CN113465767B

CN113465767B - Temperature detection circuit, gas detection device and temperature detection method

Info

Publication number: CN113465767B
Application number: CN202010242288.9A
Authority: CN
Inventors: 濱村尚宏
Original assignee: TDK Corp
Current assignee: TDK Corp
Priority date: 2020-03-31
Filing date: 2020-03-31
Publication date: 2024-03-29
Anticipated expiration: 2040-03-31
Also published as: CN113465767A

Abstract

The invention discloses a temperature detection circuit, a gas detection device and a temperature detection method, wherein the temperature detection circuit comprises: the circuit comprises a thermistor, a timer IC, a fixed resistor, an electric connector, a first capacitor, a self-oscillation circuit, a low-pass filter, a differential amplifier and an A/D converter. The gas detection device also comprises a heating device and a microcontroller. The effective temperature detection circuit is provided through the connection and the cooperation of the modules, and can be well used for gas detection.

Description

Temperature detection circuit, gas detection device and temperature detection method

Technical Field

The present invention relates to temperature detection, and more particularly, to a temperature detection circuit, a gas detection apparatus, and a temperature detection method.

Background

In the prior art, thermistors are electronic components whose resistance varies with temperature. Therefore, thermistors are widely used to measure temperature. Generally, thermistors are used to monitor the temperature inside the device so that the device can avoid overheating. However, prior art document 1 (WO 2019/188692) proposes to configure a gas sensor using a thermistor, and the gas concentration can be obtained by detecting the temperature caused by combustion heat varying with the gas using the thermistor.

Although not explicitly described for thermistors, there are other inventions available for measuring gas concentration by resistance change. For example, prior art document 2 (Japanese patent laid-open No. 2002-156350) and prior art document 3 (Japanese patent laid-open No. 2000-221152). In these prior art documents 1 to 3, in order to improve the sensitivity of the gas detection device, the gas detection method uses a heater to heat the gas for detection, which may overheat the gas.

Therefore, providing an effective temperature detection circuit and a temperature detection method are the technical problems to be solved.

Disclosure of Invention

In view of the above problems, an object of the present invention is to provide a temperature detection circuit and a temperature detection method for providing an effective means for detecting gas concentration. And more particularly to a thermistor employing a pulse-driven gas detection device, and outputting a rectangular wave like a pulse.

A first embodiment of the present invention provides a temperature detection circuit, characterized by comprising:

the device comprises a thermistor, a timer IC, a fixed resistor, an electric connector, a first capacitor, a self-oscillation circuit, a low-pass filter, a differential amplifier and an A/D converter;

Wherein the thermistor is connected between a power supply voltage terminal and a Discharge (DIS) terminal of the timer IC;

the fixed resistor is connected between the Discharge (DIS) terminal and a Threshold (THIR) terminal of the timer IC;

the electrical connector is used for connecting the threshold value (THIR) end to a Trigger (TRIG) end of the timer IC;

the first capacitor is connected between the Trigger (TRIG) terminal and a Ground (GND) terminal of the timer IC;

the self-oscillation circuit comprises a second capacitor, wherein the second capacitor is connected between a Control (CTRL) terminal of the timer IC and the Ground (GND) terminal;

the low-pass filter is arranged at the Output (OUT) end of the oscillating circuit.

A second embodiment of the present invention provides a temperature detection circuit, which is characterized in that, compared to the first embodiment:

the thermistor is connected between the Discharge (DIS) terminal and the Threshold (THIR) terminal;

the fixed resistor is connected between the power supply voltage terminal and the Discharge (DIS) terminal.

Preferably, for the above two embodiments, further comprising:

adjusting the resistor;

wherein the regulating resistor is arranged in parallel with the thermistor.

Preferably, for the second embodiment, further comprising:

an external controller connected to a RESET bar (RESET bar) end of the timer IC for controlling application of a voltage to the thermistor.

A third embodiment of the present invention provides a temperature detection circuit, characterized by comprising:

power supply, capacitor, detection resistor, thermistor

A first electrical path provided between the power source and the capacitor;

a second electrical path provided between a plurality of ends of the capacitor;

a third electrical path connected to the first path side of the detection resistor and the capacitor; and

a fourth electrical path connected to the detection resistor and the second path side of the capacitor;

wherein, a first switch, a second switch, a third switch and a fourth switch are respectively arranged in the first electric path, the second electric path, the third electric path and the fourth electric path;

the thermistor is arranged on the first electric path and the fourth electric path or the second electric path and the third electric path;

the self-oscillation circuit is used for detecting the voltage at one end of the detection resistor and executing oscillation operation;

the comparator and the trigger is connected with the output end of the comparator; and

And the low-pass filter is connected with the output end of the trigger.

A fourth embodiment of the present invention provides a temperature detection circuit, compared to the third embodiment, characterized in that:

the thermistor is arranged on the first electric path, the second electric path, the third electric path and the fourth electric path;

the thermistors are respectively arranged on the first electric path and the fourth electric path and are used for detection by a sensor; and

and thermistors arranged on the second electric path and the third electric path respectively are used for measuring the reference temperature.

Preferably, the measuring the reference temperature is implemented by using a resistance value corresponding to the reference temperature instead of the thermistor.

A further embodiment of the present invention provides a gas detection apparatus, including: a heating device, a microcontroller, and a temperature detection circuit as described in any one of the first to fourth embodiments.

Preferably, the heating means is acted upon by a rectangular waveform pulse wave generated by the oscillating circuit.

A further embodiment of the present invention provides a temperature detection method using the temperature detection circuit of the first embodiment, characterized in thatWherein D is the duty cycle of the oscillator output rectangular waveform, R _th R is the resistance value of the thermistor _B A resistance value of the fixed resistor;

changing the resistance value R of the fixed resistor _B So that the duty cycle D is linearly dependent upon the temperature change of the thermistor.

A further embodiment of the present invention provides a temperature detection method using the temperature detection circuit according to the second embodiment, characterized in thatWherein D is the duty cycle of the oscillator output rectangular waveform, R _th R is the resistance value of the thermistor _B A resistance value of the fixed resistor;

The temperature detection circuit device can effectively detect the temperature through the linear relation between the duty ratio D and the temperature of the thermistor, does not bring more power consumption and heat, reduces the heating of the thermistor, ensures that the thermistor has better sensitivity, and can be well applied to gas detection.

