TEMPERATURE REGULATION FOR ELECTRICAL HEATER

• US 3,789,190 A
• Filed: 10/17/1972
• Issued: 01/29/1974
• Est. Priority Date: 10/17/1972
• Status: Expired due to Term

• Current Assignee: Abraham J. Matlen, David J. Orosy
• Original Assignee: Abraham J. Matlen, David J. Orosy
• Inventors: Matlen, Abraham J., Orosy, David J.
• Primary Examiner(s): Gilheany, Bernard A.
• Assistant Examiner(s): Bell, F. E.
• Application Number:
  US05/298,294
• Time in Patent Office: 469 Days
• Field of Search: 219/494,497,499,501
• US Class Current: 219/497
• CPC Class Codes: G05D 23/2401 using a heating element as a sensing element

Abstract

A temperature control system for use in an electrical heating device wherein the heating element also functions as the temperature sensing element. The resistance of the heating element varies linearly with temperature and the changes in resistance, detected as voltage variations across a wheatstone bridge, regulate the heating. The system is operable in either the A.C. or D.C. mode and includes a temperature measuring circuit, a timing circuit and a control circuit.

Claims

1. A system for measuring and regulating the temperature of an electrical heating element comprising:

control means for regulating the power to an electrical heating element, including a full-wave retifier and an SCR operable for switching power to said heating element during a heating cycle and switching power away from said heating element during temperature measurement, and means for switching power away from said heating element during said heating cycle when the temperature of the heating element reaches a predetermined value including a Schmidt trigger controlling the cyclic operation of said SCR and further including logic means for preventing the turning on of said SCR to supply said heating element;

means for measuring changes in the resistance of said electrical heating element, and a timing circuit cooperating with said control means and said measuring means for measuring said resistance only when said control means ceases to supply power to said heating element.

2. The system as in claim 1, operable in the alternating current mode wherein said timing circuit comprises:

means responsive to the signal from a power supply for generating signals when nulls occur in the alternating current input, a transformer for operating said timing circuit in synchronization with said power supply, and pulse shaping and delay means coupled to said control means and said measuring means to permit temperature measurement only when no power is being provided to said heating element.

3. The system of claim 1, operable in the direct current mode, wherein said timing circuit includes:

a soUrce of clock pulses, and logic means to permit temperature movement only when no power is being supplied to said heating element.

4. The system of claim 1 operable in the alternating current mode wherein said measuring means comprises:

a wheatstone bridge having the heating element as one leg thereof;

a differential amplifier for detecting voltage variations across said bridge;

a sampling circuit responsive to the output of said differential amplifier for charging a capacitor to reflect said voltage variations; and

a comparator, adjustable to the desired heating element temperature, for comparing said voltage variations on said capacitor with the desired heating element temperature.

5. The system of claim 1 operable in the direct current mode, wherein said measuring means comprises:

a wheatstone bridge having the heating element as one leg thereof;

an oscillator coupled to said bridge;

filter means coupled to the output of said bridge for eliminating signal transients from the bridge output;

means for converting the output of said filter means into direct current signals;

a differential amplifier receiving the output of said filter means for detecting voltage variations across said bridge;

a sampling current responsive to the output of said differential amplifier for charging a capacitor to reflect said voltage variations; and

a comparator, adjustable to the desired heating element temperature, for comparing said voltage variations on said capacitor with the desired heating element temperature.