Current Measurement Circuit and Method of Diagnosing Faults in Same
First Claim
1. A current measurement circuit comprising:
- a first input node and second input node which respectively receive a voltage from either side of a resistive element through which electrical current can flow.a differential amplifier, which produces an output signal indicative of the difference in voltage between its input terminals,electrical path forming means providing a connection between each of said input nodes and a respective input terminal of said differential amplifier;
a controllable voltage source for selectively applying an offset voltage to at least one input of said differential amplifier in response to a control signal;
a control signal generator which generates said control signal applied to said voltage source such that at a second instance an offset voltage is applied which is greater than the offset voltage applied at a first instance, anda diagnostic means which identifies faults present in said electrical path between said first input node and said respective input to said amplifier by comparing the output from said amplifier at said first instant with the output at said second instant and further in which said diagnostic means produces an error signal indicating a fault in the event that said difference between the output of said amplifier at said first instant and said output at the second instant is different from a predetermined threshold level.
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Accused Products
Abstract
A current measurement circuit includes first and second input nodes which receive the respective voltages at either side of a resistive element through which electrical current can flow, a differential amplifier means which produces an output signal indicative of the difference in voltage between its input terminals, electrical path forming means providing a connection between each of the input nodes and a respective input terminal of the differential amplifiers, a controllable voltage source for selectively applying an offset voltage to at least one input of the differential amplifier in response to a control signal, a control signal generator which generates the control signal applied to the voltage source such that at a first instance an offset voltage is applied which is greater than that applied at a second instance, and a diagnostic means which is adapted to identify faults present in the electrical path between the first input node and the respective input to the amplifier by comparing the output from the amplifier at the first instant when the offset voltage is applied and at the second instant without the offset voltage.
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Citations
17 Claims
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1. A current measurement circuit comprising:
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a first input node and second input node which respectively receive a voltage from either side of a resistive element through which electrical current can flow. a differential amplifier, which produces an output signal indicative of the difference in voltage between its input terminals, electrical path forming means providing a connection between each of said input nodes and a respective input terminal of said differential amplifier; a controllable voltage source for selectively applying an offset voltage to at least one input of said differential amplifier in response to a control signal; a control signal generator which generates said control signal applied to said voltage source such that at a second instance an offset voltage is applied which is greater than the offset voltage applied at a first instance, and a diagnostic means which identifies faults present in said electrical path between said first input node and said respective input to said amplifier by comparing the output from said amplifier at said first instant with the output at said second instant and further in which said diagnostic means produces an error signal indicating a fault in the event that said difference between the output of said amplifier at said first instant and said output at the second instant is different from a predetermined threshold level. - View Dependent Claims (2, 3, 4, 5, 6, 7, 15, 16, 17)
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8. A method of diagnosing faults present in a current sensing apparatus in which a differential amplifier having a positive input and a negative input, the differential amplifier also having an output and being operable to produce an output indicative of a potential drop across a current sense resistor connected to the inputs, the method comprising the following steps:
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(a) measuring the output of the amplifier at a first instant; (b) applying an offset voltage to at least one input of the differential amplifier at a second instant; (c) measuring the output of the amplifier at a second instant; (d) comparing the output of the amplifier at the second instant to that at the first instant. (e) applying an offset voltage to at least one other input of the differential amplifier at a third instant; (f) measuring the output of the amplifier at the third instant; (g) comparing the output of the amplifier at the third instant to that at the first instant; (h) applying an offset voltage to both the positive and the negative inputs of the amplifier; (i) comparing the output of the amplifier at the fourth instant to that at the first instant; and (k) determining the difference between the outputs of the amplifier for at least one of the preceding comparisons of the amplifier outputs and comparing the resulting difference to a predetermined limit to determine whether a fault should be indicated. - View Dependent Claims (9, 10, 11)
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12. A method of diagnosing faults present in a current sensing apparatus in which a differential amplifier having a positive input and a negative input, the differential amplifier also having an output and being operable to produce an output indicative of a potential drop across a current sense resistor connected to the inputs, the method comprising the following steps:
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(a) measuring the output of the amplifier at a first instant; (b) applying an offset voltage to at least one input of the differential amplifier at a second instant; (c) measuring the output of the amplifier at a second instant; (d) comparing the output of the amplifier at the second instant to that at the first instant; and (e) determining the difference between the outputs of the amplifier that are compared in step (d) and comparing the resulting difference to a predetermined limit to determine whether a fault should be indicated. - View Dependent Claims (13, 14)
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Specification