Drawings

In order to more clearly illustrate the technical solutions of the present invention, the drawings that are needed in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and that other drawings can be obtained according to these drawings without inventive effort for a person skilled in the art.

FIG. 1 is a schematic diagram showing the general structure of a gas detection device;

FIG. 2 is a general schematic circuit diagram of a thermistor;

FIG. 3 is a schematic diagram showing the temperature-resistance relationship of NTC thermistors;

FIG. 4 is a schematic diagram showing the output characteristics of the detection circuit of FIG. 2 when an NTC thermistor is used;

fig. 5 is a diagram explaining a pulse wave and a duty cycle D;

fig. 6 is an explanatory diagram of the front-back characteristics by the low-pass filter;

fig. 7 illustrates a first embodiment;

fig. 8 illustrates a timer IC;

fig. 9 is a graph showing the temperature-duty ratio D characteristic when the duty ratio D is calculated in the first embodiment;

fig. 10 is a graph showing the results of the circuit simulation of the first embodiment and the voltage-time characteristics between a and a' of the first embodiment;

FIG. 11 shows the result of the circuit simulation of the first embodiment, and the output voltage V of the first embodiment _B -a graph of time characteristics;

FIG. 12 is a graph for comparing the characteristics of the first embodiment and the prior art, and shows the output voltage V _out And temperature;

FIG. 13 is a graph comparing the characteristics of the first embodiment and the prior art, and showing the relationship of voltage across the thermistor to temperature;

Fig. 14 illustrates a second embodiment;

fig. 15 is a graph showing the temperature-duty ratio D characteristic when the duty ratio D is obtained by calculation in the second embodiment;

fig. 16 is a graph showing the results of the circuit simulation of the second embodiment and the voltage-time characteristics between a' and a "of the second embodiment;

FIG. 17 shows the result of the circuit simulation of the second embodiment, and the output voltage V of the second embodiment _B -a graph of time characteristics;

FIG. 18 is used forComparing the characteristics of the second embodiment with those of the prior art, and displaying the output voltage V _out And temperature;

FIG. 19 is a graph comparing the characteristics of the second embodiment and the prior art, and showing the relationship between voltage and temperature across a thermistor;

fig. 20 illustrates a third embodiment;

fig. 21 illustrates a state 1 diagram in a third embodiment;

fig. 22 illustrates a state 2 diagram in the third embodiment;

fig. 23 is a diagram illustrating electrical characteristics of each of the positions in fig. 20 to 22 in the third embodiment;

fig. 24 shows the post-filter characteristic V of fig. 20 _k A relation diagram between the temperature T and the temperature;

fig. 25 illustrates a fourth embodiment;

fig. 26 is an explanatory diagram of the application of the pulse wave generated according to the present invention to the heater.

Detailed Description

The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.

In order to clearly describe the technical solutions of the embodiments of the present invention, in the embodiments of the present invention, the terms "first", "second", etc. are used to distinguish the same item or similar items having substantially the same function or effect, and those skilled in the art will understand that the terms "first", "second", etc. do not limit the number and execution order.

Referring to fig. 1, in an embodiment of the present invention, a gas detection apparatus includes: a heating section for heating the gas, a detecting section for detecting the heated gas, and a microcontroller for controlling the heating section, the microcontroller also receiving an output of the detecting circuit for correction.

The operation of the gas detection apparatus of fig. 1 includes: first, the microcontroller sends a signal to activate the heater to the heating section. Thereafter, in the heater driving circuit of the heating portion, a waveform for driving the heater is formed. Since the heater is typically driven by a pulse wave or a direct current, the heater driving circuit generates a pulse wave or a direct current voltage. Among them, the heater driving circuit is preferably provided with a power amplifier so as not to cause a voltage drop due to the load of the heater. In addition, a D/A (digital-to-analog) converter is used to generate analog values for the heater to generate waveforms. However, when a rectangular wave is acceptable, a switching element such as a MOSFET having a simple structure may be used.

By activating the heater of the heating section, the gas to be detected is heated, and the temperature of the gas is changed. Then, the heat at this time is transmitted to the thermistor of the detection portion. The temperature change of the thermistor is detected by a detection circuit and is transmitted to the microcontroller through an A/D converter. Preferably, as shown in prior art document 1, a catalyst may be used between the heater and the thermistor. The microcontroller corrects the obtained value and outputs a data value. Since the temperature change of the thermistor depends on the gas composition, the gas can be detected. The present invention will be described with emphasis on a detection circuit of a detection section in a gas detector.

In general, as shown in fig. 2, a method for arranging a fixed resistor in series with a thermistor is commonly used for a detection circuit of the thermistor. Here, the fixed resistance is a resistance whose value is constant regardless of external factors such as temperature and humidity. A temperature-dependent thermistor is connected in series with a temperature-independent fixed resistor. Then, a voltage is applied across the series circuit, and as the resistance value of the thermistor changes with temperature, the ratio of each resistance change, and the voltage applied to each resistance also changes.

Thermistors fall into two categories: NTC (negative temperature coefficient) thermistors and PTC (positive temperature coefficient) thermistors. Among them, the NTC thermistor has a characteristic that the resistance decreases with an increase in temperature, as shown in fig. 3. In contrast, PTC thermistors have the characteristic that their resistance increases with increasing temperature. For convenience of description, only a case of using the NTC thermistor will be described in this specification.

In the circuit of fig. 2, the voltage V between the resistors is fixed _sh Is the voltage division of the thermistor and fixed resistor with respect to the supply voltage. Therefore, the resistance value R of the fixed resistor is utilized ₁ Resistance value R of thermistor _th And supply voltage V _IN According to the formula

In the case of NTC thermistors, the resistance value R _th As the temperature decreases, as shown in fig. 3, the voltage V across the resistor is fixed _sh Having the characteristics shown in fig. 4. In FIG. 4, the horizontal axis represents the temperature T, and the vertical axis represents the voltage V of the fixed resistor _sh . The non-linearity is exhibited in the low temperature region or the high temperature region, but the relatively high linearity is exhibited in the temperature region between the low temperature region and the high temperature region. In this high linearity region, V _sh The relation with temperature is easy to correspond, so the usability is good. Therefore, by adjusting the characteristics of the fixed resistor or the thermistor, a range of areas of high linearity can be designed so as to be obtained in the operating temperature range. The above-described device is a known general-purpose device for detecting a thermistor.

