ELECTRONIC THERMOMETER

Abstract: A cordless electronic thermometer includes temperature sensing means (35-38) incorporating a thermistor (38) for sensing a temperature and providing over time a series of temperature related electric parameters. Data representing these parameters is stored in stored in storing means (52) which is connected to data transmitting means (50). The thermometer is provided with connector means (26) connected to the output of the data transmitting means and adapted to be connected to an associated master unit which serves as a power source and temperature display. The connector means (26) includes a command input (70) adapted to receive a command signal from the master unit, and a data output (72) via which data is transmitted to the master unit from the data transmitting means (50). Energy storage means (C1, C2) are included in the thermometer for storing electrical energy when the connector means (26) is connected to the master unit.

Description: ELECTRONIC THERMOMETER Technical Field The present invention is related to temperature measuring devices for taking the tempera¬ ture of medical patients. Background Art Electronic thermometers have recently been developed to take the place of mercury thermometers for taking the temperature of medical patients. In many of these devices, the temperature sensing probe which is placed in contact with the patient, such as under the patient's tongue, must be continuously connected to a source of power and other electronic circuitry for converting an electrical parameter of the probe to a temperature reading. This is normally done by a long cord which is attached at one end to the temperature sensing probe, and at the other end to appropriate electronics. U.S. Patent No. 4,176,556 discloses an electronic thermometer which utilizes a microproces¬ sor, a bridge circuit containing a temperature respon¬ sive transducer, a charge and discharge circuit, and an interrupt signal generating circuit. A counted value corresponding to a reference temperature is added to a counted value corresponding to the time it takes a capacitor connected to the bridge circuit to discharge, and the result is converted to a tempera¬ ture degree and displayed by the microprocessor. U.S. Patent No. 4,447,884 discloses a self contained electronic thermometer including a memory system for storing body temperature data measured by a temperature sensing element, power for the memory system being provided by a battery. The thermometer includes a graphic display for displaying the tempera¬ ture stored in the memory system. Disclosure of the Invention It is an object of the invention to provide a cordless electronic thermometer which is of simple construction and has a compact configuration. According to the invention there is provided an electronic thermometer including a temperature sensing means for sensing a temperature and providing over time a series of temperature related electric parameters, said temperature sensing means incorporat¬ ing a resistive element whose resistance varies as its temperature varies, and data storing means for storing data representing said series of temperature related electric parameters, characterized by data transmit¬ ting means having an output and connected to said data storing means for transmitting, upon command, data stored in said data storing means, connector means connected to said output of said data transmitting means and adapted to be connected to an associated power source and temperature display unit, said con¬ nector means having a command input adapted to receive a command signal from said associated unit for com¬ manding said data transmitting means to transmit data, and a data output for providing thereon data transmit¬ ted by said data transmitting means, and electrical energy storage means electrically connected to said connector means, said energy storage means being adapted to receive and store electrical energy when said connector means is connected to said associated unit, and being adapted to supply stored electrical energy to said temperature sensing means and said data storing means when said connector means is not con¬ nected to said associated unit. It will be appreciated that an electronic thermometer in accordance with the present invention can be arranged to have an extremely compact configu¬ ration since neither a battery nor a temperature display means is required to be included in the ther¬ mometer. Brief Description of the Drawings Embodiments of the present invention will now be described by way of example with reference to accompanying drawings, in which: Fig. 1 is a diagrammatic illustration of a cor -ess; electronic thermometer in accordance with the inveπtiαn together with an associated master unit; Fig. 2 is a schematic diagram of one embodiment of the electronic thermometer of Fig. 1; Fig. 3 is a schematic diagram of another embodiment of the electronic thermometer of Fig. 1; Eig. 4 is a timing diagram illustrating one method of operation of the electronic thermometer of Fig-. 