Thomas G. Hesketh

A novel micromachined accelerometer capacitive interface

In this paper a feasibility study of a novel interface concept is described for the design of a closed-loop accelerometer based upon a micromachined capacitive sensing element. The approach combines the advantages of the simple signal pick-off arrangement typically used for analogue accelerometers with those of accelerometers based upon an oversampling technique or sigma-delta modulation, which include direct digital output signal, an inherent self-test feature and improved system stability. The interface circuitry is low in component count, which makes it particularly suitable for prototype evaluation, yet has the potential for a high-performance device.

Mathematical model for a micromachined accelerometer

A mathematical model is developed for both open- and closed-loop accelerometers having capacitive sensing and electrostatic feedback. Test results on actual micromachined devices are compared with simulation employing the mathematical model.

A low cost analogue current transducer

The development and construction of a low cost current transducer is described. A simplified mathematical model is derived by filtering the limit cycle with a low pass filter. The test results were made with a variety of ferrite cores. As no Hall effect device is required, there are considerable manufacturing advantages and the device is not temperature sensitive.

Digital pressure transducer

A closed-loop digital pressure transducer is described which employs a quartz sensor embedded into a sigma delta modulator. Limit cycle analysis and test results are included for this nonlinear discrete-data system.

Control System Design Study for a Micromachined Accelerometer

Abstract In this paper an analogue, closed loop accelerometer based upon a bulk-micromachined, capacitive sensing element is described. The sensing element is embedded in a closed loop control system using electrostatic forces as a reset mechanism. A mathematical model is derived which allows to employ conventional linear control theory. The validity of the model is discussed. Particular attention is paid to the controller design; here a PID controller is used. The simulated results are compared to measurements on the actual hardware prototype.

Developments in Digital Transducers for Vehicle Control and Telemetric Instrumentation

Abstract A class of closed loop transducers is described having a digital output in form of a serial pulse stream. As representatives a current transducer and a micromachined accelerometer are introduced. In case of the accelerometer the pick-off and feedback mechanism are of special importance and are discussed in detail. The nonlinear effects inherent in certain types of micromachined control arrangements are considered and illustrated by experimental results. A novel control system strategy for the digital accelerometer is described.