However, if the size of the thermistor is reduced to reduce the size of the sensor, the thermistor generates a small amount of heat due to the voltage applied at the time of detection. This heat can cause the thermistor to detect errors. Thus, this is a factor that hinders downsizing of the sensor. In particular, in the prior art, since the DC voltage V is always supplied _IN This can lead to heating of the thermistor. Therefore, the invention provides a device for reducing the heat generation of the thermistor by adopting pulse waves to replace direct current.

Prior art document 4 (Japanese patent Sho 59-7230) proposes a method of detecting thermal sensitivity using an oscillating circuitAnd means for resistance. In prior art document 4, the temperature is estimated by driving a thermistor by an oscillation circuit and detecting the frequency of a pulse wave output from the oscillation circuit. In the prior art document 4, not only the output but also the voltage applied to the thermistor is a pulse wave. However, unlike the output, the waveform of this applied pulse wave is different from a rectangular wave. In other words, as in the prior art document 4, an arrangement using an oscillating circuit is not provided to the thermistor at all times with the direct-current voltage V _IN The heat generated by the thermistor is reduced compared to the prior art. It is noted that the separate excitation and self-excitation circuits are referred to as known circuits that handle oscillations, such as pulse waves. The individual excitation type is a method of obtaining oscillation from an externally provided oscillation device. An oscillation of a certain frequency, typically a constant frequency, is received from an oscillator or microcontroller. The characteristic change of the element can be obtained by comparing a pulse wave from the outside with a comparator or the like. The self-excited type refers to a manner in which the circuit itself oscillates, and the oscillation greatly varies due to a variation in characteristics of elements constituting the circuit. Therefore, it is possible to know the characteristic change of the element of the circuit from the oscillation state. The self-excited type changes frequency compared to the excited type alone, so that the characteristics can be dynamically changed. Therefore, the technical scheme of the application is based on a self-oscillation circuit.

Further, prior art document 4 proposes a method of setting the relationship between the temperature and the frequency of the pulse wave of the output of the oscillation circuit to be linear by connecting fixed resistors in series. That is, a method of detecting a temperature as a boundary of linearity by detecting a frequency is proposed.

However, in general, a method for detecting a frequency is not easy to implement. If the frequency is low, high-frequency pulses for comparison are generated, and the number of pulses corresponding to the high-frequency pulses is counted so that the frequency can be clarified (reciprocal method). Conventionally, in this case, since the corresponding pulse number needs to be calculated, the high-frequency pulse must be prepared for the frequency to be measured, and the counting must be performed with high accuracy. Since it is difficult to make an accurate comparison pulse and the calculation process is also complicated, it is difficult to measure a high frequency. It is possible if the output frequency of the oscillating circuit is low, but in this case the response is slow, which presents a problem. High frequencies are known to be detectable by FFT analyzers or spectrum analyzers, but in either case the configuration becomes bulky and complex, and using it to configure a gas detection device is neither cost effective nor suitable.

A rectangular waveform pulse wave can give the frequency and duty cycle due to its characteristics. Prior art document 4 focuses on frequency, but at present this application is implemented by focusing on duty cycle. As is well known, as shown in fig. 5, a rectangular pulse wave has a high voltage time T _on And a low voltage time T _off The duty ratio D is determined by the high voltage time T _on And a low voltage time T _off And (5) determining. According to the formula

Focusing on the duty cycle D has the advantage that it can be converted to a dc voltage by a low pass filter. Fig. 6 shows this state. The input is a rectangular pulse wave which is smoothed to become a direct current when passing through a low pass filter. The value of the smoothed direct voltage depends on the high voltage and the low voltage. This value is the same as the high voltage when the duty cycle D is 100%. In contrast, when the duty ratio D is 0%, the value is the same as the low voltage. At other duty cycles D, the higher the duty cycle D, the closer to the high voltage.

As described above, the output of the rectangular pulse wave is converted into a voltage level by using a low-pass filter. This is easier to detect than the measurement frequency of prior art document 4. For example, the value can be easily measured with an a/D (analog to digital) converter.

The present application also provides a first embodiment of a temperature detection circuit.

Fig. 7 shows a circuit configuration of the first embodiment, showing the detecting portion and the microcontroller of the gas detecting device, but the configuration of the heating unit is omitted. In the first embodiment, a timer IC (commonly referred to as555 Is used). Wherein the timer IC has a circuit configuration comprising a first and a second comparator and a flip-flop circuit as shown in fig. 8. Further, a thermistor is connected between a power supply voltage terminal and a Discharge (DIS) terminal of the timer IC; a fixed resistor is connected between the Discharge (DIS) terminal and a Threshold (THIR) terminal of the timer IC; the Threshold (THIR) terminal is connected to the Trigger (TRIG) terminal of the timer IC; first capacitor C ₁ A connection point between the Threshold (THIR) terminal and the Trigger (TRIG) terminal and a Ground (GND) terminal of the timer IC; second capacitor C ₂ Connected between a Control (CTRL) terminal of the timer IC and the Ground (GND) terminal; the Output (OUT) terminal is connected to the low-pass filter. An amplifier, an a/D (analog to digital) converter, a microcontroller are connected to the output of the low pass filter.

Wherein the resistor R is regulated _A And thermistor R _TH Are arranged in parallel. This resistance is fixed and independent of temperature or humidity, but will be described as regulating resistor R _A To be different from R _B . If thermistor R _TH Is larger by reducing the regulating resistor R _A Is used to perform the adjustment. Fixed resistor R _B Is one of the resistance values used when implementing an oscillating circuit using a timer IC. By adjusting thermistors R _TH Adjusting resistor R _A And a fixed resistor R _B The square pulse wave output from the oscillation circuit can be adjusted.

