Temperature control device

• US 4,053,733 A
• Filed: 07/16/1975
• Issued: 10/11/1977
• Est. Priority Date: 08/06/1974
• Status: Expired due to Term

• Current Assignee: Minolta Camera Kabushiki Kaisha
• Original Assignee: Minolta Camera Kabushiki Kaisha
• Inventors: Murata, Tomoji, Maese, Masayuki
• Primary Examiner(s): Beha, Jr., William H.
• Application Number:
  US05/596,243
• Time in Patent Office: 818 Days
• Field of Search: 219/490, 219/494, 219/497, 219/499, 219/501, 219/504, 219/505, 219/506, 323/18, 323/24, 323/19, 307/252 UA
• US Class Current: 219/494
• CPC Class Codes: G05D 23/1913 delivering a series of pulses
• CPC Class Codes: G05D 23/24 the sensing element having a resistance varying with temperature, e.g. a thermistor

Abstract

A temperature control device in which electric power to be supplied to a heating element is controlled correspondingly to pulse intervals applied to a switch circuit with the pulse intervals adapted to vary according to the temperature of the portion to be heated by the heating element, which temperature control device is further provided with a sensor for detecting the pulse intervals when the temperature of the portion to be heated has reached a predetermined level with the signal from the sensor being utilized as the signal for the completion of warming-up of the portion to be heated.

Claims

1. A temperature control device for controlling the temperature of a portion to be heated by a heating element to which electric power is supplied, the device comprising:

a pulse generating means for generating pulses with the intervals between the pulses varying in accordance with the temperature of the portion to be heated by the heating element,

a switching means coupled to said pulse generating means for being supplied with the pulses from said pulse generating means and for controlling the electric power supplied to the heating element in accordance with the pulse intervals, and

a sensing means coupled to said pulse generating means for sensing a specific pulse interval at which the temperature of the portion to be heated has reached a predetermined level and upon sensing said specific interval, said sensing means generating a signal indicative of completion of warming-up of the portion to be heated as its temperature reaches the predetermined level.

2. The temperature control device as claimed in claim 1 wherein said sensing means includes a charging circuit having a condenser, a first transistor connected to said pulse generating means and to said charging circuit, and a second transistor connected to said condenser, said first transistor discharging said condenser upon becoming conductive and said condenser being adapted to make said second transistor conductive when the temperature of the portion to be heated reaches the predetermined level, thereby providing an indication of the completion of warming-up.

3. A temperature control device for controlling the temperature of a portion to be heated by a heating element to which electric power is supplied, the device comprising:

a detecting element for detecting the temperature of the portion to be heated,

a pulse generating means including a comparison amplification control circuit associated with said detecting element for supplying to the output terminal thereof an output current proportional to the temperature detected by said detecting element, a programmable uni-junction transistor, a condenser connected to the output terminal of said comparison amplification circuit and connected to the anode of programmable uni-junction transistor for applying the terminal voltage of said condenser to the anode of said programmable uni-junction transistor, and a pulse transformer connected to the cathode of said programmable uni-junction transistor for generating pulses with the pulse intervals varying in accordance with the temperature detected by said detecting element, a switching means including a triac connected to said pulse transformer for being supplied with the pulses, said triac being adapted to be connected with the heating element so that the electric power to be supplied to said heating element is controlled in accordance with the pulse intervals, and

a sensing means for sensing specific pulse intervals at which the temperature of the portion to be heated has reached a predetermined level and including a first transistor the base of which is connected to the cathode of said programmable uni-junction transistor, a charging circuit having at least a condenser connected to the collector of said first transistor, and a comparison detection circuit having at least a second transistor and to which said charging circuit is connected, said first transistor being made conductive upon application of pulses thereto from said programmable uni-junction transistor for discharging charges in said condenser and said second transistor being made conductive by said condenser when the temperature of the portion to be heated reaches the predetermined level, and thereby indicating the completion of warming-up.

4. The temperature control device as claimed in claim 3 wherein said sensing means further includes a third transistor connected to said second transistor and a relay connected to said third transistor, said third transistor being for driving said relay when said second transistor becomes conductive, and said relay generating a signal indicative of completion of warming-up of the portion to be heated.

