Indicator diagram based AC electric energy meter

• US 4,282,576 A
• Filed: 02/08/1980
• Issued: 08/04/1981
• Est. Priority Date: 05/22/1979
• Status: Expired due to Term

• Current Assignee: ABB Power T&D Co Inc (ABB Limited)
• Original Assignee: Westinghouse Electric Corporation (Paramount Global (f/k/a ViacomCBS Inc.))
• Inventors: Elms, Robert T., Vercellotti, Leonard C.
• Primary Examiner(s): Krass, Errol A.
• Assistant Examiner(s): Chin, Gary
• Application Number:
  US06/119,686
• Time in Patent Office: 543 Days
• Field of Search: 364/483, 364/480, 364/464, 324/141, 324/142, 324/140 R, 324/76 R, 324/76 A, 361/79
• US Class Current: 702/60
• CPC Class Codes: G01R 21/133 by using digital technique

Abstract

A first input signal representative of the voltage component is integrated producing an integral signal. The integral signal is compared to fixed reference potentials. A second input signal representative of the current component is sampled when the instantaneous magnitude of the integral signal equals a reference potential. The sample value is digitized and the integrator is reset by variable width reset pulses. Successive sample values are accumulated producing totalized values representative of the time integral of the product of the current component and the time integral of the voltage component, or energy.

Claims

1. A meter apparatus computing the area of an indicator diagram for determining the value of an AC electric energy quantity defined by a voltage and a current component, comprising:

input means for producing a first input signal representative of said voltage component;

means for integrating said first input signal for producing an integral signal;

means for comparing the instantaneous magnitude of said integral signal to the magnitude of fixed and predetermined reference potentials;

processing means for producing, in response to said means for comparing, signals composed of variable width pulses;

a constant current source for resetting, in response to said width of said pulses of said signals, said means for integrating;

a second input means producing a second input signal representative of said current component;

means for sampling, in response to said pulses of said signals, said second input signal for producing sample values, said sample values input to said processing means, said processing means accumulating successive sample values thereby producing totalized values representative of the time integral of the product of said current component times the time integral of said voltage component, said processing means further producing, in response to said totalized values, an output signal representative of said AC electric energy quantity.

2. The meter apparatus of claim 1 wherein the reference potentials include a positive voltage potential and ground potential.

3. The meter apparatus of claim 2 wherein the means for comparing includes a first comparator producing an output pulse each time the instantaneous magnitude of the integral signal equals the magnitude of the constant positive voltage potential, and includes a second comparator producing an output pulse each time said instantaneous magnitude of said integral signal equals the ground potential.

4. The meter apparatus of claim 3 wherein the processing means produces, in response to the pulses produced by the first comparator, a first one of two reset signals, and produces, in response to the pulses produced by the second comparator, a second one of said two reset signals.

5. The meter apparatus of claim 3 wherein the processing means produces, in response to the pulses of both the first and second comparators, a sample control signal and a scaling control signal.

6. The meter apparatus of claim 4 wherein the processing means increases the width of predetermined pulses of the reset signals such that dither is introduced.

7. The meter apparatus of claim 4 including means for selectably connecting the constant current source to the means for integrating, said means includes a first switch electrically in parallel with a series combination of an inverter and a second switch, said first switch responsive to the width of the pulses of the first reset signal, said second switch responsive to the width of the pulses of the second reset signal.

8. The meter apparatus of claim 1 wherein the second input means includes a single turn primary current transformer having a first and sensing secondary winding.

9. The meter apparatus of claim 8 wherein the second input means includes an amplifier producing, in response to the first and sensing secondary winding, an analog signal proportional to the current flowing in the primary winding.

10. The meter apparatus of claim 9 wherein the second input means includes a second and compensating secondary winding producing, in response to the analog signal, a flux equal in magnitude and opposite in direction to the flux produced by the primary winding, and wherein said analog signal flowing through said compensating secondary winding is the second input signal.

11. The meter apparatus of claim 9 including means for producing, in response to the analog signal, a polarity signal indicating the polarity of the current flowing in the primary winding, said polarity signal input to the processing means.

12. The meter apparatus of claim 5 including a scaling means responsive to said scaling control signal, said scaling means having a first current path comprised of a switch in series with a resistor, and a second current path comprised of a switch in series with a resistor, said first current path electrically in parallel with said second current path.

13. The meter apparatus of claim 12 wherein the resistance values of the resistors varies by a factor of eight.

14. The meter apparatus of claim 12 wherein the switch of the first current path is responsive to the scaling control signal, and wherein the switch of the second current path is responsive to the inverse of said scaling control signal.

15. The meter apparatus of claim 11 including a means for rectifying having a rectifier circuit in series with a switch, said switch responsive to the inverse of the polarity signal such that only one polarity of the second input signal is applied to said rectifier circuit, and includes a bypass conductor having a switch responsive to said polarity signal such that the other polarity of said second input signal bypasses said rectifier circuit.

16. The meter apparatus of claim 5 wherein the means for sampling includes a switch, responsive to the sample control signal, in series with a capacitor, said capacitor producing the sample value.

17. The meter apparatus of claim 1 wherein the processing means produces, in response to each sample value, a digital number.

18. The meter apparatus of claim 17 wherein the processing means accumulates successive digital numbers thereby producing the totalized values.

19. The meter apparatus of claim 17 including means for inputting the sample values to the processing means, said inputting means includes a digital-to-analog converter responsive to the ditigal number in the processing means, and a comparator for producing, in response to both the means for sampling and said digital-to-analog converter, a signal updating said digital number in said processing means until said digital number equals the sample value.

20. The meter apparatus of claim 19 wherein the bits comprising the digital number are sequentially updated beginning with the most significant bit.

21. A meter apparatus computing the area of an indicator diagram for determining the value of an AC electric energy quantity defined by a voltage and a current component, comprising:

input means for producing a first input signal representative of said voltage component;

means for integrating said first input signal and producing an integral signal;

means for comparing the instantaneous magnitude of said integral signal to the magnitude of fixed and predetermined reference potentials;

processing means for producing, in response to said means for comparing, two reset signals each composed of variable width pulses, a sample control signal, and a scaling control signal;

a constant current source;

means for selectably connecting, in response to said width of said pulses of said reset signals, said means for integrating to said constant current source;

input means for producing a second input signal representative of said current component and a polarity signal indicating the polarity of said current component;

a scaling means for adjusting, in response to said scaling control signal, the magnitude of said second input signal;

means for rectifying, in response to said polarity signal and said adjusted second input signal, for producing a rectified signal;

means for sampling, in response to said sample control signal and said rectified signal, for producing sample values; and

means for inputting said sample values to said processing means, said processing means accumulating successive sample values thereby producing totalized values representative of the time integral of the product of said current component times the time integral of said voltage component, said processing means further producing, in response to said totalized value, an output signal representative of said AC electric energy quantity.