JP5288483B2 - Temperature difference detector by Seebeck current integration - Google Patents

Description

The present invention relates to a high-sensitivity temperature difference detection apparatus that increases a signal-to-noise ratio (S / N) and amplifies the temperature difference using a thermocouple. To detect the temperature difference, instead of obtaining from the magnitude of the open voltage of the thermoelectromotive force, construct a closed circuit including a thermocouple, and obtain the detected temperature difference from the Seebeck current that is the current flowing therethrough, In a so-called current detection type thermocouple, the short-circuit current is stored for a predetermined time by passing through an integration means such as converting the short- circuit current into a capacitor or the short-circuit current into a voltage and adding it on the software . The present invention provides a temperature difference detection device that can detect a temperature difference to be measured based on an output voltage. According to the present invention, a high-sensitivity temperature difference detection device with good S / N can be obtained, and can be applied to a high-sensitivity thermal infrared sensor, flow sensor, and the like.

  Conventionally, in order to detect a temperature difference, a temperature difference is formed between two junctions which are a hot junction and a cold junction of a thermocouple at a location having a detected temperature difference with respect to a certain reference temperature, and the open heat The temperature difference was obtained from the electromotive force.

The inventor previously invented the “temperature difference detection method, temperature sensor and infrared sensor using the same” (Japanese Patent Application No. 2004-026247) (Patent Document 1), and Instead of measuring the thermoelectromotive force due to the temperature difference between the two junctions, which are the contact points, with an open circuit voltage, we proposed a method to measure the temperature difference by measuring the short-circuit current, and named this a current detection type thermocouple Have demonstrated their superiority experimentally. Further, the present inventor further described "a current detection type thermocouple having a calibration method for a current detection type thermocouple and a calibration thermocouple" (Japanese Patent Application 2005-332341 (Patent Document 2), Japanese Patent Application 2006-300301 (Patent Document). 3)) has been invented and its calibration method has been proposed.

The basic principle of this current detection type thermocouple is based on the following. It is known that the Seebeck coefficient α _{s of the} semiconductor is expressed by the following formula 1 with respect to the resistivity ρ.

Here, k is a Boltzmann constant, q is an elementary charge, and in Si, ρ ₀ = 5 × 10 ⁻⁶ Ωm and m = 2.6. Conventionally, since the Seebeck coefficient α _s is larger when the resistivity ρ is larger from the above equation, a thermocouple or a thermopile tends to be produced using a semiconductor having a larger resistivity ρ. However, using a semiconductor with a too high resistivity resulted in a thermopile with extremely high internal resistance, and was looking for a compromise. However, the present inventor has realized that the above formula 1 also means the following. That is, even if the resistivity ρ is reduced by 3 to 4 digits, it means that the Seebeck coefficient α _s is reduced only by about 3 to 9 times. Conductivity, which is the reciprocal of resistivity, is proportional to the current that flows when a thermocouple (thermocouple) is short-circuited. Therefore, if a thermocouple with extremely low resistivity is created and the short-circuit current can be measured by some method, It is expected that an extremely high sensitivity and S / N can be obtained compared to the measurement of the open circuit voltage of a thermocouple or a thermopile.

Conventional short-circuit current detection type thermocouples use a virtual short circuit of an OP amplifier (operational amplifier) to measure the short-circuit current, and a feedback resistor Rf is attached to the OP amplifier to convert the short-circuit current into a voltage. The voltage drop was used as the output voltage V ₀ of the OP amplifier, and the output voltage V ₀ and the detected temperature difference ΔT were obtained from a calibration curve prepared in advance. However, in order to detect a further minute temperature difference, it is necessary to further increase the sensitivity. For this purpose, it is necessary to increase the signal-to-noise ratio (S / N).

