Low-power thermistor measurement circuit and sensor

Abstract

The application discloses a low-power thermistor measuring circuit and a sensor, and the circuit comprises a thermistor, a heating power supply branch and a working power supply branch, the heating power supply branch is used for providing heating power, and the working power supply branch is used for providing power supply power; a double-control switch, a first end of the double-control switch is connected with the thermistor, and a second end of the double-control switch is used for being connected with the heating power supply branch or the working power supply branch according to a control signal; a preheating judgment circuit, a current detection end of the preheating judgment circuit is connected with the thermistor, and a control end of the preheating judgment circuit is connected with a controlled end of the double-control switch; the preheating judgment circuit is used for detecting the temperature of the thermistor, and the second end of the double-control switch is connected with the heating power supply branch or the working power supply branch according to the detected temperature, so that the heating power supply branch is connected with the thermistor or the working power supply branch is connected with the thermistor. The application solves the problem that the power consumption of a sensor for measuring air water content (humidity) by using double thermistors is large.

Description

Technical Field

[0001] This invention relates to the field of sensors, and in particular to a low-power thermistor measurement circuit and sensor. Background Technology

[0002] Ordinary capacitive humidity sensors experience a decrease in accuracy in high humidity environments, and prolonged operation in extremely low or high humidity environments can lead to dehydration or saturation, causing sensor failure. In high humidity environments, a sensor that uses dual thermistors to measure air moisture content (humidity) can be used to measure humidity.

[0003] In sensors that use dual thermistors to measure air moisture content (humidity), the thermistors in the sensor need to operate at higher temperatures in order to improve the sensor's detection accuracy. Therefore, a fixed bias current of a large value is required for the thermistors, resulting in higher power consumption of the sensor. At the same time, the output noise of the high-voltage bias circuit is relatively large, which also affects the accuracy of the sensor measurement. Summary of the Invention

[0004] The main objective of this invention is to propose a low-power thermistor measurement circuit and sensor, aiming to solve the problem of high power consumption of sensors that use dual thermistors to measure air moisture content (humidity).

[0005] To achieve the above objectives, this invention proposes a low-power thermistor measurement circuit for use in sensors measuring air moisture content. The low-power thermistor measurement circuit includes:

[0006] Thermistor;

[0007] A heating power supply branch and a working power supply branch, wherein the heating power supply branch is used to provide heating power and the working power supply branch is used to provide power supply.

[0008] A dual-control switch, wherein the first end of the dual-control switch is connected to the thermistor, and the second end of the dual-control switch is used to connect to the heating power supply branch or the working power supply branch according to an external control signal;

[0009] A preheating judgment circuit is provided, wherein the current detection terminal of the preheating judgment circuit is connected to the thermistor, and the control terminal of the preheating judgment circuit is connected to the controlled terminal of the dual-control switch.

[0010] The preheating judgment circuit is used to detect the temperature of the thermistor, and control the second terminal of the dual-control switch to be connected to the heating power supply branch or the working power supply branch according to the detected temperature, so that the heating power supply branch is connected to the thermistor, or the working power supply branch is connected to the thermistor.

[0011] Optionally, the preheating judgment circuit is specifically used to control the second terminal of the dual-control switch to connect to the heating power supply branch when the detected current flowing through the thermistor is less than the preset current, and to control the second terminal of the dual-control switch to connect to the working power supply branch when the detected current flowing through the thermistor is greater than or equal to the preset current.

[0012] Optionally, the heating power supply branch includes a first voltage source and a first resistor, the first voltage source being connected to a first end of the first resistor; the working power supply branch includes a second voltage source and a second resistor, the second voltage source being connected to a first end of the second resistor.

[0013] The preheating judgment circuit is specifically used to control the second terminal of the dual-control switch to connect to the second terminal of the first resistor when the detected current flowing through the thermistor is less than the preset current, and to control the second terminal of the dual-control switch to connect to the second terminal of the second resistor when the detected current flowing through the thermistor is greater than or equal to the preset current.

[0014] Optionally, the low-power thermistor measurement circuit further includes a high-voltage drive circuit, the enable terminal of which is connected to the control terminal of the preheating judgment circuit, and the output terminal of which is connected to the first voltage source.

[0015] The preheating judgment circuit is also used to control the high-voltage drive circuit to provide voltage to the heating power supply branch when the detected temperature of the thermistor is lower than the preset temperature.

