GB958229A - Improvements in or relating to accelerometers - Google Patents

Abstract

958,229. Measuring electrically. LITTON INDUSTRIES Inc. Oct.31, 1960, No. 37354/60. Heading G1N. In an accelerometer, suitable for inclusion in auto-navigational systems of aircraft and missiles, comprising a floating pendulum and torquing means including a magnet for applying a null-restoring torque to the pendulum, the centre of mass,the centre of buoyancy, and the pivot axis of the pendulum are so mutually displaced that variations of the magnetic field strength of the torquing means due to temperature changes are opposed by temperature-induced variations of the density of the flotation liquid. As shown, Figs. 1, 2, and accelerometer comprises a pendulum 15 rotatably mounted in jewelled bearings 17,19, in flotation fluid within a housing 11. Angular deflection of the pendulum due to an acceleration along the axis A-A produces an output from signal generators 21, 23, the pickoff coils 25 of which are mounted on the pendulum and co-operate with exciter coil assemblies 28 mounted in the housing. This output is amplified and rectified and fed to torquer coils 35 on the pendulum which co-operate with permanent magnets 33 mounted in the cover 13 of the housing to apply a restoring torque to the pendulum. The pendulum is preferably made of non-magnetic material and the housing of a magnetic material such as cold rolled steel. Each magnet 33 has a cap 57 of high permeability material at its inner end and a ring 61 of similar material, cap and ring defining a space to receive torquer coil 35. To shield the generators 21, 23 from the fields of magnets 33, discs 60 of high coercivity, magnetised so as to nullify the undesired effects of said fields, are positioned against caps 57. To avoid variations in the scale factor of the device due to changes in the field strength of magnets 33 with temperature,by utilising density-variations of the flotation fluid, the device is so designed that 1 2 = α/γ (l 1 + l 2 ); where l 1 is the distance between the centre of mass CM (Fig. 2) of the pendulum and the point of intersection of the axis A-A and the pivot axis on the line joining CM and the centre of buoyancy CB; l 2 is the distance between said point of intersection and CB; α is the coefficient of variation of restoring torque with temperature; y is the coefficient of volume expansion of the flotation fluid. Four trim screws 37 are provided in the pendulum for adjustment purposes. Each exciter coil assembly 28 includes a yoke in recessed portions at the ends of which are located U-shaped cores having coils 45, 47, and 49, 51, Fig. 4, wound on their legs. The exciter coils are connected in series to an A.C. source, and the output of pick-up coils 25 is passed via a demodulator-amplifier 55, which may comprise valves or, advantageously, transistors, to the torquer coils 35. A resistor may be inserted in the torquer coil circuit to provide an analogue output, or an analogue-to-digital converter may be used.