Electricity: measuring and testing – Electrical speed measuring – Including speed-related frequency generator
Reexamination Certificate
2002-07-26
2003-10-21
Le, N. (Department: 2862)
Electricity: measuring and testing
Electrical speed measuring
Including speed-related frequency generator
C324S207120, C324S225000
Reexamination Certificate
active
06636033
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a sensor apparatus and a corresponding method for generating an output signal of a sensor apparatus.
BACKGROUND ART
WO 99/42789 discloses an apparatus for detecting a passage between a point on a body and a reference position. The apparatus comprises a pair of magnetic field sensors, each of the sensors generating an output signal based on the size of the magnetic field which passes through the sensor. A difference-forming circuit is provided which receives the output signals of the sensors and generates a difference signal with a peak value when the point of the body is positioned between the pair of sensors. Furthermore, a peak value detector is provided which detects the peak value in the difference signal. Moreover, the apparatus comprises a threshold value circuit which receives the difference signal, for the purpose of generating a gate signal if the magnitude of the difference signal exceeds a threshold level, the gate signal enabling the peak value pulse to be forwarded to an output terminal of the apparatus, and preventing peak value pulses from being forwarded to the output terminal of the apparatus in the absence of the gate signal. Finally, the apparatus comprises a threshold value setting circuit for setting the threshold value in accordance with the magnitude of the difference signal.
DE 197 01 262 A1 discloses a detector for passing magnetic articles with automatic gain control.
EP 0 642 029 A1 and EP 0 642 029 B1 disclose a rise-activated Hall voltage sensor. This sensor comprises a circuit branching device which is arranged in such a way that it follows a positive rise, the subsequent positive peak value of the Hall voltage is held at the detector output and the Hall voltage is applied to a comparator, so that, if, after incipient impinging [sic] of the Hall voltage from the positive maximum value, the increasing difference between the Hall voltage and the held voltage exceeds a predetermined magnitude, the resulting comparator output pulse indicates the beginning of a variation in the strength of the surrounding magnetic field at the Hall element.
Although applicable, in principle, to a wide variety of sensor apparatuses, the present invention and the problem area on which it is based are described with reference to a motor vehicle crankshaft sensor.
As is known, sensors are used to detect the movement or the positional state of rotating parts. Examples thereof are crankshaft, cam shaft, transmission and ABS sensors in motor vehicles. The sensors used are preferably Hall sensors which sense the variations in a magnetic field. For this purpose, by way of example, a permanent magnet is fitted to a stationary part in order to generate a magnetic field. This magnetic field is then modulated, depending on position, by a gearwheel fixed to the rotating part or by another ferromagnetic transmitter. In this case, the Hall sensor is preferably situated between the permanent magnet and the gearwheel or transmitter and can thus detect fluctuations in the magnetic field. By way of example, if a tooth of the gearwheel lies in the magnetic field, then a “high” output signal is supplied, while a gap between the teeth brings about a “low” output signal. In this way, the instantaneous position or annular velocity of a rotating part can be inferred from the signal output by the Hall sensor.
The signal supplied by such a sensor is significantly influenced by the operating conditions under which the sensor is used. These operating conditions include unavoidable imponderables such as, for example, operating temperature or size of the air gap, etc. Despite the fluctuations caused by the operating conditions, the sensor should supply an output signal that is defined as well as possible. In other words, the output signal should have a well-defined profile independently of the fluctuations caused by the operating conditions. The reason for this is as follows: if a sensor apparatus supplies a sinusoidal signal, for example, then a well-defined behavior of a system disturbed by the sensor apparatus can be obtained when switching operations in the system which depend on the output signal of the sensor are performed at the zero crossings of the signal. This is because these zero crossings are independent of the respective signal amplitude and, moreover, have a large edge steepness.
It goes without saying that a switching point other than zero crossing or signal center may possibly also be advantageous in the case of other signal waveforms of the output signal of the sensor.
During the evaluation of the output signal of a sensor for switching a system controlled by said sensor, a switching point should thus be complied with independently of the signal amplitude of the output signal of the sensor, which applies even to those low signals. In detail, VDI Reports 1287, 1996, pages 583 to 611, “A new generation of Hall-effect gearwheel sensors: advantages through the combination of BIMOS technology and new packaging formulations”, describes a sensor arrangement in which firstly the amplitude of the output signal of a sensor is normalized if appropriate with the aid of an analog-to-digital converter. The signal peak values are detected with the aid of two further analog-to-digital converters and with digital-to-analog converters. A switching threshold is derived and defined from said peak values. In this way, finally, it is possible to achieve a system behavior that is essentially independent of temperature fluctuations and the width of the air gap. The outlay required for this sensor arrangement is relatively high, however, since gain matching and numerous analog-to-digital converters are required.
A circuit arrangement for calibrating switching points of a decision unit driven by an analog input signal, independently of a DC component contained in the input signal besides an AC component, is known, the input signal having upper and lower signal peaks which are in a selectable fixed ratio to one another. Provision is made, in particular, of peak detectors for determining the upper and lower signal peaks of the input signal; a controllable reference unit for providing a reference signal; a computation unit for determining the average value; a comparison unit; a regulating unit for compensating for the DC component of the input signal and a second regulating unit for oppositely tracking the reference value, said second regulating unit being connected downstream of the comparison unit on the input side and being connected to the reference unit on the output side.
In particular, the output of the sensor apparatus is blocked during the calibration phase. In the case of sensor apparatuses for movement and position identification, however, it is often important to correctly identify even small movements or the beginning of a movement. In the case of sensors which do not operate in a static manner, but rather operate by means of filtering or self-calibration in order to obtain a higher accuracy, the problem can arise, therefore, that, during the transient recovery times, the system operates either only inaccurately or, alternatively, not at all, so that the initial information is lost. A known sensor apparatus needs, for example, a time of six zero crossings until it supplies correct output information after the conclusion of the calibration phase. The time through to that point is required in order to set the internal circuit parameters in such a way that the circuit has suitable operating points.
Static sensors without adaptation do not have this problem. By the same token, they usually also have reduced sensitivity, which restricts the range of use. Sensors with a filter can react to the first or second zero crossing, but usually require a relatively long time before the parameters have adapted to the current operation to an extent such that the specified accuracy is also achieved.
SUMMARY OF THE INVENTION
Therefore, it is an object of the present invention to provide a sensor apparatus and a method for generating an output signal of a sen
Aurora Reena
Infineon - Technologies AG
Jenkins & Wilson & Taylor, P.A.
Le N.
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