[0016] Optionally, the low-power thermistor measurement circuit further includes a low-voltage drive circuit, the enable terminal of which is connected to the control terminal of the preheating judgment circuit, and the output terminal of which is connected to the second voltage source.

[0017] The preheating judgment circuit is also used to control the low-voltage drive circuit to provide voltage to the working power supply branch when the detected temperature of the thermistor is greater than or equal to a preset temperature.

[0018] Optionally, there are two thermistors, referred to as the first thermistor and the second thermistor, which are connected in series between the first terminal of the dual-control switch and the ground electrode. The first output terminal of the thermistor measurement circuit is the common terminal of the first thermistor and the second thermistor.

[0019] Optionally, the first thermistor is sealed in an absolutely dry gas, while the second thermistor is not sealed.

[0020] Optionally, the low-power thermistor measurement circuit further includes a third resistor and a fourth resistor, which are connected in series between the first terminal of the dual-control switch and the ground electrode, and the second output terminal of the thermistor measurement circuit is the common terminal of the third resistor and the fourth resistor.

[0021] This invention proposes a sensor for measuring the moisture content of air, which includes the low-power thermistor measurement circuit described above.

[0022] Optionally, the sensor for measuring air moisture content further includes:

[0023] A barometric pressure sensor is used to detect the air pressure in the current environment.

[0024] Temperature sensors are used to detect the temperature in the current environment;

[0025] The processor is connected to the output terminals of the barometric pressure sensor, the temperature sensor, and the thermistor measurement circuit. The processor is used to calculate the absolute humidity of the current environment based on the output voltage of the thermistor measurement circuit. The processor is also used to calculate the relative humidity of the current environment based on the barometric pressure detected by the barometric pressure sensor, the temperature detected by the temperature sensor, and the absolute humidity of the current environment.

[0026] This invention employs a low-power thermistor measurement circuit. The preheating judgment circuit controls the corresponding power supply branch to provide bias current to the thermistor based on its temperature. When the thermistor temperature has not reached a preset value, the heating power supply branch provides a larger bias current, causing the thermistor to heat up rapidly. Once the thermistor temperature reaches the preset value, the working power supply branch provides a smaller bias current to maintain a voltage difference across the thermistor. Compared to technical solutions where the heating power supply branch continuously provides a large deviation current, the thermistor measurement circuit provided by this invention reduces damage and noise. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0028] Figure 1 This is a schematic diagram of the functional module structure of an embodiment of the low-power thermistor measurement circuit of the present invention;

[0029] Figure 2This is a schematic diagram of the circuit structure of an embodiment of the low-power thermistor measurement circuit of the present invention;

[0030] Figure 3 for Figure 1 Circuit diagram of one embodiment of the preheating judgment circuit;

[0031] Figure 4 This is a circuit structure diagram of an embodiment of the high-voltage drive circuit in the low-power thermistor measurement circuit of the present invention;

[0032] Figure 5 This is a circuit diagram of an embodiment of the low-voltage drive circuit in the low-power thermistor measurement circuit of the present invention.

[0033] Explanation of icon numbers:

[0034] label name label name 10 Working power supply branch 20 Heating power supply branch 30 Double control switch 40 Preheating detection circuit Rdry First thermistor Rair Second thermistor R1-R4 First resistor - Fourth resistor First output terminal Vout+ Second output terminal Vout- First power supply V1 Second power supply V2

[0035] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0036] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0037] It should be noted that if the embodiments of the present invention involve directional indicators (such as up, down, left, right, front, back, etc.), the directional indicators are only used to explain the relative positional relationship and movement of the components in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indicators will also change accordingly.

[0038] Furthermore, if the embodiments of this invention involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. If the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by this invention.

[0039] Existing conventional capacitive humidity sensors experience a decrease in accuracy in high humidity environments, and dehydration or saturation can occur when operating in extremely low or high humidity environments for extended periods, leading to sensor failure.

[0040] To address this, a sensor that uses dual thermistors to measure air moisture content (humidity) can be provided. To improve the sensor's detection accuracy, the thermistors in the sensor are negative temperature coefficient thermistors. The thermistors in the sensor need to operate at higher temperatures. The thermistor's resistance decreases as the temperature rises. At higher temperatures, the thermistor's resistance value is smaller, and the change in the thermistor's resistance value caused by the humidity in the air is more obvious.

