JPH0531416B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field] The present invention relates to a temperature measuring device. For more information, see Sensing and monitoring of specimens in medical circulation circuits,
Or it relates to a temperature measuring device used for sensing and monitoring in a living body. [Prior Art] In the clinical and medical fields, continuous measurement and continuous monitoring of ion concentrations, biological substance concentrations, etc. are desired. Also, awareness of continuous monitoring is increasing in general medical care.
Currently, continuous monitoring systems have not reached practical use. One of the reasons for this is that when monitoring for a long time, temperature fluctuations occur and affect measurement accuracy, making high-precision monitoring difficult. That is, in order to continuously measure highly accurate biological information, temperature measurement and temperature compensation based on the measured temperature need to be performed accurately and quickly. In particular, temperature measurement requires accuracy within ±0.01°C. However, conventional simple thermistor thermometers measure temperature by connecting a fixed resistor in series with the thermistor element to form a linearization circuit, which limits the accuracy to ±0.5°C. Purpose of the Invention The purpose of the present invention is to solve the problems of the prior art described above, and to accurately measure the temperature of a subject and measuring device in a medical circulation circuit and a fluid solution using biological fluids and biologically related solutions in real time. The object of the present invention is to provide a temperature measuring device that measures temperature. In particular, it is an object of the present invention to provide a temperature measuring device that measures temperature with an accuracy within ±0.01°C. Another object of the present invention is to provide a temperature measuring device whose temperature measuring section can be inserted into a living body. Another object of the present invention is to provide a temperature measuring device with small measurement errors due to self-heating. Structure of the Invention The temperature measuring device of the present invention that achieves the above object has the following features:
A thermistor element with a diameter of 1 mm or less, a constant current source that flows a constant current of 50 microamperes or less through the thermistor element, or a constant current source that reduces the power consumption of the thermistor element to 50 μW or less, and the thermistor element. and temperature determining means for determining the temperature by repeated calculation processing based on the resistance value of the temperature. DETAILED DESCRIPTION AND OPERATIONS OF THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 shows a block diagram of a biological information measuring device according to an embodiment of the present invention, which is composed of an input device 1, an interface 2, and an arithmetic processing device 3. is connected to the interface 2 by optical fiber cable 4.
and the arithmetic processing unit 3 are connected by an (electrical) cable 5. The processing results of the arithmetic processing device 3 are output to a display device 6 and a recording device 7. Conventionally, the input device 1 and the interface 2 were integrated, and the output part of the measurement data was isolated using a photocoupler, etc., but if the input impedance of the input device 1 is high, further insulation is required. The need arose. However, in this embodiment, the input device 1
has become smaller and uses primary or secondary batteries,
Furthermore, since the output signal is converted into an optical signal and transmitted through the optical fiber cable 4, high isolation can be ensured. This reduces noise superposition through the ground circuit and power supply, making highly accurate measurements possible. It has also become easier to measure and monitor remotely. The input device 1 measures one or more sensor outputs (electromotive force, current, resistance value, etc.). The measured value is
After performing AD conversion, the measurement data is converted into an optical signal and transferred to the interface 2 through the optical cable 4. When a single optical cable is used to transfer this measurement data, multiple sensor outputs can be transferred by a time division method. Further, a plurality of optical cables may be used. One aspect of the input device 1 includes a high input resistance voltmeter for measuring the electromotive force of the ion sensor, a temperature sensor for internal compensation of the sensor, and an output (resistance) of the temperature sensor for measuring the temperature inside the solution. By configuring it with a measuring circuit, it is possible to perform highly accurate ion concentration sensing that compensates for the effects of temperature fluctuations. FIG. 2 is a more detailed block diagram of the biological information measuring device of this embodiment. The input device 1a is an input device for measuring ion gas and enzyme concentration, and includes a high input resistance voltmeter 11 for measuring electromotive force, internal temperature measurement and solution temperature so that temperature measurement for internal compensation can be performed simultaneously. Thermometers 12 and 13 for measurement, and AD converters 13 and 1 for digitally converting their respective outputs.
