Calibration and Metering Methods for Wood Kiln Moisture Measurement

• US 20080161972A1
• Filed: 12/29/2006
• Published: 07/03/2008
• Est. Priority Date: 12/29/2006
• Status: Active Grant

• Current Assignee: Signature Control Systems, Inc.
• Original Assignee: Signature Control Systems, Inc.
• Inventors: Magill, Richard
• Granted Patent: US 7,676,953 B2
• Time in Patent Office: Days
• US Class Current: 700/275
• CPC Class Codes: G01N 27/223 for determining moisture content, e.g. humidity rain detectors on vehicle windows B60S1/0825
• CPC Class Codes: G01N 33/46 Wood

Abstract

A moisture metering calibration method and system for, e.g., determining the moisture lumber within a lumber drying kiln is disclosed. Calibration of moisture indicative electrical signals obtained from, e.g., moisture sensing capacitive plates spaced apart within a stack of drying lumber is performed, wherein long lengths (e.g., up to 1000 linear feet or more) of coaxial cable can be used for transmitting the signals, and effectively removing signal anomalies induced in such cabling so that accurate lumber moisture measurements result. Such extended cable lengths provides flexibility with respect to placement of electronic moisture metering equipment. This flexibility allows such equipment to be placed in an environmentally-controlled enclosure, rather than on the weather exposed exterior of a kiln whose lumber is being monitored.

Claims

1. A method for determining a moisture content of lumber drying, wherein signals transmitted from a moisture sensitive sensor are used to determine the lumber moisture content, comprising:

first obtaining cabling for signal communication between;

(1) a moisture sensitive sensor for measuring a capacitance of a stack of lumber being dried in which the sensor is embedded, and (2) a data acquisition device for receiving signals from the sensor in response to an excitation signal provided to the sensor via the cabling, wherein the cabling includes a conductor, and a conductive shielding surrounding the conductor;

configuring the cabling in each of one or more circuit configurations so that in each circuit configuration at least one end of the cabling is not operatively connected to each of;

the sensor, and the data acquisition device;

second obtaining, for each of the one or more circuit configurations, one or more calibration values, including at least one of the following sets of substeps;

(a) a first set of steps including;

(a-1) obtaining, for each of the circuit configurations, corresponding impedance data for a predetermined impedance load applied to the cabling; and

(a-2) determining at least one of the calibration values, by determining (i) an impedance including a parallel combination of a capacitance between the conductor and shielding, and (ii) a resistance between the conductor and the shielding, wherein the shielding is excited;

(b) a second set including the step;

(b-1) determining at least one of the calibration values by determining a capacitance between the conductor and the shielding of the cabling, wherein the shielding is grounded, and the capacitance is dependent on a length of the cabling;

storing the calibration values;

operably connecting the cabling for communicating between the moisture sensitive sensor, and the data acquisition device;

monitoring a moisture content of drying lumber, including the substeps of;

(c-1) applying the excitation signal to the conductor of the cabling;

(c-2) obtaining one or more impedance related measurements of a circuit including the cabling, the sensor, and the lumber, wherein the at least one end of the cabling is operatively connected to one of the sensor, and data acquisition device;

(c-3) determining one or more enhanced impedance related values that are substantially independent of an impedance related to at least one length of the cabling, wherein at least one of the one or more enhanced impedance related values is determined as a function of a combination of;

(i) one of the impedance related measurements, and (ii) one of the calibration values; and

(c-4) using the enhanced impedance related values for estimating a moisture content of the drying lumber.

2. The method of claim 1, wherein the cabling includes one or more cables whose combined length is greater than 50 feet in length.

3. The method of claim 1, wherein the cabling includes one or more cables whose combined length is between 100 feet and 1000 feet in length.

4. The method of claim 1, wherein the length of the cabling of (b-1), and the at least one length of the cabling of (c-3) are substantially a same portion of the cabling.

