Method and apparatus for detection signal processing

• US 6,492,821 B1
• Filed: 07/31/2000
• Issued: 12/10/2002
• Est. Priority Date: 07/31/2000
• Status: Active Grant

• Current Assignee: Banner Engineering Corporation
• Original Assignee: Banner Engineering Corporation
• Inventors: Schumacher, Neal A., Marko, Lawrence J., Rosengren, Brian P.
• Primary Examiner(s): Le, N.
• Assistant Examiner(s): KERVEROS, DEMETRIOS C
• Application Number:
  US09/629,499
• Time in Patent Office: 862 Days
• Field of Search: 324/660, 324/667, 324/678, 324/690, 324/661, 324/662, 324/671, 324/681, 324/676, 324/663, 235/383, 235/462.01, 235/492, 347/217, 280/735, 340/438, 340/545.4
• US Class Current: 324/671
• CPC Class Codes: G01D 3/02 with provision for altering or correcting the law of variation

Abstract

A system and method are disclosed for detecting the occurrence of an external event. The system eliminates the need for users to adjust amplifier offsets as well as detection thresholds by continually analyzing the signal and optimizing the offset and threshold values accordingly. Additionally, the system detects the external events in a noisy environment when the duration of the events vary by several orders of magnitude by employing cascaded difference filters.

Claims

1. A method for detecting a change in an output signal having a level that fluctuates in response to an external event, the method comprising:

amplifying the output signal using an amplifier to generate a sensed signal;

continually adjusting an offset voltage which is applied to the amplified output signal to maintain a mean value of the sensed signal at a desired voltage;

detecting an occurrence of the external event by detecting when the sensed signal changes to a value greater than a threshold value; and

continually adjusting the threshold value used to detect the occurrence of the external event to maintain the threshold value at a desired percentage of a maximum range of sensed signal values.

2. The method according to claim 1, wherein sensing circuitry is responsive to the external event, the method further comprising:

receiving from the sensing circuitry a periodic signal having a characteristic that varies when the external event occurs; and

filtering the periodic signal using a low-pass filter to generate the output signal.

3. The method according to claim 2, wherein the sensing circuitry is part of a label sensor and includes a first reference electrode, a second reference electrode, and electronic driving circuitry, wherein the first reference electrode is coupled to a first side of an opening in the sensor and a second reference electrode is coupled to a second side of the opening such that an object passes through the opening and between the first reference electrode and the second reference electrode, the method further comprising:

holding the first reference electrode at a first voltage potential;

electrically connecting the second reference electrode to a resistor that is electrically connected to a second voltage potential; and

electrically connecting the second reference electrode to an electronic driving circuit that generates the periodic signal in response to the object altering the capacitance between the first and second reference electrodes.

4. The method according to claim 3, wherein the electronic driving circuit is a monostable multivibrator circuit having a clock signal input.

5. The method according to claim 4, wherein a 2 MHz clock signal is provided to the clock signal input.

6. The method according to claim 1, wherein the method further comprises:

sampling the sensed signal using an A-to-D Converter module to generate sampled data and storing the sampled data within a memory array; and

applying cascaded difference filters to the sampled data stored within the memory array.

7. The method according to claim 6, wherein

the first time the cascaded difference filter is applied, the cascaded difference filter uses two adjacent data samples at a time from the memory array to check for the occurrence of the external event;

and

if no signal change is found, an index used by the cascaded difference filters is incremented so that the cascaded difference filters are again applied using data samples spaced at sequentially larger time intervals from the memory array until the occurrence of the external event is found or all difference filters have been executed.

8. The method according to claim 7, wherein a difference value is generated by the cascaded difference filters by subtracting the value of previously sampled data from later sampled data and wherein the difference values are compared to the threshold value to find the occurrence of the external event.

9. The method according to claim 7, wherein each data sample represents a digitally low-pass filtered value sampled from the sensed signal.

10. An apparatus for detecting a change in an output signal having a level that fluctuates in response to an external event, the apparatus comprising:

an adjustable amplifier module for generating an amplified signal and having a signal input and an offset input, the signal input being electrically connected to the output signal;

an offset adjusting module for continually adjusting the offset voltage of the adjustable amplifier module by generating an offset signal based upon the amplified signal to maintain an observed median value of the observed range for the amplified signals between a minimum and a maximum observed value, the offset signal being coupled to the offset input of the adjustable amplifier module;

cascaded difference filters module for receiving the amplified signal to detect an occurrence of the external event by detecting when the amplified signal changes to a value greater than a threshold value; and

a threshold adjusting module for continually adjusting the threshold value based upon the amplified signal to maintain the threshold value at a desired percentage of a maximum range of observed amplified signal values.

11. The apparatus according to claim 10, further comprising:

sensing circuitry responsive to the external event, the sensing circuitry generating a periodic signal having a characteristic that varies when the external event occurs; and

a low-pass filter for filtering the periodic signal to produce the output signal.

12. The apparatus of claim 11, wherein the sensing circuitry is part of a label sensor, the sensing circuitry comprising:

a first reference electrode held at a first potential;

a second reference electrode connected to a resistor that is electrically connected to a second potential; and

electronic driving circuitry electrically connected to the second reference electrode;

wherein the first reference electrode is coupled to a first side of an opening in the sensor and the second reference electrode is coupled to a second side of the opening such that an object passes through the opening and between the first reference electrode and the second reference electrode and alters the capacitance between the first and second reference electrodes; and

wherein the electronic driving circuitry generates the periodic signal in response to the altered capacitance.

13. The apparatus according to claim 12, wherein the electronic driving circuit is a monostable multivibrator circuit having a clock signal input.

