Electricity: measuring and testing – Impedance – admittance or other quantities representative of... – Lumped type parameters
Patent
1994-12-20
1997-08-05
Wieder, Kenneth A.
Electricity: measuring and testing
Impedance, admittance or other quantities representative of...
Lumped type parameters
324545, 324546, 324547, G01R 2726, G01R 3106
Patent
active
056546440
DESCRIPTION:
BRIEF SUMMARY
This application is the U.S. national-phase application of PCT International application Ser. No. PCT/EP93/01569.
BACKGROUND OF THE INVENTION
The present invention relates to a circuit for monitoring an inductive circuit which is formed as part of a signal-processing circuit or as an additional element and which is connected, through a high-ohmic input circuit or filter circuit, to the signal-processing circuit. The monitoring initiates a test cycle to determine the inductance of the circuit to be monitored, including the filter circuit, if predetermined conditions apply and/or in predetermined intervals.
A monitoring circuit of this type is disclosed in EP 0 358 887 A1. In this monitoring circuit, the duration of a test signal passing through the inductive circuit to be monitored is monitored and evaluated with respect to proper duration by means of a time-difference measuring apparatus. To this end, the time difference of the duration of a signal, which is conducted to the time-difference measuring apparatus through the inductance and a time element, is compared to the signal which is conducted directly through an equal time element to the measuring apparatus.
Circuits of this type are particularly suitable to detect short circuits in the inductive transducer of a wheel sensor. If the short circuit is in the line leading to the transducer, in its input circuit or filter circuit, the short circuit is likewise detected in the monitoring operation. A line interruption is also detected. Sensors of this type, which are required in anti-lock systems or traction slip control systems of automotive vehicles, for example, are safety-critical component parts which should be checked permanently for operability, short circuits or line interruptions. In a low-ohmic input circuit or filter circuit, a short circuit may be detected relatively easily by determining the ohmic resistance between an output of the filter circuit and ground. For a high-ohmic filter circuit, such an arrangement is not suitable in practical operations because the ohmic internal resistance of the inductive circuit is low compared to the resistors in the circuit or input circuit. Therefore, the voltage drop, which may be measured at the output of the filter circuit when a current is applied, will be changed by a short circuit only to such a minor extent that reliable evaluation of the measurement results is not possible.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a circuit for monitoring an inductive circuit which has a simple design, does not require additional terminals and permits detecting short circuits or line interruptions in a reliable manner, even if the inductive circuit is connected through a high-ohmic filter circuit or input circuit.
This object can be achieved by circuitry having the special features that, at the beginning of the test cycle, one of the two outputs of the filter circuit is connected to ground, while the second output is connected to a voltage source for a predetermined period, and the inductance is determined from the potential variation at a second output of the filter circuit.
It is expedient that the predetermined period corresponds at least to the transient time of the circuit to be monitored, including the filter circuit. Upon lapse of the predetermined time period and disconnection of the voltage source, the potential variation at the second output is evaluated to determine the inductance.
Also, symmetrically arranged filter circuits may be used, each of which has one high-ohmic series resistance in the lines leading from the inductive circuit to the signal-processing circuit, one capacitor interconnecting both outputs of the filter circuit, and one input capacitor which connects one of the outputs of the inductive circuit or one of the inputs of the filter circuit to ground.
To simplify the analysis of the signal, a d.c. voltage potential may be set for such a filter circuit by a voltage divider which is connected to a source of d.c. voltage on one side and to ground on the
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Fey Wolfgang
Zinke Olaf
Zydek Michael
Do Diep
ITT Automotive Europe GmbH
Lewis J. Gordon
Twomey Thomas N.
Wieder Kenneth A.
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