| When talking aerospace sensors, 'analogue' or 'digital' | | | | persons entering the subject. |
| become hardly necessary, being simply a matter of | | | | The word 'sensor' is derived from sentire, meaning 'to |
| method of operation, and that it is the underlying | | | | perceive' and 'transducer' is from transducere |
| physical principles that are all-important. | | | | meaning 'to lead across'. A dictionary definition |
| Classification of sensors | | | | Chambers Twentieth Century) of 'sensor' is 'a device |
| In discussing sensing devices one has to decide | | | | that detects a change in a physical stimulus and turns |
| whether to classify them according to the physical | | | | it into a signal which can be measured or recorded'; a |
| property they use (such as piezoelectric, | | | | corresponding definition of 'transducer' is 'a device |
| photovoltaic, etc.) or according to the function they | | | | that transfers power from one system to another in |
| perform (such as measurement of length, | | | | the same or in different form'. |
| temperature, etc.). In the former case one can | | | | A sensible distinction is to use 'sensor' for the sensing |
| present a reasonably integrated view of the sensing | | | | element itself, and 'transducer' for the sensing |
| process, but it is a little disconcerting when one | | | | element plus any associated circuitry. For example, |
| wishes to compare the merits of, say, two types of | | | | thermistors are sensors, since they respond to a |
| temperature sensors, if one has to look through | | | | stimulus (changes its resistance with temperature), |
| separate sections on resistive, thermoelectric and | | | | but only become transducers when connected in a |
| semiconductor devices to make the comparison. | | | | bridge circuit to convert change in resistance to |
| Alternatively, to try and differentiate devices by | | | | change in voltage, since the complete circuit then |
| function often tends to be a rather boring catalogue | | | | transduces from the thermal to the electrical domain. |
| of numerous unrelated devices. The important thing | | | | A solar cell is both a sensor and a transducer, since it |
| about them is signals are transformed from one form | | | | responds to a stimulus (produces a current or voltage |
| to another. It is also possible to discuss sensors from | | | | in response to radiation) and also transducer from the |
| the functional viewpoint, under headings such as | | | | radiant to the electrical domain. It does not require |
| length, temperature, etc., suitable for someone who | | | | any associated circuitry, though in practice an |
| actually wants to select or use a sensor for a | | | | amplifier would usually be used. All transducers thus |
| particular application rather than just read around the | | | | contain a sensor, and many (though not all) sensors |
| subject. | | | | are also transducers. |
| The words 'sensors' and 'transducers' are both widely | | | | The distinction is rather small and as soon as one |
| used in the description of measurement systems. | | | | actually uses a sensor (by applying power to it) it |
| The former is popular in the USA whereas the latter | | | | becomes a transducer. An interesting classification of |
| is more often used in Europe. The choice of words in | | | | devices can be achieved by considering the various |
| science is rather important. In recent years there has | | | | forms of energy or signal transfer. |
| been a tendency to coin new words or to misuse (or | | | | The word 'actuate' means 'to put into, or incite to, |
| misspell) existing words, and this can lead to | | | | action' and actuators are devices that produce the |
| considerable ambiguity and misunderstanding, and | | | | display or observable output in a measurement |
| tends to diminish the preciseness of the language. | | | | system such as a light-emitting diode (LED) or moving |
| The matter has been very apparent in the computer | | | | coil meter. They are of course transducers used for |
| and microprocessor areas, where preciseness is | | | | output purposes, since they transduce from one |
| particularly important, and can seriously confuse | | | | domain to another (ie. electrical to radiant for LEDs). |