5. The method of claim 1, wherein the step (c-2) includes obtaining a time series of the impedance related measurements, and the stored calibration values used in the step of determining (c-3) do not change in a time period for receiving the time series of impedance related measurements.

6. The apparatus of claim 5, wherein the time period includes one or more days.

7. The method of claim 1, wherein for at least one sequential performance of the steps (c-1), (c-2), and (c-3), the step of configuring is not performed during the sequential performance.

8. The method of claim 1, wherein the step of determining (c-3) includes determining a value that varies inversely with one of:

(i) a difference between two voltages of the impedance related measurements, each of the voltages being for the conductor at points having a load resistor therebetween; and

(ii) one of the calibration values indicative of a terminal impedance.

9. The method of claim 1, wherein the configuring step includes providing at least one of the circuit configurations by operably connecting at least one length of the cabling to a signal measurement device excluded from the circuit for obtaining the impedance related measurements.

10. The method of claim 9, wherein the excluded device includes one of:

a calibration box generating a plurality of predetermined impedances, a device for measuring impedance characteristics of the at least one circuit configuration.

11. The method of claim 1, wherein the second set of steps includes a step of balancing a bridge circuit included in one of the circuit configurations.

12. The method of claim 1, wherein the step of determining (c-3) includes a step of balancing a bridge circuit included in one of the circuit configurations.

13. The method of claim 1, wherein the step of determining (c-3) includes determining a difference between:

(i) a capacitance of the impedance related measurements, and (ii) at least one of the calibration values that is dependent on a capacitance related to the at least one length of the cabling.

14. The method of claim 1, wherein the step (b-1) includes a step of measuring, in one of the circuit configurations, the capacitance of the cabling, and in a second of the circuit configurations, measuring at least one of:

a resistance of the cabling, and an inductance of the cabling.

15. The method of claim 1, wherein at least one of the circuit configurations excludes one of:

the sensor or the data acquisition device.

16. The method of claim 1, wherein the step of configuring includes determining a terminal impedance at terminals to which the cabling attaches, wherein the cabling is detached from the terminals.

17. The method of claim 1, wherein the stored calibration values includes at least one of:

a terminal impedance, an impedance gain, an impedance offset, a phase gain, a phase offset, the capacitance for the cabling, a resistance for the cabling, an inductance for the cabling.

18. The method of claim 17, wherein the stored calibration values includes at least some of:

a terminal impedance, an impedance gain, an impedance offset, a phase gain, a phase offset, the capacitance of the cabling, a resistance of the cabling, an inductance of the cabling.

19. The method of claim 1, wherein the stored calibration values includes at least most of:

a terminal impedance, an impedance gain, an impedance offset, a phase gain, a phase offset.

20. The method of claim 1, wherein the stored calibration values includes at least most of:

the capacitance of the cabling, a resistance of the cabling, an inductance of the cabling.

21. The method of claim 1, wherein the at least one calibration value determined in (a-2) is dependent upon a result of (a-2)(i) divided by (a-2)(ii).

22. The method of claim 1, wherein for (a-2)(i), the impedance is determined using a terminal impedance at terminals for connecting to the cabling, wherein a first of the terminals is for connecting to the conductor, and a second of the terminals is for connecting to the shielding.

The method of claim 22, wherein the first and second terminals have a load resistor operably connected therebetween.

23. The method of claim 1, wherein the step of operably connecting and monitoring are performed after the step of second obtaining.

24. The method of claim 1, wherein the step of operably connecting includes establishing signal communication between the sensor and the data acquisition device via the cabling.

25. The method of claim 24, wherein the cabling includes two lengths of cabling having a multiplexer unit connected to an end of each of the two lengths of cabling, wherein communication between the sensor and the data acquisition device travels through the multiplexer unit.

26. The method of claim 25, wherein the one or more enhanced impedance related values are substantially independent of the two lengths of cabling and the multiplexer unit.