Defining the output voltage V of the oscillating circuit _B Theoretical value D of duty cycle D of (2) _theory The following are provided:

wherein R is _th Is the resistance of a thermistor, R _A Is to adjust the resistance of the resistor, R _B Is a resistance of a fixed resistance.

Due to R _th The curve shown in FIG. 2 is plotted when R _A And R is _B When the value of (2) is inappropriate, the temperature-to-temperature relationship is nonlinear, but is alwaysBy appropriately selecting R _A And R is _B It can make the value of the duty ratio D within the specified range almost linear. Referring to FIG. 9, FIG. 9 shows a reference value of the duty cycle theoretical value D _theory The calculation result of the related expression (formula (3)). The horizontal axis represents temperature, and the vertical axis represents duty cycle theoretical value D _theory . For R in formula (3) _th Values, fig. 3 gives a supplementary illustration of the curve. Wherein, the resistance value R of the resistor is adjusted _A Is fixed. Equation (3) is achieved by varying the fixed resistance R _B Is calculated from 50kΩ to 2mΩ, and the result is added to each resistance value in the graph.

As can be seen from FIG. 9, when R _B When very small (e.g., when R _B When=50kΩ), the change is small at a lower temperature, and the change is large with the increase in temperature. On the other hand, when R _B When larger (e.g., when R _B When=2mΩ), the change at low temperature is large, and the change at high temperature is small, so that the change is also nonlinear.

However, in the range of 25℃to 85℃the duty cycle theory D _theory Almost linear, during which R can be seen _B Value (R in this example) _B 200kΩ to 300kΩ).

As described above, when R _B When adjusted, there is an optimum value that can make the duty cycle D linear with temperature. Therefore, equation (3) is adjusted to be linear with temperature. Then, since the output voltage V of the oscillating circuit _B The duty cycle D of (c) is linear with temperature, and the correspondence with temperature is easily understood and will be simplified in the processing of the microcontroller in the subsequent stage.

In the present embodiment, the fixed resistance R has been described _B Is adjusted. However, the resistor R is regulated _A Also helps to obtain a linear adjustment, so that the resistor R can be adjusted _A To adjust. In general, it is difficult to obtain linearity for a thermistor with a large variation, so that the resistance value R of the parallel adjustment resistor is added _A . A high degree of linearity can be obtained despite the need to coordinate the amount of change. But, depending on the heat sensitivityResistance constant, R _A May not be necessary, equation (3) is converted into

The structure of the oscillating circuit portion in fig. 7 was verified by circuit simulation, and the results are shown in fig. 10 and 11. The simulation is performed assuming that an NTC thermistor is used, using a relationship between the approximate expression input temperature and the resistance value of the NTC thermistor. The adjustment constant is obtained in advance by using the formula (4), the duty ratio D of the output characteristic at 25 ℃ to 85 ℃ is made linear, and is input to the circuit simulation.

FIG. 10 shows the application to a thermistor R _TH The voltage versus time of (c). The horizontal axis represents time, and the vertical axis represents application to the thermistor R _TH Voltage V of (2) _A-A '. In the figure, the solid line represents the result at 25℃and the broken line represents the result at 55℃while the two-dot chain line represents the result at 85 ℃.

According to the simulation results, these waveforms show four regions, respectively, of keeping direct current 5V (supply voltage V _cc ) The voltage is rapidly decreased from 5V, the voltage is gradually decreased, and the voltage is rapidly increased to 5V.

In the region where the direct current 5V (power supply voltage Vcc) is maintained, the time does not change even if the temperature becomes 25 ℃,55 ℃, and 85 ℃. But as the temperature increases, the period becomes shorter.

According to the result shown in fig. 10, the power is large in the region where the direct current 5V (power supply voltage Vcc) is maintained. It is well known that most of the power dissipated in the resistor is used for heat generation.

Fig. 11 shows the output voltage V of the oscillating circuit _B Relationship to time. The horizontal axis represents time and the vertical axis represents the output voltage V of the oscillator _B . It can be seen that unlike fig. 10, the pulse wave is substantially rectangular.

Further, the region of fig. 10 where direct current 5V (power supply voltage Vcc) is maintained corresponds to the low voltage time T of fig. 11 _off . NamelyThat is, even if the temperature changes, the low voltage time T _off Nor is it changed. Therefore, the duty ratio D decreases with an increase in temperature. This result is consistent with the result of fig. 9.

Further, in the present invention, it is preferable to provide a low-pass filter to the oscillation circuit, and it is possible to change the change of the duty ratio D to the level of the direct-current voltage, and the change can be detected more easily. The configuration of the low-pass filter will not be limited, and an RC filter or an LC filter of a passive element, or an analog filter or a digital filter using an operational amplifier may be used. Voltage value V after passing through filter _E As the duty cycle D increases, it increases and thus decreases as the temperature increases.

Thus, if the voltage value V is detected _E The temperature characteristic can be known. Wherein a differential amplifier circuit may be provided at the output of the low pass filter as shown in fig. 7. By providing a differential amplifier circuit, unnecessary direct current components can be removed, only one necessary voltage component can be amplified, so that the voltage variation becomes large, and the microcontroller can easily obtain the voltage value.

In the differential amplifier circuit of fig. 7, when R ₂ ＝R ₄ And R is ₃ ＝R ₅ In this case, V is known to _F ＝(R ₃ /R ₂ )(V _E -V _REF ) The amplification voltage ratio may be determined. In addition, unnecessary direct current components can pass through V _F Is removed from the value of (2).

Fig. 7 shows a differential amplifier circuit using a general purpose operational amplifier. However, the present invention is not limited thereto, and an instrumentation amplifier may also be used. Various types of differential amplifiers are known to those skilled in the art. However, if the output voltage V of the low-pass filter _E The value of (c) is large enough that it is easy to receive the voltage value by the microcontroller without voltage amplification, in which case the amplifier circuit may be omitted.

Output voltage V of differential amplifying circuit _F The values are converted from analog values to digital values by an a/D converter and collected by a microcontroller. However, some microcontrollers have a built-in internal So that an external a/D converter may not be used.

