Ground fault protection circuit
First Claim
1. A protection circuit comprising:
- a main analog sensor ground terminal at which normally ground potential is provided by a sensor circuit;
a main power ground terminal, separate from said main analog sensor ground terminal, at which ground potential is provided;
a monitoring circuit having at least first and second separate input terminals, said first input terminal coupled to said main analog ground terminal and said second input terminal separately coupled to said main power ground terminal; and
means for normally providing a low resistance connection between said main analog sensor ground terminal and said main power ground terminal;
wherein the improvement comprises,current sensing means for sensing current passed through said low resistance connection, developing a signal magnitude indicative thereof and utilizing said signal magnitude to limit said current to no more than a predetermined maximum current limit; and
additional means, in addition to said current sensing means, for sensing the voltage at said main analog sensing ground terminal and, in response thereto, preventing the voltage at said first input terminal from exceeding a predetermined maximum voltage.
1 Assignment
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Accused Products
Abstract
The output terminals (15, 16) of an analog sensor (14) are monitored by a microprocessor (17). The microprocessor is DC coupled to a main analog ground terminal (16) of the sensor, while also separately being connected to a main power ground terminal (13) at which ground reference potential is provided to the microprocessor. A resistor (38), a semiconductor switch (36) and a printed circuit board metalization trace (35) provide a normal low resistance connection between the main analog sensor ground terminals (20) and the main power ground terminal (13). Current sensing circuitry (33) limits the current passed through the low resistance connection and thereby prevents excessive current from damaging printed circuit board metalization paths (34, 35) connecting the sensor analog ground terminal (16) to the main power ground terminal (13). Also, additional circuitry (32) is provided for independently sensing the voltage at the main analog sensing ground terminal (20) and preventing an excessive voltage at this terminal from being coupled (via 22) to the microprocessor. During non fault operation, the above provides low resistance, low offset voltage connections between the sensor output terminals (15, 16) and the microprocessor (17).
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Citations
15 Claims
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1. A protection circuit comprising:
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a main analog sensor ground terminal at which normally ground potential is provided by a sensor circuit; a main power ground terminal, separate from said main analog sensor ground terminal, at which ground potential is provided; a monitoring circuit having at least first and second separate input terminals, said first input terminal coupled to said main analog ground terminal and said second input terminal separately coupled to said main power ground terminal; and means for normally providing a low resistance connection between said main analog sensor ground terminal and said main power ground terminal; wherein the improvement comprises, current sensing means for sensing current passed through said low resistance connection, developing a signal magnitude indicative thereof and utilizing said signal magnitude to limit said current to no more than a predetermined maximum current limit; and additional means, in addition to said current sensing means, for sensing the voltage at said main analog sensing ground terminal and, in response thereto, preventing the voltage at said first input terminal from exceeding a predetermined maximum voltage. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15)
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Specification