27. The method of claim 1, wherein the first set of steps includes repeating the following sequence of steps:

applying a predetermined impedance load to the cabling in one of the circuit configurations (CC);

determining a resulting measurements of the one circuit configuration CC;

determining an impedance load on the circuit configuration CC using the resulting measurements; and

determining a value for one of the calibration values.

28. The method of claim 1, wherein the step of second obtaining includes:

applying a predetermined impedance load to the cabling;

determining a resulting impedance load including an impedance of the cabling;

adjusting the resulting impedance load using at least one value (V) for one of the calibration values to obtain an adjusted impedance load; and

comparing the resulting impedance load with the predetermined impedance load for determining whether the at least one value V is acceptable for use in monitoring the moisture content of the lumber.

29. The method of claim 1, wherein the circuit from which the one or more impedance related measurements are obtained includes a voltage divider circuit.

30. The method of claim 1, wherein the circuit from which the one or more impedance related measurements are obtained includes two cables, wherein one of the two cables is for transmitting the excitation signal, and the other of the two cables is for obtaining the one or more impedance related measurements.

31. The method of claim 1, wherein for providing at least one of the circuit configurations, the configuring step includes operably connecting a device for determining at least one of an inductance, a capacitance, and a resistance to the cabling in the step of second obtaining, wherein the device is excluded from the circuit from which the one or more impedance related measurements are obtained in the step of second obtaining.

32. The method of claim 1, wherein at least one of the circuit configurations includes a resistor-capacitor network circuit.

33. The method of claim 1, wherein the conductive shielding is grounded.

34. The method of claim 1, wherein the conductive shielding is excited.

35. The method of claim 1, wherein the configuring step includes providing a first circuit configuration, wherein for an end (E) of the of the cabling that transmits signals between another end of the cabling and the sensor during the monitoring step, the conductor at the end E is grounded in the first circuit configuration.

36. The method of claim 35, wherein the configuring step includes providing a second circuit configuration, wherein the end E of the cabling in the second configuration is provided in an open condition.

37. A method for determining parameters used in estimating a moisture content of lumber drying, wherein signals transmitted, via cabling, from a moisture sensitive sensor, are used to determine the lumber moisture content, comprising:

obtaining one or more values as values for a plurality of calibration parameters, the one or more values including at least one of;

(a) a first value indicative of a terminal impedance at terminals to which the cabling is connected, wherein a first of the terminals is connected to a conductor of the cabling, and a second of the terminals is connected to a shield of the cabling, the shield for shielding the conductor, and

(b) a second value indicative of a capacitance of the cabling between the conductor and the shield along a length of the cabling;

determining at least an additional one of the value for one of the parameters of the plurality of calibration parameters using at least one of the first value and the second value, wherein the additional value is the other of the first and second values, or the additional value is indicative of at least one of;

(i) an impedance gain adjustment,

(ii) an impedance offset adjustment,

(iii) an impedance phase gain adjustment,

(iv) an impedance phase offset adjustment,

(v) an inductance of the cabling; and

(vi) a resistance of the cabling;

storing the one or more values for the plurality of calibration parameters, wherein the stored one or more values are used to correct impedance values from a time series of the signals so that impedance values obtained from such correction are more indicative of the moisture in the lumber.

38. The method of claim 37, wherein the cabling includes a length for one or more coaxial cables that is greater than 50 feet in length.

39. The method of claim 37, wherein the cabling includes a length of one or more coaxial cables that is between 100 feet and 1000 feet in length.

40. The method of claim 37, wherein the obtaining step includes obtaining the first value.

41. The method of claim 40, wherein the determining step includes using the first value to determine the second value.

42. The method of claim 40, wherein the determining step includes using the first value to determine at least two values, each of the at least two values indicative of a different of one of:

(i) through (vi).

43. The method of claim 42, wherein the storing step stores each of the at least two values as a value for a different one of the calibration parameters.

44. The method of claim 42, wherein the determining step includes applying a plurality of predetermined impedance loads to the cabling for measuring a plurality of corresponding impedances for determining the at least two values.

