Self-Test for Resonant Structure Sensors Applied to a Tuning Fork Gyro and a Resonant Accelerometer

The measurement of angular rate and linear acceleration are widely used in automotive systems [1,2]. In all present applications and even more in future „x-by-wire” steering systems sensor errors or undetected sensor failures may have serious consequences. In order to achieve a higher degree of sensor safety we developed a new self-test concept for resonant structure sensors [3]. It is expected to fulfil the following conditions: no influence of the self-test on the measurement, measuring signal and test signal are simultaneous and time-continuous, a certain calibration of the sensor is possible, the self-test covers the whole measurement and dynamic range of the sensor, the self-test signal couples to the mechanical structure of the sensor and no constructive changes of the sensor element are necessary. We present properties of this self-test applied to a tuning fork angular rate sensor [4,5] and a resonant accelerometer [6]. A self-test circuit generates a special test-signature, which is applied to the actuating elements in order to generate an additional vibration on the read-out structure of the sensor. This produces an effect both equivalent to and separable from the physical quantity to be measured. This effect of the test signature on the sensor is measured and compared with the initial test signature. An intolerable deviation from the expected behaviour activates the sensor-failure-signal.