Low cutoff digital pulse filter especially useful in electronic energy consumption meters

Claim 1

In an electronic energy consumption meter comprising sources of signal variables representing voltage and current flowing in a monitored electrical circuit, a time-division multiplier for multiplying said variables and producing an analog power consumption signal, an A/D converter for producing digital pulses each representing the consumption of a predetermined unit of energy, and means for accumulating the number of digital pulses as an indication of total energy consumption, the improvement comprising a low cut-off pulse filter interposed between said A/D converter and said means for accumulating for passing only those digital pulses occurring above a predetermined cut-off repetition rate, said filter comprising: logic gate means having a first input connected to respond to said digital electrical pulses, a second input and an output for providing output electrical pulses directly corresponding to said digital pulses only when enabled by an enabling signal being applied to said second input, energy storage and dissipation means connected for short term storage and eventual dissipation at a predetermined rate of electrical energy applied thereto and for providing an averaged signal representing the amount of energy stored at any given time, a source of electrical energy, switch means connected between said source and said energy storage and dissipation means and connected for control by said digital electrical pulses for providing input pulses of energy to said energy storage and dissipation means corresponding to the occurrences of said digital electrical pulses whereby the value of said averaged signal corresponds to the repetition rate of said digital electrical signal, and trigger circuit means connected to receive said averaged signal and to provide said enabling input to the second input of said logic gate means only during the time when said averaged signal exceeds a predetermined threshold value corresponding to said predetermined repetition rate.