Design Factors Controlling the Dynamic Performance of Instruments
Charles Stark Draper, G. P. Bentley · Transactions of the American Society of Mechanical Engineers · 1940
Abstract This paper presents a generalized treatment of instruments which have a single movable index, controlled by the magnitude of a single actuating quantity. Such an instrument acts as a system with one degree of freedom and is studied by the well-known methods developed for such systems. Instruments which include servomechanisms cannot be treated as systems with one degree of freedom and are therefore excluded from consideration. From the standpoint of static indications, it is shown that the essential properties of an instrument can be specified in terms of range, scale sensitivity, calibration error, environmental error, and uncertainty. The definition and use of each of these quantities is discussed. It is shown that the response of an instrument to rapid changes in the actuating quantity can be calculated if two parameters called instrument characteristics are known. One of these parameters has the dimension of time and is called the characteristic time. The second parameter is nondimensional and is called the damping ratio. Nondimensional curves, showing instrument responses to three typical variations in the actuating quantity, are plotted for a series of values of the damping ratio. These curves are used in an illustrative example to show how the values of the instrument characteristics, required to keep dynamic errors below a given limit, can be determined in a practical case.