Measuring and testing – Instrument proving or calibrating – Speed – velocity – or acceleration
Reexamination Certificate
1997-10-16
2001-10-30
Williams, Hezron (Department: 2856)
Measuring and testing
Instrument proving or calibrating
Speed, velocity, or acceleration
Reexamination Certificate
active
06308554
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an electronic device having an acceleration-sensitive sensor.
BACKGROUND INFORMATION
The German Patent No. 37 06 765 A1 discloses a crash (impact) sensor for a vehicle that comprises a test circuit. To be able to check the reliability of the crash sensor, an electro-acoustical transducer is provided, which acoustically exposes the acceleration sensor present in the crash sensor to ultrasonic waves. The electrical signals output by the acceleration sensor are checked in an evaluation and trigger circuit with respect to defined criteria with the help of a test circuit.
In addition, the German Patent No. 37 36 294 A1 discloses a device for testing acceleration sensors for correct functioning, where one or more accelerometers are electrically excited in such a way that one of the sensors acts as a transmitter of structure-borne noise, while the other(s) receives its signals. The accelerometers are thus checked by means of an evaluation circuit for functioning, calibration and coupling into the housing structure.
The German Patent No. 35 42 397 A1 discloses an arrangement for testing piezoelectric accelerometers for correct functioning, which uses a plurality of piezoelectric elements provided with electrodes, at least one of which, as a measuring sensor, produces an electrical reaction voltage when a force caused by the acceleration to be taken up is applied to it, and in the case of which, at least one of the piezoelectric elements acts for a time as an actuator for the other piezoelement, in that an electrical test voltage is supplied to the electrodes of the actuator element.
Furthermore, the U.S. Pat. No. 3,830,091 discloses a test device for acceleration sensors, which uses an aluminum rod, which is able to be excited to vibrate by piezoelectric crystals. A reference accelerometer and the accelerometer to be tested are mounted on the end face of the aluminum rod. An evaluation circuit compares the output signals from both of the accelerometers mounted on the end face of the aluminum rod, which are excited by the vibrating aluminum rod.
In addition, the U.S. Pat. No. 3,120,622 discloses a self-calibrating accelerometer, which uses an acceleration-sensitive element and, closely associated with said element, a piezoelectric element. When electrically excited, this piezoelectric element produces mechanical vibrations and, consequently, excites the acceleration-sensitive element.
Finally, the German Patent Application No. 38 09 299 C2 discloses an electronic device having an oscillatory sensor and an evaluation circuit for evaluating an output signal from the sensor that appears when said sensor is subjected to an acceleration load. This reference uses a vibration generator in the vicinity of the sensor capable of exciting the sensor to vibrate mechanically, the sensor being able to be excited for testing purposes by the vibration generator to produce vibrations which also include the resonant frequency of the sensor.
SUMMARY OF THE INVENTION
In an especially simple manner, the present invention makes it possible to check the electronic device for reliable operation, which also includes, in particular, testing the sensor. In contrast to the solutions known from prior art, no additional voltage sources or external vibration generators are needed to perform the test. It is especially advantageous that the sensor is a frequency-determining component of a resonant circuit and is able to be excited to vibrate by appropriately designing this resonant circuit, at least during a test phase, advantageously, however, constantly during the vehicle's operating times. As soon as the sensor vibrates, one can assume that it is in working order and that it is registering accelerations acting on the vehicle. Should the sensor be damaged, e.g., in the event of a break in the ceramic substrate or separation of electrodes or the like, it will not be possible to excite the sensor to vibrate. It is especially advantageous that the sensor can be alternately excited into series or parallel resonance by means of comparatively simple circuit elements, so that the possibilities for diagnosing the functioning of the sensor are broadened. The circuit elements are preferably triggered by a microcomputer, so that diverse switching variants can be simply programmed. Another advantageous refinement made by the present invention, the resonant circuit is dimensioned to allow the sensor to be excited to vibrate at its natural frequency. However, this natural frequency is substantially higher than the frequency range within which the useful signal to be evaluated is to be expected. Since low-pass filtering is expedient to better evaluate the useful signal, the oscillator frequency of the vibrating sensor cannot be easily transmitted to the evaluation circuit. Therefore, frequency-divider circuits are provided in the advantageous refinements of the present invention, which lower the oscillator frequency to a low value that is also able to still pass through the low-pass circuits.
In one especially advantageous exemplary embodiment of the present invention, a bistable flip-flop controlled by a microcomputer is used as a frequency-divider circuit. In another advantageous exemplary embodiment of the present invention, a clock signal for controlling the entire evaluation circuit is derived from the oscillator frequency of the vibrating sensor. The lack of existence of this clock signal can be simply used as a fault-detection means in the case of a defective sensor.
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Bergfried Dietrich
Gademann Lothar
Henne Ralf
Hopf Gerald
Kursawe Frank
Fayyaz Nashmiya
Kenyon & Kenyon
Robert & Bosch GmbH
Williams Hezron
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