US 4,800,333 A · Switched-capacitor watthour meter circuit having reduced capacitor ratio

Abstract

An electronic energy consumption measuring circuit capable of being fabricated on a single integrated circuit chip employs a switched-capacitor integrator for integrating the product of first and second voltages which are proportional, respectively, to load voltage and current in an electrical system to provide a measure of the energy being consumed, and a hysteresis comparator for converting the integrator output into a pulse train wherein each pulse represents a predetermined amount of energy. The output pulses may be accumulated and displayed to provide an indication of total energy consumed. A divider at the hysteresis comparator output enables the capacitor ratio in the switched-capacitor integrator to be reduced substantially so that the capacitor values are approximately the same order of magnitude. This reduces the chip area necessary for fabricating the capacitors and improves the matching between the capacitors, thereby affording higher integration accuracy.

An electronic circuit for measuring energy consumption in an electrical system comprising:

input means for first and second signals representative, respectively, of current and voltage in the electrical system;
multiplying means for multiplying the first and second signals to provide a product signal representative of power being supplied by the electrical system;
said multiplying means comprising a time division multiplier including sampling means for sampling one of said first and second siganls and for providing samples proportional to the instantaneous value of current or voltage represented by said one signal, and switching means receiving the other of said first and second signals and an inverted form of said other signal, the switching means being controlled by said samples so as to switch between said other signal and the inverted form of said other signal to produce said product signal;
said sampling means comprising sampling signal generating means for generating a triangular waveform sampling signal, and means for comparing the amplitude of said one of the first and second signals to the sampling signal to produce said samples, the samples comprising pulses having a pulse width that is proportional to said amplitude;
said sampling signal generating means comprising a switched-capacitor integrator for providing at an output thereof said triangular waveform sampling signal, another switching means for alternately applying one of positive and negative reference voltages to an input of the switched-capacitor integrator, and comparator means for comparing the triangular waveform sampling signal from the switched-capacitor intergrator alternately with said one of the positive and negative reference voltages and for controlling said other switching means;
switched-capacitor integrator means for integrating the product signal and for providing an integrated signal representative of average energy;
converting means for converting the integrated signal into a first train of signal pulses;
and
divider means for dividing the first train of signal pulses by a preselected ratio and for providing a second train of output signal pulses, each output signal pulse representing a predetermined amount of electrical energy consumed in the electrical system, said switched-capacitor integrator means comprising an ampllifier having a first capacitor connected between an output and an input of the amplifier, a second capacitor, first switching means for alternately connecting the second capacitor to the multiplying means and to the input of said amplifier, second switching means for alternately connecting and disconnecting the second capacitor to and from ground, and clock generator means for supplying first and second clock signals for respectively controlling said first and second switching means, the clock signals being non-overlapped and out of phase, and the output signal of said amplifier being a ramp voltage having a time constant which is a function of the ratio of the values of said first capacitor to said second capacitor, said ratio of the values of said first capacitor of said second capacitor being inversely proportional to the preselected ratio by which said divider means divides said first train of pulses and limited to maintaining said first and second capacitor values within the same order of magnitude.

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Switched-capacitor watthour meter circuit having reduced capacitor ratio

Life of this patent

Switched-capacitor watthour meter circuit having reduced capacitor ratio

Life of this patent

Abstract

Claims15