Next, the first embodiment is compared with the prior art. The comparison is of the fixed resistances arranged in series in the prior art shown in fig. 2. The output voltage is also compared to the voltage across the thermistor. For comparison, R _A And R is _B The same value is set. Namely, R in FIG. 2 ₁ Is set as R _B Is a value of (2).

Fig. 12 shows the relationship between output voltage and temperature. The output of the first embodiment is the voltage V after passing through the filter _E . The output of the prior art in FIG. 2 is V _sh In the first embodiment, this trend is different from that of the related art because the output of the timer IC includes an inverter. In the first embodiment, the output voltage V _E Decreasing with increasing temperature. In the case of the prior art, however, the output voltage V _sh As the temperature increases.

Next, the voltages across the thermistors will be compared. In the first embodiment, since the waveform is a repeated wave as shown in fig. 10, the average value is calculated. The prior art feature in FIG. 12 is V shown in FIG. 2 _sh The prior art characteristic in FIG. 13 shows the voltage V across the thermistor _th . As can be seen from fig. 2, since vcc=v _th +V _sh And vcc=5v, then V shown by the prior art characteristic in fig. 13 _th Equal to Vcc-V _sh (wherein V _sh As shown in fig. 12).

The results obtained by summarizing them are shown in FIG. 13. In fig. 13, the horizontal axis represents temperature, and the vertical axis represents the average value of the voltages across the thermistor. The solid line is the result of the first embodiment and the dotted line is the result of the prior art. It can be seen that the voltage across the thermistor in the prior art is high.

In summary, the variation in the prior art is slightly larger, but in the first embodiment, the voltage across the thermistor is smaller. Because the power consumption W value of the resistor is determined byGive (V) _TH Is the voltage across the thermistor), the thermistor consumes less power and generates less heat.

As shown in fig. 13, the voltage of the present embodiment starts to have a reduced area at about 85 c, compared to the prior art. However, at temperatures below 85 ℃, the voltage of this example is lower.

According to the first embodiment of the present invention, the power consumption of the thermistor can be reduced, meaning that the generation of heat can be reduced.

The present application also provides a second embodiment of a temperature detection circuit.

Fig. 14 shows a configuration of a second embodiment in which a thermistor R _th And a regulating resistor R _A Is not connected between Vcc terminal and Discharge (DIS) terminal (between a and a '), but is connected between Discharge (DIS) terminal and Threshold (THIR) terminal (a', a "). On the other hand, a fixed resistor R _B Unlike the first embodiment, the Discharge (DIS) terminal is not connected to the Threshold (THIR) terminal (between a 'and a "), but between the Vcc terminal and the Discharge (DIS) terminal (between a and a'). Since many portions in the second embodiment are the same as those in the first embodiment, description of the same portions will be omitted.

Also for this circuit, as in the case of the first embodiment, the duty cycle theoretical value D' _theory The calculation formula of (2) is as follows:

wherein R is _th Is the resistance of a thermistor, R _A Is to adjust the resistance of the resistor, R _B Is a resistance of a fixed resistance. Fig. 15 shows a duty theoretical value D 'calculated using this calculation formula' _theory As a result of (a). The horizontal axis represents temperature, and the vertical axis represents duty cycle theoretical value D' _theory . When R is _B When the values are 50k omega, 100k omega, 200k omega, 400k omega, 600k omega, 700k omega and 1M omega, 2M omega is changed, and the theoretical value D 'of the temperature calculation duty ratio is changed' _theory 。

The difference between fig. 15 and fig. 9 of the first embodiment is that fig. 9 is downwardFig. 15 is an upward oblique view. Further, when the duty cycle theory value D of fig. 9 _theory When the duty ratio is equal to or greater than 0 and less than 1, the duty ratio theoretical value D 'of FIG. 15' _theory Is more than or equal to 0.5 and less than 1. According to FIG. 15, when R _B Is a small value (e.g. R _B =50kΩ), the slope tends to be small in the low temperature region and large in the high temperature region, being nonlinear. On the other hand, when R _B Is a large value (e.g., R _B =2mΩ), the gradient is large in one low temperature region, but tends to be small in a high temperature region, which is also nonlinear.

However, it can be seen that there is an optimum value at which R _B Approximately linear from 25 c to 85 c. When R is _B By adjusting the characteristics of this region, the relationship between duty cycle D and temperature becomes linear and the processing of the microcontroller at the subsequent stage is simplified between 400kΩ and 700kΩ.

For equation (5), the resistor R is adjusted according to the characteristics of the thermistor element as in the process of equation (3) _A May not be necessary, equation (5) is converted into

Next, as in the first embodiment, the operation is confirmed by simulation, and the result will be presented with reference to fig. 16 and 17. In the simulation, R takes into account the results of FIG. 15 _B ＝490kΩ。

FIG. 16 shows a thermistor R in a second embodiment _th Voltage waveform V between (a '-a') _A’-A” . In the figure, the solid line represents the result at 25℃and the broken line represents the result at 55℃while the two-dot chain line represents the result at 85 ℃.

The voltage waveform across the thermistor of the first embodiment is a positive voltage, as shown in fig. 10. However, as shown in fig. 16, the voltage waveform across the thermistor of the second embodiment is a waveform that switches between a positive voltage and a negative voltage.

In the first embodiment, there is a region for holding direct current 5V (power supply voltage Vcc), and even if the temperature is changed to 25 ℃, 55 ℃, and 85 ℃, the time of this region is not changed. However, there is no corresponding region in the second embodiment. In the second embodiment there are 4 regions, respectively: a region where the voltage is high but gradually decreases, a region where the voltage suddenly decreases to a negative value, a region where the voltage gradually increases from a minimum value at a negative value, and a region where the voltage rapidly increases and becomes a positive value.

In the second embodiment, the region where the voltage is high but slowly decreases is similar to the region where the direct current 5V (power supply voltage Vcc) is maintained in the first embodiment. However, when the temperature is changed to 25 ℃, 55 ℃ and 85 ℃, there is a feature that the time is not constant but gradually becomes shorter.