In this conventional short-circuit current detection type thermocouple, since the feedback resistor Rf is attached to the OP amplifier and the voltage drop is used as the output voltage V ₀ of the OP amplifier, the response speed is fast, but it is included in the input signal. Noise and induction noise were directly reflected in the output voltage V ₀ of the OP amplifier. Further, a capacitor C having an appropriate time constant is connected in parallel to the feedback resistor Rf, and a high frequency component included in the output voltage V ₀ is bypassed by the capacitor and averaged within a time constant determined by Rf and C. Therefore, the S / N was improved. Even so, it is difficult to increase the sensitivity because the output voltage V ₀ of the OP amplifier reflects the short-circuit current of the thermocouple which changes essentially from moment to moment. For this purpose, first-stage amplification with a large S / N is necessary.

Conventionally, the analog input voltage Vi is digitally converted (AD conversion) by using an OP amplifier and a capacitor C to change the analog input voltage Vi to a current through a predetermined input resistor R, and then the OP amplifier. In order to completely cancel the electric charge stored in the capacitor C so that the capacitor C provided in the capacitor is charged, converted into a voltage, and then canceled by using a known reference power source Vref. There is a method of using a clock pulse with a short time interval and obtaining it with the count number N of this clock pulse and digitizing it. However, this is not the purpose of signal amplification, but is a means of AD conversion, and further, a time for canceling it and its associated circuit are required.

Patent Application 2004-026247 Japanese Patent Application 2005-332341 Japanese Patent Application 2006-300301

The present invention further increases the S / N ratio and a large first stage amplification of a current detection type thermocouple using a thermocouple that generates only a very small voltage signal and is formed on a thin film thermally separated from a conventional substrate. It is an object of the present invention to provide an ultra-compact and highly sensitive temperature difference detection device that can be applied to a thermal infrared sensor, an atmospheric pressure sensor, a gas sensor, a flow sensor, and the like.

In order to achieve the above object, a temperature difference detection apparatus according to claim 1 of the present invention includes a Seebeck current measuring unit for measuring the Seebeck current, an integrating unit for integrating the Seebeck current, and a time for integration for a predetermined time. A setting means, an initial state returning means for returning to the initial state after the integration, and a voltage output means for holding the output of the integrating means for a predetermined period , and using an operational amplifier and its virtual short circuit as the Seebeck current measuring means, When the thermocouple is connected to the inverting input terminal of the operational amplifier and the thermocouple due to the detected temperature difference, it is inverted when the thermocouple is connected to the non-inverting input terminal. Configure a closed circuit including a thermocouple so that the Seebeck current of the short circuit current determined by the input resistance smaller than the internal resistance of the thermocouple connected to the input terminal flows. It, that the Seebeck current, it was amplified output voltage through said integrating means, using the output voltage and the output voltage is held at the voltage output means, and to determine the temperature difference, It is characterized by.

Unlike the conventional method of measuring the open thermoelectromotive force, the detection of the temperature difference in the short-circuit current detection thermocouple of the temperature difference detection apparatus according to the present invention is intended to use the thermocouple as a current detection type. However, it is better to use a measuring device such as an operational amplifier (OP amplifier) in which the internal resistance of the measuring device of the current detecting device is equivalently canceled and becomes zero. It is possible to easily measure the short-circuit current flowing through the. In addition, the internal resistance of the thermocouple varies depending on the material, dimensions, and shape of the two conductors that make up the thermocouple, and the conductor has the lowest internal resistance possible so that a large current flows for the same thermoelectromotive force. must be a combination of materials, the thermocouple emf even larger inside, i.e., it is better to use a material having a large Seebeck coefficient corresponding to the absolute thermal Den'no E _o.

In addition, as an integration means for integrating this short circuit current, charging using a capacitor and utilizing the potential difference between both ends based on the stored charge, without using a capacitor, the short circuit current signal is passed through a resistor, For example, these voltages may be added on the software every 0.1 milliseconds. Further, these output voltages may be stored in an IC memory so that they can be used.

In addition, as a time setting means for integrating for a predetermined time, an IC timer may be used to determine a predetermined time, or an externally generated clock pulse may be used to make an IC switch for each pulse. It is also possible to output an input signal from a thermocouple that changes from moment to moment by driving the switch.

