly an extremely boring catalogue of numerous unrelated devices. What is important about the subject is signals are transformed from one form to a different. Additionally it is easy to discuss Torque Sensor from your functional viewpoint, under headings such as length, temperature, etc., suitable for somebody who actually wants to select or make use of a sensor for a particular application rather than just read round the subject.
The phrase ‘sensors’ and ‘transducers’ both are widely used within the description of measurement systems. The former is popular in the USA whereas the second is much more often utilized in Europe. Deciding on a words in science is rather important. In recent years we have seen a propensity to coin new words or to misuse (or misspell) existing words, and this might lead to considerable ambiguity and misunderstanding, and is likely to diminish the preciseness in the language. The challenge has been very apparent in the computer and microprocessor areas, where preciseness is especially important, and may seriously confuse persons entering the subject.
The term ‘sensor’ is derived from sentire, meaning ‘to perceive’ and ‘transducer’ comes from transducere meaning ‘to lead across’. A dictionary definition Chambers Twentieth Century of ‘sensor’ is ‘a device that detects a big change in a physical stimulus and turns it in to a signal which is often measured or recorded’; a corresponding meaning of ‘transducer’ is ‘a device that transfers power from a single system to another inside the same or even in different form’.
A sensible distinction is by using ‘sensor’ for your sensing element itself, and ‘transducer’ for that sensing element plus any associated circuitry. For instance, thermistors are sensors, because they reply to a stimulus (changes its resistance with temperature), but only become transducers when connected in a bridge circuit to transform improvement in effectiveness against alternation in voltage, because the complete circuit then transduces through the thermal towards the electrical domain. A solar cell is both a sensor as well as a transducer, since it responds to a stimulus (produces a current or voltage responding to radiation) and also transducer through the radiant to the electrical domain. It can not require any associated circuitry, though in reality an amplifier would usually be used. All transducers thus contain a sensor, and several (though not all) sensors will also be transducers.
The distinction is quite small, and once one actually utilizes a sensor (by using capability to it) it becomes Miniature Force Sensor. An interesting classification of devices can be achieved by considering the various hdjjdy of energy or signal transfer.
The word ‘actuate’ means ‘to placed into, or incite to, action’ and actuators are devices that make the display or observable output in a measurement system for instance a light-emitting diode (LED) or moving coil meter. They are needless to say transducers used for output purposes, given that they transduce from a single domain to another (ie. electrical to radiant for LEDs).