45. The method of claim 44, further including:

applying a predetermined impedance load to the cabling;

measuring a resulting impedance load including an impedance of the cabling;

adjusting the resulting impedance load using the stored values for the calibration parameters to obtain an adjusted impedance load; and

comparing the adjusted impedance load with the predetermined impedance load for determining whether the values for the calibration parameters are acceptable for use in monitoring the moisture content of the lumber.

46. The method of claim 37, wherein the plurality of calibration parameters includes at least two parameters, one of the two parameters having one of:

the first value and the second value, and the other of the at least two parameters having a value indicative of one of (i) through (vi).

47. The method of claim 46, wherein for each parameter of the at least two parameters, said determining step includes determining a value for the parameter using the first value.

48. The method of claim 46, wherein for each of the at least two parameters, said determining step includes determining a value for the parameter using the second value.

49. The method of claim 37, wherein the plurality of calibration parameters includes at least three parameters, at least two of the three parameters having a value indicative of a different one of (i) through (vi).

50. The method of claim 37, wherein said obtaining step includes determining the first value from application of a predetermined capacitive load to the cabling, when the cabling is disconnected from a sensor from which the time series of signals is obtained.

51. The method of claim 37, wherein said at least one additional value includes two values, wherein each of the two values is for of a different one of (i) through (vi).

52. A method for determining a moisture content of lumber drying, wherein signals transmitted, via cabling, from a moisture sensitive sensor, are used to determine the lumber moisture content, comprising:

obtaining cabling for signal communication between;

(i) a moisture sensitive sensor for measuring a capacitance of a stack of lumber being dried in which the sensor is embedded, and (ii) a data acquisition device for generating an excitation signal provided to the sensor via the cabling, wherein the cabling include a conductor, and a conductive shielding surrounding the conductor;

connecting one end of the cabling to a device for providing a predetermined impedance load to the cabling, wherein the cabling is disconnected from at least one of the sensor, and the data acquisition device;

obtaining, while the device is connected to the cabling, one or more values, including at least one of the following values;

(a-1) a first value indicative of a terminal impedance at terminals to which the cabling is connected, wherein a first of the terminals connects to the conductor, and a second of the terminals connects to the conductive shielding, the shield, and

(a-2) a second value indicative of a capacitance along at least one length of the cabling between the conductor and the conductive shielding;

storing the one or more values;

disconnecting the device from the cabling;

connecting the cabling for communicating between the moisture sensitive sensor, and the data acquisition device;

monitoring a moisture content of drying lumber, including the substeps of;

(b-1) applying an excitation signal to the conductor of at least one length of the cabling;

(b-2) obtaining one or more measurements of a circuit including the at least one length of the cabling, the sensor, and lumber;

(b-3) accessing the one or more stored values;

(b-4) determining one or more impedance values that are less dependent upon an impedance for the cabling, and more indicative of an impedance for the drying lumber than the one or more measurements, wherein the one or more impedance values are determined using one of;

(i) the first value, and a difference between two voltages of the one or more measurements, and (ii) the second value, and a difference between a capacitance of the one or more measurements; and

(b-5) using the one or more impedance values for estimating a moisture content of the drying lumber.

53. The method of claim 52, wherein the cabling includes one or more cables having a combined length greater than 50 feet in length.

54. The method of claim 52, wherein the cabling includes one or more cables having a combined length of cable between 100 feet and 1000 feet in length.

55. The method of claim 52, wherein the circuit includes a voltage divider circuit.

56. The method of claim 52, wherein the circuit includes separate cables for transmitting the excitation signal and obtaining the one or more measurements.

57. The method of claim 52, wherein the circuit includes a bridge circuit.

58. The method of claim 52, wherein the conductive shielding is grounded.

59. The method of claim 52, wherein the conductive shielding is excited.

60. The method of claim 52, wherein the one or more values includes the first value.

61. The method of claim 60, wherein the determining step (b-4) includes determining an impedance by multiplying the first value by a first of the two voltages, and dividing by the difference in the two voltages.

