Abstract: An inertial measurement system for a spinning projectile includes: a first, roll gyro to be oriented substantially parallel to the spin axis of the projectile; a second gyro and a third gyro with axes arranged with respect to the roll gyro; a controller, arranged to: compute a current projectile attitude from the outputs of the first, second and third gyros, the computed attitude comprising a roll angle, a pitch angle and a yaw angle; calculate a roll angle error; provide the roll angle error as an input to a Kalman filter that outputs a roll angle correction and a roll rate scale factor correction; and apply the calculated roll angle correction and roll rate scale factor correction to the output of the roll gyro.

Abstract: A capacitive accelerometer comprises: a substantially planar proof mass mounted to a fixed substrate by flexible support legs so as to be linearly moveable in an in-plane sensing direction. The proof mass comprises first and second sets of moveable capacitive electrode fingers. First and second sets of fixed capacitive electrode fingers interdigitates with the first and second sets of moveable electrode fingers respectively. A set of moveable damping fingers extend from the proof mass substantially perpendicular to the sensing direction, laterally spaced in the sensing direction. A set of fixed damping fingers mounted to the fixed substrate interdigitates with the set of moveable damping fingers and comprises an electrical connection to the proof mass so that the interdigitated damping fingers are electrically common. The damping fingers are mounted in a gaseous medium that provides a damping effect.

Abstract: A sensor comprises a substrate 16 and a sensor element 20 anchored to the substrate 16, the substrate 16 and sensor element 20 being of dissimilar materials and having different coefficients of thermal expansion, the sensor element 20 and substrate 16 each having a generally planar face arranged substantially parallel to one another, the sensor further comprising a spacer 26, the spacer 26 being located so as to space at least part of the sensor element 20 from at least part of the substrate 16, wherein the spacer 26 is of considerably smaller area than the area of the smaller of face of the substrate 16 and that of the sensor element 20.

Abstract: An accelerometer comprises a support, a first mass element and a second mass element, the mass elements being rigidly interconnected to form a unitary movable proof mass, the support being located at least in part between the first and second mass elements, a plurality of mounting legs securing the mass elements to the support member, at least two groups of movable capacitor fingers provided on the first mass element and interdigitated with corresponding groups of fixed capacitor fingers associated with the support, and at least two groups of movable capacitor fingers provided on the second mass element and interdigitated with corresponding groups of fixed capacitor fingers associated with the support.

Abstract: An aircraft ground collision detection system comprising: an object detection device for mounting on an aircraft and arranged to detect objects and output the location of each detected object; and a processor arranged to: receive the ground speed of the aircraft and the heading of the aircraft and the detected location of each detected object; predict the aircraft's path based on the ground speed and the heading; compare the predicted aircraft path with the object locations; and output an alert based on the overlap or proximity of the predicted aircraft path with the object locations. By predicting the path of the aircraft based on detected ground speed and heading, the system can accurately assess which detected objects pose a collision threat.

Abstract: A method of compensating for signal error is described, comprising: receiving a first signal from a first sensor, said first signal indicative of a movement characteristic; applying an error compensation to said first signal to produce an output signal; applying a variable gain factor to said error compensation; receiving a second signal from a second sensor indicative of said movement characteristic; wherein said error compensation is calculated using the difference between said output signal and said second signal, and said variable gain factor is calculated using said first signal.

Abstract: A successive approximation Analogue to Digital Converter (ADC), comprising: a sample and hold device arranged to sample and hold an input signal at the beginning of a conversion cycle; a successive approximation register that sequentially builds up a digital output from its most significant bit to its least significant bit; a digital to analogue converter that outputs a signal based on the output of the successive approximation register; a comparator that compares the output of the digital to analogue converter with an output of the sample and hold device and supplies its output to the successive approximation register; and a residual signal storage device arranged to store the residual signal at the end of a conversion cycle; and wherein the successive approximation ADC is arranged to add the stored residual signal from the residual signal storage device to the input signal stored on the sample and hold device at the start of each conversion cycle.

Abstract: A MEMS sensor comprises a vibrating sensing structure formed from a semiconductor substrate layer (50). The semiconductor substrate layer (50) is mounted on a pedestal comprising an electrically insulating substrate layer (52) bonded to the semiconductor substrate (50) to form a rectangular sensor chip. The pedestal further comprises an electrically insulating spacer layer (54) for mounting the sensor chip to a housing. The electrically insulating spacer layer (54) is octagonal. When the vibrating sensing structure is excited into a cos 2? vibration mode pair, the quadrature bias arising from any mode frequency split is not affected by changes in temperature as a result of the octagonal spacer layer (54).

Abstract: A vibratory ring structure is described which comprises a ring body and at least one ring electrode secured thereto, the or each ring electrode extending over a first angular extent and: being attached to the ring body over second angular extent, wherein the first angular extent is greater than the second angular extent.

Abstract: A method for closed loop operation of a capacitive accelerometer uses a single current source (62) and a single current sink (64) to apply an in-phase drive signal V1? to a first set of fixed capacitive electrode fingers and a corresponding anti-phase drive signal V2? to a second set of fixed capacitive electrode fingers. This provides a net electrostatic restoring force on the proof mass for balancing the inertial force of the applied acceleration and maintains the proof mass at a null position.

Abstract: A sensor comprises a substrate 16 and a sensor element 20 anchored to the substrate 16, the substrate 16 and sensor element 20 being of dissimilar materials and having different coefficients of thermal expansion, the sensor element 20 and substrate 16 each having a generally planar face arranged substantially parallel to one another, the sensor further comprising a spacer 26, the spacer 26 being located so as to space at least part of the sensor element 20 from at least part of the substrate 16, wherein the spacer 26 is of considerably smaller area than the area of the smaller of face of the substrate 16 and that of the sensor element 20.

