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"present: a trends are towards instrument systems. In many more than the simple instruments mentioned. The functions of the pars of an instrument system may be categori: three systems: A sensing element, which acted upon by the variable to be measured (measurand), such as length, pressure, temperature, angle ete and which out some quantity, a signal. ; For instance, if pressure is applied to the bellows unit shown in Fig.1.1, the fee movement (x) of the free end is the output signal of the sensing element Sot Metol bellows Applied fluid pressure Fig. 1.1; Bellows used as a pressure sensing element. (b.) A signal conditioning element: The signal from the sensing element is usuall | very small, as in bellows and has to be amplified. Hence, the movement x of bellows may be converted to a much larger movement by, for example, ¢ system. Cc) An output element: The output of a system is required to do somethin be a visual output, such as the position of a pointer on a scale, liquid in a manometer, or the numerical readout on a digi eases, audible alarms may be operated as well as or instead of, : to indicate that values have reached unacceptal wa, ; measurement system may form on integral 
