Current switch with automatic calibration

• US 9,410,552 B2
• Filed: 07/31/2012
• Issued: 08/09/2016
• Est. Priority Date: 10/05/2011
• Status: Active Grant

• Current Assignee: Veris Industries LLC (Schneider Electric SE)
• Original Assignee: Veris Industries LLC (Schneider Electric SE)
• Inventors: Pierson, David
• Primary Examiner(s): Phan, Huy Q
• Assistant Examiner(s): Rhodes-Vivour, Temilade
• Application Number:
  US13/562,847
• Publication Number:
  US 20130088213A1
• Time in Patent Office: 1,470 Days
• Field of Search: 324/74, 324/76.19, 324/76.22, 324/76.41, 324/76.69, 324/674, 324/681, 324/707
• US Class Current: 1/1
• CPC Class Codes: F04D 25/08 the working fluid being air, e.g. for ventilation
• CPC Class Codes: F04D 27/001 Testing thereof; Determination or simulation of flow characteristics; Stall or surge detection, e.g. condition monitoring
• CPC Class Codes: G01N 1/00 Sampling; Preparing specimens for investigation
• CPC Class Codes: G01R 1/00 Details of instruments or arrangements of the types included in groups G01R5/00 - G01R13/00 and G01R31/00 constructional details particular to electromechanical arrangements for measuring the electric consumption G01R11/02
• CPC Class Codes: H02P 27/047 V/F converter, wherein the voltage is controlled proportionally with the frequency
• CPC Class Codes: H02P 29/027 the fault being an over-current

Abstract

A current switch that can be reset when it is not powered automatically calibrates itself when the circuit monitored by the current switch is energized.

Claims

1. A method of monitoring a drive signal having a variable frequency and a variable current, said method comprising the steps of:

(a) dividing a spectrum of said variable drive signal frequencies into a plurality of contiguous frequency ranges each bounded by a lower frequency and an upper frequency;

(b) substantially contemporaneously sampling a current and a frequency of said drive signal;

(c) determining a first frequency range that includes said drive signal sample frequency;

(d) activating an alarm if said drive signal sample current exceeds by a predetermined magnitude a current of a temporally prior sample of said drive signal having a frequency within said first frequency range;

(e) activating an alarm if said temporally prior sample of said drive signal current having a frequency within said first frequency range exceeds said sample drive signal current by a predetermined magnitude;

(f) activating an alarm if said drive signal current does not exceed a predetermined portion of a base current of said drive signal;

(g) determining a respective nominal drive current for a plurality of said frequency ranges; and

(h) adopting as said base current of said drive signal a current substantially equal to said respective nominal drive current for one of said frequency ranges if said nominal drive current for said one of said frequency ranges is substantially equal to a nominal drive current for at least one other frequency range.

2. The method of monitoring a drive signal of claim 1 wherein the step of determining a respective nominal drive signal current for each of said plurality of ranges of frequencies comprises the steps of:

(a) obtaining a plurality of substantially contemporaneous samples of said drive signal current and said drive signal frequency, a frequency of each of said plurality of samples of said drive signal current being a frequency within a single frequency range;

(b) if a predetermined number of said samples is obtained within a predetermined interval of time, approximating said plurality of current samples as said nominal drive signal current of said single frequency range.

3. The method of monitoring a drive signal of claim 2 wherein the step of approximating said plurality of current samples comprises the step of determining an average of said current samples.

4. The method of monitoring a drive signal of claim 2 wherein the step of approximating said plurality of current samples comprises the step of determining a median of said current samples.

5. A method of calibrating a current switch monitoring a drive signal having a variable frequency and a variable current, said method comprising the steps of:

(a) said current switch dividing a spectrum of said variable drive signal frequencies into a plurality of frequency ranges each bounded by a lower frequency and an upper frequency;

(b) if said current switch determines a state of a reset control has been changed, said current switch accumulating a predetermined number of samples of said drive signal current each having a frequency within a first frequency range; and

(c) if said current switch determines said predetermined number of drive signal current samples is accumulated within a predetermined time interval, said current switch adopting an approximation said predetermined number of said drive signal current samples as a nominal drive current for said first frequency range.

