US 4,876,502 AGranted

Wide dynamic range current measuring apparatus

AssigneeWestinghouse Electric Corp.

InventorsWilliam R. Verbanets, Robert T. Elms

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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 2.sup.0 to 2.sup.8, for the eight bit accurate digital signal generated by the analog to digital converter.

Claims9

Dependent claims

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.

4 more elements

Wide dynamic range current measuring apparatus comprising:

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.

5 more elements

Dependencies are inferred from the claim text.