[0041] If the thermistor operates at low temperatures, its resistance will be high. This may result in the thermistor's resistance showing little change regardless of ambient humidity, or the thermistor's resistance may only be slightly affected by humidity, leading to no significant change in the sensor's output voltage. This makes it difficult to accurately measure the absolute moisture content of the air. To obtain accurate measurement data, the thermistor needs to be at a higher temperature. This requires a large, fixed bias current, resulting in higher power consumption for the sensor. Additionally, the high-voltage bias circuit generates more output noise, which also affects the sensor's measurement accuracy.

[0042] by Figure 2 Taking the circuit structure of a dual-thermometer sensor for measuring air moisture content (humidity) as an example, if a negative temperature coefficient thermistor is used, the higher the ambient temperature, the lower the thermistor's resistance. The resistance under low humidity is denoted as Rdry, and the resistance under high humidity is denoted as Rair. (Rdry - Rair) is the difference between the two thermistor values ​​due to moisture, while (Rdry + Rair) is the sum of the two thermistor values.

[0043] Assuming that during the operation of the sensor measuring air moisture content (humidity), the ambient temperature remains constant, while the air moisture content changes, (Rday - Rair) remains constant, and (Rdry + Rair) changes with the air moisture content. The output voltage Vout = Vc * ((Rdry - Rair) / (2 * (Rdry + Rair)), where Vc is the voltage across the common terminal of Rday and R3. According to the above formula, Vc * ((Rdry - Rair)) does not change with the air moisture content. The smaller (Rdry + Rair) is, the greater the change in output voltage Vout caused by the change in air moisture, and the more accurate the measurement result of the air moisture content (humidity) sensor. Since Rdry + Rair is a negative temperature coefficient thermistor, the higher the ambient temperature of the thermistor, the lower the resistance value. Therefore, at low temperatures, the resistance value caused by humidity changes may not be obvious.

[0044] This invention proposes a low-power thermistor measurement circuit to reduce the power consumption of a dual thermistor sensor for measuring air moisture content (humidity).

[0045] Reference Figure 1 and Figure 2 In one embodiment of the present invention, the low-power thermistor measurement circuit includes:

[0046] Thermistor;

[0047] The heating power supply branch 20 and the working power supply branch 10 are provided, wherein the heating power supply branch 20 is used to provide heating bias current and the working power supply branch 10 is used to provide power supply bias current.

[0048] A dual-control switch 30, the first end of which is connected to the thermistor, and the second end of which is used to connect to the heating power supply branch 20 or the working power supply branch 10 according to an external control signal;

[0049] A preheating judgment circuit 40 is provided, wherein the current detection terminal of the preheating judgment circuit 40 is connected to the thermistor, and the control terminal of the preheating judgment circuit 40 is connected to the controlled terminal of the dual-control switch 30.

[0050] The preheating judgment circuit 40 is used to detect the current flowing through the thermistor, and control the second terminal of the dual-control switch 30 to be connected to the heating power supply branch 20 or the working power supply branch 10 according to the detected current flowing through the thermistor, so that the heating power supply branch 20 is connected to the thermistor, or the working power supply branch 10 is connected to the thermistor.

[0051] In this embodiment, since the heat exchange effect of the thermistor is more pronounced at high temperatures, and the resistance decreases as the thermistor temperature rises, it is easier to accurately measure the resistance value using a bridge circuit when the resistance is low. Therefore, when the sensor first starts working, a large heating bias current is required to ensure the thermistor operates at a high temperature. The heating power supply branch 20 provides the heating bias current to the thermistor. When the heating power supply branch 20 is connected to the thermistor, the heating bias current output by the heating power supply branch 20 to the thermistor is large, resulting in a large heating power of the thermistor and allowing its temperature to rise rapidly, thus achieving rapid heating of the thermistor.

[0052] The working power supply branch 10 provides a working bias current to the thermistor. When the thermistor is connected to the working power supply branch 10, the working bias current output by the working power supply branch 10 to the thermistor creates a voltage difference across the thermistor, causing the sensor to output a corresponding voltage. The working bias current is much smaller than the heating bias current, and the power consumed by the working power supply branch 10 connected to the thermistor is much smaller than the power consumed by the heating power supply branch 20 connected to the thermistor.

