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US 4,788,494 AGranted
Power measuring apparatus
AssigneeRefac Electronics Corporation
InventorEric Faulkner
Life of this patent
Estimating the term…
Abstract
Apparatus for measuring the mean value of instantaneous power supplied to an electrical device computes the product of two voltage signals each proportional to the instantaneous voltage and current respectively. A self-biasing current source generates a DC signal current proportional to the magnitude of one voltage signal with a mean value equal to one-half the peak-to-peak magnitude of the voltage signal. A log-antilog multiplier circuit computes the product of the DC current signal and the other input voltage signal. A current mirror connected to the multiplier cancels DC offset currents to improve accuracy of the apparatus.
Claims8
Apparatus for measuring the mean value of instantaneous power supplied to an electrical device connected to an AC power source, said apparatus characterized by:
- first circuit means for generating a first voltage signal proportional to the instantaneous voltage potential applied to said electrical device;
- said second circuit means for generating a second voltage signal proportional to the instantaneous current delivered to said electrical device;
- third circuit means responsive to said first and said second voltage signals for producing a third voltage signal representative of the product of said first and said second voltage signals and proportional to the instantaneous power supplied to said electrical device, said third circuit means including current mirror circuit means for cancelling DC error signals associated with said product of said first and second voltage signals,
- said third circuit means including a dynamic, self-biasing current source circuit means for automatically generating a range of DC quiescent current signals each of which DC quiescent current signals is different and related to and associated with the instantaneous magnitude of said second voltage signal present, and a log-antilog multiplier circuit means, said multiplier circuit means being coupled to said current source means and to said first voltage signal for computing the product of said DC current signal and said first voltage signal,
- said current source means including:
- a high pass filter comprising a resistor and a capacitor and having an input terminal coupled to said second voltage signal and an output terminal, said capacitor being connected in series between said input and output terminals, said resistor being connected between said output terminal and a reference potential, said capacitor being charged in one direciton to produce a voltage having a first polarity when said second voltage signal is positive;
- a first and second differential input instrumentation amplifier;
- a diode;
- an NPN bipolar transistor having emitter, base and collector terminals;
- said first amplifier having its non-inverting input connected to said high pass filter ouput terminal and to said second amplifier inverting input, said first amplifier having its output connected to said transistor base terminal, said first amplifier having its inverting input connected to said transistor emitter terminal and to a high-ohmic value resistance element connected between said first amplifier inverting input and a negative polarity supply voltage pontential, said first amplifier producing an output signal for biasing said transistor to conduct current through said emitter and collector terminals and said resistance element to maintain the voltage at said first amplifier inverting input equal to the magnitude of said second voltage signal appearing at said first amplifier non-inverting terminal when said second voltage signal is positive, and
- said diode having its anode connected to the output of said second amplifier and its cathode to the junction of the inverting input of said second amplifier and the non-inverting input of said first amplifier and the output terminal of said high pass filter so that said diode is forward biased and conducts current from the output of said second amplifier into said junction when said second voltage signal is negative to maintain the polarity of the voltage appearing at said high pass filter output terminal the same as said first polarity and the mean magnitude of the voltage appearing at said filter output equal to one-half the peak-to-peak magnitude of said second voltage signal, said transistor being biased to produce a collector current mean value equal to one-half its peak-to-peak collector current value so that said DC current signal is produced in the linear operating region of said transistor for all instantaneous values of said second voltage signal.
