Watt/watthour transducer and amplifier-filter therefor

An electrical power line power metering apparatus comprising:

• a. input 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 being a high impedance current source;
• b. a multiplier means connected to said input scaling means and having no substantial current path shunting the modulated current, for pulse width modulating the current from said high impedance current source with the signal from the other of said input means to provide output current pulses having an instantaneous amplitude substantially equal to the amplitude of the instantaneous signal from said high impedance current source and having a pulse width proportional to the instantaneous amplitude of the other of said signals;
• c. a dc current amplifier comprising a differential input op-amp having its inverting input coupled to the output of said multiplier means, having a dc blocking capacitance connected between its non-inverting input and its inverting input for coupling ripple from the output of said multiplier means to said non-inverting input;
• and
• d. an output impedance connected between the inverting input and the output of the op-amp;
• whereby a substantially non-shunted current path is provided serially through said high impedance current source and said output impedance and wherein the average of the current along said path is proportional to the electrical power flow through said power line.

A power transducer for providing an output current through an output load which is proportional to the power through a power line, said transducer comprising:

• a. input 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 being a high impedance current source;
• b. a multiplier means connected to said input scaling means and having no substantial current path shunting the modulated current, for pulse width modulating the current from said high impedance current source with the signal from the other of said input means to provide output current pulses having an amplitude substantially equal to the amplitude of the instantaneous signal from said high impedance current source and having a pulse width proportional to the amplitude of the other of said signals;
• c. a dc current amplifier having no substantial current path shunting the modulated current and having its input coupled to the output of said multiplier means;
• and
• d. a current conducting path serially including said output load and connected across the output of said dc current amplifier and having no substantial intermediate current shunting path;
• whereby a substantially non-shunted current loop is provided serially through said high impedance current source and said output load and wherein the current along said path is proportional to the electrical power flow through said power line.