In addition, in one region, the value is a negative value, and the value increases slowly from the minimum value, and when the temperature changes to 25 ℃, 55 ℃, and 85 ℃, the time is not constant, but becomes gradually shorter.

Fig. 17 shows the output voltage V of the oscillating circuit _B Relationship to time. The horizontal axis represents time, and the vertical axis represents the output voltage waveform V of the oscillating circuit _B This waveform is a substantially rectangular pulse wave.

The region of high voltage but slow drop in fig. 16 corresponds to the high (5V) region in fig. 18.

The region in FIG. 16 where the voltage value is negative and increases slowly from the minimum value corresponds to the low (near 0V) region in the graph of FIG. 18, where the high voltage time is T _on And the low voltage time is T _off 。

T as the temperature increases _on And T _off The duration of (2) is reduced but T _off Duration ratio T of (2) _on Shorter. Therefore, the duty ratio D increases with an increase in temperature. This trend is consistent with the results of fig. 15 based on calculated values.

As in the case of the first embodiment, the prior art is used in comparison with the second embodiment. A comparison is made of the prior art circuit shown in fig. 2 in which a thermistor is placed in series with a fixed resistor. However, the thermistors R of the first and second embodiments _th Adjusting resistor R _A FixingResistor R _B Is exchanged. Thus, in the prior art, for the circuit of FIG. 2, the thermistor R is also used _th Regulating resistor R _A And a fixed resistor R _B The positions of (3) are exchanged to make a comparison.

First, the output voltage waveforms are compared, and fig. 18 shows the result of circuit simulation. In fig. 18, the horizontal axis represents temperature and the vertical axis represents output voltage. For the prior art and the second embodiment, the resistance value R of the thermistor is used for comparison _th A regulating resistor R connected in parallel with the thermistor _A A fixed resistor R arranged in series with the thermistor _B The values of (2) are set to be the same.

In the prior art, the output voltage V _out (in the prior art, corresponding to V in FIG. 2 _sh ) Decreasing with increasing temperature. In the second embodiment, however, since an inverter is provided in the output stage of the timer IC, the voltage V is outputted _out (second embodiment, V in FIG. 14) _E ) Tends to increase with increasing temperature.

Adjusting the regulating resistor R _A And a fixed resistor R _B So that in the second embodiment the relationship between output voltage and temperature is linear over the range 25 c to 85 c.

Next, the voltages across the thermistors will be compared. In the second embodiment, as shown in the result of fig. 16, since the positive voltage and the negative voltage are switched, the thermistor consumes the voltage and generates heat when the voltage is positive and negative. Thus, for V shown in FIG. 16 _A ′-V _A Waveform, absolute value is calculated first, then average value is calculated. The result is indicated by a solid line in fig. 19.

In addition, the thermistor R in the prior art method is compared _th Is a position of (c). Adjusting resistor R _A And a fixed resistor R _B Switching from the circuit of fig. 2. Since the results are identical to those of fig. 18, the broken line representation of fig. 19 appears identical to the prior art results of fig. 18.

From the results shown in fig. 18 and 19, it can be seen that the degree of variation is greater in the prior art, but the voltage applied across the thermistor is smaller in the second embodiment. That is, in the second embodiment, the power consumption of the thermistor is small, and heat generation of the thermistor can be suppressed more than in the prior art.

In addition, the second embodiment is superior to the first embodiment in that the voltage of the Discharge (DIS) terminal is almost 0V when the timer IC is in the reset state, and thus the potential difference between a '-a and a' -a "(between the Discharge (DIS) terminal and the Ground (GND) terminal) is almost 0V, and no voltage needs to be applied to the thermistor during the reset operation. If the thermistor is driven continuously, the thermistor itself generates a small amount of self-heating, which may affect the measurement of the thermistor. However, this problem can be avoided by setting the potential applied to the thermistor to almost 0 volts.

In the case of the circuit in fig. 14, the microcontroller is connected to the RESET bar (RESET bar) terminal of the timer IC, and sends a low signal from the microphone and the controller to the timer to stop the operation of the timer IC and simultaneously apply the signal to the thermistor. It is possible to bring the applied potential close to 0V, that is, the second embodiment is suitable for the case of performing the reset operation when it is unnecessary for a long time because heat generation can be reduced.

The first embodiment, the second embodiment, and the thermistor detection method using the duty ratio D of the timer IC have been described. In the above description, the case where the number of thermistors of the sensor is 1 has been described. However, the number of thermistors of the sensor is not limited to one, and two or more thermistors may be configured as described above. Further, for simplicity of explanation, the timer IC is described as a timer IC. However, since the configuration is based on the internal circuit of the timer IC, if the product is not what is called a timer IC, the same internal circuit configuration as the timer IC can be used. A circuit configuration such as an ASIC may be used. Similar circuits may also be designed by a combination of comparators and flip-flops.

The present application also provides a third embodiment of a temperature detection circuit.

The above-described first and second embodiments have described a setting method using a timer IC. However, another oscillating circuit may be used. The following means that the technical solution using an H-bridge will be described as the third embodiment and the fourth embodiment. The H-bridge has a circuit configuration comprising four switches, typically used to control the current direction of the motor, also known as an oscillating circuit configuration. In the third and fourth embodiments, the present invention will describe an example to which the H-bridge type oscillating circuit is applied.

Fig. 20 shows a circuit of the third embodiment. In the figure, a first electrical path and a second electrical path are respectively connected to a power supply Vcc. Each of them is connected with a capacitor C _H Is connected to opposite sides of the frame. Detection resistor R _d The other end of which is grounded, and the third and fourth electrical paths. Then, the third and fourth electrical paths are connected to the capacitor C _H Is provided on the opposite side of (a).

Further, a switch is provided in each of the first electrical path, the second electrical path, the third electrical path, and the fourth electrical path. The switch on the first electrical path is switch 1 (SW 1), the switch on the second electrical path is switch 2 (SW 2), the switch on the third electrical path is switch 3 (SW 3), and the switch on the fourth electrical path is switch 4 (SW 4). The four switches used in the H-bridge are controlled by the output Q or Q bar of the flip-flopAnd (5) controlling. Q and Q bar are positive and negative theories, respectively, in the digital circuit domain. When the voltage is indicated by high (high voltage) and low (low voltage), Q bar is low when Q is high; when Q is low, Q bar is high. Switch 1 (SW 1) and switch 4 (SW 4) are connected to Q, respectively, and switch 2 (SW 2) and switch 3 (SW 3) are connected to Q bar, respectively.