4 and 15, a multiplexer 16 for selecting an AD-converted value, and an optical transmission circuit 17 for converting the digital value into an optical signal and transmitting it. The power supply has one for isolation from ground and commercial power.
A second battery was used. FIG. 3 is used as a high input resistance voltmeter for measuring electromotive force. This is an example of a high input resistance differential amplifier for an ion sensor. High input resistance voltmeter 11
is a high input impedance (10 ¹¹ Ω or higher), low drift (2 μV/°C or lower) differential amplifier with a commercially available operational amplifier (for example, Burr-Brown).
ODA111BM, manufactured by Texas Instruments
TLC-27L2) was used. AD converter 1
3, 14, and 15 used a double-integration type 41/2-digit AD converter (ICL7135CPI manufactured by Intersil).
The multiplexer 16 and digital circuitry use CMOS logic ICs to reduce current consumption.
The AD converters 13, 14, and 15 are started at the same time approximately every 400 ms, and a header character is added to each output value for serial conversion. FIG. 4 is an example of a temperature measurement circuit. For thermometers 12 and 13, high precision constant current sources were fabricated using commercially available operational amplifiers. This constant current source is preferably set to 70 μA or less, particularly preferably 10 to 50 μA. As a constant current source, a circuit may be provided so that the power consumption of the temperature sensor (thermistor) element is 50 μW or less. In this case, it is possible to set the power consumption of the temperature sensor (thermistor) element to 20 μW. preferable. The voltage when the constant current was passed through the temperature sensor (thermistor) was measured by the AD converter 14 or 15. During instrument calibration,
A signal indicating this is generated from the switch 27 and communicated from the multiplexer 16 to the interface 2. Now, in order to continuously measure highly accurate biological information with a biological information measuring device to which the temperature measuring device of this embodiment is applied, temperature measurement and temperature compensation using the measured temperature must be performed accurately and quickly. There is. In particular, temperature measurement requires accuracy within ±0.01°C. Therefore, for temperature measurement in this example, a thermistor was used instead of a thermocouple or platinum resistor, which requires a high-performance device with a small output voltage value. In addition, the thermistor is a small thermistor inserted into an insulating tube, taking into consideration its insertion into a living body.In order to reduce errors caused by self-heating, in this example, the constant current value flowing through the thermistor is set to 50 μA. It was set to However, in conventional simple thermistor thermometers, a fixed resistor is connected in series with the thermistor element to form a linearization circuit to measure temperature, so the accuracy is limited to ±0.5°C.
This is determined by the temperature T from the resistance value R (Ω) of the thermistor.
This can be understood from the following formula for calculating ( ⁰ K). 1/T-1/T ₀ = 1/Bln (R/R ₀ ) Here, the resistance value at temperature T ₀ ( ⁰ K) is R ₀
(Ω) is the standard. Also, B has a very narrow temperature range (e.g. ±2℃)
Although it can be considered a constant, it is actually a function of temperature. Therefore, a wide temperature range (e.g. 0 to 50℃)
As mentioned above, the linearization circuit cannot perform highly accurate measurements. B can be expressed as follows in the temperature range T ₀ to T ₁ ( ⁰ K). B=B ₀ +C(X-X ₀ )+E・T ₀ (T-T ₁ ) +F・T ₀ (T-T ₀ )(T+T ₀ +T ₁ ) However, X=ln(T/T ₀ )/1 /T ₀ -1/T B ₀ , C, X ₀ , E, F are constants,
This is a physical property value related to the composition of the thermistor. In this embodiment, the resistance value from the thermistor is converted into a decimal value by AD converters 14, 15, and 22,
The temperature is sent to the arithmetic processing unit 3 via the optical fiber cable 4, interface 2, and cable 5, and the temperature is calculated quickly and accurately in the arithmetic processing unit 3 according to a calculation program to be described later. The input device 1b is an input device for measuring O ₂ concentration by measuring, for example, a polarographic electrolytic current of O ₂ and includes a microammeter 18, a thermometer 19 for temperature measurement, and AD converters 20, 21. , a multiplexer 22 and an optical transmission circuit 23. The microammeter 18 was composed of a constant voltage source of -0.5V to -0.7V and a circuit that converts a microcurrent of 10 ^-6 to ^{10 -11} A into voltage. FIG. 5 shows an example of a polarographic microcurrent measuring circuit. Other thermometers 19
