CA1048298A - Electronic thermometer with automatic on-off switching - Google Patents

Abstract

Abstract of the Disclosure An electronic thermometer system comprising a temperature sensing circuit for measuring temperature variations and providing a first signal representative thereof; a temperature measuring circuit responsive to the first signal for producing a second signal representative of the temperature being sensed; a display circuit for indicating the measured temperature for a predetermined period; a power supply; an actuator device; and an automatic electronic switch responsive to the actuator to turn on and provide power from the power supply to the circuits during an interval at least as long as the predetermined period and to automatically turn off at the end of the interval, cease providing power to the circuits and end the display.

Description

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This invention rela~es to an ~lectronic th~rmome~r having an auto-matic electronic switch for independently holding the syst~m on for a limited time and then automatically turning it off to conserve power.
Recent advances in technology have made more appealing the wide-spread use o~ electronic ~hermometers to measure temperatureJ especially in the medical ~ield. Typically such sys~ems include a thermomster uni~ and a temperature sensing probe unit which may be used with disposable covers.
These systems are initially relatively expensive compared to mercury khermo-meters but over th~ useful life they cost considerably less ~o use and are less consuming of the time of scarce and e~pensive medical personnel. However, since these thermometers are electronic they require electrical power for their operation which i5 supplied in the form of batteries to promote the portability of the electronic thermometer systems. The system requires sub-stantial electrical power to operate the sensing and measuring circuits and to operate the display; as a result the batteries n~y be relatively quite large and heavy in order to provide sufficient power for operating the system ; over a reasonable period of ti~e. Periodically the batteries are removed and replaced with new ones at addi~ional cost or ~he system is removed from ser- ;
vice while the batteries are recharged. Poorer battery duty cycles result if the user habitually unnecessarily extends the measuring and display period or ~, inadvertantly fails to swi~ch ~ff the system at the end of its use.
It is therefore an object of this i~vention to provide an improved electronic thermo~eter system extremely conservative of elec~ric power.
It is a further object of this invention to provide such a syste~
which independently, automatically turns off the system, including the display, a predetermined time after the system is energized.
The invention features an electronic thermometer system comprising a ~emperature sensing circuit for sensing temperature variations and providing a ~irst signal representative thereof and a temperature measuring circuit which is responsive to the first signal for producing a second signal representative ' :

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;;~8 o~ the tempera~ure being sensed. The inven~ion also comprises a ti~
measurlng circuit; a display circuit responsive to said time meas~ring cir-cui~ and said temperature measuring circuit, for indicating the measured temperature during one period and the measured time during a~other period;
a power supply; an actuator; and an automatic electronic switch responsive to an initial operation of said actuator to provide power from said power supply to said circuits and to continue to provide power from said power supply to said circuits independent of further operation of said actuator during an interval at least as long as the combined periods and automatically and independently of further operation of said actuator, at th~ end of said interval, to cease providing power to said circuits and end the display.
In preferred embodiments the system may also include a time measur~
ing circuit whose output will be displayed by the display circuit during another period of time. Typicaliy the time is displayed during a first period and the temperature during the next period.
Other objectsJ features and advantages will occur from the follow-ing description of a preferred embodimen~ and the accompanying drawings, in ` which: -Figure 1 is a block diagram of an electronic thermometer system using an automatic on-off electronic switch according to this invention;
Figure 2 is a more detailed block diagram illustrating one implemen-- tation of the system of Figure l; and - Figure 3 is a more detailed schematic diagram of the automatic on-off electronic switch shown in Figures 1 and ~.
; There is shown in Figure 1 an electronic th rmometer system 10 according to this invention including a temperature sensing circuit 12 which ~` senses variations in temperature and provides a signal representative thereof -~ to measuring circuit 14 which responds by providing a signal representative of the measured temperature to control and display circuit 16. Power is supplied to circuits 12, 14 and 16 from power supply 17 under the control of automatic on-off electronic switch 1~

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In preferrecl embodiments measuring circuit 14 may include a voltage to rate converter or similar analog to digital convert0r which provides a s~ries of pulses representing the measured temperature to control and display circuit 16. Control and display circuit 16 may include counting circuits for ' '` ' ` ' ' :'' :