3T during its data collecting mode; and Fig. 5 is a timing diagram illustrating an alternate method of operation of the electronic ther¬ mometer of Fig. 3 during its data collecting mode. Best Mode for Carrying Out the Invention Fig. 1 is a diagrammatic illustration of a cordless electronic thermometer and its master unit which includes the present invention. The thermometer unit 10 includes a thermometer probe 12 and a housing portion 14 for housing the electronics of the thermom¬ eter unit. The master unit 16 includes a thermometer receiving portion 18, a temperature readout display 20 and a data entry key pad 22. The thermometer receiv¬ ing portion 18 of the master unit 16 includes a con¬ nector portion 24 which mates with a corresponding connector portion 26 in the housing 14 of the elec¬ tronic thermometer unit 10. The master unit 16 fur¬ ther includes a central processing unit 28 and a memory 30. Prior to use, a nurse places the thermometer unit 10 in the thermometer receiving portion 18 of the master unit 16 and mates the connector unit portions 24 and 26 together to make an electrical connection. - 4 - As will be discussed, the electronics in the housing portion 14 are then prepared by a charging cycle to receive temperature data from a patient. When the charging cycle of the preparation of the electronics is completed, the thermometer unit 10 is removed from the master unit 16 and the temperature probe 12 is covered with a throw away protective sheath 32 and placed under the tongue of a patient, the protective sheath 32 having been previously sterilized. The nurse is now free to perform other duties while the patient's temperature is being measured by the thermometer unit 10. After an appropriate length of time, the nurse removes the thermometer unit 10 from the mouth "of the patient and plugs it into the thermometer receiving portion 18 of the master unit 16, once again mating the connector portions 24 and 26. The nurse may make appropriate entries in the data entry key pad 22, such as the patients number, time-of-day, nurse identification, or other information needed for the proper recording of the patients temperature. Then, under the control of the CPU 28, the readings taken by the thermometer unit 10, as will be discussed, are used to calculate the patient's temperature. The calculated temperature may be displayed on the temper¬ ature display 20, and stored in the memory 30 along with the previously entered data for later readout and permanent storage. The master unit 16 may either be a central unit located at a nurses station, or it may be a nurses portable unit which is carried by the nurse. Fig. 2 presents a schematic diagram of one embodiment of the electronic thermometer unit 10 of Fig. 1. The thermometer probe 12 (also shown in Fig. 1) includes a bridge circuit made up of resistors 35, 36 and 37, and a thermistor 38. It will be understood that with power applied across the bridge circuit of thermometer probe 12 and the thermometer probe 12 placed under the tongue of a patient, the voltage reading across the bridge circuit will change as the resistance of the thermistor 38 changes in response to the heat of the patient. It will further be understood that with the sheath 32 over the thermometer probe 12 (see Fig. 1), the sheath 32 will act as an insulator thereby delay¬ ing the transfer of heat from the patient to the thermistor 38. Algorithms are known in which a plu¬ rality of temperature related measurements may be made over a period of time, and the measurements compared to a temperature-versus-time curve to predict, very accurately, what the final temperature will be. Thus, it is unnecessary to wait until the temperature of the probe 12 reaches its final value as long as sufficient temperature related readings are made over a period of time. In this' case, the temperature related readings are the various voltage drops across the bridge cir¬ cuit. The electronic thermometer unit 10 also includes an analog-to-digital converter 40 for con¬ verting the voltage readings across the bridge circuit of probe 12 to digital information. This digital information is transmitted from the analog-to-digital converter circuit 40 over a bus 42 to a data control circuit 44. The data control circuit 44 is driven by a clock 46 which times the various functions of the circuit 44. The data control circuit 44 also includes a central processing unit 48, a read only memory (ROM) 49, and a universal asynchronous receiver transmitter (UART) 50. The CPU 48 controls the various data transfer functions, to be described, as programmed by a set of instructions stored in the ROM 49. In the data collecting mode, the CPU 48 controls the analog-to-digital converter 40 to trans- fer data over bus 42 and data bus 53, to be stored in a random access memory (RAM) 52. The electronic thermometer unit 10 also includes a 1000 microfarad, 10 volt capacitor C2 for supplying power to the various electronic components of the unit, and a 100 microfarad, 2.5 volt capacitor Cl which provides power to a switch 66 and a light emitting diode (LED) 68 to be discussed. When the electronic thermometer unit 10 is connected, via connector portions 24 and 26, to the master unit 16, as discussed in connection with Fig. 1, a source of power is connected at a connector pin 55, and a con¬ nector pin 56 is grounded to charge the capacitor C2. A voltage source is also connected at a pin 57 to charge the capacitor Cl. The electronic thermometer unit 10 is then removed from the master unit 16 and placed under the tongue of a patient to take the patient's temperature. The now disconnected capacitor C2 supplies power to the clock 46 and a voltage reference circuit 60 over conductor 61. Capacitor C2 also provides power to the data control circuit 44, the RAM 52, and the analog- to-digital converter 40 over conductors 62 and 63 respectively. The electronic thermometer unit 10 is now in the data collecting mode wherein voltage readings across the bridge circuit of the probe 12 are convert¬ ed to digital readings by the analog to digital con¬ verter 40. The CPU 48 