5. A temperature control device for detecting zero crossing points of an A.C. power source and for generating pulse signals at zero crossing times of the A.C. power source, for integrating a control input voltage and for producing an output of zero crossing signals after the integrated value of said control input voltage has exceeded a predetermined value, said temperature control device comprising a switching element for passing a half cycle of the A.C. power source to a heating element, a rectifier coupled to the A.C. power source, a Zener diode, an output terminal of said rectifier being connected to said Zener diode for developing trapezoidal form waves of rectified full waves across said Zener diode, a first capacitor and a diode connected to each other in series and connected to opposite sides of said Zener diode, a first transistor, the common junction of said first capacitor and said diode being connected to the base of said first transistor with said first capacitor and said first transistor forming a differential circuit so as to develop differential pulses at the base of said first transistor upon the rise of said trapezoidal form waves, series-connected resistors connected to the collector of said first transistor for developing zero crossing signals at a common junction of said series-connected resistors upon momentary conduction of said first transistor due to said differential pulses and for determining a comparison voltage, a programmable uni-junction transistor, to which said common junction of said series-connected resistors is connected, a pulse transformer to the primary winding of which the cathode of said programmable uni-junction transistor is connected for developing pulses for turning on said switch element and the secondary winding of said pulse transformer being connected to the control terminals of said switching element, a temperature sensor element disposed in the vicinity of said heating element for detecting the temperature of a heating apparatus to be heated by said heating element, one terminal of said temperature sensor element being connected to an output terminal of said rectifier, a second transistor, the other terminal of the temperature sensor element being connected to the base of said second transistor, a third transistor and a plurality of resistors connected to the collector and emitter of said second transistor and the collector of said third transistor to form with said second transistor a differential amplifier, a further plurality of resistors connected between the other terminal of said temperature sensor element and another terminal of said rectifier, series-connected resistors connected, at a common junction thereof, to the base of said third transistor for biasing said third transistor, a fourth transistor for a constant current source having the emitter thereof connected to the collector of said second transistor and the base thereof connected to the collector of said third transistor for receiving the output of said differential amplifier with the collector of said fourth transistor being connected to the anode of said programmable uni-junction transistor, a second capacitor for integration and to which the collector of said fourth capacitor is connected, and a smoothing capacitor coupled to said rectifier.

6. A temperature control device as claimed in claim 5, wherein said switching element is a three electrode A.C. control element.

7. A temperature control device as claimed in claim 6, wherein said three electrode A.C. control element is a triac.

8. A temperature control device as claimed in claim 5, wherein said temperature sensor element is a thermistor.

9. In a temperature control device in which electric power to be supplied to a heating element is controlled corresponding to pulse invervals applied to a switching element with the pulse intervals adapted to vary according to the temperature of a portion to be heated by the heating element, and in which a temperature sensor element is provided to detect the pulse intervals when the temperature of said portion to be heated has reached a predetermined level with the signal from said sensor element being utilized as signal for completion of warming-up of said portion to be heated, a temperature control circuit comprising said switching element which is coupled between an A.C. power source and said heating element, a transformer, a rectifier coupled to the A.C. power source through said transformer, a Zener diode, said rectifier having an output terminal connected to said Zener diode for developing trapezoidal form waves of rectified full waves across said Zener diode, series-connected resistors coupled to opposite sides of said Zener diode, a programmable uni-junction transistor, the common junction of said series-connected resistors being connected to the gate of said programmable uni-junction transistor for dividing the voltage of said trapezoidal form waves and for applying the same to said gate to enable phase control synchronized with the wave forms of the A.C. power source, a pulse transformer having the primary winding connected to the cathode of said programmable uni-junction transistor and the secondary winding of said pulse transformer being connected to the control terminals of said switching element, a comparison amplification control circuit connected between said output terminal of said rectifier and the anode of said programmable uni-junction transistor, said temperature sensor element being connected in parallel to said comparison amplification control circuit, a first capacitor connected to an output terminal of said comparison amplification control circuit and to the anode of said programmable uni-junction transistor for integrating output current from said comparison amplification control circuit and applying the voltage across said first capacitor to the anode of said programmable uni-junction transistor, a first transistor having the base connected to the cathode of said programmable uni-junction transistor, a charging circuit composed of a series connected resistor and a second capacitor, a second transistor, the common junction of said resistor and said second capacitor being connected to the collector of said first transistor and the base of said second transistor for rendering said first transistor conducting whenever a pulse from said programmable uni-junction transistor is applied to said first transistor so as to discharge said second capacitor, a plurality of resistors connected to said second transistor for forming a comparison and detecting circuit for comparing and detecting the potential of said second capacitor, a third transistor, to which the collector of said second transistor is connected, a warming-up completion detection relay coupled to said third transistor for being driven thereby by amplification of the output current from said second transistor, said relay having a self-holding contact and another contact for generating a signal, and a smoothing capacitor coupled to said rectifier.

10. A temperature control device as claimed in claim 9, wherein said switching element is a three electrode A.C. control element.

11. A temperature control device as claimed in claim 10, wherein said three electrode A.C. control element is a triac.

12. A temperature control device as claimed in claim 9, wherein said temperature sensor element is a thermistor.

13. A temperature control device as claimed in claim 9, wherein said comparison amplification control circuit further comprises a bridge circuit composed of said temperature sensor element and three resistors connected in series thereto, and a comparison amplifier composed of a fourth and fifth transistors and a plurality of resistors, voltage at a common junction of said sensor element and one of said three resistors being applied to the base of said fourth transistor with voltage at a common junction of the other two of said three resistors being applied to the base of said fifth transistor for amplifying difference of said voltages in said comparison amplifier, and a sixth transistor to which said difference of said voltages is applied as an input thereto, which input is in turn applied to said first capacitor as a constant current.

14. A temperature control device as claimed in claim 9, wherein said temperature control circuit further comprises a third capacitor and a diode connected in series with each other, said third capacitor and diode being connected to opposite sides of said Zener diode, a seventh transistor to the base of which is connected the common junction of said third capacitor and said diode, the collector of said seventh transistor being connected to one end of said series-connected resistors coupled to said Zener diode with the emitter of said seventh diode.