This book contains a selection of papers and articles in instrumentation previously pub- lished in technical periodicals and journals of learned societies. Our selection has been made to illustrate aspects of current practice and applications of instrumentation. The book does not attempt to be encyclopaedic in its coverage of the subject, but to provide some examples of general transduction techniques, of the sensing of particular measurands, of components of instrumentation systems and of instrumentation practice in two very different environments, the food industry and the nuclear power industry. We have made the selection particularly to provide papers appropriate to the study of the Open University course T292 Instrumentation. The papers have been chosen so that the book covers a wide spectrum of instrumentation techniques. Because of this, the book should be of value not only to students of instrumen- tation, but also to practising engineers and scientists wishing to glean ideas from areas of instrumentation outside their own fields of expertise. In recent years instrumentation has emerged as a discipline in its own right rather than as an adjunct to traditional science and engineering disciplines. This development has been driven partly by the needs of industries for new and improved sensing techniques, and partly by new technological developments such as microprocessors, optical fibres and in- tegrated silicon sensors which are revolutionising sensing and signal processing practice.