ELECTRONIC WATTMETER INCLUDING A SOLID-STATE LOGARITHMIC MULTIPLIER

• US 3,764,908 A
• Filed: 03/06/1972
• Issued: 10/09/1973
• Est. Priority Date: 03/06/1972
• Status: Expired due to Term

• Current Assignee: Robert T. Elms
• Original Assignee: Robert T. Elms
• Inventors: Elms, Robert T.
• Primary Examiner(s): Smith, Alfred E.
• Application Number:
  US05/232,025
• Time in Patent Office: 582 Days
• Field of Search: 324/142 307/229 328/160 235/194
• US Class Current: 324/142
• CPC Class Codes: G01R 21/00 Arrangements for measuring electric power or power factor G01R7/12 takes precedence
• CPC Class Codes: G06G 7/24 for evaluating logarithmic or exponential functions, e.g. hyperbolic functions for multiplication, division or for evaluating powers or roots using logarithmic functions; gamma correction in television systems H04N5/20, H04N9/69

Abstract

An electronic wattmeter includes a solid-state logarithmic multiplier of the single quadrant type for measuring true instantaneous values alternating current power. The logarithmic multiplier computes the product of the instantaneous absolute values of a current component and a voltage component defining an alternating current power quantity to be measured. The logarithmic multiplier includes compensating and sensitivity corrections for increasing accuracy and reliability. A product of the polarity logic senses the relative states of polarity of the voltage and current components. A polarity restorer inverts the logarithmic multiplier output signal in response to opposite polarity states of the voltage and current components as sensed in the logic. The electronic wattmeter output signal is provided at the polarity restorer output so as to be indicative of the true instantaneous values of the alternating current.

Claims

1. An electronic wattmeter comprising:

first and second input circuits adapted for connection to voltage and current components of a source of alternating current energy to be measured;

first and second rectifier circuits connected to said first and second input circuits, respectively, for developing common polarity voltage and current sensing analog signals responsive in magnitude and phase relationship to said voltage and current components;

a logarithmic multiplier circuit including first and second logarithmic computing devices, a balancing and compensating logarithmic computing device, and an anti-logarithmic Computing device, each of said devices having an input and an output with said anti-logarithmic computing device input connected with the outputs of said first and second logarithmic computing devices so as to develop a computed output current responsive to the product of current flow in the inputs of said first and second logarithmic devices;

means for coupling said input of the first logarithmic computing device to said voltage analog signal;

means for coupling said input of the second logarithmic computing device to said current analog signal whereby said output of the antilogarithmic computing device develops the computed output current so as to have varying values responsive to the product of the absolute values of said voltage and current components;

means connected to said first and second rectifier circuits for developing first and second digital pulse signals each having either of two different magnitudes with each magnitude corresponding to one of the positive or negative polarity states of said voltage and current components, respectively;

means responsive to said two magnitudes of each of said first and second pulse signals for comparing the magnitudes of said first and second digital pulse signals so as to establish a third pulse signal having first, second and third levels, said first level being established by the magnitudes of said first and second digital pulse signals indicating either of common polarity states of said voltage and current components, and said second and third levels being established by the opposite polarity states of said voltage and current components;

means for developing a fourth pulse signal in response to said first, second and third levels of said third pulse signal, said fourth pulse signal having either of two signal levels such that one level is developed when the magnitudes of the first and second pulse signals correspond to opposite polarity states of said voltage and current components and the other level is developed when the magnitude of the first and second pulse signals correspond to common polarity states of said voltage and current components;

a pair of output terminals connected with said output of said anti-logarithmic computing device; and

an inverting circuit connected between said output of said antilogarithmic computing device and said pair of output terminals, said inverting circuit being responsive to said third pulse signal such that said one level thereof renders said inverting circuit operative to reverse the phase of said computed output current by reversing the direction of current normally generated through said pair of output terminals by said antilogarithmic computing device, whereby current through said pair of output terminals is responsive to the true instantaneous value of power of said voltage and current components.

2. The electronic wattmeter as claimed in claim 1 wherein said logarithmic multiplier circuit includes solid state devices wherein said first and second logarithmic computing devices are input transistors having diode connected base and collector electrodes, said balancing and compensating computing device is a third transistor having a diode connected base and collector electrodes, and said anti-logarithmic computing device is an output transistor having a base to emitter input circuit connected in series with said input transistors and said third transistor and an emitter to collector output circuit.

3. The electronic wattmeter as claimed in claim 2 wherein said means for establishing said third pluse signal includes a pair of saturating amplifiers each including a constant current source, one transistor means with base, emitter and collector electrodes and another transistor means of the field effect type with gate, source and drain electrodes, wherein the emitter to collector circuit of each one transistor is connected in series with the source to drain circuit of one of said another transistor and with one of said constant current sources, wherein said first and second pulse signals are each applied to a separate one of said drain electrodes, and wherein said third pulse signal is developed across said collector electrodes, and said means for developing said fourth pulse signal further includes a logic circuit means responsive to said third pulse signal so as to generate one of said two signal levels when the levels of magnitude of said third pulse signal correspond to either of said states of opposite polarity of said voltage and current components and to generate the other signal level when the level of magnitude of said third pulse signal corresponds to said voltage and current components having a common polarity.

4. The electronic wattmeter as claimed in claim 3 wherein said means for developing said fourth pulse signal includes an exclusive OR function circuit having a pair of transistors with base, emitter and collector electrodes connected together in a differential amplifier configuration with each base electrode of a differential amplifier transistor connected to the collector electrode of a separate one of said one transistor means, and wherein a junction between said collector electrodes of said pair of differential amplifier transistors is effective to develop said fourth pulse signal in response to the three levels of magnitude of said fourth pulse signal.

