Abstract: A sensing structure for an accelerometer includes a support and a proof mass mounted to the support by flexible legs for in-plane movement in response to an applied acceleration along a sensing direction. The proof mass includes a plurality of moveable electrode fingers extending substantially perpendicular to the sensing direction and spaced apart in the sensing direction. The structure also includes at least one pair of fixed capacitor electrodes comprising first and second sets of fixed electrode fingers extending substantially perpendicular to the sensing direction and spaced apart in the sensing direction; the first set of fixed electrode fingers arranged to interdigitate with the moveable electrode fingers with a first offset in one direction from a median line therebetween, and the second set of fixed electrode fingers arranged to interdigitate with the moveable electrode fingers with a second offset in the opposite direction from a median line therebetween.

Abstract: A closed loop method of controlling a capacitive accelerometer uses two servo loops. A Vcrit servo loop uses an output signal (S2) modulated by a sine wave signal (S1). The Vcrit control signal adjusts the magnitude of the PWM drive signals applied to the fixed capacitor electrodes of the accelerometer, thereby optimising open loop gain.

Abstract: An inertial sensor includes a substantially planar, rotationally symmetric proof mass, a capacitive pick-off circuit connected to the proof mass, an electrical drive circuit connected to the four pairs of electrodes. The drive circuit is arranged to apply first in-phase and anti-phase pulse width modulation (PWM) drive signals with a first frequency to the first and third electrode pairs, such that one electrode in each pair is provided with in-phase PWM drive signals and the other electrode in each pair is provided with anti-phase PWM drive signals and to apply second in-phase and anti-phase PWM drive signals with a second frequency, different to the first frequency, to the second and fourth electrode pairs, such that one electrode in each pair is provided with in-phase PWM drive signals and the other electrode in each pair is provided with anti-phase PWM drive signals.

Abstract: An inertial sensor includes a substantially planar, rotationally symmetric proof mass, a capacitive pick-off circuit connected to the proof mass, an electrical drive circuit connected to the four pairs of electrodes. The drive circuit is arranged to apply first in-phase and anti-phase pulse width modulation (PWM) drive signals with a first frequency to the first and third electrode pairs, such that one electrode in each pair is provided with in-phase PWM drive signals and the other electrode in each pair is provided with anti-phase PWM drive signals and to apply second in-phase and anti-phase PWM drive signals with a second frequency, different to the first frequency, to the second and fourth electrode pairs, such that one electrode in each pair is provided with in-phase PWM drive signals and the other electrode in each pair is provided with anti-phase PWM drive signals.

Abstract: A sensing structure for an accelerometer includes a support and a proof mass mounted to the support by flexible legs for in-plane movement in response to an applied acceleration along a sensing direction. The proof mass includes a plurality of moveable electrode fingers extending substantially perpendicular to the sensing direction and spaced apart in the sensing direction. The structure also includes at least one pair of fixed capacitor electrodes comprising first and second sets of fixed electrode fingers extending substantially perpendicular to the sensing direction and spaced apart in the sensing direction; the first set of fixed electrode fingers arranged to interdigitate with the moveable electrode fingers with a first offset in one direction from a median line therebetween, and the second set of fixed electrode fingers arranged to interdigitate with the moveable electrode fingers with a second offset in the opposite direction from a median line therebetween.

Abstract: A closed loop method of controlling a capacitive accelerometer uses two servo loops. A Vcrit servo loop uses an output signal (S2) modulated by a sine wave signal (S1). The Vcrit control signal adjusts the magnitude of the PWM drive signals applied to the fixed capacitor electrodes of the accelerometer, thereby optimising open loop gain.

Abstract: An angular velocity sensor or gyroscope has a ring and a primary drive transducer arranged to cause the ring to oscillate in a primary mode substantially at the resonant frequency of the primary mode of the ring. A primary control loop receives primary pick-off signals from the primary pick-off transducer and provides primary drive signals to the primary drive transducer so as to maintain resonant oscillation of the ring. The primary control loop includes a demodulator arranged to determine the amplitude of the fundamental frequency of the primary pick-off signals and a demodulator arranged to determine the amplitude of the second harmonic frequency of the primary pick-off signals and a drive signal generator arranged to produce the primary drive signals with an amplitude that is dependent on a ratio of the amplitude of the second harmonic frequency of the primary pick-off signal over the amplitude of the fundamental frequency of the primary pick-off signal as derived by a divider.

Abstract: An angular velocity sensor or gyroscope has a ring and a primary drive transducer arranged to cause the ring to oscillate in a primary mode substantially at the resonant frequency of the primary mode of the ring. A primary control loop receives primary pick-off signals from the primary pick-off transducer and provides primary drive signals to the primary drive transducer so as to maintain resonant oscillation of the ring. The primary control loop includes a demodulator arranged to determine the amplitude of the fundamental frequency of the primary pick-off signals and a demodulator arranged to determine the amplitude of the second harmonic frequency of the primary pick-off signals and a drive signal generator arranged to produce the primary drive signals 116 with amplitude that is dependent on a ratio of the amplitude of the second harmonic frequency of the primary pick-off signal over the amplitude of the fundamental frequency of the primary pick-off signal as derived by a divider.

Abstract: The accelerometer has a base (2), an outer planar ring-like support frame (17) fixedly bonded to the base (2), and an inner planar ring-like support frame (18) flexibly suspended within the outer frame (17) by mounts (19) connecting the inner frame (18) to the outer frame (17) so that the inner frame (18) is spaced from the base (2), co-planar with the outer support fram (17) so as to provide flexible suspension for the inner support frame (18) reducing compressive and/or tensile forces on mounting legs (4) flexibly mounting a proof mass (3) in the inner support frame (18).

Abstract: In an open loop rate sensor clockwise (CW) and counterclockwise (CCW) beams from a common source 10 pass in opposite directions around a coil 20 of optical fiber and recombine on a detector 24. A phase modulator 22 applies a stepped phase modulation in which each step is of duration equal to the transit time of the coil 20 and in which alternate steps are zero. The intermediate steps increase linearly from zero to 2.pi.. Without modulation, the CW and CCW beams combine on the detector with a combined intensity which varies as a cosine of rate. The above modulation causes two points to either side of the cosine fringe to be sampled which move progressively farther as the amplitude of the stepped modulation increases. The sample data is processed to determine the rate applied to the rate sensor.