62. The method of claim 60, wherein the determining step (b-4) includes determining a current of the circuit by dividing the difference in voltages by the first value.

63. The method of claim 60, further including determining at least one additional value of the one or more values using the first value, wherein the additional value is indicative of at least one of:

(i) an impedance gain adjustment,

(ii) an impedance offset adjustment,

(iii) an impedance phase gain adjustment,

(iv) an impedance phase offset adjustment,

(v) an inductance of the cabling; and

(vi) a resistance of the cabling.

64. The method of claim 60, further including determining at least one additional value of the one or more values using the first value, wherein the additional value is indicative the second value.

65. The method of claim 64, wherein the determining step (b-4) includes determining a corrected resistance by subtracting from a resistance of the measurements at least one of:

a value indicative a resistance of the cabling, and a value indicative an inductance of the cabling.

66. The method of claim 52, wherein the one or more values includes the second value.

67. The method of claim 66, further including determining at least one additional value of the one or more values using the second value, wherein the additional value is indicative of at least one of:

(i) an impedance gain adjustment,

(ii) an impedance offset adjustment,

(iii) an impedance phase gain adjustment,

(iv) an impedance phase offset adjustment,

(v) an inductance of the cabling; and

(vi) a resistance of the cabling.

68. The method of claim 66, further including determining the first value using the second value.

69. The method of claim 52, wherein the step of determining (b-4) includes using the one or more stored values to repeatedly determine an instance of the impedance values for a time series of the signals from the circuit, wherein the time series spans at least a plurality of days.

70. A method for determining a moisture content of drying lumber in a kiln using a meter, wherein the meter receives signals from at least one capacitor plate of a pair of capacitor plates spaced apart by a portion of the lumber, and wherein the meter uses measurements of the signals to obtain values indicative of the moisture content of the lumber, comprising:

obtaining cabling for transmitting the signals from the at least one capacitor plate to the meter, wherein the cabling includes a signal conductor, and a conductive shielding surrounding the conductor;

subsequent to said step of obtaining, and for a circuit including at least one length of the cabling, determining a terminal impedance using at least two of;

(a) a predetermined capacitive load applied to the circuit, wherein the capacitive load is applied to the signal conductor of the at least one length of the cabling, and the shielding therefor;

(b) a voltage difference across a resistor operably connected between the signal conductor, and the shielding of the at least one length of the cabling;

(c) a capacitance between the signal conductor of the cabling, and the shielding of the at least one length of the cabling, the capacitance dependent on the at least one length of the cabling;

receiving, at the meter, the signals from the at least one capacitor plate;

generating adjusted measurements of the measurements of the signals using the terminal impedance, wherein the adjusted measurements have a reduced dependence on the at least one length of the cabling; and

deriving, from the adjusted measurements, values indicative of the moisture content of the lumber.

71. An apparatus for determining a moisture content of lumber drying, wherein signals transmitted from a moisture sensitive sensor are used to determine the lumber moisture content, comprising:

one or more lengths of cabling for signal communication between;

(1) a moisture sensitive sensor for measuring a capacitance of a stack of lumber being dried in which the sensor is embedded, and (2) a data acquisition device for receiving signals from the sensor in response to an excitation signal provided to the sensor via at least one of the lengths (L) of the cabling, wherein the at least one length of the cabling L includes a conductor extending substantially an entire length of the at least one length of the cabling L, and a conductive shielding surrounding the conductor for substantially the entire length of the at least one length of the cabling L;

one or more circuit configurations, wherein each circuit configuration includes the one or more lengths of the cabling, and wherein one or more calibration values are obtained when a predetermined impedance load is applied to the circuit configuration, the one or more calibration values obtained by one of;

(a-1) determining (i) a first difference between the predetermined impedance loads for two of the circuit configurations, and (ii) a second difference between the corresponding impedance data for the different circuit configurations;