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counting pulses from moasuring circuit 14 and a digital display for displaying the measured temp~rature. Control and display circuit may also include a time measuring circuit and control circuitry for displaying the time during one period and the te~perature during another.
In one specifie e~bodiment temperature s~nsing circuit 12 may include : :
a probe 20, Figure 2~ for sensing a t~mperature to be measured and producing a signal representative thereQ~ which is submitted through int~rnal reerence ;~;
circuit 22 to bridge circuit 24. Intornal reference circuit 22 selectivoly `:
connects a matching circuit to bridge circuit ~4 in place o~ the input from probe 20 so ~hat the accuracy and operation of ~he syste~ can be veriied.
Bridge circuit 24 provides a reference ou~put on li~9 26 and on line 28 pro-vides a va~ying output as a functi~n of the bTidge i~balance~ an analog sig-nal which is a func~ion of tho temperature sensed by probo 20, In this system used primarily to take thc ~emperatures of humans the moasurement range is from 90F to 110F. Thus reference output 26 of bridge circuit 24 repressnts the levçl of 90F; when output 28 of bridge circuit 24 îs equal to reference output 26 thermometer probe 20 is measurin~ a temperature o 90F. When out~
put 28 is at a predetorminod devia~ on from the le~el of output 26 probe 20 is measuring 110F. Output 28 is fed to anticipation circuit 30 which senses ~; :
the ~ate of change of the ~emperature bein~ sensed by probe 20 and adds to the ` signal on output 28 fro~ ~ridge circuit 24, thoreby providing a signal at :
: summing point 32 in voltage to ra~e converter 14 represcntative of the final value of the temperature being sensed in advance of thc actual sensing of that :: final value.
:: In measuring circui~ 14 the signal at summing point 32 is directed to the negati~e input of integrator circuit 34 ~hose positivo input receives reference output 26 rom bridge circuit 24. A dif~erence between suDming point . 32 and reference output 26 at the input to integrator 34 causes it to provide : .~
a positive slope ramp at its output to constant width pulse generator 36, which provides a negative going output pulse of ~ixed width when the ramp reaches a .~ :

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pr~det~rmined voltage lev~l. The fixed width pulse is deliv~red alon~ feed-back line 38 to r~ference current switch 40 which produces a positive going pulse having fixed width and fixed amplitude and delivers it to summing point 32. The presence of this pulse t~mporarily restores summing point 32 to the level of output 26 causing the integrator circuit output to drop resulting in a sawtooth output signal. Constant width pulse generator 36 then produces no further pulses to reference current switch 40. Tharefore no pulses are de-livered to summing point 32 and the level at summing point 32 once again moves away from ~hat at the reference output 26. This causes integrator circuit 34 ~ 10 to provide another positive ramp and the cycle to begin again. Since the pulse ; fed back to summing point 32 has fixed width and fixed amplitude it is the rate of those pulses which must adjust to the relative imbalance between summing point 32 and reerence output 26. Thus ~he greater the difference between these two inputs to integrator circuit 34 the higher will be the repetition rate of ~he pulses provided at the output of canstant width pulse generator 36; this repetition rate is proportional to the temperature being sensed by brobe 20. The illustrated configuration of measuring circuit 14 in Fi~ure 2 which includes su~ing point 32, integrator circuit 34, constant width pulse genera~or 36, feedback line 38 and reference current switch 40 is but one exa~ple of a vol~age to rate converter which may be usedO For example a vol-tage controlled oscillator or other means for producing an output whose fre-: . .
quency varies in proportion to an analog input signal may be used.
` Control and display circuit 16 includes digital counting and decoding circuit 42 which counts the digital pulses provided at the output of constant width pulse generator 36 and decodes that count to display the measured tem-perature on digital display 44.
Pre~ision voltage regulator 40 provides regulated voltage, PVR to bridge circuit 24, reference current switch 40J integrator circuit 34, constant s width pulse gene~ator 36 and low battery voltage sensing circuit 52. The o~her .
-, 30 input to low battery voltage sensing circuit 52 is ~he unregulated power sup~