In addition, after the integration, as an initial state return means for returning the initial state, the switch in parallel with the capacitor as the integration means is connected, and when the switch is closed, the charge accumulated in the capacitor is discharged. Thus, the capacitor may be returned to the initial state by making it empty. Alternatively, the addition on the software or the value on the memory may be cleared to return to the initial state.

Temperature difference detecting apparatus according to claim 2 of the present invention uses a capacitor as an integral unit, and a case where a switch connected in parallel to said capacitor as an initial condition returning means.

The use of a capacitor as the integration means has a practical advantage since it has a very simple configuration. The capacitor can integrate the short-circuit current by connecting to the OP amplifier instead of the conventional feedback resistor _Rf . For example, the capacitance is C, if the short-circuit current of the thermocouple due to the detected temperature difference ΔT and the Is, the output voltage V ₀ which OP amp when is integrated for a predetermined time t, as in Equation 2 Expressed. In addition, since the conventional temperature difference detection device uses R _f , the output voltage V _{00 at} that time can be expressed by Equation 3 . Therefore, these ratios, V ₀ / V _00, are expressed by Equation 4 .

Thus, certain short-circuit current Is flows into the capacitor C, and when the output V ₀ which OP amplifier is obtained, rather than conventional way capacitor C, in the case of using a feedback resistor R _f of the OP amp Since the ratio to the output voltage V ₀₀ is expressed as in Equation 4 , for example, the integration time t is 10 milliseconds (msec), the capacitor C is 1000 picofarads (pF), and the feedback resistance R _f is 100. Assuming kilo ohms (kΩ), V ₀ / V ₀₀ is 100, which means that 100 times the sensitivity can be obtained. Thus, since the response has an integration period of the short-circuit current, a response faster than the integration period cannot be expected, but an increase in sensitivity can be expected. When applied to a thermal infrared sensor, there is virtually no problem if the integration time is selected to be about the thermal time constant of the infrared light receiving section.

Further, since the integration of the short-circuit current in the capacitor C is used, the noise within the integration time is superimposed on the short-circuit current as a signal. Generally, however, the noise is zero when the positive and negative are mixed and averaged. Therefore, the noise within the integration time tends to be positive and negative, and the S / N is large. Thus, it is suitable as a first stage amplifier having a large S / N.

The temperature difference detecting apparatus according to claim 3 of the present invention is the case where the clock pulse is used as the time setting means and the initial state returning means is driven for each clock pulse.

A clock pulse generator, for example, as an integration means attached to an OP amplifier so as to drive an analog switch with a rectangular wave pulse signal having a voltage amplitude of 5 V, 10 milliseconds (msec), and a duty ratio of 1: 1. Capacitor C is charged and discharged. The analog switch is opened (off), and the charge stored in the capacitor C at this time generates a voltage across the capacitor C (this voltage forms the output voltage V ₀ of the OP amplifier). When the analog switch is closed (on) and discharged, the output voltage V ₀ becomes zero and returns to the initial state. In this way, when the clock pulse is applied and the analog switch is opened (off), the short-circuit current integration starts, and when the analog switch is closed (on), the discharge starts. The period during which the analog switch is open (in this case, 10 milliseconds) is the integration time. The integration time can be extended or shortened by adjusting the width of the clock pulse. If the internal resistance when the analog switch is closed (on) is small, the discharge time can be shortened. Since it is good, an almost continuous output voltage of the OP amplifier can be obtained.

The temperature difference detection apparatus according to claim 4 of the present invention is a case where a peak hold circuit is used as the voltage output means.

As described above, the analog switch is closed (ON) and the capacitor starts discharging, so that the voltage across the capacitor immediately before it becomes maximum. Measuring the maximum voltage, which is the voltage across the last capacitor in the open (off) period of this analog switch, is optimal for high sensitivity, and this maximum voltage is the analog switch immediately after that. When the discharge starts in the closed (on) state, the output voltage V ₀ of the OP amplifier suddenly starts to decrease, so that a peak is formed as a waveform. Therefore, this maximum voltage can be measured by using a known peak hold circuit. The detected temperature difference ΔT can be obtained by using a calibration curve prepared in advance between the output voltage V ₀ and the detected temperature difference ΔT.