14. The apparatus according to claim 13, wherein a 2 MHz clock signal is provided to the clock signal input.

15. The apparatus according to claim 10, wherein the apparatus further comprises:

an A-to-D Converter module electrically connected to the amplified signal for sampling the amplified signal to generate sampled data; and

a memory array for storing the sampled data generated by the A-to-D Converter module; and

wherein the cascaded difference filters module processes the sampled data stored within the memory array.

16. The apparatus according to claim 15, wherein

the first time the cascaded difference filters module is applied, the cascaded difference filters module uses two adjacent data samples at a time from the memory array to check for the occurrence of the external event;

if no signal change is found, an index used by the cascaded difference filters module is incremented so that the filter uses data samples spaced at sequentially larger time intervals from the memory array to check for the occurrence of the external event.

17. The apparatus according to claim 16, wherein a difference value is generated by the cascaded difference filters module by subtracting the value of previously sampled data from later sampled data;

and wherein the difference value is compared to the threshold value to find the occurrence of the external event.

18. The apparatus according to claim 16, wherein each data sample represents a digitally low pass filtered value sampled from the amplified signal.

19. A system for providing a capacitive label sensor having a ground plate coupled to a first side of an opening in the sensor and a sensor signal plate coupled to a second side of the opening such that an object passes between the ground plate and the sensor signal plate, the system comprising:

means for electrically connecting the ground plate to a system ground;

means for electrically connecting the sensor signal plate to a first end of a first resistor at a first connection and to an electronic driving circuit receiving an input signal emanating from the sensor signal plate and generating a periodic signal, wherein the first resistor is electrically coupled between the first connection and a supply voltage;

means for filtering the periodic signal using a low-pass filter to generate a filtered periodic signal;

means for amplifying the filtered periodic signal to generate a sensed capacitance signal;

means for continually adjusting an offset voltage which is applied to the amplified and filtered periodic signal to maintain a mean value of the sensed capacitance signal at a desired voltage;

means for sampling the sensed capacitance signal using an A-to-D Converter module to generate sampled data and storing the sampled data within a memory array;

means for applying cascaded difference filters to the sampled data stored within the memory array;

means for determining an observed edge of a label passing through the opening in the label sensor by determining when the sensed capacitance signal changes to a value greater than a threshold value; and

means for continually adjusting the threshold value to maintain the threshold value at a desired percentage of the maximum range of sensed capacitance signals;

wherein the input signal is a periodically rising signal having an RC time constant based upon the first resistor and the sensor capacitance within the opening of the sensor.

20. A computer program product for detecting a change in an output signal having a level that fluctuates in response to an external event, wherein the computer program product configured to implement acts comprising:

amplifying the output signal using an amplifier to generate a sensed signal;

continually adjusting an offset voltage applied to the amplified output signal to maintain a mean value of the sensed signal at a desired voltage; and

detecting an occurrence of the external event by detecting when the sensed signal changes to a value greater than a threshold value.

21. A computer program product for detecting a change in an output signal having a level that fluctuates in response to an external event, the computer program product configured to implement acts comprising:

amplifying the output signal using an amplifier to generate a sensed signal;

detecting an occurrence of the external event by detecting when the sensed signal changes to a value greater than a threshold value; and

continually adjusting the threshold value used to detect the occurrence of the external event to maintain the threshold value at a desired percentage of a maximum range of sensed signal values.

22. A computer program product for detecting a change in an output signal having a level that fluctuates in response to an external event, the computer program product configured to implement acts comprising:

amplifying the output signal using an amplifier to generate a sensed signal;

detecting an occurrence of the external event by detecting when the sensed signal changes to a value greater than a threshold value; and

wherein the external event is detected by application of cascaded difference filters for quantifying the change in signal over multiple time intervals.

23. A computer program product for detecting a change in an output signal having a level that fluctuates in response to an external event, the computer program product configured to implement acts comprising:

amplifying the output signal using an amplifier to generate a sensed signal;

continually adjusting an offset voltage which is applied to the amplified output signal to maintain a mean value of the sensed signal at a desired voltage;

detecting an occurrence of the external event by detecting when the sensed signal changes to a value greater than a threshold value;

continually adjusting the threshold value used to detect the occurrence of the external event to maintain the threshold value at a desired percentage of a maximum range of sensed signal values; and

wherein the external event is detected by application of cascaded difference filters for quantifying the change in signal over multiple time intervals.

24. An apparatus for detecting a change in an output signal having a level that fluctuates in response to an external event, the apparatus comprising:

an adjustable amplifier module for generating an amplified signal and having a signal input and an offset input, the signal input being electrically connected to the output signal; and

an offset adjusting module for continually adjusting the offset voltage of the adjustable amplifier module by generating an offset signal based upon the amplified signal to maintain an observed median value of the observed range for the amplified signals between a minimum and a maximum observed value, the offset signal being coupled to the offset input of the adjustable amplifier module; and

a processor for receiving the amplified signal to detect an occurrence of the external event by detecting when the amplified signal changes to a value greater than a threshold value.

25. An apparatus for detecting a change in an output signal having a level that fluctuates in response to an external event, the apparatus comprising:

an adjustable amplifier module for generating an amplified signal and having a signal input, the signal input being electrically connected to the output signal; and

a cascaded difference filters module for receiving the amplified signal to detect an occurrence of the external event by detecting when the amplified signal changes to a value greater than a threshold value.

26. An apparatus for detecting a change in an output signal having a level that fluctuates in response to an external event, the apparatus comprising:

an adjustable amplifier module for generating an amplified signal and having a signal input, the signal input being electrically connected to the output signal;

a threshold adjusting module for continually adjusting the threshold value based upon the amplified signal to maintain the threshold value at a desired percentage of a maximum range of observed amplified signals; and

a processor for receiving the amplified signal to detect an occurrence of the external event by detecting when the amplified signal changes to a value greater than a threshold value.