(a-2) determining at least one of the calibration values by determining a capacitance between the conductor and the shielding of the cabling, wherein the shielding is grounded, and the capacitance is dependent on a length of the cabling;

a data store for storing the one or more calibration values;

a signal measurement correction component, included in the data acquisition device or operably connected thereto, for;

(b-1) receiving a time series of impedance related measurements from a circuit including the one or more lengths of the cabling, the sensor, and the lumber when an excitation signal is applied to the conductor, and

(b-2) determining a plurality of enhanced impedance related values that are substantially independent of an impedance related to the one or more lengths of the cabling, wherein each of the plurality of enhanced impedance related values is determined as a function of;

(i) one of the impedance related measurements, and (ii) one of the calibration values;

wherein the one or more enhanced impedance related values are used for estimating a moisture content of the lumber.

72. The apparatus of claim 71, wherein for (a-1), the first and second difference are combined for obtaining at least one of the calibration values.

73. The apparatus of claim 71, wherein for at least one of the circuit configurations, one of the lengths of cabling is configured differently from the circuit including the one or more lengths of the cabling, the sensor, and the lumber, wherein the one length of cabling.

74. The apparatus of claim 71, wherein the data store includes one of a data file, and a database.

75. The apparatus of claim 71, wherein the one or more lengths of cabling includes at least two lengths of cabling for a communication channel between the sensor, and the data acquisition device, wherein each of the two lengths of cabling are operably connected to a multiplexer.

76. The apparatus of claim 75, wherein there are a plurality of communication channels, with each communication channel including two lengths of cabling for communicating between the data acquisition device and a corresponding sensor for the communication channel, and wherein the two lengths of cabling are operably connected to the multiplexer.

77. The apparatus of claim 71, wherein for at least one of circuit configurations at least one end of one of the lengths of cabling is not operatively connected to one of the components:

the sensor, and the data acquisition device, and the one length of cabling is operatively connected to the component in the circuit.

78. The apparatus of claim 71, wherein the stored calibration values used in the step of determining (b-2) do not change in a time period for receiving the time series of impedance related measurements.

79. The apparatus of claim 71, wherein the time period includes one or more days.

80. An apparatus for determining a moisture content of lumber drying, wherein signals transmitted from a moisture sensitive sensor are used to determine the lumber moisture content, comprising:

one or more lengths of cabling for signal communication between;

(1) a moisture sensitive sensor for measuring a capacitance of a stack of lumber being dried in which the sensor is embedded, and (2) a data acquisition device for receiving signals from the sensor in response to an excitation signal provided to the sensor via at least one of the lengths (L) of the cabling, wherein the at least one length of the cabling L includes a conductor extending substantially an entire length of the at least one length of the cabling L, and a conductive shielding surrounding the conductor for substantially the entire length of the at least one length of the cabling L;

one or more circuit configurations, wherein each circuit configuration includes the one or more lengths of the cabling, and wherein one or more calibration values are obtained when a predetermined impedance load is applied to the circuit configuration, the one or more calibration values obtained by one of;

(a-1) determining (i) a first difference between the predetermined impedance loads for two of the circuit configurations, and (ii) a second difference between the corresponding impedance data for the different circuit configurations;

(a-2) determining at least one of the calibration values by determining a capacitance between the conductor and the shielding of the cabling, wherein the shielding is grounded, and the capacitance is dependent on a length of the cabling;

a data store for storing the one or more calibration values;

signal measurement correction means, included in the data acquisition device or operably connected thereto, for;

(b-1) receiving a time series of impedance related measurements from a circuit including the one or more lengths of the cabling, the sensor, and the lumber when an excitation signal is applied to the conductor, and

(b-2) determining a plurality of enhanced impedance related values that are substantially independent of an impedance related to the one or more lengths of the cabling, wherein each of the plurality of enhanced impedance related values is determined as a function of;

(i) one of the impedance related measurements, and (ii) one of the calibration values;

wherein the one or more enhanced impedance related values are used for estimating a moisture content of the lumber.