METHOD AND SYSTEM OF MEASURING CURRENT IN AN ELECTRIC METER

• US 20120032666A1
• Filed: 08/04/2010
• Published: 02/09/2012
• Est. Priority Date: 08/04/2010
• Status: Active Grant

• Current Assignee: Sensus Spectrum, LLC (Xylem, Inc.)
• Original Assignee: Sensus Spectrum, LLC (Xylem, Inc.)
• Inventors: Hamo, David
• Granted Patent: US 8,847,577 B2
• Time in Patent Office: Days
• US Class Current: 324/120
• CPC Class Codes: G01R 1/203 Resistors used for electric measuring, e.g. decade resistors standards, resistors for comparators, series resistors, shunts resistors in general H01C; microwave or radiowave terminations H01P1/26; coupling devices H01R
• CPC Class Codes: G01R 19/0092 measuring current only all subgroups of G01R19/00 take precedence
• CPC Class Codes: G01R 35/005 Calibrating; Standards or reference devices, e.g. voltage or resistance standards, "golden" references G01R33/0035, G01R35/002 take precedence

Abstract

A method and system for measuring the current flowing through an electric meter. The electric meter includes a reactive sensor positioned in series with a bus bar contained in the meter. The reactive sensor includes an inductor and the voltage across the inductance is measured. A control unit contained in the electric meter calculates the current based on the detected voltage and the value of the inductor. The value of the inductor is determined by passing a reference current through the inductor at a known frequency, such as 50 Hz or 60 Hz, and the voltage drop across the inductor is measured. Once the value of the inductor is determined, the value is stored in the control unit.

Claims

1. A system for measuring the amount of current flowing through an electric meter coupled to the utility source through at least one bus bar, the system comprising:

an inductor positioned in series with the bus bar;

a voltage detector positioned to detect the voltage across the inductor; and

a control unit coupled to the voltage detector and operable to calculate the current flowing through the electric meter based on the value of the inductor and the detected voltage.

2. The system of claim 1 wherein the value of the inductor is predetermined and stored in the control unit.

3. The system of claim 1 wherein the control unit is mounted to a circuit board contained within the electric meter, wherein the inductor is formed on the circuit board.

4. The system of claim 1 wherein the inductor is formed on the bus bar.

5. The system of claim 3 wherein the inductor includes a plurality of turns.

6. The system of claim 1 wherein the inductor includes a combination of self-inductance and mutual inductance required to measure current.

7. The system of claim 1 wherein the voltage detector includes an analog to digital converter.

8. A method of measuring the current flowing through an electric meter, the method comprising the steps of:

positioning an inductor in series with a bus bar contained in the electric meter;

detecting the voltage across the inductor; and

calculating the current flowing through the electric meter based on a value of the inductor and the detected voltage.

9. The method of claim 8 further comprising the steps of:

supplying a known reference current to the electric meter;

detecting the voltage across the inductor; and

calculating the value of the inductor based on the known reference current and the detected voltage.

10. The method of claim 9 wherein the known reference current supplied to the electricity meter is supplied at a known frequency and the value of the inductor is calculated based on the known reference current, the known frequency and the detected voltage.

11. The method of claim 10 further comprising the steps of:

storing the calculated value of the inductor in a control unit of the electric meter; and

calculating the current based on the calculated value of the inductor, the known frequency and the detected voltage.

12. The method of claim 8 wherein the current is calculated in a control unit mounted to a circuit board contained in the electric meter.

13. The method of claim 12 wherein the inductor is formed on the circuit board.

14. The method of claim 8 wherein the inductor is formed on the bus bar.

15. The method of claim 8 wherein the inductor is part of the bus bar construction.

16. The method of claim 8 wherein the inductor is between 100 nH and 200 nH.

17. The method of claim 11 further comprising the steps of:

determining the phase shift between the current and the detected voltage; and

storing the phase shift in the control unit.

21. The system of claim 15 wherein the inductor is formed on the bus bar.

18. An electric meter, comprising:

at least one bus bar to connect the electric meter to a source of utility provided power having a frequency;

an inductor positioned in series with the bus bar;

a voltage detector positioned to detect the voltage across the inductor; and

a control unit coupled to the voltage detector and operable to calculate the current flowing through the electric meter based on the value of the inductor, the frequency and the detected voltage.

19. The system of claim 18 wherein the value of the inductor is predetermined and stored in the control unit.

20. The system of claim 18 wherein the control unit is mounted to a circuit board contained within the electric meter, wherein the inductor is formed on the circuit board.

22. The system of claim 18 wherein the inductor includes a plurality of turns.

23. The system of claim 18 wherein the voltage detector includes an analog to digital converter.