The AD converters 20 and 21, the multiplexer 22, and the optical transmission circuit 23 are the same as those in the input device 1a. The interface 2 converts the optical signal from the input device 1 into an electrical signal using an optical receiving circuit 24 having a plurality of input channels (for example, 5 channels), and then converts the signal data of the channel selected by the multiplexer 25 into an I/O signal. It is transmitted to the arithmetic processing unit 3 through the O interface 26. After the signal data is converted into density units by the arithmetic processing unit 3, it is output to the display device 6 and the recording device 7. In addition to outputting the information to the display device 6 and the recording device 7, it may also be stored in a storage device so that it can be read out at any time.
The measurement data received from the input device 1 may be directly sent to the arithmetic processing device 3, but the interface 2 includes a RAM 320, and the measurement data is organized by a program stored in the ROM 321 and temporarily stored. If you do this, the arithmetic processing unit 3
This reduces the burden on people. Multiplexer 25 is 8
The bit CPU is used to convert the received data into character and numerical codes, which are stored for each channel.
Data is transferred in response to a data request from the O interface 26. I/O interface 26
The IEEE-488 bus interface was used for
General-purpose RS-232C or the like can also be used. The arithmetic processing unit 3 includes a CPU 331, a ROM 332 for storing processing programs, and an auxiliary RAM 333.
It is converted into units of ion concentration and gas partial pressure (concentration) by calculation according to a calibration curve created in advance. Additionally, the sensor temperature can be used to compensate for temperature fluctuations in the sensor. As the arithmetic processing unit 3, a personal computer having an 8-bit CPU, a 16-bit CPU, etc. can be used. By assembling the interface 2 on a board, it can be built into an expansion slot of a personal computer. As the display device 6, a monitor device for a personal computer can be used. FIG. 6 shows a schematic diagram when the temperature measuring device of the embodiment is applied to a biological information measuring device. FIG. 7 is a flowchart of the control program of the arithmetic processing unit 3 stored in the ROM 332, and FIG. 8 a and b are
It is a flowchart of a control program for the interface 2 stored in the ROM 321. First, in step S71, the device is initialized. In step S72, an interrupt is generated to prompt the interface 2 to transmit measurement data, and in step S73, reception of measurement data from the interface 2 is awaited. On the other hand, the interface 2 normally scans and receives measurement data from the input device 1 in accordance with the procedure shown in FIG. 8a. Wait for reception of measurement data from input device 1 in step S101, and then proceed to step S101.
In step S102, different storage addresses are set depending on the connection position of the input device 1, and in step S103, each input device 1 is stored in the storage area of the RAM 320. Steps S101 to S103 are repeated to sequentially scan all the input devices 1 and store the measured data.
Although different storage addresses are set depending on the connection position to distinguish the difference in the biometric information to be measured, the measurement data from the input device 1 may include an identification code for identifying the type of biometric information. This way,
Since the type of biometric information can be identified without considering the connection location, the degree of freedom in control is increased. When there is an interruption prompting the transmission of measurement data from the arithmetic processing unit 3, processing is performed according to the procedure shown in FIG. 8b. First, in step S104, the measurement data stored in step S103 of the normal procedure is read out and transmitted to the arithmetic processing unit 3 in step S105.
