JP2005342376A - Infrared ray clinical thermometer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an infrared ray clinical thermometer which can cancel a violent change in atmospheric temperature and a disturbing influence from the front side of a sensor to allow accurate determination of temperature, is easy to handle, and can be manufactured at a lower price. <P>SOLUTION: The infrared ray clinical thermometer comprises the sensor consisting of a thermopile and a thermistor, a heater for heating the back of the sensor, a thermopile output measurement AD converting circuit for converting the analog output signal of the thermopile to the digital signal, a thermistor temperature measurement AD converting circuit for converting the analog signal of the thermistor to the digital signal, a heating control circuit for heating by the heater, and a microcontroller for controlling each of the circuits to operate and displaying and/or outputting the temperature of an subject to determine, wherein the microcontroller detects a point where the heater heats the sensor to have a thermopile output of zero and measures the thermistor temperature at the point to determine the temperature of the subject. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a thermometer that measures the surface temperature of a human body with or without contact with the tip of a thermometer, and in particular, the temperature of the eardrum is measured by inserting a probe tip into an ear hole, referred to as an ear-type thermometer. The present invention relates to a non-contact infrared thermometer.

  Infrared thermometers that use a thermopile as a sensor can be broadly classified into a non-heating type and a heating type. In any type, there is a possibility that the output greatly fluctuates or exhibits abnormal output characteristics due to a sudden change in ambient temperature or exposure (when it is directed to a high-temperature measurement object for a long time).

For this reason, in the non-heating type infrared thermometer, the following countermeasures are taken as countermeasures against a sudden change in ambient temperature and beating.
(1) The sensor is covered with a metal frame so that it is not directly affected by sudden temperature changes or beatings.
(2) To alleviate the effects of sudden temperature changes and beatings, keep the distance between the sensor and the object to be measured, and attach a metal pipe as thin as possible in front of the sensor.
(3) By making the lead wire of the sensor as thin or thin as possible, the heat conduction of the lead wire does not affect the sensor.

  In detail, the infrared absorber of the thermopile (the part where the infrared absorbing film and the hot junction are integrated) absorbs the infrared rays from the measurement object, and the temperature rises, but the thermopile can head also becomes an infrared absorber. In contrast, infrared rays are emitted. In normal usage, the wall surface of the can can be regarded as the same temperature as the thermopile itself, but if a sudden temperature change is applied from the outside, a temperature difference occurs between the head of the can and the sensor part, The thermopile output becomes transiently unstable and outputs an unnecessary voltage. As a measure against such a sudden temperature change from the outside, the thermopile is installed in a metal holder (sensor frame) with good thermal conductivity so that the temperature change is uniformly and slowly applied to the thermopile, and air is used as a heat insulator. -It is configured to be surrounded by plastic (probe). In addition, a metal tube plated with gold so that the emissivity is as low as possible is provided on the front surface of the thermopile to reduce the influence of thermal radiation from the measurement target (human body).

  Semiconductor sensors and thermistors are used as cold junction (waveguide) temperature compensation sensors, but thermistors are overwhelmingly used because of their low production costs and high accuracy. If the thermal coupling between the thermopile cold junction and the thermistor is poor, there will be a temperature difference between the cold junction and the thermistor, making accurate measurement impossible. For this reason, by installing the thermistor and the thermopile in the same can, the thermal coupling degree between the thermopile cold junction and the thermistor is increased. It is an effective method that both thermistor and thermopile can be arranged closer to each other by downsizing. However, even with the same standard thermistor, the B constant (a constant representing the magnitude of the change in resistance value obtained from the temperature at any two points in the resistance temperature characteristic) varies, so it is difficult to maintain accuracy over a wide environmental temperature range. However, it is not enough for measuring body temperature. In addition, the non-heating type infrared thermometer with such countermeasures cannot be attached to the probe tip, and the structure thereof becomes complicated, resulting in high cost.

On the other hand, in the heating type infrared thermometer, the following measures are taken as a measure against a sudden change in ambient temperature and a beating.
(1) The entire sensor package is heated to increase the stability against temperature changes.
(2) Use a material with good thermal conductivity for the sensor package.
(3) A structure in which the heat of the heater can be uniformly distributed over the entire package.