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g8 plied a~ the outpu~ of au~omAtlc on-off electronic switch 18. When ~he un-regulated power s-lpply voltage d~creases to a predetermined level relative to the regulate~ voltage output provided by prscision voltage regulator 50, low battery voltage s~nsing circuit 52 provides a signal to digital counting and decoding circuit 42 causing it to extinguish the least significaat digit of the temperature appearing in digi~al display 44.
The speciic embodiment of electronic tharmomet~r system 10 illustra-ted in Figure 2 operates in two modes: a time display mode and a temperature display mode Digital control logic 54 supervises sys~em performance in each }o of th~se modes and controls ~he ~ransition between the~ as a function of control and display circuit 16. In the time display mode digital control logic 54 passes pulses from clock 56 to digital counting and decoding circuit ; 42; while in the temperature display mode digital control logic 54 directs pulses from constant width pulse generator 36 to digital counting and decoding circuit 42. The system is operated by actuation of start switch 58 In operation when start switch 58 is actuated automatic on-off elec-tronic swi~ch 18 is turned on to supply power from power supply 46 to the rest of the system and digital control logic 54 and digîtal counting and decoding ~` circuits 42 are reset. Probe 20 in contact with the patiqnt whose temperature ~0 is to be measured begins to sense the temperature As the probe temperature T increases, the voltage E at output 28 of bridge circuit 24 decreases, in-creasin~ the negative current I at summing point 32. The difference in levels of output 26 and sum~ing point 32 causes pulses to be generated a~ the output of constant width pulse generator 36 at a repetition rate required to restore summing point 32 to the proper level. The repetition rate of the pulses at -~
the output of const~nt width pulse generator 36 stabilizes in a short period of time to represent the final value of the temperature being sensed. This time may be reduced still further by the use of anticipation circuit 30 as explained previously.
Simultaneously wi~h this action3 upon the actuation of start switch .: ~ ' ' ' ~Lr~ 3~

48, au~omatic on-off electronic switch 18 latches i~self to stay on for a predetermined period of time after the start switch 58 has been operated.
In this particular embodiment, where there is both a time and a temp~rature ~easurement and display ~he interval of opera~ion includes both the period of the time display mode and the period of the temperature display mode e.g.
20 seconds and 10 seconds, resp~ctively, A signa~ to automatic on-off elec-tronic swi~ch 18 on line 60 signifies the end of the period ~f thc time dis_ play mode and the start o the temperature display mode.
Simultaneously with the actua~ion of start switch 58 digi~al control logic 54 passes clock pulses from clock 56 to digital counting and decoding circuit 42. These clock pulses may have a duration of 100 milliseconds so that a count of ten such clock pulses by digital counting and decoding circuit 42 indicates one second. At the end o each second so accumulated digital dis~lay 44 is enabled to display the number 1 through 19 representing the time.
At the end of the twentleth second digital control logic 54 transfers the system into the temperature display mode by permitting passage, for the period - of one clock pu}se, of the pulses at the output of constant width pulse ge~era-tor 36 ~o digital counting and decoding circuit 42 which accumulates and de-~i codes the count and causes the temperature to be displayed, Preferably automatic on-off electronic switch 18 includes switching circuit 70, Figure 3, including transistor 72 having its emitter 74 connected to the positive terminal 76 of power supply 17 and its collector 78 connected to the positive power line 80. Transistor 72 is held normally in a non-conducting state by means of resistor 82 which is connected between base 84 ~'~ and emitter 74 and which keeps base 8~ within six ~enths ~0.6) of a volt of emit~er 74. In switching circuit 70 resistor 86 holds base 88 of transistor 9Q within six tenths ~0.6) of a volt of ground so that transis~or 90 is also noImally in a non-conduc~ing state. The emitter g2 of transistor 90 is con-nected ~o ground and the collector 94 is connected through resistor 96 to the base 84 of trancistor 72~ When start switch 58 is closed thevoleage at resis-1~41~91~