then transfers the digital readings over buses 42 and 53 for storage in the RAM 52. After sufficient readings have been stored, the CPU sends a signal over conductor 67 to instruct the switch 66 to close, thereby energizing the LED 68. It will be noted, that the LED 68 is powered by the capacitor Cl so as to not place an additional burden on the capacitor C2 supplying power for the other electronics. The lighting of the LED 68 indicates that the thermometer unit 10 is finished taking tem¬ perature readings and that it may be returned to the master unit 16. When the electronic thermometer unit 10 has been returned to the master unit 16 and the connector portions 24 and 26 have been mated, the master unit 16 issues a command over a conductor 70 to the CPU 48 of the data control circuit 44. Upon receiving the command from conductor 70, the CPU 48 reads the stored digital readings from the RAM 52 and instructs the UART 50 to transmit the digital readings over a data line 72 to the master unit 16 for processing. As is known, the UART 50 performs the parallel-to-series conversions necessary to transmit the data from the RAM 52 over line 72 in a serial fashion to the master unit 16. As previously discussed in connection with Fig. 1, the CPU 28 of the master unit 16 may analyze the periodic digital readings from the electronic thermometer unit 10 to calculate and display a temper¬ ature reading on temperature display 20 and store the calculated reading in memory 30 for entry into the patient's permanent records. Fig. 3 is a schematic diagram of another embodiment of the electronic thermometer unit 10 of Fig. 1. In the device of Fig. 3, a large reference or source capacitor CR is provided to transfer a small charge to a series of small measuring capacitors C__ι through C_- n . The charge is transferred through a thermistor 80, having a resistance R(t), which is a function of time following the placement of the elec¬ tronic thermometer unit under the tongue of a patient, and which is connected to each small capacitor for a time in the order of one-half of the time constant of Ci R(t) wherein Ci represents any of the capacitors c l,l through Cι_ n and R(t) represents all expected values of the resistance of the thermistor 80. In this fashion, each individual small capacitor can be charged by an amount that is a sensitive function of the temperature of the thermistor 80 at the time a switch Si through S n corresponding to one of the individual small capacitors Cι f ι through / Ti is closed, simultaneously with the closing of a thermis¬ tor switch S-~. The circuit of Fig. 3 shows the mentioned source capacitor CR, which is a 0.1 microfarad capaci¬ tor, and a second capacitor Cp, which is a 50 micro¬ farad capacitor rated at about 10 volts. A typical value for the small capacitors C _ι through Cι_ n is 10 picofarads. A line 82 denoted AMPL POWER is connected to an output amplifier 84 and a switch sequencer integrated circuit 86. The switch sequencer 86, when activated, sequentially closes switches Si through S n one after the other in a timed sequence, as will be explained. When the electronic thermometer of Fig. 3 is plugged into the master unit 16 as described in con¬ nection with Fig. 1, the source capacitor CR is charged through pin 87 of the connector portions 24 and 26. Also, the capacitor Cp is charged through pin 88 of the mated connector portions 24 and 26. It will also be noted that the AMPL POWER line 82 is energized by pin 89, which voltage prevents the activation of the switch sequencer circuit 86. When the thermome¬ ter unit of Fig. 3 is removed from the master unit 16 as described in connection with Fig. 1, the connection between mated connector portions 24 and 26 is broken and the switch sequencer 86 senses the voltage on AMPL POWER line 82 dropping to zero, which instructs the switch sequencer 86 to begin its data collection mode. Figs. 4 and 5 show two possible alternatives for the operation of the switch sequence circuit 86. In Fig. 4, the switch S-p is precisely controlled, while the switches Si through S n are sequentially closed, each during a period which overlaps with one of the closings of switch S< ~ . The waveform 120 illus¬ trates the operation of the switch S->, with the posi¬ tive going edges of the pulses of waveform 120 showing the closing of switch S<~, and the negative going edges showing the opening of the switch S<~. The switch S ~ « is closed for a known precise time, on the order of one-half of the time constant CiR(t). The thermistor resistance R(t) will be a function of the temperature, but will not vary by a large amount over the tempera¬ ture range of importance. The resistance of the thermistor 80 is approximately 0.1 megohm, and the CiR(t) time constant is approximately one microsecond. Thus, an appropriate length of time for closure of the switch S<- in the operation of Fig. 4, would be about 400 nanoseconds. In this operation, the switch sequencer circuit 86, powered by the capacitor Cp, closes and opens the switch S<- n times, once while each of the switches S through S n is closed. In Fig. 4, the waveforms 122, 124 and 126 show the operation of the switches Si, S2 and S n respectively. In this method of operation, S-- would define the exact duration of the connection between the source capacitor CR and each of the storage capacitors Cι_ι through Cι. n . One of the advantages of the operation of Fig. 4 is that only the switch S<*r> would require pre¬ cise timing. The other switches Si through S n could then be a crude set of multiplexer or selector switch¬ es requiring