VARIABLE SENSING USING FREQUENCY DOMAIN

• US 20080114557A1
• Filed: 11/12/2007
• Published: 05/15/2008
• Est. Priority Date: 11/14/2006
• Status: Active Grant

• Current Assignee: 2 Bit Incorporated
• Original Assignee: 2 Bit Incorporated
• Inventors: Lambert, Rodney J.
• Granted Patent: US 8,060,325 B2
• Time in Patent Office: Days
• US Class Current: 702/77
• CPC Class Codes: H03M 1/1042 the look-up table containing corrected values for replacing the original digital values H03M1/1052 takes precedence
• CPC Class Codes: H03M 1/122 Shared using a single converter or a part thereof for multiple channels, e.g. a residue amplifier for multiple stages

Abstract

Embodiments of a method and apparatus for variable sensing using the frequency domain are taught herein. An exposure of a system to a physical variable is determined by periodically sensing the physical variable to produce a plurality of digital samples. The plurality of digital samples is converted to respective frequency domain representations. The exposure is calculated using the frequency domain representations.

Claims

1. A method for monitoring an exposure of a system to a physical variable, the method comprising:

periodically sensing the physical variable to produce a plurality of digital samples;

converting the plurality of digital samples to respective frequency domain representations; and

calculating the exposure using the frequency domain representations.

2. The method according to claim 1, further comprising:

producing the plurality of digital samples by converting each sensed value for the physical variable to a corresponding digital sample.

3. The method according to claim 1, further comprising:

applying a weighting function to the frequency domain representations before calculating the exposure.

4. The method according to claim 3, further comprising:

determining a fundamental frequency; and

wherein applying the weighting function comprises applying a weighting factor to each of the frequency domain representations based on the fundamental frequency.

5. The method according to claim 1, further comprising:

filling a first data window with the plurality of digital samples; and

wherein calculating the exposure using the frequency domain representations includes calculating a first exposure using the frequency domain representations of the plurality of digital samples in the first data window;

periodically sensing the physical variable to produce a second plurality of digital samples;

filling a second data window with the second plurality of digital samples while calculating the first exposure;

converting the second plurality of digital samples to respective frequency domain representations; and

calculating a second exposure using the frequency domain representations of the second plurality of digital samples in the second data window after calculating the first exposure.

6. The method according to claim 5, further comprising:

calculating a recent exposure by adding the first exposure and the second exposure.

7. The method according to claim 1 wherein periodically sensing the physical variable to produce a plurality of digital samples further comprises periodically sensing the physical variable for a first period, the method further comprising:

filling a first data window with the plurality of digital samples;

wherein calculating the exposure using the frequency domain representations includes calculating a first exposure using the frequency domain representations of the plurality of digital samples in the first data window;

filling a first portion of a second data window with certain of the plurality of digital samples occurring at an end of the first period;

periodically sensing the physical variable for a second period to produce a second plurality of digital samples;

filling a third data window with the second plurality of digital samples while calculating the first exposure; and

filling a second portion of the second data window with certain of the second plurality of digital samples occurring at a beginning of the second period simultaneously with filling the third data window.

8. The method according to claim 7, further comprising:

calculating a second exposure using frequency domain representations of samples stored in the second data window after filling the second data window and while filling the third data window.

9. The method according to claim 7, further comprising:

scaling each digital sample before using the digital sample to fill a position in a respective data window, the scaling based on the position in the respective data window.

10. The method according to claim 1 wherein calculating the exposure using the frequency domain representations further comprises:

calculating a plurality of exposure values using the frequency domain representations;

counting occurrences where an individual value of the plurality of exposure values is outside a desired range; and

calculating a lifetime exposure using a count of the occurrences.

11. The method according to claim 1, further comprising:

outputting the exposure as a logic level or as a proportional analog value.

12. The method according to claim 1 wherein converting the plurality of digital samples to respective frequency domain representations comprises:

performing a Fourier transform on each of the plurality of digital samples to obtain a respective complex Fourier coefficient at a respective frequency; and

calibrating each complex Fourier coefficient to obtain the respective frequency domain representations.

13. The method according to claim 1, further comprising:

sequentially filling a plurality of windows with the plurality of digital signals;

calculating a first exposure value using frequency domain representations corresponding to digital signals of a first one of the plurality of windows; and

deciding whether to store at least one of the first exposure value and the digital signals of the first one of the plurality of windows based on the first exposure value.

14. The method according to claim 13, further comprising:

storing the digital signals of the first one of the plurality of windows when the first exposure value exceeds a preset level or the first exposure value is outside an envelope of values.

15. The method according to claim 13 wherein calculating the first exposure value comprises performing a correlation function on the frequency domain representations corresponding to the digital signals of the first one of the plurality of windows and a user-defined pattern, the method further including:

storing the digital signals of the first one of the plurality of windows when the first exposure value exceeds a preset level.

16. The method according to claim 13, further comprising:

calculating a second exposure value for a second window of the plurality of windows;

comparing the second exposure value to the first exposure value;

deciding whether to store at least one of the second exposure value and data of the second window based on a result of the comparing.

17. An apparatus for monitoring an exposure of a system to a physical variable, the apparatus comprising:

means for periodically sensing the physical variable to produce a plurality of digital samples;

means for converting the plurality of digital samples to respective frequency domain representations; and

means for calculating the exposure using the frequency domain representations.

18. The apparatus according to claim 17 wherein the physical variable is acceleration and wherein the means for periodically sensing the physical variable to produce the plurality of digital samples further comprises:

an accelerometer sensing the acceleration in three directions; and

means for converting each sensed acceleration value to a corresponding digital sample.

19. The apparatus according to claim 17 wherein the means for calculating the exposure using the frequency domain representations further comprises:

means for calculating a first exposure in a first direction using frequency domain representations corresponding to a first plurality of digital samples;

means for calculating a second exposure in a second direction using frequency domain representations corresponding to a second plurality of digital samples;

means for calculating a third exposure in a third direction using frequency domain representations corresponding to a third plurality of digital samples; and

means for calculating a weighted exposure based on the first exposure, the second exposure and the third exposure.

20. The apparatus according to claim 17, further comprising:

means for determining a fundamental frequency; and

means for scaling each of the frequency domain representations based on the fundamental frequency prior to calculating the exposure.

21. The apparatus according to claim 17 wherein the means for periodically sensing the physical variable to produce the plurality of digital samples further comprises means for periodically sensing the physical variable for a first period, the apparatus further comprising:

memory including a plurality of windows for storing a same number of digital samples;

means for filling a first data window with the plurality of digital samples;

wherein the means for calculating the exposure using the frequency domain representations includes means for calculating a first exposure using the frequency domain representations of the plurality of digital samples in the first data window;

means for filling a first portion of a second data window with certain of the plurality of digital samples occurring at an end of the first period;

means for periodically sensing the physical variable for a second period to produce a second plurality of digital samples;

means for filling a third data window with the second plurality of digital samples while calculating the first exposure;

means for filling a second portion of the second data window with certain of the second plurality of digital samples occurring at a beginning of the second period simultaneously with filling the third data window; and

means for calculating a second exposure using frequency domain representations of samples stored in the second data window after filling the second data window and while filling the third data window.

22. The apparatus according to claim 17 wherein the means for calculating the exposure further comprises means for calculating a plurality of exposure values using the frequency domain representations, the apparatus further comprising:

memory configured to store at least certain of the exposure values.

23. The apparatus according to claim 22 wherein the memory is further configured to store each of the exposure values over a predetermined time period as respective counts in a histogram.