In step S106, it is determined whether all measurement data have been transmitted. If not, the process returns to step S104 and steps S104 to S106 are repeated. On the arithmetic processing unit 3 side, the steps S104 to
The measurement data transmitted in step S74 is received and stored in the RAM 333. Next, step
Different analyzes are performed depending on the type of measurement data stored in steps S75, S84, etc. Note that only typical ion sensors and gas sensors will be explained here. Other biometric information is processed in the same manner. In the case of an ion sensor, the process goes from step S75 to step S76, and the temperature at the time of ion measurement is calculated from the temperature measurement data from the same input device as the ion sensor. In step S77, it is determined whether or not PH is to be measured. If PH is to be measured, the PH value is calculated from the measured data in step S78, and in step S79, the PH value is calculated from the measured data.
Correct the PH value based on the temperature calculated in
The corrected PH value is stored in step S80. If it is determined in step S77 that PH measurement is not being performed, the process goes to steps S81 to S83, where the ion concentration of other ions is calculated, temperature compensated, and stored. For gas sensors, proceed from step S84.
Proceeding to S85, the temperature measured by the gas sensor is calculated from the temperature measurement data of the same input device in step S85, and the gas temperature is calculated in steps S86 to S88, temperature compensated, and stored. In step S89, various memorized measurement results are arranged according to the output format of the display device 6 and storage device 7, and in step S90, the various measurement results stored in the display device 6 and storage device 7 are arranged.
output to the output device. Determine whether the measurement is finished in step S91, and if it is not finished, proceed to step S91 again.
Repeat S71 to S91 and output the measurement results at the next point in time. Incidentally, even if the measurement results are output at a fixed timing, various controls such as outputting the measurement results when predetermined biological information exceeds a permissible value can be performed. Next, a flowchart for calculating the measured temperature in steps S76, S85, etc. is shown in FIG. Here, m is the number of counters, and m is the number of repetitions of calculation related to calculation accuracy. First, in step S91, m=0,
Set a predetermined number to constants T ₀ , T ₁ , B ₀ , R ₀ , X ₀ ,
Set C, E, F. Next, in step S92,
In step S74, the thermistor resistance value R received and stored from the interface 2 is read out along with other measured values. In step S93, T is calculated based on R from T=1/[{l _o (R/R ₀ )}/B ₀ +1/T ₀ ], and in step S94, T is calculated based on T calculated in step S93. , X=(l _o (T/T ₀ )}/(1/T ₀ -1/T)
Based _on T _{calculated in step S94 and} B is calculated from T+T ₀ +T ₁ ). Step S96
A new T is calculated based on T calculated in S93 and B calculated in step S95. m in step S97

[Table] It was found that an accuracy of 1/100°C was already obtained in the first calculation loop. Also, for comparison, the values measured with D632 agree well with a difference of 0.002°C, and high-accuracy and rapid temperature measurement is possible (measurement time is 100 msec or less). Similar results were obtained using a constant current source that reduces the power consumption of the thermistor element to 20 μW or less. (Experimental Example 2) Using the system shown in FIGS. 1 and 2, ion concentration measurement and temperature measurement were performed simultaneously to perform temperature-compensated ion concentration measurement. The input device 1a includes a high input resistance voltage type 11 for measuring ion concentration, a temperature measuring circuit 12 similar to that in Experimental Example 1,
13, the output of each of which passes through a multiplexer 16, and performs optical data communication with the interface 2 through the optical fiber 4 in a time division manner. The interface 2 is for inputting data to the arithmetic processing unit 3, and is for inputting data to the arithmetic processing unit 3.