only that they be of sufficiently high impedance when off to avoid undue leakage of the stored charge from storage capacitors C f through -l,n- Another method of operation of the switch sequence circuit 86 is shown in Fig. 5 wherein the switch ST is closed throughout ' the sequential closings of the switches Si through S n . The waveform 128 illustrates the closing of the switch S ~ >, and the waveforms 130, 132 and 134 illustrate the closing of the switches Si, S2 and S n respectively. In this method of operation, the switches Si through S n con¬ trol the timing, with each switch going closed at a precisely known time and staying closed for the men¬ tioned approximately 400 nanoseconds. Thus, in the method of operation shown in Fig. 5, S<- acts as a routing switch, switching the storage capacitors Cι_ι through Cι_ n to the source capacitor CR during the data collection phase. In either of the operations of Fig. 4 or Fig. 5, the switch S«- remains open in the data transmitting mode, to be described. As the thermometer unit heats up, each small capacitor receives a different charge. Thus, the charge stored on each of the small capacitors Cι_ι through Cι, n provides an accurate measure of the temperature when each was charged. The self- discharge time constant for each small capacitor Cι_ι through Cι_ n is many hours, and the leakage of the switches Si through S n is less than 10~" amps. Thus, the small capacitors Cι_ through Cι_ n will have a voltage change of approximately one volt in three hours. This time is more than sufficient to hold the charge while the thermometer unit is being transferred to the master unit 16 of Fig. 1. After a time, at the most a few minutes, the nurse retrieves the thermometer unit 10 and reconnects it to the master unit 16 as described in connection with Fig. 1. The AMPL POWER line 82 is reenergized, providing a signal to the switch sequencer circuit 86 to go into its data transfer mode. If desired, a timer circuit can be included to supply information to the amplifier 84 which would indicate the total elapsed time since the completion of the measuring sequence. In its data transmitting mode, the switch sequencer circuit 86 closes switch S&, and sequential¬ ly closes each of the switches Si through S n in a timed sequence, to deliver the stored data to the amplifier for conditioning and transfer to the master unit 16. As mentioned previously, the switch ST remains open during the data transmitting mode. The amplifier 84 may be linear, merely transferring a measure of the actual voltage stored on each of the capacitors Cι f ι through Cι. n , or it may transfer a measurement of the ratio between the volt¬ age on each of the small capacitors Cι_ι through Cι. n and the voltage VREF from pin 87 over line 100 to the amplifier 84. This would have the advantage of relax¬ ing the required constancy of the voltage VREF, since the charge transferred to each small capacitor Cι,ι through Cι_ n can be made proportional to the voltage VREF' regardless of the absolute value of V EF. The data on data line 102 from the amplifier 84 may be supplied through pin 104 to an analog-to- digital converter in the master unit 16 for processing as previously described. The small capacitors Cι_ι through Cι fn can be of any low-leakage type sufficiently small to be included in the probe. The type considered optimal for the design would be MOS elements directly on the surface of an integrated circuit containing the MOS transistor switches ST, S^, and Si through S n . In addition, the switch sequencer circuit 86 and the amplifier 84 may be on the same integrated circuit chip. As previously mentioned, the capacitor CR has a value of 0.1 microfarads and the value for the small capacitors Cι f ι through Cι, n is typically 10 pico¬ farads. The capacitor CR supplies the source charge to be transferred to the individual small capacitors Cl,l through Ci- n . If there are ten nearly identical small capacitors, then even if each small capacitor was fully charged during the data collection opera¬ tion, the charge on the source capacitor CR would decrease by only about 0.1 percent in the typical case. The capacitor Cp is the power source for the switch sequencer circuit 86 and can be a fairly crude electrolytic or other high energy storage type, rated for about ten volts and having a capacity of 50 micro¬ farads, as previously mentioned. If the leakage of the switches Si through S n is not made small enough, but is predictable, the accuracy of the data can be preserved in two ways. First, the data sent by the switch sequencer circuit 86 may include the elapsed time following the measure¬ ment and before reconnection to the master unit 16. This elapsed time can be interpreted by programming in the master unit 16 to correct the data. Second, a controlled leak can be placed across the source capac¬ itor CR SO that its voltage will drop at a rate to compensate for the loss of the charge of the capaci¬ tors Ci-i through Cι /n through the switches Si through S n , as explained. If the amplifier measures the ratio of voltage on the small capacitors Ci i through Ci I1 to that on the capacitor CR, a more accurate tempera¬ ture measurement will result. Small capacitors Cι r ι through Cι_ n which are external to the switch sequencer circuit 86 may also be provided, thus allowing small capacitors of much larger value. In this case, a much larger capacitor CR is required. Also, the use of external small capacitors Cι f ι through ι f T1 requires more terminal pads on the integrated circuit of the switch sequencer circuit 86.