In the temperature difference detection apparatus of the present invention, a thermocouple (or a thermopile, which is a set of a plurality of thermocouples) can be easily obtained by using an operational amplifier (OP amplifier) as a short-circuit current measuring means and a capacitor as an integrating means. Since the short-circuit current is integrated for a predetermined time, the output voltage of the OP amplifier after integration can be increased. Therefore, there is an advantage that the detected temperature difference can be detected with high sensitivity.

In the temperature difference detection device of the present invention, a capacitor as an integration means can be used, so that the noise contained in the short circuit current or the positive / negative change of the induction noise cancels each other, so that the S / N can be increased. There are advantages.

In the temperature difference detection device of the present invention, the clock pulse is used as the time setting means, and the analog switch as the initial state returning means can be easily turned on and off, so that the circuit configuration is small and simple. There are advantages. Since the clock pulse generator can also be constituted by a simple circuit such as a known IC timer, it is easy to reduce the size of the temperature difference detection device on which it is mounted.

In the temperature difference detection apparatus of the present invention, since a known peak hold circuit can be used as the voltage output means, there is an advantage that the temperature difference detection apparatus can be easily configured.

It is a circuit structure schematic diagram showing one example at the time of applying a temperature difference detection device of the present invention to a temperature detection part of a thermal type infrared sensor. Example 1 It is the conventional circuit structure schematic explaining operation | movement at the time of utilizing a thermocouple as a short circuit current detection type thermocouple. Example 1 It is the schematic of the thermocouple part in the circuit structure which shows another Example for demonstrating the temperature difference detection apparatus of this invention. (Example 2) It is the circuit structure schematic which shows another Example for demonstrating the temperature difference detection apparatus of this invention. (Example 3)

Hereinafter, embodiments of the temperature difference detection device of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a schematic circuit configuration diagram showing an embodiment in which the temperature difference detection device of the present invention is applied to a temperature difference detection unit of a thermal infrared sensor.

When the thermocouple 10 of the short-circuit current detection type thermocouple used in the temperature difference detection apparatus of the present invention is used and implemented as a thermal infrared sensor, referring to FIG. 1, for example, as follows . A thin n-type high-concentration SOI layer (for example, 5 μm in thickness) of the SOI substrate is formed as a slender cantilever by forming a cavity below the MEMS layer using the MEMS technique, and is used as a conductor 10B constituting a thermocouple. The thin n-type high-concentration SOI layer conductor 10B is thermally oxidized to form a thin insulating film of silicon oxide film. Then, via this, a conductor 10A (for example, nickel Ni) thin film joined to the conductor 10B near the tip of the cantilever is formed by sputtering deposition or the like, and the cantilever type thermocouple 10 is formed. Then, an infrared absorption film is formed in the entire region of the cantilever type thermocouple 10 or in the vicinity of the tip thereof, and this is used as the infrared light receiving unit 100. In general, the absolute thermoelectric power of a high-concentration n-type semiconductor is larger than that of metal, and the hot junction 60 has a positive potential with respect to the cold junction 70. In the Ni thin film metal, the hot junction 60 having a voltage opposite to that of the n-type semiconductor has a negative potential with respect to the cold junction 70. Therefore, in the arrangement of the thermocouple 10 as shown in FIG. 1, the infrared light receiving unit 100 that receives infrared rays rises in temperature and acts as a hot junction 60. At this time, the short-circuit current Is flows from the inverting input terminal (−) B of the operational amplifier (OP amplifier) 20 serving as the short-circuit current measuring means 1 to the non-inverting input terminal (+) A through the thermocouple 10.

