Watt/watt hour transducer having current signals and a modulator therefor

An electrical power line metering apparatus comprising:

• a. scaling means connected to a power line and including a current input means and a voltage input means for providing electrical signals proportional to the instantaneous voltage and current of said power line, at least one of said input means effectively being a high impedance current source;
• b. a watt section load means comprising an amplifier and filter circuit means having an input port which is the input port of said watt section load means and an output port and having no substantial shunt current path, for smoothing the current through it, and a watt output impedance connected across the output port of said amplifier and filter circuit means, said watt section load means providing an output proportional to the instantaneous power through said line;
• c. a watthour integrator load means for providing an output proportional to the time integral of power through said line;
• and
• d. a multiplier circuit including a pulse width modulating switching means having an input port connected to said high impedance current source and an output port having said watt section load means and said watthour integrator load means series connected thereto, said multiplier circuit also having a control port connected to the other of said input means for chopping pulses of current source current through said series load means with chopping intervals proportional to the signal amplitude at said control port.

An electrical power line combination watt and watthour metering apparatus of the type having a current input scaling means and a voltage input scaling means for providing a pair of electrical signals proportional to the instantaneous voltage and current of said power line, a multiplier connected to said scaling means for providing an output signal having an average value substantially equal to the instantaneous power through said power line, and an integrator means for integrating said output signal over a selected period of time to provide a signal corresponding to watthours of energy through said power line, wherein the improvement is a multiplier which includes:

• a. a single pole, double throw switching means having a wiper terminal, a control input port and a pair of output terminals alternatively connectable to said wiper terminal, said switch means having no substantial interterminal leakage;
• b. an amplifier load means connected to one of the output terminals of said switching means and a common for providing an output signal proportional to the instantaneous power through said power line;
• c. said integrator means connected as a load means to the other output terminal of said switching means and said common;
• d. a first one of said scaling means coupled at its output to said wiper terminal and said load means for at times driving current through said load means and having at least one dc block capacitance in its coupling path for maintaining a zero average current flow through said first scaling means;
• and
• e. an analog to pulse width converter means having an input connected to the output of the other of said scaling means for providing a series of pulses at a rate greater than the frequency of said power line and having a pulse width proportional to the amplitude of the output of said other scaling means, the output of said converter means connected to the control input of said switching means.