The measurement accuracy of the heating-type infrared thermometer with such measures is high. However, since a large amount of electric power is required to heat the entire package and heating time is required, there is a problem that the time required for measurement becomes long. Moreover, when using as a thermometer, with heating power large, you have to consider the safety | security with respect to a human body at the time of abnormal operation | movement, and has become a hindrance in productization.
http://www.healthcare.omron.co.jp/medical/pdf/thermometer_2001_01.pdf

  The present invention provides an infrared thermometer that can accurately measure the temperature by canceling out the influence of the drowning against the sudden change in ambient temperature and the blurring from the front of the sensor, and is easy to handle and can be manufactured at a lower cost. To do.

  The infrared thermometer according to the present invention is a sensor comprising a thermopile and a thermistor for measuring the temperature of the cold junction of the thermopile, a heater for heating the back of the sensor, and an analog output signal from the thermopile of the sensor. Thermopile output measurement AD conversion circuit for converting to a signal, thermistor temperature of the sensor is measured, thermistor temperature measurement AD conversion circuit for converting the analog signal indicating the thermistor temperature into a digital signal, and heating by the heater A heating control circuit for controlling, and a microcontroller (MCU) for controlling the operation of each of the above-mentioned circuits and displaying and / or outputting the temperature to be measured based on a digital signal from a thermistor temperature measurement AD conversion circuit It consists of.

  The microcontroller detects the point where the thermopile output becomes zero by heating the sensor with a heater, and determines the temperature to be measured by measuring the thermistor temperature at that time, or the sensor is heated by the heater. Then, a point at which the thermistor temperature change becomes stable is detected, and the temperature of the measurement object is determined by measuring the thermistor temperature and the thermopile output at that time.

  The infrared thermometer according to the present invention also includes a thermistor temperature measurement AD conversion circuit comprising an analog switch controlled by a microcontroller, a CR time constant circuit, and a switching transistor for controlling charging and discharging of a capacitor of the CR time constant circuit. It can also be configured. The common contact of the analog switch is connected to the capacitor of the CR time constant circuit. Each contact point of the analog switch is a sensor thermistor that constitutes a resistor for the CR time constant circuit, a first reference resistor having a resistance value smaller than the resistance value of the thermistor, and a resistance value larger than the resistance value of the thermistor. Are respectively connected to the second reference resistors. The microcontroller connects the analog switch to each contact sequentially, while turning on and off the switching transistor at each connection to measure the discharge time of the capacitor, and by calculating the resistance value of the thermistor based on each measured value Determine the temperature to be measured.

  The infrared thermometer according to the present invention further includes an analog switch controlled by a microcontroller, a CR time constant circuit, one input terminal connected to a common contact of the analog switch, and the other input terminal to a CR time constant circuit. A thermopile output measurement AD conversion circuit can also be configured by a connected comparator and a switching transistor for controlling charging and discharging of the capacitor of the CR time constant circuit. The thermopile output of the sensor, the voltage at the time of thermopile output 0, and the voltage at the time of maximum thermopile output are applied to each contact of the analog switch. The microcontroller connects the analog switch to each contact in sequence, and at the time of each connection, turns on and off the switching transistor to measure the capacitor charging time and calculates the thermopile output value based on each measured value. Determine the target temperature.

  The infrared thermometer of the present invention configured as described above is basically used in two types of measurement methods, a continuous measurement method and a short-time measurement method.

1. Continuous measurement method This measurement method inserts a sensor into the ear canal for a long time and continuously measures the eardrum temperature. The microcontroller operates the AD conversion circuit of the thermopile circuit and continuously measures the infrared sensor output. Based on the measured infrared sensor output, the duty ratio of the timer output of the heating control circuit is varied to control the thermopile output to be always zero. On the other hand, the thermistor temperature in the infrared sensor is measured by operating the AD conversion circuit of the thermistor circuit. When the thermopile output becomes zero, there is no temperature difference between the sensor and the measurement target, and the thermistor temperature reaches a stable state, so that it can be read as the measurement target temperature. The measured thermistor temperature is displayed on the display or output as external output data.