Here, since it is implemented as a thermal infrared sensor, the junction between the conductor 10A and the conductor 10B of the thermocouple 10 near the tip of the thin-film cantilever is used as the hot junction 60. In this case, although not shown here, the SOI substrate supporting the cantilever-shaped thermocouple 10 becomes the cold junction 70. The temperature of the cold junction 70 is preferably matched with the room temperature, which is the ambient temperature. In such a case, since the circuit components used in the temperature difference detection device of the present invention are also at room temperature, the operational amplifier (OP amplifier) 20 as the short-circuit current measuring means 1 is also at the same temperature as the cold junction 70, The detected temperature difference ΔT is a temperature difference between the hot junction 60 and the cold junction 70. As a result, due to the virtual short-circuit effect of the OP amplifier 20, the thermoelectromotive force of the thermocouple 10 and the thermocouple 10 due to the detected temperature difference ΔT. The short-circuit current Is determined by the internal resistance flows through the capacitor 25 of the integrating means 2, and this short-circuit current Is is integrated.

Although not shown here, a cantilever or a bridge structure having an infrared absorption film for the infrared light receiving unit 100 near the hot junction 60 of the thermocouple 10, and further an image sensor having a diaphragm as an array and each pixel. It may be used as

The operation of the temperature difference detection apparatus of the present invention when it is implemented as a thermal infrared sensor will be described in detail with reference to FIG. First, the above-described thermocouple 10 that receives infrared rays at room temperature (for example, 20 ° C.) rises in temperature by the detected temperature difference ΔT, and has a value obtained by dividing the thermoelectromotive force of the thermocouple 10 at that time by its internal resistance. The short-circuit current Is flows through the capacitor 25 of the integrating means 2 connected to the OP amplifier 20 when the switch 40 which is the initial state returning means 4 is in the open state (off state). When the capacitor 25 has an empty charge, the potential difference between both ends thereof is zero, so the output voltage V ₀ of the OP amplifier 20 is also zero. However, as the short-circuit current Is is time elapses starts to flow into the capacitor 25, accumulated time integral of the partial charge of the short-circuit current Is gradually capacitor 25, the output voltage V ₀ which OP amplifier 20 also increases with it. For example, the switch 40 of the initial state return means 4 connected in parallel to the capacitor 25 is turned on when a predetermined integration time t, for example, 10 milliseconds (msec) has elapsed since the short-circuit current Is started to flow through the capacitor 25. When in the closed state (on state), the charge stored in the capacitor 25 through the switch 40 is discharged with a time constant expressed by the product of the capacitance C of the capacitor 25 and the internal resistance (on resistance) of the switch 40. Therefore, the charge of the capacitor 25 returns to zero again. Here, this return is referred to as initial state return. By repeating the switch 40 periodically opened (OFF state) and the closed state (ON state), the capacitor 25 is charged and discharged, the output voltage V ₀ which OP amplifier 20 be periodically synchronized It will vary from zero to the maximum value. The maximum value (peak value) of the output voltage V ₀ is immediately before the switch 40 is closed (ON state). The peak value of the output voltage V ₀ can be measured as, for example, the output voltage V _0p at the output terminal of a known peak hold circuit connected to the output terminal of the OP amplifier 20. The detected temperature difference ΔT can be measured using a calibration curve of the output voltage V _0p thus obtained and the detected temperature difference ΔT prepared in advance.

For example, when the switch 40 is periodically opened (off state) and closed (on state), for example, the switch 40 is an analog switch, and a clock pulse as the time setting means 3 having a 5 V amplitude is applied to its input terminal. This can be achieved. Since the internal resistance of the analog switch is small, it is possible to make the discharge time constant as extremely small as several microseconds. Therefore, it is not always necessary to set the duty ratio of the clock pulse to 1: 1. (Off state) is set to 10 milliseconds, and the closed state (on state) is set to 10: 1 such as 1 millisecond so that the output voltage V _{0p of} the substantially continuous peak hold circuit can be obtained. Can do. In this example, clock pulses are introduced by a clock pulse generator attached to the outside. Of course, a device incorporating a clock pulse generator may be used.

