Electronic digital read-out circuit for a clinical thermometer

• US 3,872,726 A
• Filed: 01/19/1972
• Issued: 03/25/1975
• Est. Priority Date: 01/19/1972
• Status: Expired due to Term

• Current Assignee: Ludwig Kauffeld, Perry V. Holst
• Original Assignee: Ludwig Kauffeld, Perry V. Holst
• Inventors: Kauffeld, Ludwig, Holst, Perry V.
• Primary Examiner(s): Swisher, S. Clement
• Assistant Examiner(s): Shoon, Frederick
• Application Number:
  US05/218,787
• Time in Patent Office: 1,161 Days
• Field of Search: 73/362R,362AR 338/28 235/92MT,92NT 340/347NT
• US Class Current: 374/169
• CPC Class Codes: G01K 7/42 Circuits effecting compensation of thermal inertia; Circuits for predicting the stationary value of a temperature
• CPC Class Codes: H03M 1/00 Analogue/digital conversion; Digital/analogue conversion conversion of analogue values to or from differential modulation H03M3/00
• CPC Class Codes: H03M 1/08 of noise H03M1/0617 takes precedence

Abstract

An electronic circuit for digitally displaying the temperature sensed by a thermistor element and especially adapted for use in monitoring human or animal temperature. An analog voltage signal developed from the thermistor is converted into a digital representation which is used to drive a visual display. In order to decrease the time necessary for obtaining a temperature reading, electronic circuits are provided for forecasting the ultimate temperature that will be sensed by the thermistor prior to the time that the thermistor reaches this temperature.

Claims

1. In an electronic instrument having an input for receiving from a transducer a voltage that is proportional to a condition such as temperature that is being sensed by the transducer, electronic circuits comprising:

means including an integrating capacitor for integrating said voltage from a transducer, said integrating means being connected to said input for charging said capacitor an amount proportional to the magnitude of said voltage from thE transducer, a free running binary counter having an output signal each cycle of the counter upon its reaching a predetermined count, said counter connected so that the periods between each of successive output signals are exactly the same, means connected to said integrating means for providing a discharge path for said capacitor, means for connecting said discharge means to said capacitor in response to each of said counter output signals, means responsive to the voltage across said capacitor for disconnecting said discharge means and for immediately beginning charging of said capacitor responsive to said input voltage when the capacitor voltage reaches a certain predetermined minimum, means for detecting the count of said binary counter upon operation of said discharge disconnecting means when said voltage reaches said predetermined minimum level, whereby the detected count of said counter is a measure of the capacitor discharge time and is proportional to the input voltage being measured.

2. The electronic instrument of claim 1 which additionally comprises a voltage power supply source level that is connected to both the instrument input for supplying the transducer and to the capacitor discharge means for providing a potential to which the capacitor is connected during the periods where said discharge means are connected, whereby variations in the voltage output of said source do not affect the detected count of said binary counter during the capacitor discharge.

3. In an electronic instrument having an input for receiving from a transducer a voltage that is proportional to a condition such as temperature that is being sensed by the transducer, electronic circuits comprising:

means including measuring integrating capacitor for integrating said voltage from a transducer, said integrating means being connected to said input for charging said capacitor an amount proportional to the magnitude of said voltage from the transducer, a free running binary counter having an output signal each cycle of the counter upon its reaching a predetermined count, means connected to said integrating means for providing a discharge path for said capacitor, said discharge path means includes at least two different impedance values that are selectable by an external connection to distinct terminals of said instrument input, whereby a discharge time constant of said capacitor is controlled, means for connecting said discharge means to said capacitor in response to each of said counter output signals, means responsive to the voltage across said capacitor for disconnecting said discharge means and for immediately beginning charging of said capacitor responsive to said input voltage when the capacitor voltage reaches a certain predetermined minimum, means for detecting the count of said binary counter upon operation of said discharge disconnecting means when said voltage reaches said predetermined minimum level, whereby the detected count of said counter is a measure of the capacitor discharge time and is proportional to the input voltage being measured.

