Low-frequency sensitive force-balance linear standard accelerometer

Abstract

An accelerometer based on an automatic force-balance principle has been developed with a view to measuring linear acceleration from 0.01 to 1.0 g, with overall accuracy of 0.1% under static as well as dynamic conditions in the frequency range from 0 to 70 Hz. The analysis of errors of components of various blocks and its experimental verification, the exact determination of damping ratio, and the phenomenon of reduction of undamped natural frequency arising out of the so called 'piston effect', caused by the highly viscous damping fluid, are some of the highlights in the determination of the performance. Finally, it is concluded that this linear accelerometer, using a new technique of calibration and an accurate measuring device, can be considered as a standard accelerometer. Principal symbolsA = gain of the /1-circuit {} = Bl = gain of the B-circuit B = flux density b = coefficient of damping D = diameter of feedback coil h = damping factor /," = current in calibrating coil I O ut -current in feedback coil K o = stiffness of the spring Kp = introduced stiffness K v = A 2 A 3 A^A S m = mass of the movable system n = transformation ratio n e = ratio of applied frequency to equivalent frequency n 0 = ratio of applied frequency to natural frequency N = number of turns of the feedback coil N t = number of turns on the primary side of transformer N 2 -number of turns on the secondary side of transformer R = matched output resistance on the secondary side of the transformer R in = input resistance of the transformer on primary side of the transformer a = relative value of actuating quantity £ 0 = damping ratio (open-loop) Paper 4933A (S4), first £ e = damping ratio (closed-loop) co = applied frequency cop = introduced frequency (closed-loop system) co e = equivalent frequency (closed-loop system) co 0 -undamped natural frequency (open-loop system)

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