Variable gain oven temperature control circuit
First Claim
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1. A circuit for controlling the temperature in an oven, comprising:
- a quick warm-up heater and a steady state heater, each comprising an electrical resistance element, located in the oven;
sensing means located in the oven for sensing the temperature;
steady-state amplifier means having an input and having an output connected to control the power supplied to the steady-state heater;
quick warm-up amplifier means having an input and having an output connected to control the power supplied to the quick warm-up heater;
an input means connected between the sensing means and the input of the steady-state amplifier means, the input means being also coupled to the input of the quick warm-up amplifier means;
a low-gain feedback means coupled between the quick warm-up amplifier means and the input means;
a high-gain feedback means coupled between the steady-state amplifier means and the input means;
the circuit being operative responsive to the sensing means sensing a large difference in temperature in the oven below a predetermined set temperature to fully turn on the quick warm-up amplifier means to apply a maximum power to the quick warm-up heater, until the sensed temperature rises to a value which causes the quick warm-up amplifier means to reduce the power in the quick warm-up heater in a continuous range, causing the low-gain feedback means to become effective, until the sensed temperature reaches a value which causes the quick warm-up amplifier means to be turned off with no significant power in the quick warm-up heater, which causes the high gain feedback means to become effective with the steady-state amplifier means applying power in a continuous range to the steady-state heater, which is then effective to control the temperature very near to the set temperature.
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Abstract
The frequency of an electronic oscillator is controlled by a crystal located in the oven. The heaters in the oven include resistance elements for quick warm-up, and steady state. The circuit allows the quick warm-up power to be reduced incrementally as the set temperature is approached and effects a smooth transition to the steady-state heater. This is accomplished by circuit features which reduce the control loop gain when high power is applied to the heaters and increase the gain as the warm-up power decreases.
38 Citations
9 Claims
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1. A circuit for controlling the temperature in an oven, comprising:
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a quick warm-up heater and a steady state heater, each comprising an electrical resistance element, located in the oven; sensing means located in the oven for sensing the temperature; steady-state amplifier means having an input and having an output connected to control the power supplied to the steady-state heater; quick warm-up amplifier means having an input and having an output connected to control the power supplied to the quick warm-up heater; an input means connected between the sensing means and the input of the steady-state amplifier means, the input means being also coupled to the input of the quick warm-up amplifier means; a low-gain feedback means coupled between the quick warm-up amplifier means and the input means; a high-gain feedback means coupled between the steady-state amplifier means and the input means; the circuit being operative responsive to the sensing means sensing a large difference in temperature in the oven below a predetermined set temperature to fully turn on the quick warm-up amplifier means to apply a maximum power to the quick warm-up heater, until the sensed temperature rises to a value which causes the quick warm-up amplifier means to reduce the power in the quick warm-up heater in a continuous range, causing the low-gain feedback means to become effective, until the sensed temperature reaches a value which causes the quick warm-up amplifier means to be turned off with no significant power in the quick warm-up heater, which causes the high gain feedback means to become effective with the steady-state amplifier means applying power in a continuous range to the steady-state heater, which is then effective to control the temperature very near to the set temperature. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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Specification