Electricity: measuring and testing – Fault detecting in electric circuits and of electric components – In an ignitor or detonator
Reexamination Certificate
1998-02-18
2001-09-11
Metjahic, Safet (Department: 2858)
Electricity: measuring and testing
Fault detecting in electric circuits and of electric components
In an ignitor or detonator
C324S547000, C324S525000, C324S550000, C324S649000
Reexamination Certificate
active
06288551
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an arrangement for checking the resistance of a load, preferably the squib of an air bag, connected to the secondary winding of a transformer.
BACKGROUND INFORMATION
Such an arrangement is described in German Patent No. 38 12 633 A1. According to this related art, a rotary transformer is used, for example, for signal transmission between a controller and an air bag built into the steering wheel of a vehicle. The functionality of an air bag must be tested on an ongoing basis to ensure that it is ready to operate in an emergency situation. For this purpose, the resistance of the squib, which should typically be between 1.8 &OHgr; and 2.5 &OHgr;, is periodically measured. The transmission of signals using inductively coupled windings of the rotary transformer depends on the distance between the two windings, i.e., the size of the gap between the pot-type cores of the windings. Assembly and manufacturing tolerances of the steering wheel, on which the secondary-side pot-type core of the rotary transformer is installed, can distort the measured resistance value of the squib. In order to avoid such measuring signal distortions, the aforementioned related art provides an oscillating circuit on the secondary side of the rotary transformer, which is excited by a control signal from the primary side. After the control signal is switched off, the decay of the response signals of the oscillating circuit is retransmitted back to the primary side and the secondary side resistance is obtained from the time constant of the decaying response signal.
SUMMARY OF THE INVENTION
According to the present invention, the resistance of a load, preferably the squib of an air bag, connected to the secondary side of a rotary transformer, is checked using an additional resistor connected in parallel to the load. The input resistance of the transformer, measured on the primary side, is a single-valued function of the load resistance. This input resistance is measured and, if it differs from a predefined value, it is signaled that a load malfunction has occurred. The additional resistor can be transformed into the primary side of the transformer using an additional secondary winding. It is convenient that the additional secondary winding be made from a wire that has this additional resistance. The additional resistor can, however, also be designed as a ring arranged on the secondary side. One advantage of the arrangement according to the present invention is that it can be implemented with a very simple circuit and allows reliable conclusions to be drawn regarding the changes in the load resistance.
REFERENCES:
patent: 4837501 (1989-06-01), Fry
patent: 4851761 (1989-07-01), Matsuno
patent: 5341102 (1994-08-01), Akiyama
patent: 3540031 (1987-02-01), None
patent: 3812633 (1989-10-01), None
patent: 38 12 633 (1989-10-01), None
patent: 2576109 (1986-07-01), None
patent: WO 87/07388 (1987-02-01), None
Dukart Anton
Zabler Erich
Deb Anjan K
Kenyon & Kenyon
Metjahic Safet
Robert & Bosch GmbH
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