Used IB interface. Arithmetic processing unit 3
A personal computer, NEC PC-9801VM4 manufactured by NEC Corporation, was used. In an ion-selective electrode, the ion concentration [Ion] and the electromotive force E generally follow the Nernst equation, and for cations, E=E ⁰ +RT/ _nFlo [Ion] [Ion]=exp{nF/RT(E-E ⁰ )} Therefore, if temperature T and electromotive force E can be measured, highly accurate ion concentration measurement is possible without being affected by temperature changes. As a specific example, continuous measurement of hydrogen ion concentration will be described. Measure the potential difference E of the PH sensor in buffer solutions of three known temperatures and PH, and calculate the coefficient a of the calibration formula E=a・T+b・T・PH+C…(1) (where T: absolute temperature), Calculate b and c and create a calibration formula. Next, a PH sensor and a thermistor are set in the circulating standard serum (manufactured by Prechireham Boehringer Mannheim). The potential difference E of the PH sensor and the temperature T (=θ+273.15) of the thermistor are input to the input device 1a, the multiplexer 16, the optical fiber 4,
It is input to the arithmetic processing unit 3 through the interface 2, and the PH value of the circulating fluid is calculated from equation (1). As shown in Figure 10, the results show that even if the circulating fluid temperature θ changes,
It was found that PH values can be measured with high accuracy. The + mark in the figure indicates a commercially available PH sensor (manufactured by Radiometer).
This is the value measured using ABL3). As described above, according to the present invention, a small thermistor (diameter of 1 mm or less, more preferably 0.6 mm or less) is used for temperature setting and temperature compensation, so it has a small heat capacity and can respond quickly to temperature changes. respond. In addition, ion sensors, gas sensors,
Alternatively, since it can be stored and used inside the enzyme sensor, temperature compensation can be performed with high accuracy. Because the thermistor uses a constant power source that only flows a current of 50 μA or less, or a constant current source that consumes less than 20 μW, the self-heating caused by the thermistor itself can be ignored, making it possible to measure resistance with high precision, which means temperature measurement. is possible. By repeatedly calculating and processing this resistance value using a computer at high speed, it is possible to quickly and accurately convert the resistance value into temperature even in a system that changes continuously. and,
Using this temperature, it is possible to accurately compensate the temperature of the ion sensor or gas sensor. Specific Effects of the Invention According to the present invention, it is possible to provide a temperature measuring device that accurately measures the temperature of a subject and a measuring device in a medical circulation circuit using a biological fluid and a biologically related solution and in a fluid solution in real time. In particular, it is possible to provide a temperature measuring device that measures temperature with an accuracy within ±0.01°C. Furthermore, it is possible to provide a temperature measuring device whose temperature measuring section can be inserted into a living body. Furthermore, it is possible to provide a temperature measuring device with small measurement errors due to self-heating.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of the biological information measuring device of the embodiment, FIG. 2 is a more detailed block diagram of the biological information measuring device of the embodiment, and FIG. 3 is an example diagram of a high input resistance differential amplifier for an ion sensor. FIG. 4 is an example diagram of a temperature measurement circuit, FIG. 5 is an example diagram of a polarographic microcurrent measurement circuit, FIG. 6 is a schematic diagram of the biological information measuring device of the embodiment, and FIG. 7 is a control of the arithmetic processing unit 3. Flowchart of the program; FIGS. 8a and 8b are flowcharts of the control program of the interface 2; FIG. 9 is a flowchart of the program for calculating the measured temperature; FIG. 10 is the temperature value measured by the biological information measuring device of the embodiment. FIG. 3 is a diagram showing measurement results of temperature-compensated PH values. In the figure, 1, 1a, 1b...input device, 2...interface, 3...arithmetic processing unit, 4...optical fiber cable, 5...cable, 6...display device, 7...recording device, 12, 13, 19...temperature Total, 14, 15,
22...A/D converter, 331...CPU, 332...
ROM, 333...RAM.

Claims (1)

[Claims] 1. A thermistor element with a diameter of 1 mm or less, a constant current source that flows a constant current of 50 microamperes or less through the thermistor element, or a constant current source that reduces the power consumption of the thermistor element to 50 μW or less, and the above-mentioned What is claimed is: 1. A temperature measuring device comprising: temperature determining means for determining the temperature by repeated calculation processing based on the resistance value of the thermistor element.