Fault detection circuit for sensors

Details Fault detection circuit for sensors Fault detection circuit for sensors

1994-12-22

2001-11-06

Swarthout, Brent A. (Department: 2632)

Communications: electrical

Land vehicle alarms or indicators

Internal alarm or indicator responsive to a condition of the...

C073S121000, C303S122000, C324S535000, 37, C701S076000

Reexamination Certificate

active

06313741

ABSTRACT:

The present invention relates, in general, to sensors which are normally employed in safety-related devices and, more particularly, this invention relates to a fault detection circuit for inductive and/or capacitive-type sensors, which during a testing cycle will feed a test signal into the sensor circuit.
BACKGROUND OF THE INVENTION
It is generally recognized that a sensor-fault detection circuit of this type is required in any instance where such sensors are to be employed in conjunction with safety-related devices. One particularly well known area where this applies is when these sensors are utilized in a vehicle anti-locking brake system. As a rule, inductive-type sensors are employed in such vehicle anti-lock brake system to measure the rotational speed of the wheels on such vehicle. In this application, it is obvious that these sensors are subjected to a number of undesirable conditions. These undesirable conditions include dirt, moisture and rather high vibration at times. Therefore, these sensors will exhibit a relatively high susceptibiity to failure. Consequently, it is imperative that any failure occurring in such a sensor be detected as quickly as possible. Such early detection being desirable in order to substantially eliminate a serious malfunctioning in the control of such anti-lock brake system.
A fault detection circuit for a vehicle anti-lock brake control system has been taught in the prior art. See, for example, German patent publication DE-OS 31 26 102. The fault detection circuit taught in this particular reference monitors the anti-lock brake control system while the vehicle is stopping. In order to accomplish this, a safety circuit disconnects each of the respective wheel speed sensing devices. After the wheel speed sensors are disconnected by the safety circuit, the same test signals are fed into one pair of control channels each. In this system, identical test signals pass through each of the two pairs of control circuits. At this point the fault detection circuit will compare the signals which are generated at the output end in each pair of such control circuits. During this comparison, the fault detection circuit makes the assumption that in the case of a properly functioning control circuit the generated signals will be the same at the respective points. However, in this known fault detection circuit, as soon as a non-agreement of these generated signal sequences can be detected such fault detection circuit causes a warning or switch signal to be produced. A check of the wheel speed sensors proper does not take place.
A fault detection circuit for a skid control system is also taught in German patent publication DE-OS 32 34 637. In this particular prior art fault detection circuit, the wheel speed sensors are also monitored with an astable multivibrator while the vehicle wheels are stopped. When the wheel speed sensor is connected and functioning properly in this system, a low-level natural frequency is produced. This low-level natural frequency is interrupted, however, in the case of a sensor malfunctioning. Such interruption occurs either by a short-circuit or by disconnection. Consequently, this will result in a different signal sequence as compared to the other operative wheel speed sensor circuits. This different signal sequence is perceived as a malfunction in this fault detection circuit. A major drawback with this fault detection circuit is that it is relatively complicated.
SUMMARY OF THE INVENTION
The present invention provides an improved sensor-fault detection circuit. Such sensor-fault detection circuit is particularly useful in conjunction with either an inductive or capacitive-type sensor. For testing purposes, the sensor-fault detection circuit feeds a test signal into the sensor circuit in a manner such that the transit time of the test signal passing through such sensor can be analyzed by means of a timing device.
OBJECTS OF THE INVENTION
It is, therefore, one of the primary objects of the present invention to provide an improved fault detection circuit for a sensor which is relatively simplistic in design.
Still another object of the present invention is to provide an improved fault detection circuit for a sensor which is either an inductive or capacitive-type sensor which can be connected to a time difference measuring device so that the impedance of such sensor can be exploited for the existence of a-fault being present in the sensor circuit.
An additional object of the present invention is to provide an improved fault detection circuit for a sensor in which both interrupt faults and any short-circuit faults which may exist within the sensor circuit can be detected by such fault detection circuit.
In addition to the specific objects and advantages of the fault detection circuit for a sensor described above, various other objects and advantages of the present invention will become more readily apparent to those persons who are skilled in the electronic sensor art from the following more detailed description of the present invention, particularly when such description is taken in conjunction with the attached drawing FIGS. and with the appended claims.


REFERENCES:
patent: 4085979 (1978-04-01), Leiber et al.
patent: 4546437 (1985-10-01), Bleckman et al.
patent: 3234637 (1984-03-01), None

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