Accurate hand-held digital readout thermometer

Claim 2

A hand-held thermometer comprising: thermocouple means having a measuring junction and a reference junction for providing a millivolt range electrical signal systematically related to temperature according to a nonlinear response curve; power supply means having a source of supply voltage and including a plurality of diodes on a single substrate for providing a substantially stable and temperature independent reference voltage difference, means for defining a stable ground, and means responsive to ambient temperature for generating a temperature dependent compensating voltage for compensating for variations in said millivolt range electrical signal occasioned by variations in the temperature of said reference junction; means for combining said millivolt range electrical signal and said temperature dependent compensating voltage to produce a compensated electrical signal; differential first amplification means including a plurality of integrated circuit amplifiers on a single substrate for providing a substantially temperature independent constant gain for amplifying said compensated electrical signal to produce a first amplified signal in the range of tenths of volts to volts; second amplification means responsive to said first amplified signal and providing a gain that changes at preselected signal levels of said first amplified signal in order to provide a piecewise linear approximation to said nonlinear response curve whereby the output signal from said second amplification means is a second amplified signal substantially linearly related to the measured temperature of said measuring junction within preselected tolerances; analog/digital conversion means responsive to said second amplified signal for providing digital signals representing the temperature at said measuring junction; latching comparator means, comprising a Schmitt trigger and an exclusive OR-gate, responsive to said supply voltage and said reference voltage difference for detecting a low power supply voltage condition by producing a low voltage signal indicative thereof; and display means responsive to said digital signals for indicating the measured temperature in digital form and responsive to said low voltage signal for indicating low voltage condition.

Claim 3

A hand-held thermometer comprising: thermocouple means having a measuring junction and a reference junction for providing a millivolt range electrical signal systematically related to temperature according to a nonlinear response curve; power supply means having a supply voltage and including a plurality of diodes on a single substrate for providing a substantially stable and temperature independent reference voltage difference, means for defining a stable ground, and means responsive to ambient temperature for generating a temperature dependent compensating voltage for compensating for variations in said millivolt range electrical signal occasioned by variations in the temperature of said reference junction; means for combining said millivolt range electrical signal and said temperature dependent compensating voltage to produce a compensated electric signal; differential first amplification means including a plurality of integrated circuit amplifiers on a single substrate for providing a substantially temperature independent constant gain for amplifying said compensated electrical signal to produce a first amplified signal in the range of tenths of volts to volts; second amplification means responsive to said first amplified signal and providing a gain that changes at preselected signal levels of said first amplified signal in order to provide a piecewise linear approximation to said nonlinear response curve whereby the output signal from said second amplification means is a second amplified signal substantially linearly related to the measured temperature of said measuring junction within preselected tolerances; scale selection means operable by a user for providing scale selection signals corresponding to the temperature scale selected by the user; analog/digital conversion means responsive to the said amplified signal and said scale selection signals for providing digital signals representing the temperature at said measuring junction according to the temperature scale selected by the user; latching comparator means, comprising a Schmitt trigger and an exclusive OR-gate, responsive to said supply voltage and said reference voltage difference for detecting a low power supply voltage condition by producing a low voltage signal indicative thereof; and display means responsive to said digital signals for indicating the measured temperature in digital form according to the temperature scale selected by the user and responsive to said low voltage signal for indicating low voltage condition.

Claim 4

A hand-held thermometer comprising: thermocouple means having a measuring junction and a reference junction for providing a millivolt range electrical signal systematically related to temperature according to a nonlinear response curve; power supply means having a supply voltage and including a plurality of diodes on a single substrate for providing a substantially stable and temperature independent reference voltage difference, means for defining a stable ground, and means responsive to ambient temperature for generating a temperature dependent compensating voltage for compensating for variations in said millivolt range electrical signal occasioned by variations in the temperature of said reference junction; means for combining said millivolt range electrical signal and said temperature dependent compensating voltage to produce a compensated electric signal; differential first amplification means including a plurality of integrated circuit amplifiers on a single substrate for providing a substantially temperature independent constant gain for amplifying said compensated electrical signal to produce a first amplified signal in the range of tenths of volts to volts; second amplification means responsive to said first amplified signal and providing a gain that changes at preselected signal levels of said first amplified signal in order to provide a piecewise linear approximation to said nonlinear response curve whereby the output signal from said second amplification means is a second amplified signal substantially linearly related to the measured temperature of said measuring junction within preselected tolerances; scale selection means operable by a user for providing scale selection signals corresponding to the temperature scale selected by the user; analog/digital conversion means responsive to the said amplified signal and said scale selection signals for providing digital signals representing the temperature at said measuring junction according to the temperature scale selected by the user; latching comparator means, comprising a Schmitt trigger and an exclusive OR-gate, responsive to said supply voltage and said reference voltage difference for detecting a low power supply voltage condition by producing a low voltage signal indicative thereof; and display means responsive to said digital signals for indicating the measured temperature in digital form according to the temperature scale selected by the user and responsive to said low voltage signal for indicating low voltage condition.

Claim 5

A hand-held thermometer according to claim 2 wherein said scale selection means includes an exclusive OR-gate and an inverter.

Claim 6

In a hand-held thermometer comprising at least one battery that supplies voltage to a power supply means which generates a substantially stable and temperature independent reference voltage difference, the thermometer also comprising a display means, comprising an analog/digital display driver outputting a square wave that drives the backplane of a liquid crystal display having a low battery input terminal, capable of indicating a low battery condition, the improvement comprising a latching comparator which responds to the battery supplied voltage and the reference voltage difference to cause said display means to indicate a low battery condition when the battery voltage is less than a predetermined multiple of said reference voltage difference, said latching comparator being a Schmitt trigger which outputs into an exclusive OR-gate having the square wave as another input, causing the exclusive OR-gate to output an inverted square wave during a low battery condition, the inverted square wave being connected to the low battery input terminal of said liquid crystal display.

Claim 7

In a hand-held thermometer comprising at least one battery that supplies voltage to a power supply means which generates a substantially stable and temperature independent reference voltage difference, the thermometer also comprising a display means, comprising an analog/digital display driver outputting a square wave that drives the backplane of a liquid crystal display having a low battery input terminal, capable of indicating a low battery condition, the improvement comprising a latching comparator which responds to the battery supplied voltage and the reference voltage difference to cause said display means to indicate a low battery condition when the battery voltage is less than a predetermined multiple of said reference voltage difference, said latching comparator being a Schmitt trigger which outputs into an exclusive OR-gate having the square wave as another input, causing the exclusive OR-gate to output an inverted square wave during a low battery condition, the inverted square wave being connected to the low battery input terminal of said liquid crystal display.