6. The method of monitoring a drive signal of claim 5 wherein the step of approximating said predetermined number of said drive signal current samples comprises the step of determining an average of said drive signal current samples.

7. The method of monitoring a drive signal of claim 5 wherein the step of approximating said predetermined number of said drive signal current samples comprises the step of determining a median of said drive signal current samples.

8. A current switch for monitoring a drive signal having a variable frequency and a variable current, said current switch comprising:

(a) a current transducer producing a transducer signal indicating said frequency of said drive signal and indicating a magnitude of said drive signal current;

(b) a processing unit for executing a process according to a program instruction;

(c) a reset control operable to indicate to said processing unit one of a first state and a second state of said reset control, said indicated reset control state preserved until said reset control is operated to indicate the other of said first state and said second state;

(d) a memory storing a program instruction and data including a datum designating an indicated state of said reset control and a datum quantifying at least one drive signal current; and

(e) a program instruction stored in said memory and executable by said processing unit, said program instruction causing said processing unit to change a value of said datum quantifying said at least one drive signal current if a state of said reset control presently indicated to said processing unit differs from a state of said reset control stored in said memory.

9. A current switch for monitoring a drive signal having a variable frequency and a variable current, said current switch comprising:

(a) a current transducer producing a transducer signal having a frequency related to said frequency of said drive signal and a magnitude related to said current of said drive signal;

(b) a processing unit for executing a process according to a program instruction;

(c) a memory storing a program instruction and data including a datum quantifying at least one nominal current of said drive signal; and

(d) a program instruction stored in said memory and executable by said processing unit, said program instruction causing said processing unit to;

(i) determine a frequency and a current of a sample of said drive signal from said transducer signal;

(ii) identifying a first frequency range which includes said frequency of said drive signal sample, said first frequency range one of a plurality of contiguous frequency ranges comprising a spectrum of potential frequencies for said variable frequency drive signal;

(iii) repeating steps (d)(i) and (d)(ii) to accumulate a predetermined number of samples of said drive signal current each having a frequency within said first frequency range; and

(iv) if said predetermined number of samples is accumulated within a predetermined interval of time, adopting as a nominal drive signal current for said first frequency range an approximation of said predetermined number of said samples of said drive signal current.

10. The current switch of claim 9 wherein the program instruction causing the processing unit to approximate said predetermined number of samples of said drive signal current causes said processing unit to find an average of said samples of said drive signal current.

11. The current switch of claim 9 wherein the program instruction causing the processing unit to approximate said predetermined number of samples of said drive signal current causes said processing unit to find a median of said samples of said drive signal current.

12. The current switch of claim 9 further comprising a program instruction stored in said memory and executable by said processing unit to cause said processing unit to activate an alarm if said sample of said drive signal current exceeds by a predetermined magnitude a temporally prior sample of said drive signal current having a frequency within said first frequency range.

13. The current switch of claim 9 further comprising a program instruction stored in said memory and executable by said processing unit to cause said processing unit to activate an alarm if a temporally prior sample of said drive signal current having a frequency within said first frequency range exceeds said sample of said drive signal current by a predetermined magnitude.

14. The current switch of claim 9 further comprising a program instruction stored in said memory and executable by said processing unit to cause said processing unit to activate an alarm if said sample of said drive signal current does not exceed a nominal drive signal current for a second frequency range bounded by an upper frequency that does not exceed a lower frequency of said first frequency range.

15. The current switch of claim 9 further comprising a program instruction stored in said memory and executable by said processing unit to cause said processing unit to activate an alarm if said sample of said drive signal current does not exceed a predetermined portion of a base current approximating a nominal drive signal current for a second frequency range, said nominal drive signal current for said second frequency range being substantially equal to a nominal drive signal current for at least one other frequency range.

16. The current switch of claim 9 further comprising a program instruction stored in said memory and executable by said processing unit to cause said processing unit to activate an alarm if said sample drive signal current exceeds a nominal drive signal current for said first frequency range by a predetermined amount.

17. The current switch of claim 9 further comprising a reset control operable to indicate one of a first state and a second state, said reset control preserving said indicated state until operated to indicate the other of said first state and said second state;

said processing unit arranged to compare said indicated state of said reset control with a stored state of said reset control and to accumulate said predetermined number of samples if said indicated state differs from said stored state.