When a high signal is input to Q, the switch 1 (SW 1) and the switch 4 (SW 4) are turned on, and when a low signal is input to Q, the switch 1 (SW 1) and the switch 4 (SW 4) are turned off. That is, when the switch 1 (SW 1) and the switch 4 (SW 4) are turned on, the switch 2 (SW 2) and the switch (SW 3) are turned off. In contrast, when the switch 1 (SW 1) and the switch 4 (SW 4) are turned off, the switch 2 (SW 2) and the switch (SW 3) are turned on.

The switch used herein is a switch that can be electrically controlled to be on/off, more specifically, a MOS-FET, bipolar transistor, thyristor, relay, or the like. However, as one skilled in the art will appreciate, there are numerous ways. For example, there are products for performing various operations, such as complementary products of P-ch and N-ch in MOS-FETs. This description will not be read in a one-to-one manner for the sake of brevity. What is important is the operation of the switches 1 (SW 1) to 4 (SW 4). For example, if the P-ch MOSFET is for the high side and the N-ch MOSFET is for the low side, Q bar is connected to switch 1 (SW 1), Q is connected to switch 2 (SW 2), Q bar is connected to switch 3 (SW 3), and Q is connected to switch 4 (SW 4). In addition, Q and Q bar are reversed when passing through the inverter, which is common knowledge of those skilled in the art, and will be omitted in the following description.

Although a circuit after the low-pass filter is omitted in fig. 20, a differential amplifier, an a/D converter, a microcontroller, and the like are provided after the output stage K of the circuit, as shown in the connection of fig. 7 and 14.

Next, other operations of the third embodiment will be described in two states.

The first state is that switch 1 (SW 1) and switch 4 (SW 4) are on, and switch 2 (SW 2) and switch 3 (SW 3) are off. In this state, the second electric path and the third electric path through which no current flows can be considered, and therefore, equivalently, the circuit shown in fig. 21 can be used. For convenience, this state will be described as state 1.

The second state is that the switch 1 (SW 1) and the switch 4 (SW 4) are off, and the switch 2 (SW 2) and the switch 3 (SW 3) are on. This state may be equivalently illustrated in fig. 22, where the first electrical path and the fourth electrical path may be omitted. For convenience, this state will be described as state 2.

In state 1, i.e. in the case of fig. 21, sensor 1 and sensor 2 are connected in series with switch 1 (SW 1) and switch 4 (SW 4). Wherein, the thermistor 1R _TH1 Is connected to the sensor 1, thermistor 2R _TH2 Is connected to the sensor 2. This point is electrically different from state 2 (i.e., the case of fig. 22). That is, the resistance value on the circuit is higher in state 1 than state 2 due to the increased resistance of the thermistor.

This operation will be described with reference to fig. 23. After Q goes high, that isState 1I ₁ Flows in the positive direction. At the same time, charge is gradually accumulated in the capacitor C _H In such a way that the current I ₁ And become smaller. Thus, flow through R _d Gradually decreasing the current of V _H And also gradually decreases.

One end of the input end of the comparator is connected to V _cmp The other end is connected to R from the ground _d Is provided on the opposite end of the housing. The output is connected to the clock of the flip-flop. When R is _d The voltage between them drops to V _cmp The comparator outputs an output signal. Because the output signal is the input of the flip-flop clock, the output of the flip-flop is inverted. That is, if Q is a high signal, it will become a low signal.

When the Q signal switches from a high signal to a low signal, the state transitions from state 1 (fig. 21) to state 2 (fig. 22). In state 2, the current flows along I ₂ ＝-I ₁ The absolute value of the present current value becomes larger when the state is changed than when state 1 is transitioned. This is because the resistance of the circuit from Vcc to ground is lower in state 2. In state 2, the current flows through the sense resistor R _d Is charged in capacitor C _H Is reduced by accumulation of V _H And also gradually decreases.

Then, when V _H Is lower than V _cmp When the comparator outputs an output signal. Since the output signal is input to the flip-flop clock, the output of the flip-flop is inverted. That is, if Q is a low signal, it will become a high signal. Then, the state is switched from state 2 (fig. 22) to state 1 (fig. 21).

As described above, the state 1 and the state 2 are alternately repeated. By repeating, the oscillation continues. However, in the case of state 1, since the thermistor is present in the electrical path, the resistance value from Vcc to ground is large, so V _H Down to V _cmp Requiring time. Therefore, the high period of Q becomes longer. In other words, the duty cycle D of the signal Q increases. Since the duty ratio D depends on the resistance of the thermistor, the thermistor R can be detected by reading the value of the duty ratio D _TH1 And R is _TH2 Is a value of (2).

As described in the first embodiment and the second embodiment, the value of the duty ratio D is easily detected by converting to a direct current level using a low-pass filter. Through the filter to the voltage V _k The values are shown in fig. 24. When the temperature increases, the resistance value of the NTC thermistor decreases, and thus the difference between the resistance values of the state 1 and state 2 paths gradually decreases. Thus, T of Q _on And T is _off The time differences of (2) gradually approach. Wherein Vcc value is set to 5V in fig. 20-22, V corresponding to duty ratio d=50% in fig. 24 _k =2.5v. It can be seen that as the temperature increases, the value approaches the duty cycle d=50%.

Wherein R in FIGS. 20 and 21 ₂₁ And R is ₂₂ Is the tuning resistor described in the first embodiment as well as the second embodiment. Adjusting resistors for improving T-V _k Linearity of the characteristic. By adjusting the resistor R ₂₁ And R is ₂₂ By choosing the appropriate value, linearity will be improved. However, the voltage V _k The amount of change after passing through the filter, deltaV _k With adjusting the resistor R ₂₁ And R is ₂₂ Is reduced by a reduction in the value of (2). When the signal becomes smaller, it is difficult for the a/D converter to detect it, and thus Δv is not caused _k Very small. Preferably, the resistor R is regulated ₂₁ And R is ₂₂ Is to weigh the linearity and DeltaV _k The value is determined.