In the above description, the clock pulse is introduced and the switch 40 is periodically turned off and on. However, if necessary, the time can be adjusted or the switch 40 can be turned on and off once or multiple times. The state operation may be performed.

FIG. 2 is a schematic circuit diagram for explaining the operation of a conventional short-circuit current detection type thermocouple, which is an example applied to an infrared detection device of a thermal type infrared sensor. In this conventional embodiment, a feedback resistor Rf is attached to the OP amplifier 20. In this case, response speed is substantially determined by the thermal time constant determined by heat capacity and thermal conductance of the infrared receiver 100, the output voltage V ₀ which OP amplifier 20, the product of the short-circuit current Is flowing therethrough and a feedback resistor Rf. Therefore, even when a time sufficiently longer than the thermal time constant has elapsed, if the short-circuit current Is is constant, the output voltage V ₀ also becomes a constant value. When short-circuit current Is is small, the output voltage V ₀ becomes a constant value in the value smaller. On the other hand, in the temperature difference detection device of the present invention, as described above, the time integration of the short-circuit current Is is performed, so that the output voltage V ₀ increases with time. Therefore, a large output voltage V ₀ can be obtained. For example, if the predetermined integration time t is 10 milliseconds (msec), the capacitor C is 1000 picofarads (pF), and the feedback resistance _Rf is 100 kilohms (kΩ), a constant short-circuit current Is flows. The output voltage ratio, V ₀ / V _{00 at that time} is 100, which is 100 times more sensitive than the method shown in FIG. 2, which is the operation of a conventional short-circuit current detection type thermocouple. Here, V ₀₀ is the output voltage of the OP amplifier 20 of the conventional short-circuit current detection type thermocouple. Further, in the temperature difference detection device of the present invention, since the capacitor C is inserted instead of the conventional feedback resistor _Rf , the noise component that fluctuates positive and negative is canceled out, and the infrared sensor has a large S / N.

In the temperature difference detection device of the present invention, when formed in the same light receiving area, a thermopile in which a short-circuit current detection type thermocouple using a thermocouple 10 having a small internal resistance is connected in series with many thermocouples. As compared with the case where the short-circuit current is detected in the same manner, the short-circuit current Is becomes large and a large charge is stored in the capacitor 25 of the integrating means 2, so that a large output voltage V ₀ can be obtained. Of course, at this time, the output voltage V _0p of the peak hold circuit 50 of the voltage output means 5 similarly increases.

  FIG. 3 is a schematic view of a thermocouple portion in a circuit configuration showing another embodiment for explaining the temperature difference detecting device of the present invention. An example is shown in which two thermocouples 10 made of the same thermoelectric material and a thermocouple 110 are connected in series to measure the temperature difference ΔT between the point P and the point Q. The terminal B ′ of the conductor 10B of the same thermoelectric material of these two thermocouples 10 and 110 and the terminal A ′ of the conductor 110B correspond to the OP amplifier 20 shown in FIG. By connecting to the inverting input terminal B and the non-inverting input terminal A, respectively, the temperature difference ΔT between the point P and the point Q can be measured with high sensitivity as described in the first embodiment. In the two thermocouples 10 and 110, the thermoelectric material conductor 10B and the conductor 10A of the thermocouple 10 are the same material as the thermoelectric material conductor 110B and the conductor 110A of the corresponding thermocouple 110, respectively. ing.

In FIG. 3 of the second embodiment, in order to measure the temperature difference ΔT between the point P and the point Q, two thermocouples 10 and a thermocouple 110 are connected in series, and an input terminal of a single OP amplifier 20 is used. In this example, two thermocouples 10 and 110 are connected to the input terminals of independent OP amplifiers 20 as shown in FIG. May be requested.