4. The electronic instrument of claim 1 wherein the input voltage remains connected to continuously charge said capacitor even during the periods that the capacitor is connected to said discharge means, whereby said capacitor begins charging immediately after said discharge means is disconnected from said capacitor without any additional switching being necessary. 5. In an electronic instrument having an input for receiving from a transducer a voltage that is proportional to a condition such as temperature that is being sensed by the transducer, electronic circuits comprising:

means including an integrating capacitor for integrating said voltage from a transducer, said integrating means being connected to said input for charging said capacitor an amount proportional to the magnitude of said voltage from the transducer, a free running binary counter having an output Signal each cycle of the counter upon its reaching a predetermined count, means connected to said integrating means for providing a discharge path for said capacitor, means for connecting said discharge means to said capacitor in response to each of said counter output signals, means responsive to the voltage across said capacitor for disconnecting said discharge means and for immediately beginning charging of said capacitor responsive to said input voltage when the capacitor voltage reaches a certain predetermined minimum, means for detecting the count of said binary counter upon operation of said discharge disconnecting means when said voltage reaches said predetermined minimum level, whereby the detected count of said counter is a measure of the capacitor discharge time and is proportional to the input voltage being measured, means monitoring the rate of change of said input voltage and emitting an electrical signal when said rate of change falls below a predetermined value, whereby said electrical signal is usable to indicate when the instrument is in a state to give a measurement of said condition, and means for increasing a value of impedance in said capacitor discharge means, whereby a steady state value of the input voltage is forecasted by the detected count of said counter in response to said control signal in advance of the input voltage reaching said steady state value.

6. In an electronic thermometer having a temperature sensing element connected to a voltage supply in a manner to develop a signal voltage level that is proportional to the temperature of said sensing element, electronic measuring and display circuits comprising:

means receiving said signal voltage level for integrating said signal voltage level, said integrating means including an electrical storage element that is alternately charged to a level proportional to the value of said signal voltage level and then discharged to a given voltage supply level, means for alternately switching said storage element between its charging and discharging states without any interval therebetween, said switching means maintaining every complete cycle of charging and discharging the storage element at exactly the same total time duration regardless of the signal voltage level developed by the temperature sensing element, and means for measureing the time duration that said storage element is in its discharge state, whereby said time duration is proportional to the temperature of said sensing element.

7. The electronic thermometer of claim 6 wherein said voltage supply that is connected to said temperature sensing element also provides said given voltage supply level to which said storage element is connected during discharge, whereby the discharge time of the storage element is substantially independent of the output of said voltage supply.

8. The electronic thermometer of claim 6 wherein said switching means includes a free running binary counter with an overflow signal connected to switch the storage element from its charging to its discharging states at the occurrence of every counter overflow signal.

9. An electronic thermometer, comprising:

a temperature transducer, a voltage terminal connected to be supplied by a battery electrical power source, means receiving power from said voltage terminal electrically connected to said transducer for developing a voltage that is proportional to the temperature of said transducer, and means connected to said transducer voltage developing means for integrating said temperature proportional voltage, said integrating means including a capacitor that is alternately charged in response to said temperature proportional voltage and discharged by connection to the voltage of said voltage terminal, whereby a change in battery output voltage over time is self-compensating.

10. An electronic thermometer comprising:

a bridge circuit including a temperature transducer and three resistances connected In a closed loop wherein an output voltage proportional to the temperature of the transducer is generated, a capacitor connected to be charged an amount proportional to the voltage output of said bridge, a free running binary counter having an overflow signal each time said counter is reset to zero, the time between each of the overflow signals being exactly the same, means initiated by each of said counter output signals for periodically connecting a discharging circuit to said capacitor without disconnecting said capacitor from said bridge, thereby to maintain recurring cycles of capacitor charge and discharge exactly the same, means for disconnecting the discharge circuit from said capacitor when the voltage thereacross reaches a predetermined level, and thereby to cause the capacitor to begin charging again from the voltage output of said bridge, and means responsive to said discharge circuit disconnecting means for reading and storing the count of said free running counter at the time that the capacitor discharge has ended.

11. An electronic thermometer, comprising:

a bridge circuit including a temperature transducer and three resistances connected in a closed loop wherein an output voltage proportional to the temperature of the transducer is generated, a free running binary counter having an output signal at a certain binary count, a capacitor connected to be charged an amount proportional to the voltage output of said bridge, means responsive to the output signal of said counter for periodically initiating a discharge of said capacitor, means for terminating the discharge of said capacitor when the voltage thereacross reaches a predetermined level, means responsive to said discharge terminating means for reading and storing the count of said free running counter at the time that the capacitor discharge has terminated, means responsive to the output voltage of said bridge for observing a temperature change of the transducer per unit time for either upward or downward temperature change, means responsive to said temperature change observing means for causing a temperature reading to occur when the bridge output voltage change per unit time becomes less than a predetermined value said temperature reading proportional to the count of said counter held by said reading and storing means, and means for adjusting the discharge time of said capacitor to add on a value of capacitor discharge time to that which would normally occur, whereby temperature of the body to be measured is forecasted in advance of the transducer becoming equalized in temperature therewith.

