Heater control device

• US 4,636,619 A
• Filed: 06/14/1985
• Issued: 01/13/1987
• Est. Priority Date: 05/31/1982
• Status: Expired due to Term

• Current Assignee: Hideo Sugimori
• Original Assignee: Hideo Sugimori
• Inventors: Sugimori, Hideo
• Primary Examiner(s): PASCHALL, MARK H
• Application Number:
  US06/744,886
• Time in Patent Office: 578 Days
• Field of Search: 219/494, 219/499, 219/497, 219/501, 219/486, 219/508, 219/506, 323/321, 323/235, 323/236
• US Class Current: 219/497
• CPC Class Codes: D06F 75/26 Temperature control or indicating arrangements
• CPC Class Codes: G05D 23/1909 whose output amplitude can only take two discrete values
• CPC Class Codes: G05D 23/2401 using a heating element as a sensing element

Abstract

A heater control device in which a heater is made to double as a temperature sensor so as to eliminate the leading wires used exclusively for the temperature sensor. The heater control device includes a zero-crossing detector which generates a short duration pulse signal each time an AC power voltage is crossing the zero-level. The heater acts as a temperature sensor only for the short duration of the pulse signal.

Claims

1. A heater control device in which a heater element to be temperature-controlled doubles as a temperature sensor, said heater element being supplied from an AC power source through an AC power switching element except when said heater element is acting as said temperature sensor, said heater control device comprising:

a zero-crossing detector means for generating a pulse signal each time an instantaneous absolute voltage value of said AC power source becomes smaller than a predetermined value, said pulse signal causing said heater element to act as said temperature sensor;

a DC power source for supplying current for operating said heater control and for providing a temperature sensing circuit voltage to said heater element when said element is being utilized as a temperature sensor;

a DC current switching element for providing a sensing excitation voltage in accordance with said pulse signal generated by said zero-crossing detector means;

a circuit means connected to said heater element and responsive to said sensing excitation voltage for providing a reference voltage corresponding to a predetermined control temperature value, and for sensing a temperature sensing signal which corresponds to an exciting sensing voltage from said heater element when said element is being utilized as a temperature sensor;

a comparator means for comparing said temperature sensing signal with said reference voltage;

wherein said AC power switching element is operated by said comparator means in accordance with the polarity of the difference between said temperature sensing signal and said reference voltage;

wherein said circuit means is a bridge circuit which comprises;

a variable voltage-divider circuit for generating said reference voltage in one leg of said bridge circuit;

a resistor connected in series with a load impedance, said load impedance, connected in parallel with said heater element, wherein said resistor, said load impedance and said heater element constitute another leg of said bridge circuit;

and a means for preventing an AC voltage from said AC power source to be imposed on said reference voltage and on said temperature sensing signal;

and wherein said preventing means comprises;

a first diode connected in series between said resistor and said heater element, an anode of said first diode being connected to a connecting point of said heater element and said AC power switching element;

a second diode connected in series between said resistor and said load impedance, an anode of said second diode being connected to said load impedance;

a third diode connected in series between said DC current switching element and said variable voltage-divider circuit, a cathode of said third diode being connected to said DC current switching element;

and wherein said temperature sensing signal is generated at a connecting point between said load impedance and said second diode.