[0053] The preheating judgment circuit 40 has the function of detecting the temperature of the thermistor. It can also control the heating power supply branch 20 to provide a heating bias current to the thermistor, or the working power supply circuit to provide a working bias current to the thermistor, based on the thermistor's temperature. For example, when the temperature detected by the preheating judgment circuit 40 is lower than a preset value, the thermistor's temperature is low, and the heating power supply branch 20 needs to be connected to rapidly heat the thermistor. When the temperature detected by the preheating judgment circuit 40 is higher than or equal to the preset temperature value, the thermistor's temperature is high, meeting the sensor's operating requirements. In this case, the working power supply branch 10 needs to be connected to maintain a voltage drop across the thermistor. Since the bias current provided by the working power supply branch 10 is less than the bias current provided by the heating power supply branch 20, the sensor consumes less power in this situation.

[0054] Specifically, the first terminal of the double-control switch 30 is fixedly connected to the thermistor, and the second terminal of the double-control switch 30 is connected to the heating power supply branch 20 or the working power supply branch 10 according to the control signal of the preheating judgment circuit 40. When the temperature of the thermistor reaches the preset temperature, the preheating judgment circuit 40 controls the second terminal of the double-control switch 30 to connect to the working power supply branch 10. When the temperature of the thermistor does not reach the preset temperature, it can be considered that the temperature of the thermistor has not reached the preset temperature, and at this time, the second terminal of the double-control switch 30 is controlled to connect to the heating power supply branch 20.

[0055] It should be noted that the current flowing through the thermistor remains unchanged at the instant the dual-control switch is switched. Whether the thermistor switches from being connected to the heating power supply branch 20 to the working power supply branch 10, or vice versa, the heating bias current provided by the heating power supply branch 20 and the working bias current provided by the working power supply branch 10 are the same during the switchover. Because the output current of the corresponding power supply branch remains unchanged, the circuit operates more stably, and the corresponding noise is reduced. Furthermore, the corresponding sensor output voltage also remains unchanged, which improves the stability of the sensor measurement results and thus enhances the sensor's measurement accuracy.

[0056] Specifically, with Figure 2 Taking the circuit structure in the example, V1, V2, R1, and R2 are pre-set with corresponding parameters so that the current flowing through resistors Rdry, Rair, R3, and R4 remains unchanged when the double-control switch 30 is switched.

[0057] Optionally, there are two thermistors, referred to as the first thermistor Rdry and the second thermistor Rair, which are connected in series between the first terminal of the dual-control switch 30 and the ground. The first output terminal Vout+ of the thermistor measurement circuit is the common terminal of the first thermistor Rdry and the second thermistor Rair. The first thermistor Rdry is sealed in an absolutely dry gas, while the second thermistor Rair is not sealed.

[0058] It should be noted that the low-power thermistor measurement circuit in this embodiment is applied to a sensor for measuring air moisture content. Existing ordinary capacitive humidity sensors experience a decrease in accuracy in high humidity environments, and long-term operation in extremely low or high humidity environments can lead to dehydration or saturation, causing sensor failure. The thermistor measurement circuit in this embodiment, applied to a sensor for measuring air moisture content, detects air moisture content by detecting the voltage at the common terminal of a first thermistor Rdry and a second thermistor Rair. One thermistor (Rdry) is sealed in an absolutely dry gas, while the other thermistor (Rair) is not sealed and is in contact with the gas being measured. When current flows through the thermistors, the resistors heat up, and their resistance decreases. Eventually, the heat generated by the current and the heat dissipated by the thermistors equalize, reaching thermal equilibrium, and the final temperature remains constant. Because the air in the measured environment contains moisture, the heat exchange rate differs from that of completely dry gas, resulting in different temperatures for the two thermistors in their final stable states. By measuring and comparing the resistance values ​​of the two thermistors at their final stable state, the moisture content in the measured gas can be calculated. The sensor can be tested using a standard absolute humidity meter and a constant temperature and humidity chamber. Different absolute humidity levels can be adjusted, and the sensor output voltage can be recorded. The relationship between the sensor output voltage and the absolute humidity can be measured, and the relationship between the absolute humidity and the sensor output voltage can be derived from the sensor output voltage.

[0059] Optionally, the low-power thermistor measurement circuit further includes a third resistor and a fourth resistor, which are connected in series between the first terminal of the dual-control switch 30 and the ground electrode. The second output terminal Vout- of the thermistor measurement circuit is the common terminal of the third resistor and the fourth resistor.

[0060] The third and fourth resistors, together with the first thermistor Rdry and the second thermistor Rair, form a bridge circuit. The second output terminal Vout- is located at the common terminal of the third and fourth resistors, and outputs a stable voltage signal. By comparing the voltage at the first output terminal Vout+ with the voltage at the second output terminal Vout-, the bridge circuit can measure minute changes in the voltage at the first output terminal Vout+, thus achieving higher measurement accuracy.