Claims: CLAIMS 1. An electronic thermometer including a temperature sensing means for sensing a temperature and providing over time a series of temperature relat¬ ed electric parameters, said temperature sensing means incorporating a resistive element (38) whose resis¬ tance varies as its temperature varies, and data storing means (52) for storing data representing said series of temperature related electric parameters, characterized by data transmitting means (50) having an output and connected to said data storing means for transmitting, upon command, data stored in said data storing means (52), connector means (26) connected to said output of said data transmitting means and adapt¬ ed to be connected to an associated power source and temperature display unit (16), said connector means having a command input (70) adapted to receive a command signal from said associated unit for command¬ ing said data transmitting means (50) to transmit data, and a data output (72) for providing thereon data transmitted by said data transmitting means, and electrical energy storage means (Cl, C2) electrically connected to said connector means (26), said energy storage means being adapted to receive and store electrical energy when said connector means (26) is connected to said associated unit, and being adapted to supply stored electrical energy to said temperature sensing means (38) and said data storing means (52) when said connector means is not connected to said associated unit. 2. An electronic thermometer according to claim 1, characterized in that said temperature sens¬ ing means comprises a bridge circuit (35-38) including a thermistor (38), and an analog-to-digital converter (40) for converting the voltage across said bridge to a digital representation. 3. An electronic thermometer according to claim 2, characterized by processing means (48) con¬ nected to said analog-to-digital converter (40), and a random access memory device (52) which forms said data storing means and which is connected to said process¬ ing means, said processing means being arranged to receive periodic digital representations of the volt¬ age across said bridge circuit and to store them in said random access memory device. 4. An electronic thermometer according to claim 3, characterized in that said data transmitting means (50) comprises a universal asynchronous receiver transmitter (UART) connected to said processing means (48), said UART being arranged to receive the digital representations of the voltages across said bridge circuit (35-38) in parallel fashion, and to transmit * them in serial fashion on said data output (72) of said connector means (26). 5. An electronic thermometer according to either claim 3 or claim 4, characterized by visual indicating means (68) connected to said processing means (48) for providing a visual indication of the receipt and storage by said processing means of a set number of periodic digital representations of the voltages across said bridge circuit (35-38). 6. An electronic thermometer according to any one of the preceding claims, characterized in that said electrical energy storage means are formed by capacitor means (Cl, C2). 7. An electronic thermometer according to claim 1, characterized in that said data storing means comprises a plurality of storage capacitors (Cι_ι- c l,n) each being arranged to receive an electrical charge transferred through said resistive element (80) as an indication of the temperature of said element at the time the electrical charge was transferred there¬ through, a plurality of corresponding switches (Sι~ S n ), and switch control means (86) for controlling the closing of said plurality of switches such that an electrical charge is transferred through said resis¬ tive element to each of said storage capacitors in a set order. 8. An electronic thermometer according to claim 7, characterized in that said electrical energy storage means includes a source capacitor (CR) for storing the electrical charge to be transferred to each of said storage capacitors (Cι / ι-Cι. n ), and a further switch (S ) connected between said source capacitor (CR) and said plurality of switches (Sι-S n ), said further switch being arranged to close for a set length of time and to provide, when closed, for the transfer of the electrical charge through said resis¬ tive element (80) to said storage capacitors. 9. An electronic thermometer according to either claim 7 or claim 8, characterized in that said data transmitting means includes amplifier means (84) arranged to transmit data representing the charge stored by each of said storage capacitors (Cι f ι-Cι fI ) to said data output (72) of said connector means (26). 10. An electronic thermometer according to claim 9, characterized by amplifier switch means (S&) connected between said amplifier means (84) and said plurality of switches (Sι-S n ) and controlled such that, upon the receipt of said command signal by said command input (70), said amplifier switch closes, said switch control means (86) being arranged to control the closing of said plurality of switches (Sι~ - 16 - S n ) such that the electrical charges stored on the corresponding ones of said storage capacitors (Cι_ι- c l,n) are transferred to said amplifier means in a set order.

Inventors: PACKARD ROGER ERWIN, THOMAS JACOB EARL, PACKARD, ROGER, ERWIN, THOMAS, JACOB, EARL
Applicants: NCR CO, NCR CORPORATION
Application year: 1986
Main classification: G01K1
IPC codes: G01K1, G01K7, G01K13