Food preparation electric thermometer alarm circuit

Claim 2

A condition-responsive circuit of the type having impedance means for supplying an indication of external conditions to be sensed, said circuit comprising: a. a pair of input supply terminals for supplying a source of alternating current; b. a four-leg impedance bridge network having first and second common terminals coupled across the input supply terminals and two comparison terminals intermediate respectively the first and second legs of the bridge network and the third and fourth legs; c. a programmable unijunction transistor having a cathode connected to the first common bridge network terminal, an anode connected to the first common bridge network terminal, an anode connected to the terminal intermediate the first and second legs, and a gate connected to the terminal intermediate the third and fourth legs such that said programmable unijunction transistor functions as a null detector in said bridge network; d. said sending means being removably coupled in circuit with one of said legs adjacent said second common terminal of the bridge network; and e. indication means coupled between the second common network terminal and the anode of the programmable unijunction transistor and being responsive to the switched-on state of the programmable unijunction transistor to become operative.

Claim 3

The circuit of claim 1 wherein the sensing means is adapted to be in circuit with the first leg of the impedance bridge and is an impedance with a negative temperature coefficient.

Claim 4

The circuit of claim 1 wherein the sensing means is adapted to be in circuit with the third leg of the impedance bridge and is an impedance with a positive temperature coefficient.

Claim 5

The circuit of claim 2 wherein the impedance with a negative temperature coefficient is a temperature-sensitive thermistor.

Claim 6

The circuit of claim 2 wherein the impedance is a photo-sensitive resistor.

Claim 7

The circuit of claim 2 wherein the impedance is a pressure-sensitive resistor.

Claim 8

A condition-responsive circuit of the type having thermistor means for supplying an indication of an external temperature to be sensed, comprising: a. a pair of input supply terminals for supplying a source of alternating current; b. a four-leg impedance bridge network having first and second common terminals coupled across the input supply terminals and two comparison terminals intermediate respectively the first and second legs of the bridge network and the third and fourth legs; c. a programmable unijunction transistor having a cathode connected to the first common bridge network terminal, an anode connected to the terminal intermediate the first and second legs, and a gate connected to the terminal intermediate the third and fourth legs such that said programmable unijunction transistor functions as a null detector in said bridge circuit; d. said thermistor means having a negative temperature coefficient being removably coupled in circuit with the first leg of the bridge network such that the self-heat of said thermistor provides a latching effect to insure the continued firing of said programmable unijunction transistor once started; and e. indication means coupled between the second common network terminal and the anode of the programmable unijunction transistor and being responsive to the switched-on state of the programmable unijunction transistor to become operative.

Claim 9

A condition-responsive circuit of the type having thermistor means for supplying an indication of an external temperature to be sensed, comprising: a. a pair of input supply terminals for supplying a source of alternating current; b. a four-leg impedance bridge network having first and second common terminals coupled across the input supply terminals and two comparison terminals intermediate respectively the first and second legs of the bridge network and the third and fourth legs; c. a programmable unijunction transistor having a cathode connected to the first common bridge network terminal, an anode connected to the terminal intermediate the first and second legs, and a gate connected to the terminal intermediate the third and fourth legs such that said programmable unijunction transistor functions as a null detector in said bridge circuit; d. said thermistor means having a negative temperature coefficient being removably coupled in circuit with the first leg of the bridge network such that the self-heat of said thermistor provides a latching effect to insure the continued firing of said programmable unijunction transistor once started; and e. indication means coupled between the second common network terminal and the anode of the programmable unijunction transistor and being responsive to the switched-on state of the programmable unijunction transistor to become operative.

Claim 10

A temperature-responsive alarm control circuit of the type having probe means, including a temperature-sensitive thermistor, to be inserted into food being cooked for monitoring the interior temperature thereof, the circuit comprising: a. a pair of input supply terminals foR supplying a source of alternating current; b. a four-leg impedance bridge network having first and second common terminals coupled across the input supply terminals and two comparison terminals intermediate respectively the first and second legs and the third and fourth legs of the bridge network; c. a programmable unijunction transistor having a cathode connected to the first common bridge network terminal, an anode connected to the terminal intermediate the first and second legs, and a gate connected to the terminal intermediate the third and fourth legs such that said programmable unijunction transistor functions as a null detector in said bridge network; d. the temperature-sensitive thermistor of the probe means having a negative temperature coefficient and being removably coupled in circuit with the first leg of the bridge network such that the self-heat of said thermistor provides a latching effect to insure the continued firing of said programmable unijunction transistor once started; e. a manually variable resistor connected serially in circuit with the thermistor in the first leg; f. a buzzer alarm device, coupled serially with the second common network terminal and the anode of the programmable unijunction transistor and being responsive to the switched-on state of the programmable unijunction transistor to become operative; and g. a zener diode coupled serially between said alarm device and said second common network terminal for allowing a slight back current to flow through said alarm device to result in increase magnetomotive force variation therein.

Claim 11

A temperature-responsive alarm control circuit of the type having probe means, including a temperature-sensitive thermistor, to be inserted into food being cooked for monitoring the interior temperature thereof, the circuit comprising: a. a pair of input supply terminals foR supplying a source of alternating current; b. a four-leg impedance bridge network having first and second common terminals coupled across the input supply terminals and two comparison terminals intermediate respectively the first and second legs and the third and fourth legs of the bridge network; c. a programmable unijunction transistor having a cathode connected to the first common bridge network terminal, an anode connected to the terminal intermediate the first and second legs, and a gate connected to the terminal intermediate the third and fourth legs such that said programmable unijunction transistor functions as a null detector in said bridge network; d. the temperature-sensitive thermistor of the probe means having a negative temperature coefficient and being removably coupled in circuit with the first leg of the bridge network such that the self-heat of said thermistor provides a latching effect to insure the continued firing of said programmable unijunction transistor once started; e. a manually variable resistor connected serially in circuit with the thermistor in the first leg; f. a buzzer alarm device, coupled serially with the second common network terminal and the anode of the programmable unijunction transistor and being responsive to the switched-on state of the programmable unijunction transistor to become operative; and g. a zener diode coupled serially between said alarm device and said second common network terminal for allowing a slight back current to flow through said alarm device to result in increase magnetomotive force variation therein.

Claim 12

The circuit of claim 8 wherein the buzzer alarm device is of very low impedance as compared with the impedances of the individual legs of the bridge network.