In addition, in FIGS. 20 to 22, the thermistor 1R _TH1 And a thermistor 2R _TH2 Shown as sensor 1 and sensor 2, respectively, but they need not be used alone as separate sensors. Both sensors may be incorporated into the same sensor and used to detect the same gas. Therefore, the thermistor 1R _TH1 And a thermistor 2R _TH2 May be adjacently arranged or may be thermistors that do not have the same characteristics.

Fourth embodiment

The third embodiment shows an arrangement using an H-bridge and a thermistor that is active in the case of state 1 and inactive in the case of state 2. However, a configuration may be employed in which the thermistor contributes to both state 1 and state 2. That is, the circuit diagrams of both state 1 and state 2 may include thermistors. As a fourth embodiment, a description will be given of an arrangement in which both state 1 and state 2 have thermistors.

Fig. 25 is a diagram showing a fourth embodiment. One thermistor is provided in each of the first to fourth electrical paths. Wherein it is assumed that the thermistor on the first electrical path is arranged adjacent to the thermistor on the fourth electrical path, functioning as a sensor. Further, it is assumed that the thermistor on the second electrical path and the thermistor on the third electrical path are set to measure the reference temperature. Wherein the reference temperature is a temperature to be compared with a value of the sensor, and may be a room temperature. However, since the temperature may vary at room temperature, the reference temperature may be a constant temperature heated by a heater or the like.

When the NTC thermistor is used as the thermistor, if the temperature of the NTC thermistor of the sensor is lower than the reference temperature, the resistance value of the first and fourth electrical paths having the sensor is greater than the second and third electrical paths that are measuring the reference temperature, and thus the duty ratio D becomes 50% or more. In contrast, if the temperature of the NTC thermistor of the sensor is higher than the reference temperature, the resistance values of the first and fourth electrical paths having the sensor are smaller than those of the second and third electrical paths in which the reference temperature is being measured, and thus the duty ratio D becomes 50% or less. Depending on whether the duty ratio D is 50% or more or 50% or less, comparison with the reference temperature can be achieved, so that a plurality of gases can be compared, or one of them can be made into general air and compared with the gas.

If the reference temperature is known in advance, a resistance value corresponding to the reference temperature may be provided into the second electrical path and the third electrical path. In this case, since it is not necessary to measure the temperature, the arrangement can be simplified. The resistance value corresponding to the reference temperature may be a fixed resistance or an electrically adjustable value.

In the above description, the first and fourth electrical paths and the second and third electrical paths are clearly shown for convenience of explanation. Since the same effect can be obtained by the connection, the connection can be reversed.

As described above, from the first embodiment to the fourth embodiment, the present application proposes a temperature detection circuit that can be used for a gas detection device, which is a method of detecting a thermistor using a self-oscillation circuit. Since all of the oscillating circuits of the first to fourth embodiments output rectangular waveform pulse waves, it is applicable to the heater of the heating unit of fig. 1. As shown in the prior art document, a pulse wave is typically used to drive a heater. Therefore, the circuit can be simplified by adding the pulse wave according to the present invention.

Fig. 26 is a diagram for explaining a method of supplying a pulse wave generated by the present invention to a heater. The output of the oscillating circuit and the pulse shape before the low pass filter are used for the heater. The amplitude and duty cycle D of the pulse wave contribute to the heater. That is, as the amplitude of the pulse wave increases and the duty ratio D increases, the heater is heated. The compensator has a configuration related to pulse wave control, and has a function of performing operations such as controlling amplitude, inverting the duty ratio D using an inverter, and providing delay. For example, the duty ratio D-temperature characteristic of the first embodiment and the duty ratio D-temperature characteristic of the second embodiment exhibit opposite trends with respect to temperature. However, by providing an inverter in the compensator, the high and low voltages can be reversed, so that this trend can be reversed.

While the foregoing is directed to the preferred embodiments of the present invention, it will be appreciated by those skilled in the art that changes and modifications may be made without departing from the principles of the invention, such changes and modifications are also intended to be within the scope of the invention.

Claims

1. A temperature detection circuit, comprising:

power supply, capacitor, detection resistor, thermistor

A first electrical path provided between the power source and the capacitor;

a second electrical path provided between a plurality of ends of the capacitor;

a low pass filter connected to the output of the trigger;

the first electrical path and the second electrical path are connected to the power source, respectively, the first electrical path and the second electrical path being connected to opposite sides of the capacitor; one end of the detection resistor is grounded, and the other end of the detection resistor is connected with the third electric path and the fourth electric path, and the third electric path and the fourth electric path are respectively connected to opposite sides of the capacitor.

2. The temperature detection circuit of claim 1, wherein:

3. The temperature detection circuit of claim 2, wherein:

the reference temperature is measured by adopting a resistance value corresponding to the reference temperature to replace a thermistor.

4. A gas detection apparatus, comprising: a heating device, a microcontroller, and a temperature detection circuit as claimed in any one of claims 1 to 3.

5. The gas detection apparatus according to claim 4, wherein the heating means is acted on by a pulse wave of a rectangular waveform generated by the self-oscillation circuit.

6. A temperature detection method, wherein the temperature detection method employs a temperature detection circuit, the temperature detection circuit comprising:

The low-pass filter is arranged at the Output (OUT) end of the oscillating circuit;

the temperature detection method uses a formulaWherein D is the duty ratio of the self-oscillation circuit to output rectangular waveform, R _th R is the resistance value of the thermistor _B For the fixation ofThe resistance value of the resistor;

7. A temperature detection method, wherein the temperature detection method employs a temperature detection circuit, the temperature detection circuit comprising:

the fixed resistor is connected between the power supply voltage end and the Discharge (DIS) end;

the temperature detection method uses a formulaWherein D is the duty ratio of the self-oscillation circuit to output rectangular waveform, R _th R is the resistance value of the thermistor _B A resistance value of the fixed resistor;