A number of digital thermometer exist which have accuracy limitations
A number of digital thermometer exist which have accuracy limitations on the order of one to one hundred milli-degre centigrade. The accuracy limitations of such digital thermometers is mainly due to quantizing error and noise of analog-to-digital convertors which follow thermistor bridges, or by inherent limitations associated with other arrangements and techniques.
U.S. Pat. No. 3,781,869 to Sudnick et al discloses a transducer amplifier with automatic balance for strain gages and other transducers in quarter, half or full bridge configurations which provides an analog output suited for measurement, control or display purposes. The amplifier includes temperature compensation provided by a silicon PN junction whose voltage-temperature characteristic is used to effect the offset of an integrated circuit amplifier stage. A signal for zero balance is derived from the amplifier output which is sampled and retained in an analog to digital converter and reconverted to analog form.
U.S. Pat. No. 4,022,063 to West et al discloses an electromechanical digital thermometer. In operation, temperature probe 10 is placed in a patient’s mouth causing the thermistor therein to change resistance. This causes unbalance in bridge 13 amplified by amplifiers 14 and 15 and thus driving motor 21. Shaft 25 then takes up a new position until resistance of potentiometer 26 fed back to the bridge balances the new value of the thermistor resistance. The angular portion of the shaft 25 and coding disc 22 is indicative of the temperature of the thermistor.
U.S. Pat. No. 4,443,117 to Muramoto et al discloses a measuring apparatus wherein an amplifier is connected between a bridge circuit and an analog to digital converter followed by a data processor and display device.
U.S. Pat. No. 4,618,848 to Parfitt discloses an analog to digital converter circuit which uses a CMOS multiplexer, an analog to digital convertor and an operational amplifier buffer which is controlled by a single chip microprocessor.
U.S. Pat. No. 4,679,162 to Ferber et al discloses a wide range linear to log converter with a microcomputer control. The microcomputer provides slope corrections and applies the output corrections for offsets due to the circuit components and ambient temperature compensation for increased precision.
U.S. Pat. No. 4,814,692 to Baumann discloses a circuit for measuring and digitizing the value of a resistance. The resistance to be measured is both a component of an A/D converter which operates in accord with the charge balancing network and is also a component of the resistance network bridge. The circuit permits both a pure resistance measurement and attainment of a composite measured value from a plurality of measured values.
In spite of the developments and advance in the prior art, there remains a need for a high resolution digital thermometer capable of measuring temperature difference on the order of several micro-degrees centigrade.
Although the present invention has been described with reference to particular means, material and embodiments, from the foregoing description, one skilled in the art can easily ascertain the essential characteristics of the present invention and various changes and modifications may be made to adopt the various uses and conditions without departing from the spirit and scope of the present invention as described by the claims which follow.
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