Wide dynamic range current measuring apparatus
First Claim
1. Wide dynamic range current measuring apparatus comprising:
- a current transformer having a primary winding and a secondary winding in which a secondary current proportional to a current flowing in the primary winding is induced;
an analog to digital converter having a plurality of discrete selectable reference voltages providing a plurality of resolutions for a digital signal generated thereby;
an amplifier with programmable gain and with means generating an overrange signal when the amplifier output exceeds a preset limit;
means applying a signal proportional to said secondary current to said amplifier;
means applying the output of the amplifier to said analog to digital converter to generate said digital signal; and
control means responsive to said overrange signal selecting the highest programmable gain of the amplifier which does not produce an overrange signal, selecting in response to the magnitude of the digital signal generated by the analog to digital converter the selectable reference voltage for the analog to digital converter which provides the greatest resolution of said digital signal and providing an output signal including said digital signal and a scale factor which is a function of both the selected gain of said amplifier and the selected reference voltage of the analog to digital converter.
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Accused Products
Abstract
Apparatus for measuring current over a wide range generates an eight bit accurate, 16-bit dynamic range digital signal from a current transformer secondary. Two signals proportional to the rectified secondary current, one generated by a large burden resistor and the other by an amplifier with programmable gain and an overrange indication, are applied through a multiplexer to an eight bit analog to digital converter which has three selectable reference voltages. A microprocessor selects the input signal, converter reference voltage, and one of four levels of amplifier gain which provide the greatest resolution for the magnitude of the current being measured, and provides an appropriate scale factor, from 20 to 28, for the eight bit accurate digital signal generated by the analog to digital converter.
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Citations
9 Claims
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1. Wide dynamic range current measuring apparatus comprising:
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a current transformer having a primary winding and a secondary winding in which a secondary current proportional to a current flowing in the primary winding is induced; an analog to digital converter having a plurality of discrete selectable reference voltages providing a plurality of resolutions for a digital signal generated thereby; an amplifier with programmable gain and with means generating an overrange signal when the amplifier output exceeds a preset limit; means applying a signal proportional to said secondary current to said amplifier; means applying the output of the amplifier to said analog to digital converter to generate said digital signal; and control means responsive to said overrange signal selecting the highest programmable gain of the amplifier which does not produce an overrange signal, selecting in response to the magnitude of the digital signal generated by the analog to digital converter the selectable reference voltage for the analog to digital converter which provides the greatest resolution of said digital signal and providing an output signal including said digital signal and a scale factor which is a function of both the selected gain of said amplifier and the selected reference voltage of the analog to digital converter.
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2. Wide dynamic range current measuring apparatus comprising:
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a current transformer having a primary winding and a secondary winding in which a secondary current proportional to a current flowing through the primary winding is induced; means converting the current flowing in the secondary winding to a voltage signal; an analog to digital converter having a selectable reference voltage which provides selectable resolution of a digital signal generated thereby; means applying said voltage signal to said analog to digital converter for conversion into a digital signal; means responsive to the magnitude of the secondary current for selecting the reference voltage of the analog to digital converter to provide the greatest resolution of the digital signal; and means providing an output signal including the digital signal generated by the analog to digital converter and a scale factor generated as a function of the reference voltage selected. - View Dependent Claims (3)
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4. Wide dynamic range current measuring apparatus comprising:
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a current transformer having a primary winding and a secondary winding in which secondary current is induced by current flowing through the primary winding; an analog to digital converter for converting applied voltage signals to a digital signal; a first burden resistor connected in series with said secondary winding and having an ohmic value which produces a first voltage signal for said analog to digital converter having a full range value at a preselected low value of said secondary current; current limiting means limiting current through the first burden resistor to said preselected low value of secondary current; means generating a reference current proportional to having a magnitude less than said secondary current; amplifier means generating a second voltage signal proportional to said reference current; and microprocessor means programmed to apply said first voltage signal to said analog to digital converter for conversion to said digital signal when said secondary current is below said preselected low value, to apply said second voltage signal to the analog to digital converter for conversion to said digital signal when said secondary current is above said preselected low value, and to generate an output signal which includes said digital signal and a scale factor dependent upon which of said first and second voltage signals is converted to said digital signal. - View Dependent Claims (5, 6, 7, 8, 9)
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Specification