tor 86 moYes toward the leYel of positive powor supply terminal 76 incroasing the voltage at base 88 of transistor 90 causing that transistor to conduct.
This causes current to be drawn through resistor 96 driving th~ base 84 of transistor 72 toward ground and oausing it ~o conduct and supply power to the rest of the eircuit on line 80, The pressing and releasing of start switch 58 provides a positive pulse on line 98 ~o timing cireui~ 100 which includes flip-~lop 102, The signal on line 9~ is delivered to the set inputs of flip-flop 102 causing its Q output 104 to go high, With Q output 104 high diode ln6 is forward biased and a signal is provided on line 108 which charges capacitor llO in timing circuit 111 and is fed back through amplifier 112 and resistor 114 in latch circuit 116 ~o tlle base 88 of transistor 90> thereby keeping it conducting --even af~er start switch 58 has been released. In this condition transistor . .
72 continues to ronduc~ and automatic on-off electronic switch 18 maintains itself in the on condition independent of external signals. Resistor 118 connects one pole of start switch 58 to ground and resistor 120 similarly ~ connects the reset input R of fllp-flop 102 with ground. After a predeiter--~ mined time, in the specific system shown in Figure 2, a signal is provided on ~-~ line 122 signifying the end of the ~ime display mode and resetting flip-flop ~ ;~
102. Diode 106 is now back biased by the lower signal on Q ou~pu~ 104 and so ', capacitor 110 discharges through resistor 124 for a predetermined period of ; time e.g. ten seconds while the ~emperature is being displayed in the tempera-ture mode. When the voltage on line 108 falls, the voltage fed back through latch circuit 116 to base 88 of transistor 90 also falls turning off transis- ;
~, tor 90 and transîstor 7Z and automatically turning off power to the xest of the system. The inter~al during which automa~ic on-off electronic switch 18 ;;
remams energized need not necessarily include two periods; it may include only one period or more than two periods. If the temperature display period is the only one utilized, the temperature display period may be delayed for ~ 30 a short time after the interval begins in order to permit the temperature ,. .~. .
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Z~8 measuring circuit of the system to stabilize at a ~inal temperature value.
Other embodiments will occur to those skilled in the art and are within the following claims.

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Claims (3)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. An electronic thermometer system comprising: a temperature sensing circuit for sensing temperature variations and providing a first signal re-presentative thereof; a temperature measuring circuit responsive to said first signal provided by said temperature sensing circuit for producing a second signal representative of the temperature being sensed; a time measur-ing circuit; a display circuit responsive to said time measuring circuit and said temperature measuring circuit, for indicating the measured temperature during one period and the measured time during another period; a power supply;
an actuator; and an automatic electronic switch responsive to an initial operation of said actuator to provide power from said power supply to said circuits and to continue to provide power from said power supply to said circuits independent of further operation of said actuator during an interval at least as long as the combined periods and automatically and independently of further operation of said actuator, at the end of said interval, to cease providing power to said circuits and end the display.

2. An electronic thermometer system comprising: a temperature sensing circuit for sensing temperature variations and providing a first signal representative thereof; a temperature measuring circuit responsive to said first signal provided by said temperature measuring circuit for producing a second signal representative of the temperature being sensed; a time measuring circuit; a display circuit, responsive to said time measuring circuit and said temperature measuring circuit, for indicating the measured time during a first period and the measured temperature during the next period; a power supply; an actuator; and an automatic on-off electronic switch responsive to an initial operation of said actuator to turn on and provide power from said power supply to said circuits and to continue to provide power from said power supply to said circuits independent of further operation of said actuator during an interval at least as long as the combined periods and to automatical-ly and independently of further operation of said actuator turn off at the end of said interval, cease providing power to said circuits and end the display.

3. An electronic thermometer system comprising: a temperature sensing circuit for sensing temperature variations and providing a first signal representative thereof; a temperature measuring circuit responsive to said first signal provided by said temperature measuring circuit for producing a second signal representative of the temperature being sensed; a time measuring circuit; a display circuit, responsive to said time measuring circuit and said temperature measuring circuit, for indicating the measured time during a first period and the measured temperature during the next period; a power supply; an actuator; and an automatic electronic switch including a switching circuit responsive to operation of said actuator for providing power from said power supply to said system; a first timing circuit responsive to operation of said actuator to switch to a first condition and responsive to a signal from said time measuring circuit indicating that said system has reached the end of said first period to switch to a second con-dition; a second timing circuit responsive to the change of said first timing circuit from said first condition to said second condition to define said next period; and a latching circuit responsive to said first timing circuit in said first condition to enable said switching circuit to continue to provide power from said power supply to said system during said first period independent of further operation of said actuator and subsequently, responsive to said second timing circuit, to continue to provide power from said power supply to said system during said next period independent of further operation of said actuator and to automatically and independently of further operation of said actuator turn off at the end of said next period, cease providing power to said system and end the display.