In FIG. 4, the operational amplifier (OP amplifier) 20 of the short-circuit current measuring means 1 of FIG. 1 in the first embodiment is used as a non-inverting amplifier, and the input resistance 7 (inside thereof) smaller than the internal resistance of the thermocouple or thermopile 11. When the resistor R) is connected to the inverting input terminal B side and an equivalent short-circuit current Is of a thermocouple or thermopile is generated and integrated, the input of the operational amplifier (OP amplifier) 20 in FIG. The vicinity of the terminal is shown in the center, and the other circuit portions are omitted. Thus, in this case, the inverting input terminal B of the input terminal that becomes a virtual short circuit is connected to the input resistance 7 smaller than the internal resistance of the thermocouple or the thermopile 11 to increase the equivalent short circuit current Is. This is a case where a Seebeck short-circuit current detection circuit is used, and a case where a thermocouple or a thermopile 11 as a temperature difference sensor is connected between the non-inverting input terminal A to which almost no electric potential flows and only a potential is applied and the ground. By connecting the input resistance 7 smaller than the internal resistance of the thermocouple or thermopile 11, a large short-circuit current Is can be obtained, so that the amplification can be improved and the amplification can be fixed. is there. Also in this case, the operation is almost the same as that in the case of FIG.

As described above, the temperature difference detection device of the present invention short-circuits a thermocouple having an extremely small internal resistance, so that a large short-circuit current Is flows even with a small thermoelectromotive force. Further, this large short-circuit current Is Is integrated for a predetermined time, so that it becomes a highly sensitive temperature difference sensor with a simple circuit configuration, and the integration cancels out noise components that fluctuate positively and negatively, resulting in a large S / N signal amplification. Therefore, it is promising as a temperature difference sensor for infrared radiation thermometers, particularly ear-type thermometers, which need to measure minute temperature differences with high accuracy and high sensitivity. It is most suitable for temperature difference measurement such as gas detection such as hydrogen by measurement of minute calorific value in combustible gas sensors such as, heat conduction type gas sensor, Pirani vacuum gauge, pressure sensor such as thermal type humidity sensor and atmospheric pressure sensor.

DESCRIPTION OF SYMBOLS 1 Short circuit current measurement means 2 Integration means 3 Time setting means 4 Initial state return means 5 Voltage output means 7 Input resistance 10 Thermocouple 10A, 10B Conductor 11 Thermocouple or thermopile 20 Operational amplifier (OP amplifier)
25 Capacitor 30 Clock pulse 40 Switch 50 Peak hold circuit 60 Hot junction 70 Cold junction 110 Thermocouple 110A, 110B Conductor 100 Infrared light receiver 200 Temperature difference detector of thermal infrared sensor

Claims (4)

In a temperature difference detection device that detects a temperature difference using a Seebeck current of a thermocouple, a Seebeck current measurement unit that measures the Seebeck current, an integration unit that integrates the Seebeck current, a time setting unit that integrates for a predetermined time, An initial state return means for returning to the initial state after the integration, a voltage output means for holding the output of the integration means for a predetermined period, an operational amplifier and its virtual short circuit as the Seebeck current measurement means, and a detected temperature difference When the thermocouple is connected to the inverting input terminal of the operational amplifier and when the thermocouple is connected to the non-inverting input terminal, the internal resistance of the thermocouple is connected to the inverting input terminal. A closed circuit including a thermocouple is configured so that a short-circuit current Seebeck current determined by the input resistance smaller than the internal resistance of the connected thermocouple flows. Things, the Seebeck current, it was amplified output voltage through said integrating means, using the output voltage and the output voltage is held at the voltage output means, we have to determine the temperature difference The temperature difference detection apparatus characterized by these. 2. The temperature difference detecting device according to claim 1, wherein a capacitor is used as the integrating means , and a switch connected in parallel to the capacitor is used as the initial state returning means. 3. The temperature difference detecting device according to claim 1, wherein the clock pulse is used as the time setting means, and the initial state returning means is driven every time the clock pulse is used. 4. The temperature difference detection device according to claim 1, wherein the voltage output means is a peak hold circuit.