Current controller for resistive heating element
First Claim
1. Apparatus for controlling the flow of heating current through a resistive element in order to heat the resistive element from ambient temperature to a desired temperature, said apparatus comprising:
- heating current supply means for supplying the resistive element with heating current;
measuring means for measuring the resistance of the resistive element;
detection means connected to said measuring means for detecting changes in the resistance measured by said measuring means in order to determine when the resistive element is at ambient temperature, said detection means including detection circuit means for generating a first logic signal indicative of ambient temperature conditions in the resistive element;
computing means connected to said measuring means and said detection means for computing the predicted resistance of the resistive element at the desired temperature, said computing means including a first computing circuit means responsive to said first logic signal for receiving the value of said resistance measured by said measuring means when the resistive element is at ambient temperature, said computing means also including a second computing circuit means for computing said predicted resistance as a function of the desired temperature and said value of said resistance received by said first computing circuit means; and
comparison means connected to both said measuring means and said computing means for comparing said predicted resistance with said resistance measured by said measuring means, said comparison means including a control signal means for generating a control signal as a function of the difference between said predicted resistance and said resistance measured by said measuring means, said comparison means also including a control circuit means connected to said control signal means for conducting heating current through the resistive element in response to said control signal.
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Accused Products
Abstract
A controller for regulating current flow through a resistive heating element in order to adjust the temperature thereof is disclosed. The controller includes a means for periodically measuring the resistance of the heating element. During controller calibration, the rate of change of the measured heating element resistance is ascertained in order to determine whether the heating element is at ambient temperature. Computations are performed on the value of the measured heating element resistance associated with ambient temperature conditions, enabling the controller to predict the value of the heating element resistance at a desired temperature. Current is then conducted through the heating element to generate heat, while periodic measurements of the heating element resistance are performed. The resistance values obtained during these latter resistance measurements are compared with the predicted resistance of the heating element associated with the desired temperature and the difference between the predicted resistance and each measured resistance is used to generate a control signal which regulates the flow of heating current through the heating element until desired temperature is reached.
138 Citations
15 Claims
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1. Apparatus for controlling the flow of heating current through a resistive element in order to heat the resistive element from ambient temperature to a desired temperature, said apparatus comprising:
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heating current supply means for supplying the resistive element with heating current; measuring means for measuring the resistance of the resistive element; detection means connected to said measuring means for detecting changes in the resistance measured by said measuring means in order to determine when the resistive element is at ambient temperature, said detection means including detection circuit means for generating a first logic signal indicative of ambient temperature conditions in the resistive element; computing means connected to said measuring means and said detection means for computing the predicted resistance of the resistive element at the desired temperature, said computing means including a first computing circuit means responsive to said first logic signal for receiving the value of said resistance measured by said measuring means when the resistive element is at ambient temperature, said computing means also including a second computing circuit means for computing said predicted resistance as a function of the desired temperature and said value of said resistance received by said first computing circuit means; and comparison means connected to both said measuring means and said computing means for comparing said predicted resistance with said resistance measured by said measuring means, said comparison means including a control signal means for generating a control signal as a function of the difference between said predicted resistance and said resistance measured by said measuring means, said comparison means also including a control circuit means connected to said control signal means for conducting heating current through the resistive element in response to said control signal. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. Apparatus for controlling the flow of heating current through a resistive element in order to heat the resistive element to a desired temperature, said apparatus comprising:
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heating current supply means for periodically supplying heating current to the resistive element; measuring current supply means for periodically supplying measuring current to the resistive element; logic means connected to said heating current supply means and said measuring current supply means for respectively enabling said heating current supply means and said measuring current supply means to supply the resistive element with heating current and measuring current in alternating fashion; measuring means for measuring the voltage drop across the resistive element as measuring current flows therethrough and for responsively generating a measured resistance signal indicative of the actual resistance of the resistive element; computing means for computing the predicted resistance of the resistive element at the desired temperature and for generating a computed resistance signal indicative of said predicted resistance, said computing means including a memory means for storing an ambient resistance value representing the resistance of the resistive element at ambient temperature, said computing means also including a computing circuit means connected to said memory means for generating said computed resistance signal as a function of the desired temperature and said ambient resistance value; and comparison means connected to both said measuring means and said computing means for comparing said computed resistance signal with said measured resistance signal, said comparison means including a control signal means for generating a control signal as a function of the difference between said predicted resistance and said actual resistance of the resistive element, said comparison means also including a control circuit means connected to said control signal means for conducting heating current through the resistive element in response to said control signal. - View Dependent Claims (10, 11)
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9. Apparatus for controlling the flow of heating current through a resistive element in order to heat the resistive element to a desired temperature, said apparatus comprising:
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timing means for generating timing signals which define operating cycles for said apparatus, each said operating cycle including first and second intervals of predetermined duration; measuring current supply means connected to receive said timing signals for supplying the resistive element with a measuring current during said first interval of each said operating cycle; heating current supply means connected to receive said timing signals for supplying the resistive element with heating current during said second interval of each said operating cycle; measuring means for measuring the voltage drop across the resistive element as measuring current flows therethrough and for responsively generating a measured resistance signal indicative of the actual resistance of the resistive element; computing means for computing the predicted resistance of the resistive element at the desired temperature and for generating a computed resistance signal indicative of said predicated resistance, said computing means including a memory means for storing an ambient resistance value representing the resistance of the resistive element at ambient temperature, said computing means also including a computing circuit means connected to said memory means for generating said computed resistance signal as a function of the desired temperature and said ambient resistive value; and comparison means connected to both said measuring means and said computing means for comparing said computed resistance signal with said measured resistance signal, said comparison means including a control signal means for generating a control signal as a function of the difference between said predicted resistance and said actual resistance of the resistive element, said comparison means also including a control circuit means connected to said control signal means for conducting heating current through the resistive element during said second interval of each said operating cycle in response to said control signal.
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12. Apparatus for controlling the flow of heating current through a resistive element having a plurality of resistive segments in order to heat each of said plurality of resistive segments to a desired temperature, said apparatus comprising:
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heating current supply means for supplying the resistive element with heating current; measuring means for respectively measuring the resistances of each of the plurality of resistive segments; detection means connected to said measuring means for determining when the resistive segments are at ambient temperature; computing means for respectively computing the predicted resistances of each of the resistive segments at the desired temperature, said computing means including a first computing circuit means which receives the value of the resistance measured by said measuring means for each resistive segment when each resistive segment is at ambient temperature as determined by said detection means, said computing means also including a second computing circuit means which respectively computes said predicted resistance for each resistive segment as a function of the desired temperature and said value of said resistance of each resistive segment as measured by said measuring means at ambient temperature; and comparison means connected to both said measuring means and said computing means for respectively comparing each of said predicted resistances computed by said computing means with a corresponding one of said resistances measured by said measuring means, said comparison means including a control signal means for generating a plurality of control signals as a function of the respective differences between each of said predicted resistances computed by said computing means and each of said resistances measured by said measuring means, said comparison means also including a control cirucit means connected to said control signal means for selecting individual resistive segments and for conducting heating current through the individual resistive segments so selected in response to said plurality of control signals. - View Dependent Claims (13, 14, 15)
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Specification