2. Short-time measurement method This measurement method is a type that holds the value measured by the measurement button after turning on the infrared thermometer, or holds the temperature automatically measured after the thermometer is turned on. Applies to type ones. When the power is turned on, the microcontroller starts the temperature measurement of the infrared sensor by operating the AD conversion circuit of the thermistor circuit. When the thermistor temperature is extremely lower than the assumed temperature to be measured, the sensor pre-heating is started immediately, and for example, the sensor is heated so that the difference between the temperature to be measured and the temperature in the sensor is within 10 ° C.

  The operation of the microcontroller will be described. At the start of measurement, the microcontroller measures the thermistor temperature and thermopile output to determine the sensor heating status. If it is determined that the sensor is heated heavily, the microcontroller performs heating control by changing the duty ratio of the timer output of the heating control circuit, and obtains the temperature to be measured from the thermistor temperature and the thermopile output.

  A method that has been used for a long time as a method of AD converting the thermistor temperature and taking it into the MCU as a digital numerical value has been to oscillate the thermistor as part of the CR oscillation circuit and read the oscillation frequency into the microcontroller. Although this method has a merit that the number of effective bits of conversion data can be increased with a simple circuit, it has a disadvantage that it takes time to count. For this reason, the thermistor temperature measurement AD converter circuit of the present invention enables high-accuracy conversion in a short time measurement, and the voltage is brought to the threshold level of the microcontroller port while discharging the capacitor of the CR time constant circuit. The time to reach is measured, and the time is used as the AD conversion value of the thermistor temperature. The threshold level of the microcontroller port depends on the power supply voltage of the MCU.

  On the other hand, the thermopile output measurement AD conversion circuit according to the present invention measures the time until the voltage reaches the voltage to be measured while charging the capacitor of the CR time constant circuit, and uses the time as the AD conversion value of the thermopile output.

Countermeasures for thermistor temperature range The infrared thermometer of the present invention responds to the exposure from the front of the sensor approaching the temperature to be measured by heating from the back. The thermistor temperature of the sensor attached to the front face of the probe approaches the temperature to be measured due to the blow from the front face. At this time, the thermistor temperature further approaches the measurement target temperature by heating the sensor from the back surface. As a result, the temperature measurement range of the thermistor is limited to a narrow range, and the measurement error factor by the thermistor can be reduced.

Environmental temperature countermeasures and environmental temperature change countermeasures In order to realize a highly accurate body temperature measurement infrared thermometer that reduces the change in reading due to the influence of the environment temperature and has little error due to the environment temperature change, the infrared thermometer of the present invention is By heating the sensor from the back side against the blow from the sensor, the sensor temperature approaches the measurement target temperature, and the influence of the environmental temperature and the influence of the environmental temperature change can be drastically reduced.

Anti- blurring thermopile output and thermistor output from the front of the sensor are monitored, and the overburst (heating by infrared rays and heat conduction) received by the thermopile is measured. Heat is applied to the heating element attached to the back of the thermopile sensor. As a guideline for heating, it is preferable that the difference (relative temperature) between the measurement object and the thermistor temperature is within 10 ° C. The temperature change of the thermistor is kept within a certain value (range in which the thermopile does not cause a large error) (stable state), and the temperature (body temperature) of the measurement object is obtained from the thermistor temperature and thermopile output in the stable state. Accordingly, by heating the sensor from the back side against the blow from the front side, the influence from the front side is canceled from the back side, and the influence on the blow can be greatly reduced. Instead of keeping the thermistor temperature in a stable state, heating is performed until the thermopile output becomes zero, and the temperature to be measured can be obtained from the thermistor temperature at that time.

  1 to 4, an infrared thermometer according to an embodiment of the present invention includes a sensor 10 including a thermopile TH1 and a thermistor R1 for measuring the temperature of the cold junction of the thermopile TH1, and a back surface of the sensor 10. A heater 20 for heating, a thermopile output measurement AD conversion circuit 30 for converting an analog output signal from the thermopile TH1 of the sensor into a digital signal, and a thermistor temperature of the sensor (actually, the resistance value of the thermistor R1) Thermistor temperature measurement AD conversion circuit 40 for measuring and converting an analog signal indicating the thermistor temperature into a digital signal, a heating control circuit 50 for controlling heating by the heater 20 of the sensor, and the operation of each of the above circuits Control and digital signal from thermistor temperature measurement AD converter circuit 40 Composed of the microcontroller 60. for displaying and / or outputting a measured temperature based on the signal. What is indicated by reference numeral 70 is a display or an externally connected device for displaying and / or recording the temperature to be measured.

