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Method and apparatus for calibration and controlling multiple heaters

  • US 5,521,850 A
  • Filed: 01/18/1994
  • Issued: 05/28/1996
  • Est. Priority Date: 11/05/1990
  • Status: Expired due to Term
First Claim
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1. A process of calibrating and running a multiple positive temperature coefficient electrical resistance heater system comprising:

  • a. energizing a first heater;

    b. sampling the energized heater to determine voltage across the heater and current through the heater;

    c. calculating the heater resistance;

    d. assigning a temperature to the calculated resistance to establish a calibrated normalized resistance value;

    e. repeating steps a-d for each of the heaters;

    f. establishing set points for each of the heaters;

    g. sampling the first heater for current and voltage;

    h. calculating the resistance of said first heater;

    i. dividing the calculated resistance of step c by the calculated resistance determined in step h to determine a normalized resistance ratio;

    j. comparing the normalized resistance ratio of step "i" to a table of normalized resistance ratios at specific temperatures for the heater material;

    k. controlling heater energization based on the comparison of step "j";

    l. repeating steps a-k for each of the heaters; and

    ,m. continuously sampling each of the heaters in sequence and repeating steps g-k at each sampling.

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