12. An electronic thermometer comprising a bridge circuit including a temperature transducer and three resistances connected in a closed loop wherein an output voltage proportional to the temperature of the transducer is generated, wherein said bridge circuit and said transducer comprise an entity that is physically and electrically disconnectible from the remaining portion of the electronic thermometer, at least one of said bridge resistances being adjustable for matching the bridge individually to its associated transducers for making the electrical output of the bridge substantially linear in a desired region of interest, a capacitor connected to be charged an amount proportional to the voltage output of said bridge, a free running binary counter having an overflow signal each time said counter is reset to zero, the time between each of the overflow signals being exactly the same, means initiated by each of said counter output signals for periodically connecting a discharging circuit to said capacitor without disconnecting said capacitor from said bridge, thereby to maintain recurring cycles of capacitor charge and discharge exactly the same, means for disconnecting the discharge circuit from said capacitor when the voltage thereacross reaches a predetermined level, and thereby to cause the capacitor to begin chargiNg again from the voltage output of said bridge, a visual temperature display means, means connected to said free running binary counter for applying to said display means the count of said counter at the instant that the discharge means is disconnected from the capacitor, thereby to visually display a reading of the temperature of said transducer.

13. An electronic thermometer according to claim 12 wherein said capacitor discharging circuit includes two distinct impedance values and further wherein the physical entity of the bridge circuit and transducer includes means responsive to connection of said physical entity with the rest of the electronic thermometer circuit for selecting one of said two distinct impedance values, thereby to control the rate of capacitance discharge during its discharge cycle, whereby a single electronic thermometer can be used for direct measurements in degrees Centigrade or degrees Fahrenheit by merely substituting one integral bridge and transducer assembly for another.

14. An electronic thermometer comprising:

a bridge circuit including a temperature transducer and three resistances connected in a closed loop wherein an output voltage proportional to the temperature of the transducer is generated, an integrating analog-to-digital converter for generating pulses at periodic intervals, the width of each pulse being proportional to the output voltage of said bridge circuit, and means for measuring and displaying the width of said pulses, thereby to visually display a reading of the temperature of said transducer, means responsive to the output voltage of said bridge for observing a temperature change rate of the transducer for either upward or downward temperature change, means responsive to said temperature change observing means for developing a temperature acceptance signal when the bridge output voltage change rate becomes less than a predetermined value, and means for adjusting the width of each of said pulses by a fixed amount so that the temperature reading displayed at the time of the acceptance signal is that of the body with which the transducer is in contact before the temperature of the transducer is equalized with the temperature of the body being measured.

15. An electronic thermometer according to claim 14 which additionally comprises a mode control switch for selectively activating said temperature mode circuit, said mode control switch including a bi-stable element having two resistance-capacitive circuits connected therewith of different time constants so that when power is interrupted from the mode control switch for a substantial length of time said bi-stable element will switch to one of its states upon reapplying power to the circuit while a shorter discontinuance of power to the mode control switching circuit will cause the bi-stable element to switch to its second state upon resumption of application of power thereto.

16. An electronic thermometer comprising:

a temperature transducer, means responsive to changing electrical characteristics of said transducer for generating pulses at periodic intervals wherein each pulse has a width that is proportional to the temperature of the transducer, means for measuring the width of each of said pulses and displaying said widths directly in terms of temperature of the transducer, means responsive to the changing electrical characteristics of said transducer for monitoring the rate of temperature change of said transducer when increasing, means responsive to the changing electrical characteristics of said transducer for monitoring the rate of temperature change of said transducer when decreasing, means responsive to said increasing monitoring means and to said decreasing monitoring means for developing an electrical signal at an instant when either of said monitoring means detect a rate of change of the transducer temperature to be less than a predetermined value, whereby said electrical signal is usAble to indicate when the temperature being measured can be read, and means for adding onto the temperature reading at said instant a proportional amount which predicts the temperature to which the transducer will equalize with its new surroundings.

17. An electronic thermometer for measuring temperature with a temperature transducer, comprising:

means responsive to changing electrical signal characteristics of said transducer for displaying its temperature, means responsive to the changing electrical characteristics of said transducer for monitoring the rate of temperature change of said transducer when increasing, means responsive to the changing electrical characteristics of said transducer for monitoring the rate of temperature change of said transducer when decreasing, means responsive to said increasing monitoring means and to said decreasing monitoring means for developing an electrical signal at an instant when either of said monitoring means first detects a rate of change of the transducer temperature to be less than a predetermined value, but more than zero, whereby said electrical signal is usable to indicate when the temperature being measured can be read, and means for adding onto a temperature signal from the transducer a signal proportional to the difference between the transducer temperature at said instant and its ultimate temperature, thereby predicting the temperature to which the transducer would equalize with its new surroundings if given enough time.

18. The electronic thermometer of claim 17 which additionally comprises means normally blanking said display means for unblanking said display means in response to said electrical signal.