Electronic thermometer

Claim 2

An electronic thermometer comprising a housing, a variable resistor disposed within said housing, means for varying the resistance of said resistor, a temperature sensing probe adapted to change resistance in response to changes in temperature a digital temperature indicating scale calibrated according to a range of temperatures adapted to be sensed by said probe, said scale being movable in response to varying said resistor, a light source within said housing and positioned to illuminate at least a portion of said scale, an electrical power supply within said housing, a plurality of operational amplifiers within said housing, circuit means connecting said operational amplifiers, said variable resistor, said light source and said probe to said power supply, said circuit means being effective to actuate said light source when said scale indicates the temperature being sensed by said probe in response to varying said resistor, a cord reel supported for rotation within said housing, said circuit means includes an elongated flexible conductor wound on said reel and connected to said temperature sensing probe, a portion of said conductor being arranged to twist relative to the axis of said reel in response to extension and retraction of said conductor and probe, and spring means for urging said reel in a direction to retract said conductor.

Claim 3

An electronic thermometer comprising a housing, a variable resistor disposed within said housing, means for varying the resistance of said resistor, a temperature sensing probe adapted to change resistance in response to changes in temperature, a digital temperature indicating scale calibrated according to a range of temperatures adapted to be sensed by said probe, means for indicating a temperature on said scale, an electrical power supply within said housing, circuit means connecting said variable resistor and said probe to said power supply, said circuit means including a plurality of operational amplifiers, an input resistor and a feedback resistor connected to said operational amplifiers, reference resistor means connected to said input resistors, said circuit means being effective to actuate said indicating means for indicating on said scale the temperature being sensed by said probe in response to varying said resistor, said sensing probe comprises a thermistor connected in series with said variable resistor and a variable trim resistor, and a precision resistor connected to control the level at which said operational amplifiers operate with respect to the reference established by said reference resistor means.

Claim 4

An electronic thermometer comprising a housing, a variable resistor disposed within said housing, means for varying the resistance of said resistor, a temperature sensing probe adapted to change resistance in response to changes in temperature, a digital temperature indicating scale calibrated according to a range of temperatures adapted to be sensed by said probe, means for indicating a temperature on said scale, an electrical power supply within said housing, circuit means connecting said variable resistor and said probe to said power supply, said circuit means including a plurality of operational amplifiers, an input resistor and a feedback resistor connected to said operational amplifiers, reference resistor means connected to said input resistors, said circuit means being effective to actuate said indicating means for indicating on said scale the temperature being sensed by said probe in response to varying said resistor, said sensing probe comprises a thermistor connected in series with said variable resistor and a variable trim resistor, and a precision resistor connected to control the level at which said operational amplifiers operate with respect to the reference established by said reference resistor means.

Claim 5

An electronic thermometer as defined in claim 2 wherein said means for indicating a temperature on said scale include means defining an opening within said housing, a rear projection screen within said opening, and means for projecting and enlarging the temperature numbers from said scale to said screen.

Claim 6

An electronic thermometer comprising a housing, a variable resistor disposed within said housing, means for varying the resistance of said resistor, a temperature sensing probe adapted to change resistance in response to changes in temperature for producing a temperature input signal, digital temperature indicating means, an electrical power supply within said housing, circuit means connecting said variable resistor and said probe to said power supply, said circuit means including a plurality of operational amplifiers, an input resistor and a feedback resistor connected to each of said operational amplifiers for establishing a stable closed-loop voltage gain, reference resistor means connected to said input resistors for establishing a reference signal, said operational amplifiers connEcted to sense simultaneously said input signal with respect to said reference signal, a precision resistor connected to control the level at which said operational amplifiers operate with respect to said reference signal, and said circuit means being effective to actuate said temperature indicating means according to the temperature being sensed by said probe in response to varying said variable resistor.

Claim 7

An electronic thermometer comprising a housing, a variable resistor disposed within said housing, means for varying the resistance of said resistor, a temperature sensing probe adapted to change resistance in response to changes in temperature for producing a temperature input signal, digital temperature indicating means, an electrical power supply within said housing, circuit means connecting said variable resistor and said probe to said power supply, said circuit means including a plurality of operational amplifiers, an input resistor and a feedback resistor connected to each of said operational amplifiers for establishing a stable closed-loop voltage gain, reference resistor means connected to said input resistors for establishing a reference signal, said operational amplifiers connEcted to sense simultaneously said input signal with respect to said reference signal, a precision resistor connected to control the level at which said operational amplifiers operate with respect to said reference signal, and said circuit means being effective to actuate said temperature indicating means according to the temperature being sensed by said probe in response to varying said variable resistor.