  As shown in FIG. 2, the thermopile output measurement AD converter circuit 30 includes an analog switch 31 controlled by a microcontroller 60, a CR time constant circuit composed of a resistor R2 and a capacitor C1, and an analog switch connected to one input terminal. 31 is connected to the common contact Ptm via the operational amplifier OP1, and the other input terminal is connected to the CR time constant circuit. The comparator CMP1 is connected to the CR time constant circuit and the switching transistor for controlling the charging and discharging of the capacitor C1. Q1. At the three contacts P1 and P2 of the analog switch 31, the voltage V1 at the thermopile output 0 of the sensor obtained by dividing the reference voltage Vref generated by the constant voltage diode Dref by the resistors R3, R4 and R5 and the thermopile The maximum output voltage V2 is applied, and the thermopile TH1 is connected to the contact P3, and the thermopile output voltage V3 is applied.

  As shown in FIG. 3, the thermistor temperature measurement AD conversion circuit 40 includes an analog switch 41 controlled by a microcontroller 60, a CR time constant circuit including a thermistor R1 or a resistor R7 or R8, and a capacitor C2, and a CR And a switching transistor Q2 for controlling charging / discharging of the capacitor C2 of the time constant circuit. The common contact Pth of the analog switch 41 is connected to the capacitor C2 of the CR time constant circuit. The three contacts P4, P5, and P6 of the analog switch have a sensor thermistor R1, a first reference resistor R7 having a resistance value smaller than the resistance value of the thermistor R1, and a resistance value larger than the resistance value of the thermistor. 2 is connected to the reference resistor R8. The capacitor C2 can also be connected to a position as indicated by a dotted line.

  As shown in FIG. 4, the heater 20 includes a diode D <b> 1 installed on the back surface of the sensor 10. The heating control circuit 50 is configured by a switching transistor Q3 for turning on / off energization to the diode D1 serving as a heater. The switching transistor Q3 is controlled by a pulse sent from the microcontroller 60.

  Next, the control relationship of each circuit performed by the microcontroller 60 will be described.

Thermistor Temperature Calibration Cycle FIG. 5 is a diagram for explaining the operation of the thermistor temperature measurement AD conversion circuit 40. While the analog switch 41 is connected to the contact P4 (first reference resistor R7), the switching transistor Q2 is turned on to discharge the capacitor C2. Due to the discharge of the capacitor C2, the voltage VA at the point A rises, becomes higher than the high level input voltage of the port of the microcontroller 60, and finally rises to almost the power supply voltage Vcc. When the discharge of the capacitor C2 is completed, the switching transistor Q2 is turned off and at the same time a timer in the microcontroller 60 is started. While the capacitor C2 is charged by the first reference resistor R7, VA decreases and becomes equal to or lower than the high level input voltage of the port of the microcontroller 60. When the threshold level of the microcontroller input port is reached, the microcontroller 60 timer is automatically stopped. When the timer of the microcontroller 60 is stopped, the microcontroller 60 is interrupted, the count value of the timer is read, and the count value is set to 1.

  Similarly, the analog switch is set to the position P5, the switching transistor Q2 is turned on, and the capacitor C2 is discharged by the second reference resistor R8. The timer in the microcontroller 60 is started simultaneously with turning off the switching transistor Q2. As the capacitor C2 is charged, the voltage VA at the point A decreases, reaches the threshold level of the port of the microcontroller 60, and automatically stops the timer of the microcontroller 60. When the timer of the microcontroller 60 is stopped, the microcontroller 60 is interrupted to read the count value of the timer and set the value as the count value 2.

