Feedback in instruments and its applications
B.E. Jones · Journal of Physics E Scientific Instruments · 1979
Instruments can be considered as systems, and there are only a few structural schemes employed in the construction of such systems; one such scheme is the use of feedback. The general mode of operation of feedback-measuring systems is ascertained, and the reasons for applying feedback to a measurement situation are established. Using feedback it is possible to improve accuracy and speed of measurement, reduce the effect of interfering and modifying inputs, and allow remote indication and non-contact measurement. The property of inversion assists instrument design, and can provide for digital indication. Basic methods of stability assessment are given. The common balance variables are listed, and a wide range of instruments is discussed, making explicit the general properties of feedback. Measuring devices having a frequency output maintained by feedback, and the use of feedback for control purposes in instruments, are considered. The pedagogic implications are referred to, and an extensive list of references is provided.