US 5,397,874 A · Electric automatic temperature control

Abstract

A temperature control circuit is disclosed utilizing automatically either the electric heating (or cooling) element or a separate sensor to measure the instantaneous temperature of the thermal load device. Either a pulsating dc or an ac electric power source may be used with the temperature sensing occurring at near-zero points of the source voltage waveform. The sensor forms one element of a Wheatstone bridge which when unbalanced by a value lower than a chosen reference value, causes a monostable oscillator to flip for at least several cycles of the source power. This turns on a power SCR to feed electric current to the thermal load to increase its temperature (and resistance) until the bridge is again balanced to reverse the state of the monostable oscillator and turn off the SCR. A simple, reliable two step, user friendly calibration circuit is provided for the temperature selecting component. For multiple channel applications the circuit need be reiterated only in part whereby major portions thereof remain common to the various channels and need not be duplicated, thereby minimizing manufacturing cost, component space, heat generation, and power consumption.

Claims20

Dependent claims

Automatic temperature control and power switching circuit for a thermo-electric load comprising:

AC power means for energizing the thermo-electric load, said power source means for having an alternating current waveform that periodically crosses through zero voltage;
temperature control circuit means for sensing a temperature representing that of the thermo-electric load;
power switching means responsive to said temperature control circuit means for selectively connecting said power source means to the thermo-electric load for a predetermined minimum number of half cycle waveforms selected to minimize DC bias build up due to one or several odd half cycles of conduction of one polarity of said alternating current;
and
timing control circuit means connected to said power source means for preventing said switching means from operating unless said alternating current waveform of said power source means is below a predetermined amplitude.

2 more elements

Automatic temperature control and power switching circuit for a thermo-electric load, comprising;

power source means having an alternating current or pulsed DC waveform that periodically approaches zero voltage;
temperature control circuit means for sensing a temperature representing that of the thermo-electric load, said temperature control circuit means including means for independently setting high and low temperature range limits;
switching means responsive to said temperature control circuit means for selectively connecting said power source means to the thermo-electric load wherein the duration of such connection is controlled by said temperature control circuit means;
and
timing control means connected to said switching means for preventing said switching means from operating unless the waveform of said power source means is below a predetermined level.

2 more elements

Automatic temperature control and power switching circuit for a plurality of thermo-electric loads comprising:

power source means for energizing the thermo-electric load, said power source means having an alternating current or pulsed DC waveform that periodically approaches zero voltage;
first and second temperature control circuit means for sensing temperatures respectively representing that of first and second thermo-electric loads;
first and second power switching means respectively responsive to said first and second temperature control circuit means for selectively connecting said power source means to the first and second thermo-electric loads;
and
timing control circuit means connected to said power source means for preventing said switching means from operating unless said waveform of said power source means is below a predetermined amplitude.

2 more elements

Automatic temperature control and power switching circuit for a plurality of thermo-electric loads comprising:

common alternating current power source means for energizing the thermo-electric loads, said power source means having an alternating current waveform that periodically crosses through zero voltage;
first temperature control circuit means for sensing a temperature representing that of a first thermo-electric load, said temperature control circuit means including means for independently setting high and low calibration temperature limits;
first power switching means responsive to said first temperature control circuit means for selectively connecting said common alternating current power source means to a first thermo-electric load for a predetermined minimum number of half cycle waveform;
second temperature control circuit means for sensing a temperature representing that of a second thermo-electric load, said second temperature control circuit means including means for independently setting high and low calibration temperature limits;
second power switching means responsive to said second temperature control circuit means for selectively connecting said common alternating current power source means to a first thermo-electric load for a predetermined minimum number of half cycle waveform;
and
common timing control circuit means connected to said common alternating current power source means for preventing said first and second switching means from operating unless said waveform of said power source means is below a predetermined amplitude.

4 more elements

Dependencies are inferred from the claim text.

Electric automatic temperature control

Life of this patent

Electric automatic temperature control

Life of this patent

Abstract

Claims20