Coasting power supply for AC power system waveform measuring instrument

• US 5,742,153 A
• Filed: 12/28/1993
• Issued: 04/21/1998
• Est. Priority Date: 08/18/1992
• Status: Expired due to Fees

• Current Assignee: Basic Measuring Instruments, Inc.
• Original Assignee: Basic Measuring Instruments, Inc.
• Inventors: Hord, Bryan D., McEachern, Alexander
• Primary Examiner(s): BERHANE, ADOLF D
• Application Number:
  US08/173,922
• Time in Patent Office: 1,575 Days
• Field of Search: 323/282, 323/283, 323/349, 323/351, 363/62, 363/78, 363/39
• US Class Current: 323/282
• CPC Class Codes: G01R 21/133 by using digital technique
• CPC Class Codes: G05F 1/56 using semiconductor devices in series with the load as final control devices G05F1/461 takes precedence
• CPC Class Codes: H02J 7/34 Parallel operation in networks using both storage and other dc sources, e.g. providing buffering H02J7/14 takes precedence

Abstract

A power supply for an instrument that measures waveforms on AC (alternating current) power systems. Under ordinary circumstances, the power supply draws its power from the signal that the instrument measures. The power supply includes energy storage means. When the instrument must make a precise measurement that could be affected by the power drawn by its power supply, the instrument temporarily disconnects its power supply from the measured signal and draws power from its energy storage means, effectively coasting on the stored energy. At the conclusion of the precise measurement, the instrument reconnects its power supply to the signal being measured.

Claims

1. A power supply for an electronic circuit that measures an AC (alternating current) power line signal, the power supply drawing its power from the same power line signal that the electronic circuit is measuring, comprising:

a. means for receiving the AC power line signal from a power line, said means for receiving coupled to the power line;

b. means for converting the AC power line signal received from the power line to DC (direct current) power, said means for converting coupled to the means for receiving;

c. means for supplying the electronic circuit with the DC power from the means for converting, said means for operating coupled to the means for converting and to the electronic circuit;

d. means for storing DC power to be used by the electronic circuit, said means for storing coupled to the means for converting and to the electronic circuit; and

e. means for disabling the means for supplying and furnishing power to the electronic circuit from the means for storing for a pre-determined interval of time;

said means for disabling coupled to the means for supplying and the means for storing.

2. The power supply as claimed in claim 1 wherein the conversion means is comprised of a first transformer coupled to the AC power line and a second transformer coupled to the first transformer and to the electronic circuit.

3. The power supply as claimed in claim 1 wherein the storage means is comprised of a capacitor.

4. The power supply as claimed in claim 1 wherein the pre-determined interval of time is less than fifteen seconds.

5. The power supply as claimed in claim 2 wherein the means for disabling is comprised of a transistor, a resistor and a control signal from a microprocessor.

6. The power supply as claimed in claim 2 wherein the means for disabling is comprised of gated rectifiers and a control signal from a microprocessor.

8. A power supply for electronic circuit that measures an AC (alternating current) power line voltage waveform having a period, the power supply comprising:

a. conversion means for converting AC power obtained from the power line to DC (direct current) power to operate the electronic circuit;

b. storage means for storing sufficient DC power to operate the electronic circuit for a first interval of time, the first interval of time being longer than one-half the period of the AC power line voltage waveform;

c. means for disabling the conversion means for a second interval of time, the second interval of time less than the first interval of time;

d. means for operating the electronic circuit using DC power from the storage means during the second interval of time; and

e. means for re-enabling the conversion means at the conclusion of the second interval of time.

7. The power supply as claimed in claim 8 wherein the means for disabling is comprised of an electromechanical relay and a control signal from a microprocessor.

9. The power supply as claimed in claim 8 wherein the conversion means is comprised of a first transformer coupled to the AC power line and a second transformer coupled to the first transformer and to the electronic circuit.

10. The power supply as claimed in claim 8 wherein the storage means is comprised of a capacitor.

11. The power supply as claimed in claim 9 wherein the second interval of time is less than fifteen seconds.

12. An electronic instrument for measuring a waveform generated by a power source, wherein the power source supplies operating power to the electronic instrument via a power supply signal path, the instrument comprising:

a. a control circuit coupled to the power source for receiving and measuring the waveform via an attenuating signal path;

b. a switch for decoupling the control circuit from the power supply signal path when the waveform is being measured; and

c. a storage element coupled to provide operating power to the control circuit when the control circuit is decoupled from the power source.

13. The electronic instrument according to claim 12 wherein the switch decouples the control circuit from the power supply signal path in response to a control signal generated by the microprocessor.

14. The electronic instrument according to claim 12 wherein the switch comprises a resistor-biased transistor coupled to receive a control signal from the control circuit.

15. The electronic instrument according to claim 12 wherein the storage element comprises a capacitor, further wherein the capacitor is charged by the power source via the power supply pathway and wherein the capacitor supplies power to the control circuit when the switch decouples the control circuit from the power supply signal path.

16. The electronic instrument according to claim 12 wherein the storage element comprises a DC battery.

17. The electronic instrument according to claim 16 wherein the DC battery is charged by the power source via the power supply signal path and wherein the DC battery supplies power to the control circuit when the switch decouples the microprocessor from the power supply signal path.

18. The electronic instrument according to claim 12 wherein the power supply signal path includes a voltage regulator and an AC-to-DC converter for converting AC voltages to an input voltage for the microprocessor.

19. The electronic instrument according to claim 12 wherein the attenuating signal path includes an analog-to-digital converter and an attenuator for converting the waveform into digital values.

20. The electronic instrument according to claim 12 wherein the control circuit comprises a microprocessor.

21. An electronic instrument for measuring a waveform generated by a power source, wherein the power source supplies operating power to the electronic instrument via an AC-DC converter, the instrument comprising:

a. a microprocessor coupled to the power source for receiving and measuring the waveform via an attenuating signal path, wherein the attenuating signal path includes (i) an attenuator for reducing voltage of the waveform and (ii) an analog-to-digital converter coupled to the attenuator for converting the waveform into digital signals;

b. a switch coupled between the microprocessor and the AC-DC converter for decoupling the microprocessor from the AC-DC converter when the waveform is being measured, wherein the switch is configured to respond to a control signal from the microprocessor; and

c. a storage element coupled to provide operating power to the microprocessor when the microprocessor is decoupled from the power source.

22. The electronic instrument according to claim 21 wherein the switch comprises an enhancement mode power field-effect transistor.