Abstract: A method for closed loop operation of a capacitive accelerometer comprising: a proof mass; first and second sets of both fixed and moveable capacitive electrode fingers, interdigitated with each other; the method comprising: applying PWM drive signals to the fixed fingers; sensing displacement of the proof mass and changing the mark:space ratio of the PWM drive signals, to provide a restoring force on the proof mass that balances the inertial force of the applied acceleration and maintains the proof mass at a null position; detecting when the mark:space ratio for the null position is beyond a predetermined upper or lower threshold; and further modulating the PWM drive signals by extending or reducing x pulses in every y cycles, where x>1 and y>1, to provide an average mark:space ratio beyond the upper or lower threshold without further increasing or decreasing the mark length of the other pulses.

Abstract: A sensor comprises a substrate (16) and a sensor element (20) anchored to the substrate (16), the substrate (16) and sensor element (20) being of dissimilar materials and having different coefficients of thermal expansion, the sensor element (20) and substrate (16) each having a generally planar face arranged substantially parallel to one another, the sensor further comprising a spacer (26), the spacer (26) being located so as to space at least part of the sensor element (20) from at least part of the substrate (16), wherein the spacer (26) is of considerably smaller area than the area of the smaller of face of the substrate (16) and that of the sensor element (20).

Abstract: A vibratory gyroscope is provided comprising a plurality of secondary pickoff transducers which are each sensitive to the secondary response mode, wherein: at least two of the secondary pickoff transducers comprise skew transducers designed to be sensitive to the primary mode which produce an induced quadrature signal in response thereto. A method of using the gyroscope is provided comprising the steps of arranging electrical connections between the secondary pickoff transducers and a pickoff amplifier so that in use the induced quadrature signal is substantially rejected by the amplifier in the absence of a fault condition, and the amplifier outputs an induced quadrature signal when a fault condition disconnects one of the skew transducers from the amplifier, and a comparator compares the quadrature output from the pickoff amplifier with a predetermined threshold value and provides a fault indication when the predetermined threshold is exceeded.

Abstract: An accelerometer comprises a support (12), a proof mass (14) supported for movement relative to the support (12) by a plurality of mounting legs (16), a plurality of fixed capacitor fingers associated with the support (12) and a plurality of movable capacitor fingers associated with the proof mass (14), the fixed capacitor fingers being interdigitated with the movable capacitor fingers, the mounting legs (16) being of serpentine shape, each mounting leg (16) comprising at least a first generally straight section (16a), a second generally straight section (16a), and an end section (16b) of generally U-shaped form interconnecting the first and second generally straight sections (16a), wherein the thickness Te of the end section (16b) is greater than the thickness Tc of a central part (16c) of both of the first and second generally straight sections (16a).

Abstract: A method of processing an amplitude-modulated analog signal at a carrier frequency Fc comprises: digitizing the analog signal to produce an input bit stream that represents the amplitude of the analog signal; generating an in-phase reference bit stream that is synchronous to the carrier frequency Fc and represents an in-phase digital reference signal substantially in the form of a sine and/or cosine wave; and multiplying the input bit stream with the in-phase reference bit stream to produce an output bit stream representing the amplitude modulation of the analog signal.

Abstract: A method of tuning a vibratory ring structure is described which comprises determining an angular spacing for a pair of fine tuning holes (16) of substantially the same size, located on or near the neutral axis of the vibratory ring structure (10), the angular offset being selected to reduce to an acceptable level the frequency split between the target normal mode and a further normal mode which Is angularly offset relative to the target normal mode, and forming the pair of fine tuning holes (16) in the vibratory ring structure (10) at the determined angular spacing, A ring structure, for example a gyroscope, tuned or balanced in this manner is also disclosed.

Abstract: A MEMS sensor comprises a vibrating sensing structure formed from a semiconductor substrate layer (50). The semiconductor substrate layer (50) is mounted on a pedestal comprising an electrically insulating substrate layer (52) bonded to the semiconductor substrate (50) to form a rectangular sensor chip. The pedestal further comprises an electrically insulating spacer layer (54) for mounting the sensor chip to a housing. The electrically insulating spacer layer (54) is octagonal. When the vibrating sensing structure is excited into a cos 2? vibration mode pair, the quadrature bias arising from any mode frequency split is not affected by changes in temperature as a result of the octagonal spacer layer (54).

Abstract: An exemplary vibrating structure gyroscope includes a ring structure, an external frame and a flexible support including a pair of symmetrical compliant legs arranged to retain the ring structure within the external frame. A metal track is provided on an upper surface of the ring structure, the compliant legs and the external frame, over an insulating surface oxide layer. Each flexible support is arranged to carry a metal track associated with a single drive or pick-off transducer. The metal track is repeated for eight circuits, one circuit for each transducer. Each circuit of metal track associated with a transducer begins at a first bond-pad on the external frame, runs along a first compliant leg, across an eighth segment of the ring structure and back along the other compliant leg to a second bond-pad on the external frame.

Abstract: An accelerometer comprises a support, a first mass element and a second mass element, the mass elements being rigidly interconnected to form a unitary movable proof mass, the support being located at least in part between the first and second mass elements, a plurality of mounting legs securing the mass elements to the support member, at least two groups of movable capacitor fingers provided on the first mass element and interdigitated with corresponding groups of fixed capacitor fingers associated with the support, and at least two groups of movable capacitor fmgers provided on the second mass element and interdigitated with corresponding groups of fixed capacitor fingers associated with the support.