Claim 8

An electronic thermometer as defined in claim 4 wherein said power supply comprises a first battery having a predetermined voltage rating for operating said circuit means, and a second battery having a lower voltage rating than said first battery and connected for operating said light source.

Claim 9

An electronic thermometer as defined in claim 4 wherein said closed loop voltage gain is at least 1,000.

Claim 10

An electronic thermometer as defined in claim 4 wherein said housing includes a head portion and a handle portion, said handle portion being adapted to be held in one hand, said means for varying said resistor including a dial member positioned to be rotated by the thumb of the hand holding said handle portion, and said circuit means include a normally open switch positioned to be actuated by a finger of the hand holding said handle portion.

Claim 11

An electronic thermometer as defined in claim 4 including resistor means connected to one of said operational amplifiers and being effective to set the input reference of said one operational amplifier slightly different than the input reference of the other said operational amplifier.

Claim 12

An electronic thermometer as defined in claim 4 wherein the outputs of said operational amplifiers are connected to a first switching transistor for actuation of said first switching transistor in response to a difference between said output of said operational amplifiers, a second switching transistor connected to control said temperature indicating means, and said second transistor being controlled by the operation of said first transistor.

Claim 13

An electronic thermometer as defined in claim 4 wherein said circuit means include a variable trim resistor connected to calibrate the circuit to said temperature sensing probe, said variable trim resistor is connected in series with said temperature sensing probe and said variable resistor, said circuit means being effective to present substantially the same input conditions to each of said operational amplifiers when the resistance sum of said trim resistor, said sensing probe and said variable resistor equals a predetermined fixed resistance.

Claim 14

An electronic thermometer comprising a housing, a variable resistor disposed within said housing, means for varying the resistance of said resistor and including a dial member having a substantially cylindrical outer surface, a temperature sensing probe adapted to change resistance in response to changes in temperature, an elongated flexible tape-like scale member extending around said outer surface of said dial member, a series of longitudinally spaced multiple digit numbers on said scale member and being calibrated according to a range to temperatures adapted to be sensed by said probe, a light source within said housing and positioned to illuminate at least a portion of said scale member, an electrical power supply within said housing, circuit means connecting said variable resistor and said probe to said power supply, said circuit means including a plurality of operational amplifiers, an input resistor and a feed back resistor connected to each of said operational amplifiers for establishing a stable closed-loop voltage gain, reference resistor means connected to said input resistors for establishing a reference signal, said operational amplifiers connected to sense simultaneously said input signal with respect to said reference signal, and said circuit means being effective to actuate said light source when said scale member indicates the temperature being sensed by said probe in response to varying said variable resistor.

Claim 15

An electronic thermometer comprising a housing, a variable resistor disposed within said housing, means for varying the resistance of said resistor and including a dial member having a substantially cylindrical outer surface, a temperature sensing probe adapted to change resistance in response to changes in temperature, an elongated flexible tape-like scale member extending around said outer surface of said dial member, a series of longitudinally spaced multiple digit numbers on said scale member and being calibrated according to a range to temperatures adapted to be sensed by said probe, a light source within said housing and positioned to illuminate at least a portion of said scale member, an electrical power supply within said housing, circuit means connecting said variable resistor and said probe to said power supply, said circuit means including a plurality of operational amplifiers, an input resistor and a feed back resistor connected to each of said operational amplifiers for establishing a stable closed-loop voltage gain, reference resistor means connected to said input resistors for establishing a reference signal, said operational amplifiers connected to sense simultaneously said input signal with respect to said reference signal, and said circuit means being effective to actuate said light source when said scale member indicates the temperature being sensed by said probe in response to varying said variable resistor.

Claim 16

An electronic thermometer as defined in claim 11 wherein said dial member includes a light transmittable hollow cylindrical portion having said outer surface, said scale member is light transmittable, and said light source is positioned to project light through said scale member and said cylindrical portion of said dial member to illuminate the indicated temperature.