5. The electronic wattmeter as claimed in claim 1 wherein said inverting circuit includes a diode serially connected to said output terminals, a pair of field effect transistors each having gate, source and drain electrodes, and a voltage source, wherein said drain and source electrodes of one field effect transistor are connected across a first series circuit thereof including said diode and said output terminals and said gate thereof is connected to said fourth pulse signal for rendering the one field effect transistor conductive when in said one signal level to thereby shunt normal current flow of said diode away from said output terminals, wherein the other field effect transistor is connected with the drain and source electrodes in parallel to both said first series circuit and a second series circuit including said output terminals and said voltage source, and wherein said pair of field effect transistors are connected together so that current through said other field effect transistor is substantially identical to the current through the one field effect transistor and said current through said output terminals is in one direction when said one field effect transistor is nonconductive and in an opposite direction when said one field effect transistor is conductive.

6. The electronic wattmeter as claimed in claim 1 wherein said inverting circuit includes a diode serially connected between said output of said anti-logarithmic computing device and said output terminals for conducting current in one direction thereto, one field effect transistor having source and drain electrodes connecting the junction between said diode and the anti-logarithmic computing device output in a shunt path and further having a gate electrode connected to said third pulse signal for rendering the associated field effect transistor conductive when in said one signal level and nonconductive when in said other signal level, another field transistor having source, drain and gate electrodes wherein said source and drain electrodes are connected in series with a junction of said diode adjacent said pair of output terminals, a source of voltage being connected between said source and drain electrodes of said another field effect transistor and said output terminals, resistor means connecting said gate electrode thereof to said voltage source, and a biasing means connecting said drain electrodes of said one and another field effect transistors such that current through both field effect transistors are substantially identical when said one field effect transistor is rendered conductive and concurrently said diode is rendered nonconductive and the current through the output terminals is in an opposite direction relative when said diode is conductive.

7. The electronic wattmeter as claimed in claim 2 wherein said logarithmic multiplier circuit includes an error reduction circuit for adjusting the collector to emitter current level of said output transistor so as to maintain a predetermined minimum of error producing variations thereof while generating a higher predetermined current level at said output terminals, said error reduction circuit including two dual connected transistors with the transistors of each dual having commonly connected emitter electrodes and commonly connected base electrodes, said base electrodes of a first dual connected to one collector electrode of one transistor therein and to said collector to emitter circuit of said output transistor, said emitter electrodes of the first dual connected to the base electrodes of a second dual and to a collector electrode of one transistor in the second dual, and said remaining collector electrodes of the two dual connected transistors connected together so that the common junction thereof develops said higher predetermined current level, and a field effect transistor having source and drain electrodes connected in series between the common collector junction and said output terminals and having the source electrode and a gate electrode connected across the emitter and collector electrodes of said second dual connected transistor to maintain minimum voltage variations thereacross.

8. An electronic wattmeter as claimed in claim 2 including a field effect transistor having source and drain electrodes connected in series with said collector to emitter circuit of said output transistor and the source electrode and a gate electrode connected across the collector to emitter circuit of said output transistor to maintain minimum voltage variations at the collector electrode of said output transistor.

9. An electronic wattmeter as claimed in claim 2 including one field effect transistor having source and drain electrodes connected in series with said collector to emitter circuit of said output transistor, another field effect transistor operated in a high gain amplifier mode wherein said another field effect transistor has a gate electrode connected to the collector of said output transistor and a feedback transistor means having a base biasing circuit connected in series with the source and drain electrodes of said another field effect transistor and an emitter to collector circuit connected to the gate electrode of said one field effect transistor whereby increasing voltage variations at the collector of said output transistor is decreased by said feedback transistor biasing said one field effect transistor so as to oppose such voltage variations.

10. A logarithmic multiplier circuit having first and second input transistors each having diode connected base and collector electrodes and the collector and an emitter electrodes connected in series adding relationship, each of said first and second transistors developing a voltage logarithmically related to current applied therethrough, a third compensating transistor having diode connected base and collector electrodes and the collector and an emitter electrodes connected in series with the first and second transistor, a constant current means connected across the collector and emitter electrodes of said third transistor, a fourth output transistor having base and emitter electrodes serially connected between said first and second transistors and said third transistor so as to develop a base current directly related to the combined voltages across said first and second transistors, said output transistors having emitter and collector electrodes developing a current through the collector to emitter circuit associated therewith anti-logarithmically related to said base current thereof, and a beta error reduction circuit comprising a fifth transistor substantially identical to said output transistor, said fifth transistor having a collector tO emitter circuit connected in series with said collector to emitter circuit of said output transistor, and sixth and seventh transistors having commonly connected emitters, diode connected base and collector electrodes of said sixth transistor connected in turn to the base electrode of said fifth transistor and the base electrode of said seventh transistor and the collector and emitter electrodes of said seventh transistor connected between the collector electrode of said fifth transistor and the base electrode of said output transistor, whereby error producing currents related to the beta characteristic of said output transistor are substantially reduced in the base current of said output transistor by duplicating said error producing currents through the collector electrode of said seventh transistor in opposing relationship thereto.

11. The electronic wattmeter as claimed in claim 2 wherein said means for comparing said first and second pulse signals including a pair of saturating amplifiers, each of said pair of saturating amplifiers having an output responsive to one of said first and second pulse signals such that said third pulse is established across both of said outputs of the saturating amplifiers, and wherein said means for developing said fourth pulse signal includes an exclusive OR logic function circuit having inputs connected across said outputs of said pair of saturating amplifiers.