Thermistor temperature measurement cycle Next, the analog switch is set to the position P6. The switching transistor Q2 is turned on to discharge the capacitor C2. The timer in the microcontroller 60 is started simultaneously with turning off the switching transistor Q2. As the capacitor C2 is charged, the voltage at the point A drops, reaches the threshold level of the port of the microcontroller 60, and automatically stops the timer of the microcontroller 60. When the timer of the microcontroller 60 is stopped, the microcontroller 60 is interrupted and the count value of the timer is read. The value is set to a count value 3. Thus, since the resistance values of the first and second reference resistors R7 and R8 and the capacitance of the capacitor C2 are known, the resistance value of the thermistor R1 in the sensor 10 is calculated from the values of the count value 1, the count value 2, and the count value 3. Can be requested. Here, it should be noted that the resistance value of the thermistor means the thermistor temperature.

  By including a calibration cycle when measuring the thermistor temperature, it is possible to eliminate error factors such as fluctuations in the measurement circuit voltage Vcc, fluctuations due to temperature changes in the capacitor C2, and threshold level fluctuations due to the temperature of the microcontroller 60 port. Accurate thermistor temperature measurement is possible with a timer count of 3 cycles.

Thermopile output calibration cycle FIG. 6 is a diagram for explaining the operation of the thermopile output measurement AD conversion circuit. When the analog switch 31 is connected to the contact P1, the voltage at the contact P1 is amplified by the operational amplifier OP1, and becomes the comparison target voltage / measured voltage (VC) of the comparator CMP1. When the switching transistor Q1 is turned on and the capacitor C1 is discharged, the other input voltage VB of the comparator CMP1 becomes 0V. When the discharge of the capacitor C1 is completed, the switching transistor Q1 is turned off, and at the same time, a timer in the microcontroller 60 is started. As the capacitor C1 is charged, the voltage VB rises and reaches the other input voltage level VC of the comparator CMP1, inverting the comparator output. The microcontroller timer is automatically stopped by reversing the microcontroller port input. The microcontroller is interrupted by stopping the timer of the microcontroller, the count value of the timer is read, and the value is set to the count value 4.

  Similarly, the analog switch 31 is set to the position of the contact P2, the switching transistor Q1 is turned on, and the capacitor C1 is discharged. A timer in the microcontroller is started simultaneously with turning off the switching transistor Q1. As the capacitor C1 is charged, the voltage VB rises, reaches the other input voltage level VC of the comparator CMP1, and inverts the comparator output. By reversing the port input of the microcontroller 60, the microcontroller timer is automatically stopped. Interrupt the microcontroller by stopping the timer of the microcontroller and read the count value of the timer. The value is set to a count value of 5.

Thermistor output measurement cycle The analog switch 31 is set to the position of the contact P3, the switching transistor Q1 is turned on, and the capacitor C1 is discharged. A timer in the microcontroller is started simultaneously with turning off the switching transistor Q1. As the capacitor C1 is charged, the voltage VB rises and reaches the other input voltage level VC of the comparator CMP1, inverting the comparator output. By reversing the port input of the microcontroller 60, the microcontroller timer is automatically stopped. When the timer of the microcontroller 60 is stopped, the microcontroller is interrupted and the count value of the timer is read. At this time, the values of the voltages V1 and V2 applied to the contacts P2 and P3 are accurate and stable values obtained by dividing the reference voltage Vref by the reference resistors R3, R4, and R5. The output of the operational amplifier OP1 can be obtained from the value of the count value 3, and the thermopile output of the sensor 10 can be obtained from the output of the operational amplifier OP1. The thermopile output of the sensor is converted to temperature inside the microcontroller.

  By including a calibration cycle when measuring thermopile output, fluctuation due to temperature change of capacitor C1, offset voltage fluctuation due to temperature of comparator CMP1, offset error of comparator CMP1, offset voltage fluctuation due to temperature of operational amplifier OP1, offset error of operational amplifier OP1, operational amplifier An error factor such as a gain (N) error of the amplifier circuit can be removed. For this reason, thermopile output measurement with high accuracy is possible with a timer count of 3 cycles including a calibration cycle.

  In the heating circuit 20, the timer output of the microcontroller 60 is connected to the base of the switching transistor Q3 via an integration circuit (resistor R9, capacitor C3). A diode D1 for sensor heating is connected to the emitter of the switching transistor Q3 via a resistor R10, and an emitter follower circuit in which the heating current increases as the base voltage of the switching transistor Q3 increases. By varying the duty ratio of the timer output of the microcontroller 60, the current flowing through the diode D1 can be precisely controlled. Although it is possible to control the heating of the diode D1 without passing through an integration circuit, it is preferable to integrate the timer output in order to prevent inadvertent noise from being mixed into the sensor circuit.

