Claims
- 1. A method of predicting failure of a resistive element heater comprising the steps of:compiling a historical database of design and construction variables that effect the life of a resistive element heater during service operation based on testing of a lab standard heater; assigning a ratiometric life factor to each variable within the representative set of design and construction variables for a given heater and creating a simplified model by factoring the individual life factors together; normalizing actual service time on a given heater to an equivalent time on the laboratory standard heater; measuring the thermal profile of the resistive element heater by measuring the heater temperature at set time intervals and assigning each interval an element temperature related stress oxidation life factor based on the historical database and defining a cumulative life factor; mathematically manipulating the ratiometric life factor, the normalized service time, and the cumulative life factor in such a manner to predict fractional life remaining; and wherein the compiling step comprises the sub-steps of: compiling historical test data on the effect of a resistive element alloy on the life of a resistive element heater; compiling historical test data on the effect of a resistive element's page on the life of a resistive wire heater; compiling historical data on the effect of a heater type on the life of a resistive element heater; compiling historical data on the effect of a heater element formation on the life of a resistive heater; consolidating the historical data for wire alloy, wire gauge, element type and element formation into an indexable data base; and assigning factors to each data element for varying operating temperatures representative of the data element's effect on operating life when subjected to said temperatures.
- 2. The method of claim 1, where assigning a ratiometric life factor to each variable is based on (1) a fixed thermo-physical operating profile; and (2) each variable's characteristic reaction when subjected to said operating profile.
- 3. The method of claim 1, where measuring the actual thermal profile comprises the steps of:measuring the resistive element sheath temperature; and calculating the heater element temperature using a Fourier heat transfer function based on known heater construction and thermo-physical properties.
- 4. The method of claim 3, where calculating the element temperature comprises the steps of:operating on heater formation variables with a Fourier heat transfer function to obtain a heat transfer factor; calculating the thermal conductivity of the sheath and a given insulator based on known values for their respective materials; measuring the sheath temperature; and mathematically manipulating the heat transfer factor, the thermal conductivity, and the sheath temperature in such a fashion to determine the element temperature.
- 5. The method of claim 1, where normalizing the actual service time is performed by normalizing the measurement operating time interval with the oxidation life factor.
- 6. The method of claim 1, where the mathematical manipulation is performed by factoring the life factors and the service time function together.
- 7. The method of claim 1, wherein the measuring step is approximated by predicting an estimated temperature profile based on an intended service application.
- 8. An apparatus that performs the method of claim 1.
Parent Case Info
This application is a divisional of application Ser. No. 09/316,803 filed May 21, 1999, now U.S. Pat. No. 6,336,083.
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