A sensor records some kind of real-world measurement into a form which can be registered by an instrument (or displayed on a dial).
A transducer takes one form of energy (chemical, physical, optical) and converts it to another one (typically but not limited to electrical energy).
The real difference is that a sensor can be made up of multiple transducers (A glass pH electrode has 4 transducers but is regarded as a single sensor).
A sensor can also be comprised of a single transducer, so in some cases sensor and transducer are truly interchangeable.
But then, this has all been said byother posters too.
Shane.
you naughty boy