  The configuration proposed in the present invention can be applied not only to an infrared thermometer but also to various non-contact thermometers. In that case, it will be easily understood that various values such as a resistance value and a capacitance are changed to values according to the measurement object. Further, in the above description, the number of reference resistors in the thermopile output measurement AD conversion circuit 30 and the thermistor temperature measurement AD conversion circuit 40 is set to one value above and below the planned measurement value, but the number of reference resistors is increased. It will be readily understood that this can be configured to calculate more accurate measurements.

It is a block diagram of the infrared thermometer by the Example of this invention. It is a figure which shows the outline | summary of the thermopile output measurement AD conversion circuit in the infrared thermometer of this invention. It is a figure which shows the outline | summary of the thermistor temperature measurement AD conversion circuit in the infrared thermometer of this invention. It is a figure which shows the outline | summary of the heating circuit in the infrared thermometer of this invention. It is a figure for demonstrating operation | movement of the thermistor temperature measurement AD converter circuit. It is a figure for demonstrating operation | movement of a thermopile output measurement AD converter circuit.

Explanation of symbols

10 Sensor 20 Heater 30 Thermopile output measurement AD conversion circuit 40 Thermistor temperature measurement AD conversion circuit 50 Heating control circuit 60 Microcontroller 70 Display or external connection device TH1 Thermopile R1 Thermistor

Claims (4)

A sensor composed of a thermopile and a thermistor for measuring the temperature of the cold junction of the thermopile, a heater for heating the back surface of the sensor, and an analog output signal from the thermopile of the sensor for converting to a digital signal A thermopile output measurement AD conversion circuit, a thermistor temperature measurement AD conversion circuit for measuring the thermistor temperature of the sensor and converting an analog signal indicating the thermistor temperature into a digital signal, and for controlling heating by the heater A heating control circuit and a microcontroller for controlling the operation of each circuit and displaying and / or outputting the temperature to be measured based on the digital signal from the thermistor temperature measurement AD conversion circuit;
An infrared thermometer in which the microcontroller detects a point where the thermopile output becomes zero by heating the sensor with a heater, and determines the temperature to be measured by measuring the thermistor temperature at that time.   The said microcontroller heats a sensor with a heater, detects the point where a thermistor temperature change becomes stable, and determines the temperature to be measured by measuring the thermistor temperature and the thermopile output at that time. Infrared thermometer. The thermistor temperature measurement AD conversion circuit includes an analog switch controlled by a microcontroller, a CR time constant circuit, and a switching transistor for controlling charging and discharging of a capacitor of the CR time constant circuit,
The common contact of the analog switch is connected to a capacitor of a CR time constant circuit, and each contact of the analog switch has a resistance value smaller than a resistance value of the thermistor of the sensor that constitutes a resistance for the CR time constant circuit. And a second reference resistor having a resistance value larger than the resistance value of the thermistor, respectively.
The microcontroller sequentially connects the analog switch to each contact, and at the time of each connection, the switching transistor is turned on / off to measure the discharge time of the capacitor, and the resistance value of the thermistor is calculated based on each measured value. The infrared thermometer according to claim 1 or 2, wherein the temperature to be measured is determined by the method. The thermopile output measurement AD converter circuit is an analog switch controlled by a microcontroller, a CR time constant circuit, and one input terminal is connected to the common contact of the analog switch and the other input terminal is connected to the CR time constant circuit. And a switching transistor for controlling charging / discharging of the capacitor of the CR time constant circuit,
The thermopile output of the sensor, the thermopile output voltage at 0 and the maximum thermopile output voltage are applied to each contact point of the analog switch,
The microcontroller sequentially connects the analog switches to the respective contacts, and at the time of each connection, the switching transistor is turned on / off to measure the charging time of the capacitor, and the thermopile output value is calculated based on the measured values. The infrared thermometer according to claim 1, 2, or 3, wherein the temperature to be measured is determined.

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