8 more elements
Apparatus for computing the product of the instantaneous magnitude of two voltage signals characterized by:
- means for producing a first and a second voltage signal;
- self-biasing current source circuit means for automatically generating a range of DC quiescent current signals each of which is related to and associated with the instantaneous magnitude of said second voltage signal present, and
- log-antilog multiplier circuit means, said mulitplier circuit means being coupled to said current surce means and to said first voltage signal for computing the product of said DC current signal and said first voltage signal;
- said current source circuit means including a high pass filter comprising a resistor and capacitor and having an input terminal coupled to said second voltage signal and an output terminal, said capacitor being connected in series between said input and output terminals, said resistor being connected between said output terminal and a reference potential, said capacitor being charged in one direction to produce a voltage having a first polarity when said second voltage signal is positive;
- a first and second differential input instrumentation amplifier;
- a diode;
- an NPN bipolar transistor having emitter, base and collector terminals;
- said first amplifier having its non-inverting input connected to said high pass filter output terminal and to said second amplifier inverting input, said first amplifier having its output connected to said transistor base terminal, said first amplifier having its inverting input connected to said transistor emitter terminal and to a high-ohmic value resistance element connected between said first amplifier inverting input and a negative polarity supply voltage potential, said first amplifier producing an output signal for biasing said transistor to conduct current through said emitter and collector terminals and said resistance element to maintain the voltage at said first amplifier inverting input equal to the magitude of said second voltage signal appearing at said first amplifier non-inverting terminal when said second voltage signal is positive, and
- said diode connected to the output of said second amplifier and its cathode to the junction of the inverting input of said second amplifier and the non-inverting input of said first amplifier and the output terminal of said high pass filter so that said diode is forward biased and conducts current from the output of said second amplifier into said junction when said second voltage signal is negative said output current tending to maintain the polarity of the voltage appearing at said high pass filter output terminal the same as said first polarity and the mean magnitude of the voltage appearing at said filter output equal to one-half the peak-to-peak magnitude of said second voltage signal, said transistor being biased to produce a collector current mean value equal to one-half its peak-to-peak collector current value so that said DC current signal is produced in the linear operating region of said transistor for all instantaneous values of said second voltage signal.
6 more elements
Apparatus for measuring the mean value of instantaneous power supplied to an electrical device connected to an AC power source, said apparatus characterized by:
- first circuit means for generating a first voltage signal proportional to the instantaneous voltage potential applied to said electrical device;
- second circuit means for generating a second voltage signal proportional to the instantaneous current delivered to said electrical device;
- third circuit means responsive to said first and said second voltage signals for producing a third voltage signal representative of the product of said first and said second voltage signals and proportional to the instantaneous power supplied to said electrical device, said third circuit means including current mirror ciruit means for cancelling D.C. error signals associated with said product of said first and second voltage signals;
- a dynamic, self-biasing current source circuit means for automatically generating a range of DC quiescent current signals each of which is related to and associated with the instantaneous magnitude of said second voltage signal present;
- a log-antilog multiplier circuit means, said multiplier circuit means being coupled to said current source means and to said first voltage signal for computing the product of said second voltage signal and said first voltage signals;
- a high-pass filter comprising a resistor and capacitor and having an input terminal coupled to said second voltage signal and an output terminal, said capacitor being connected in series between said input and output terminals, said resistor being connected between said output terminal and a reference potential, said capacitor being charged in one direction to produce a voltage having a first polarity when said second voltage signal is positive;
- a first and second differential input instrumentation amplifier;
- a diode;
- an NPN bipolar transistor having emitter, base and collector terminals;
- said first amplifier having its non-inverting input connected to said high pass filter output terminal and to said second amplifier inverting input, said first amplifier having its output connected to said transistor base terminal, said first amplifier having its inverting input connected to said transistor emitter terminal and to a high-ohmic value resistance element connected between said first amplifier inverting input and a negative polarity supply voltage potential, said first amplifier producing an output signal for biasing said transistor to conduct current through said emitter and collector terminals and said resistance element to maintain the voltage at said first amplifier inverting input equal to the magnitude of said second voltage signal appearing at said first amplifier non-inverting terminal when said second voltage signal is positive, and
- said diode having its anode connected to the output of said second amplifier and its cathode to the junction of the inverting input of said second amplifier and the non-inverting input of said first amplifier and the output terminal of said high pass filter so that said diode is forward biased and conducts current from the output of said second amplifier into said junction when said second voltage signal is negative to maintain the polarity of the voltage appearing at said high pass filter output terminal the same as said first polarity and the mean magnitude of the voltage appearing at said filter output equal to one-half of the peak-to-peak magnitude of said second voltage signal, said transistor being biased to produce a collector current mean value equal to one-half its peak-to-peak collector current so that said DC current signal is produced in the linear operating region of said transistor for all instantaneous values of said second voltage signal.
8 more elements
Dependencies are inferred from the claim text.