Wood kiln moisture measurement calibration and metering methods

• US 8,104,190 B2
• Filed: 01/06/2010
• Issued: 01/31/2012
• Est. Priority Date: 12/29/2006
• Status: Active Grant

• Current Assignee: Signature Control Systems, Inc.
• Original Assignee: Signature Control Systems, Inc.
• Inventors: Magill, Richard
• Primary Examiner(s): GRAVINI, STEPHEN MICHAEL
• Application Number:
  US12/683,023
• Publication Number:
  US 20100171513A1
• Time in Patent Office: 755 Days
• Field of Search: 342/82, 345/22, 343/89, 343/96, 34/90, 343/10, 342/18, 342/42, 431/321, 147/17, 700/275, 700/150, 705/14, 144/380, 144/363, 73/73, 738/66
• US Class Current: 34/282
• 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 sensor are used to determine the lumber moisture content, comprising:

first obtaining cabling for signal communication between (1) and (2) following;

(1) a sensor for providing signals related to a capacitance of a stack of drying lumber when the sensor is embedded therein, and

(2) a data acquisition device for receiving the signals from the sensor in response to an excitation signal provided to the sensor via the cabling, and determining a measurement related to the lumber moisture content from the signals received;

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 the sensor, and not operatively connected to the data acquisition device;

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

(a) the first set of substeps including (a-1) and (a-2) following;

(a-1) providing, for the circuit configuration, corresponding impedance data for a predetermined impedance load applied to the cabling; and

(a-2) obtaining at least one of the calibration values, by determining an impedance including a parallel combination of;

(i) a capacitance between the conductor and the shielding, and (ii) a resistance between the conductor and the shielding, wherein the shielding is excited;

(b) the second set of one or more substeps, including the step;

(b-1) obtaining at least one of the calibration values, CV, 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;

wherein for an operative circuit configuration, CC, that varies from the circuit configuration by each end of the cabling being operatively connected to one of the sensor and the data acquisition device, and the operative circuit configuration CC includes the drying lumber, the at least one calibration value CV, for modifying values for the signals, is determined according to the operative circuit configuration being modeled as a voltage divider circuit;

storing the calibration values;

after the second obtaining step, a step of operably connecting the cabling for communicating between the sensor, and the data acquisition device to thereby provide an operable circuit configuration, including the drying lumber, which is identical to the operative circuit configuration CC of step (b-1) above when the second set of steps is performed;

monitoring a moisture content of the drying lumber using the operable circuit configuration, including the substeps of;

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

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

(c-3) obtaining 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) the at least one calibration value from one of (a-2) and (b-1) above; and

(c-4) using the one or more enhanced impedance related values for estimating the 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 second set of steps is performed, and 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 obtaining (c-3) do not change in a time period for receiving the time series of the 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 obtaining (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 two 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 one or more circuit configurations by operably connecting at least one length of the cabling to a signal measurement device excluded from the operable circuit configuration for obtaining the impedance related measurements.

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

providing one or more 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 values 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;

accessing the one or more values for the plurality of calibration parameters, wherein the 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 content in the drying lumber.

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

cabling for signal communication between;

(i) a sensor for measuring a capacitance of a stack of drying lumber 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 includes a conductor, and a conductive shielding surrounding the conductor;

wherein the cabling, sensor, the drying lumber, and data acquisition device form an operative circuit configuration for estimating the moisture content of the drying lumber;

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

wherein, while the device is connected to the cabling, one or more values are obtained, including at least one of the following values of (a-1) and (a-2);

(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, wherein the second value is determined according to the operative circuit configuration being modeled as a voltage divider circuit;

wherein when the cabling is disconnected from the device and connected to the sensor and the data acquisition device to thereby provide a particular operable circuit configuration, the particular operable circuit including the at least one length of the cabling, the sensor, and the drying lumber, then the particular operable circuit configuration is operably identical to the operative circuit configuration for obtaining the second value;

wherein a moisture content of the drying lumber is monitored using in the operative circuit configuration, the monitoring resulting in (b-1), (b-2), and (b-3) following;

(b-1) obtaining one or more measurements of the operative circuit configuration;

(b-2) 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-3) using the one or more impedance values for estimating the moisture content of the drying lumber.