Digital circuit and method for measuring AC voltage values

• US 9,488,683 B2
• Filed: 09/28/2012
• Issued: 11/08/2016
• Est. Priority Date: 12/19/2011
• Status: Active Grant

• Current Assignee: Johnson Controls Tyco IP Holdings LLP (Johnson Controls International plc)
• Original Assignee: Tyco Safety Products Canada Limited (Johnson Controls International plc)
• Inventors: Bucsa, Andrei, Fosty, Stephen D. W.
• Primary Examiner(s): Betsch, Regis
• Assistant Examiner(s): PETERS, LISA E
• Application Number:
  US13/630,986
• Publication Number:
  US 20130158924A1
• Time in Patent Office: 1,502 Days
• Field of Search: 219/497, 361/160, 361/154, 361/18, 361/21, 361/6, 315/224, 315/307, 322/28, 322/73, 322/32, 320/163, 323/259, 327/58, 327/62, 702/78, 714/47.1, 714/745
• US Class Current: 1/1
• CPC Class Codes: F16H 59/105 consisting of electrical switches or sensors
• CPC Class Codes: G01B 7/003 for measuring position, not involving coordinate determination coordinate measuring G01B7/004
• CPC Class Codes: G01B 7/14 for measuring distance or clearance between spaced objects or spaced apertures G01B7/30 takes precedence
• CPC Class Codes: G01D 5/2457 Incremental encoders having reference marks
• CPC Class Codes: G01R 19/00 Arrangements for measuring currents or voltages or for indicating presence or sign thereof G01R5/00 takes precedence; for measuring bioelectric currents or voltages A61B5/24
• CPC Class Codes: G01R 23/02 Arrangements for measuring frequency, e.g. pulse repetition rate; Arrangements for measuring period of current or voltage
• CPC Class Codes: G06F 17/00 Digital computing or data processing equipment or methods, specially adapted for specific functions information retrieval, database structures or file system structures therefor G06F16/00
• CPC Class Codes: H02H 3/06 with automatic reconnection
• CPC Class Codes: H02H 3/087 for dc applications
• CPC Class Codes: H02J 7/0068 Battery or charger load switching, e.g. concurrent charging and load supply H02J7/0013 takes precedence

Abstract

An AC measurement circuit includes a rectifier for receiving an AC signal; a peak detection circuit; and a voltage divider, interconnected with an output of the rectifier, and the input of the peak detection circuit to provide the peak detection circuit with a voltage value equal to a fraction of the AC signal. An analog to digital converter, has its analog input interconnected with an output of the peak detection circuit, for providing a digital output corresponding to its analog input. A summing circuit sums n samples of the digital output. The voltage divider is configured so that the summing circuit calculates an average measurement of the AC signal by summing n samples and without floating point division.

Claims

1. An AC measurement circuit to provide an average measurement of an AC signal, the circuit comprising:

a rectifier for receiving said AC signal and providing a rectified output, the AC signal having an expected voltage range;

a peak detection circuit for detecting peak values of an input voltage;

an analog to digital converter, having its analog input interconnected with an output of said peak detection circuit, for providing a digital output corresponding to detected peak values of said input voltage and to provide n samples of said digital output, n having been selected based on a ratio of the maximum peak value of said expected voltage range and the dynamic range of said analog input;

a voltage divider, interconnected with an output of said rectifier, and the input of said peak detection circuit to provide said peak detection circuit with said input voltage equal to a fraction of said rectified output, said fraction being a reciprocal of a multiple of n; and

a processing circuit to calculate said average measurement of said AC signal by summing said n samples of said digital output.

2. The AC measurement circuit of claim 1, wherein said processing circuit calculates said average measurement without floating point operation.

3. The AC measurement circuit of claim 1, wherein said average measurement is an average root mean square measurement of the voltage of said AC signal, said fraction equals η

, and wherein η and

n are chosen so that the ratio

4. The AC measurement circuit of claim 1, wherein said average measurement is an average peak voltage measurement of said AC signal, said fraction equals η

, and wherein η and

n are chosen so that the ratio

5. The AC measurement circuit of claim 1, wherein said processing circuit is calibrated to account for any voltage drop across said rectifier.

6. The AC measurement circuit of claim 1, further comprising a circular buffer in communication with said analog to digital converter to store said n samples of said digital output.

7. The AC measurement circuit of claim 6, wherein said processing circuit sums values stored in said circular buffer.

8. The AC measurement circuit of claim 1, wherein said processing circuit and said analog to digital converter form part of a processor.

9. A method of determining an average measurement of an AC signal, the method comprising:

providing said AC signal to a rectifier to provide a rectified output, the AC signal having an expected voltage range;

providing said rectified output to the input of a voltage divider that outputs a fraction of said rectified output;

detecting a peak of said output of said voltage divider over time;

sampling said peak of said output at an analog to digital converter to produce at least n digital values, n having been selected based on a ratio of the maximum peak value of said expected voltage range and the dynamic range of said analog input;

summing n of said digital values to calculate said average measurement of said AC signal by at least one processor;

wherein said voltage divider is configured so that said fraction is a reciprocal of a multiple of n.

10. The method of claim 9, wherein said average measurement of said AC signal is calculated without floating point operations.

11. The method of claim 9, wherein said detecting said peak, said sampling and said summing are repeated.

12. The method of claim 9, wherein said average measurement is an average root mean square measurement of the voltage of said AC signal, said fraction equals η

, and wherein η and

n are chosen so that the ratio

13. The method of claim 9, wherein said average measurement is an average peak voltage measurement of said AC signal, said fraction equals η

and wherein η and

n are chosen so that the ratio

14. The method of claim 9, wherein said summing accounts for any voltage drop across said rectifier.

15. The method of claim 9, wherein said n of said digital values are stored in a circular buffer.

16. The method of claim 14, wherein said summing n of said digital values by at least one processor comprises summing values stored in said circular buffer.