Heating element condition monitor

• US 6,956,489 B2
• Filed: 07/17/2002
• Issued: 10/18/2005
• Est. Priority Date: 07/17/2002
• Status: Expired due to Term

• Current Assignee: Hitachi, Ltd., Kanthal Thermal Process, Inc. (Sandvik AB)
• Original Assignee: Sandvik Thermal Process, Inc. (Sandvik AB)
• Inventors: Berdner, Thomas J, McEntire, William D., Peck, Kevin B., Johnson, Noel H.
• Primary Examiner(s): NGUYEN, HUNG T
• Application Number:
  US10/196,160
• Publication Number:
  US 20040012498A1
• Time in Patent Office: 1,189 Days
• Field of Search: 340/640, 340/654, 340/655, 340/825.22, 340/825.23, 340/870.16, 340/870.17, 340/870.28, 340/825.08, 340/825.1, 250/311, 250/306, 250/338.1, 250/214.1
• US Class Current: 340/640
• CPC Class Codes: G01N 17/00 Investigating resistance of materials to the weather, to corrosion, or to light
• CPC Class Codes: H05B 1/0233 for semiconductors manufacturing
• CPC Class Codes: H05B 1/0291 Tubular elements

Abstract

A method for monitoring the condition of an electric current-carrying heating element involving installing the heating element in a location and setting the initial composition C_i of the material as a reference baseline at an initial time T_i corresponding to said installation of the heating element. Data is then collected reflecting the subsequent composition C_s of the heating element material after a subsequent time T_s at the installed location and any change in the material composition of the heating element between T_i and T_s is monitored. An alarm is sent when the change reaches a threshold value indicating a possible failure condition. According to one embodiment, an impedance monitor is provided that calculates and compares impedance at the required levels of accuracy to determine changes in material composition. The impedance monitor, or portions thereof may be embedded within a microcontroller for increased portability and functionality.

Claims

1. A method for monitoring the condition of an electrical current-carrying heating element comprising:

determining an initial composition of a material of the heating element as a reference baseline at an initial time;

collecting data reflecting the subsequent composition of the heating element material after a time interval;

setting a threshold level of change in the subsequent composition from the initial composition;

monitoring a change between the subsequent composition and the initial composition occurring after the time interval has passed; and

sending a signal to a decision making authority if the change has reached or exceeded the threshold level of change.

2. The method of claim 1, wherein the initial composition is determined to be an alloy having an initial composition of approximately 72.2% iron, 22.0% chromium, and 5.8% aluminum.

3. The method of claim 2, wherein the threshold level is set such that a signal is sent to the decision making authority when the alloy reaches a composition having approximately 2.5% of aluminum.

4. The method of claim 1, wherein the step of monitoring comprises monitoring a change in a resistance ratio X_R of the heating element.

5. The method of claim 4, wherein the heating element material comprises an alloy having an initial composition of approximately 72.2% iron, 22.0% chromium, and 5.8% aluminum and X_R is approximately 1.042 at the initial time.

6. The method of claim 5, wherein the threshold level is set such that X_R is approximately 1.250, which corresponds to a condition where the heating element has reached approximately 2.5% aluminum content.

7. The method of claim 4, where X_R is defined as R_h/R_c where R_h is the hot resistance of the heating element and R_c is the cold resistance of the heating element.

8. An apparatus for monitoring the condition of a material of an electric current-carrying heating element comprising:

means for determining an initial composition of the material as a reference baseline at an initial time;

means for collecting data reflecting a subsequent composition of the heating element material after a specified time interval;

means for setting a threshold level of change in the subsequent composition from the initial composition;

means for monitoring a change in the data after the interval has passed; and

means for sending a signal to a decision making authority if the change has reached or exceeded the threshold level of change.

9. The apparatus of claim 8, wherein the means for setting the initial composition sets an alloy composition of approximately 72.2% iron, 22.0% chromium and 5.8% aluminum.

10. The apparatus of claim 9, wherein the threshold level comprises a level corresponding to the composition of the heating element material containing approximately 2.5% of aluminum.

11. The apparatus of claim 8, wherein the data collected includes a change in resistance ratio X_R of the heating element.

12. The apparatus of claim 11, wherein X_R is approximately 1.042 at the initial time.

13. The apparatus of claim 11, wherein the means for setting sets a threshold level corresponding to a value for X_R of approximately 1.250.

14. The apparatus of claim 11, wherein the heating element resistance ratio X_R is defined as R_h/R_c, where R_h is the resistance of the heating element at hot temperatures and R_c is the resistance of the heating element at cold temperatures.

15. The apparatus of claim 8, wherein the data collected by the means for collecting includes a voltage value.

16. The apparatus of claim 15, wherein the data collected by the means for collecting includes an instantaneous voltage.

17. The apparatus of claim 8, wherein the data collected by the means for collecting includes a current value.

18. The apparatus of claim 8, wherein the data collected by the means for collecting includes an element temperature value.

19. The apparatus of claim 8, wherein the apparatus is embedded within a microcontroller as an embedded system.

20. The apparatus of claim 8, wherein the means for collecting data comprises a microcontroller.

21. The apparatus of claim 8, wherein the means for monitoring comprises a microcontroller.

22. The apparatus of claim 8, further comprising a decision making authority for responding to the means for sending, once the threshold level has been reached or exceeded.

23. The apparatus of claim 22, wherein the decision making authority comprises a microcontroller.

24. The apparatus of claim 8, wherein the means for collecting data comprises a sensing mechanism for sensing conditions of a heating element.

25. The apparatus of claim 24, wherein the sensing mechanism senses electrical characteristics of a heating element.

26. The apparatus of claim 25, wherein the sensing mechanism comprises an embedded active sensor, which is embedded within a microcontroller.