Communications: electrical – Condition responsive indicating system – Specific condition
Patent
1999-02-24
2000-03-21
Lefkowitz, Edward
Communications: electrical
Condition responsive indicating system
Specific condition
340653, 363 17, 361 93, 324706, G08B 2100
Patent
active
060407794
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to a method and a circuit arrangement for monitoring the function of a symmetrical sensor bridge circuit having sensor elements, which are connected in a full bridge circuit. A semiconductor sensor in the form of a symmetrical bridge circuit, known from the prior art, and a differential amplifier circuit, which generates an output signal of the sensor bridge circuit, are often used for detecting a physical quantity, for example pressure, velocity, acceleration or the like. Within a defined measuring voltage range, this output signal from the sensor bridge circuit indicates the physical quantity to be measured, for example the pressure, as a mostly linear function.
When employing such a sensor bridge circuit in a safety-related measuring device, for example in the anti-blocking system of a motor vehicle, it is very important for the safety of the motor vehicle and its occupants that the function of the sensor be continuously monitored during its operation, and that, in case of a malfunction of the sensor, it is possible to immediately generate an alarm signal which indicates this malfunction. In this connection it is important that not only disruptions in the lines leading to and from the sensor bridge circuit, the supply lines and similar can be detected, but also malfunctions which can cause the outage of the pressure sensor, so that slowly occurring changes, for example changes of the characteristic curve of the pressure sensor, the amount of amplification of the integrated amplifiers, etc., which degrade the accuracy of the measurement, can be detected.
A known sensor error detection device for detecting a line break or a short circuit, known from U.S. Pat. No. 4,845,435, has a resistor for generating a sensor compensation output signal between an output connection on the ground side of a sensor and the sensor. A comparison of the sensor output signal generated in this way with a reference voltage makes possible the drawing of a conclusion regarding the status or the functional ability of the sensor by means of the output state of a comparator employed for this. If, for example, a sensor is connected with an A/D-converter, the dependability of the known arrangement for the detection of interruptions of the respective voltage supply connections, the output connections and the ground connections of the sensors is not assured.
SUMMARY OF THE INVENTION
It is the object of the invention to make possible a method and a circuit arrangement for monitoring the function of a symmetrical sensor bridge circuit having sensor elements which are connected in a full bridge circuit, in such a way, that it is automatically possible to monitor the sensor signal in all operational states without disruption of the chain of measured signals and, at low cost expenditure, not only the sensor input lines, the supply voltage lines, the bonded connections, but also the bridge resistors, all of the amplifiers and the adjustment and compensation modules of the chain of measured signals.
A method in accordance with the invention for monitoring the function of a symmetrical sensor bridge circuit, by means of which the above objects are attained, is distinguished by the following steps: half-bridge circuit; the bridge supply voltage while forming a difference signal; so that it corresponds to the full bridge signal if the sensor bridge circuit operates correctly; and from the full bridge signal in an unacceptable manner.
In accordance with the invention this method is advantageously further developed in that the full bridge signal is amplified and the output signal of the sensors is formed from it, and that the alarm signal is generated with a fixed level, a fixed frequency or the like and is superimposed on the output signal of the sensor.
The level of the alarm signal is advantageously selected in such a way that in case of an alarm the output signal of the sensor is placed outside the normal operating range of the sensor.
Furthermore, the amplified difference signal and the ful
REFERENCES:
patent: 4845435 (1989-07-01), Bohan, Jr.
patent: 4947309 (1990-08-01), Jonsson
patent: 5734269 (1998-03-01), Sakai et al.
Keller Herbert
Pfaff Georg
Lefkowitz Edward
Robert & Bosch GmbH
Striker Michael J.
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