[0061] This invention employs a low-power thermistor measurement circuit. The preheating judgment circuit 40 controls the corresponding power supply branch to provide a bias current to the thermistor based on its temperature. When the thermistor temperature has not reached a preset value, the heating power supply branch 20 provides a larger bias current to the thermistor, causing it to heat up rapidly. When the thermistor temperature reaches the preset value, the working power supply branch 10 provides a smaller bias current to maintain a voltage difference across the thermistor. Compared to a technical solution where the heating power supply branch 20 continuously provides a large deviation current, the thermistor measurement circuit provided by this invention reduces damage and noise.

[0062] In one embodiment of the present invention, the preheating judgment circuit 40 is specifically used to control the second terminal of the double-control switch 30 to connect to the heating power supply branch 20 when the detected current flowing through the thermistor is less than a preset current, and to control the second terminal of the double-control switch 30 to connect to the working power supply branch 10 when the detected current flowing through the thermistor is greater than or equal to the preset current.

[0063] In this embodiment, the preheating judgment circuit 40 can detect the temperature of the thermistor by detecting the current flowing through it. When the current flowing through the thermistor reaches the preset current, it can be considered that the temperature of the thermistor has reached the preset temperature. At this time, the second terminal of the double-control switch 30 is connected to the working power supply branch 10. When the current flowing through the thermistor does not reach the preset current, it can be considered that the temperature of the thermistor has not reached the preset temperature. At this time, the second terminal of the double-control switch 30 is connected to the heating power supply branch 20.

[0064] Reference Figure 2 In one embodiment of the present invention, the heating power supply branch 20 includes a first voltage source and a first resistor, the first voltage source being connected to a first end of the first resistor, and the working power supply branch 10 includes a second voltage source and a second resistor, the second voltage source being connected to a first end of the second resistor.

[0065] The preheating judgment circuit 40 is specifically used to control the second terminal of the dual-control switch 30 to connect to the second terminal of the first resistor when the detected current flowing through the thermistor is less than the preset current, and to control the second terminal of the dual-control switch 30 to connect to the second terminal of the second resistor when the detected current flowing through the thermistor is greater than or equal to the preset current.

[0066] In this embodiment, the working power supply branch 10 and the heating power supply branch 20 include corresponding power supply voltage sources and voltage divider resistors. Due to the presence of the voltage divider resistors, the thermistor's resistance will not decrease and the current will not increase uncontrollably as the temperature rises. Even if the thermistor's temperature is very high, its resistance is very small, and the heat generated by the thermistor current and the heat dissipated outward will eventually be equal, reaching thermal equilibrium, and the final temperature will remain constant.

[0067] Reference Figure 3 and Figure 4 In one embodiment of the present invention, the low-power thermistor measurement circuit further includes a high-voltage drive circuit, the enable terminal of the high-voltage drive circuit is connected to the control terminal of the preheating judgment circuit 40, and the output terminal of the high-voltage drive circuit is connected to the first voltage source.

[0068] The preheating judgment circuit 40 is also used to control the high-voltage drive circuit to provide voltage to the heating power supply branch 20 when the detected temperature of the thermistor is lower than the preset temperature.

[0069] In this embodiment, the high-voltage drive circuit provides voltage to the first power supply V1 of the heating power supply circuit. When the high-voltage drive circuit does not output drive voltage, the first power supply V1 is not powered on, and the heating working branch cannot work. When the thermistor detected by the preheating judgment circuit 40 has not reached the preset temperature, the high-voltage drive circuit provides voltage to the first voltage source, and the heating power supply circuit works. When the thermistor reaches the preset temperature, the power supply to the heating power supply branch 20 is stopped, and the heating power supply branch 20 does not work.

[0070] Reference Figure 3 and Figure 5 In an embodiment of the present invention, the low-power thermistor measurement circuit further includes a low-voltage drive circuit, the enable terminal of the low-voltage drive circuit is connected to the control terminal of the preheating judgment circuit 40, and the output terminal of the low-voltage drive circuit is connected to the second voltage source.

[0071] The preheating judgment circuit 40 is also used to control the low-voltage drive circuit to provide voltage to the working power supply branch 10 when the detected current flowing through the thermistor is greater than or equal to a preset current.

[0072] In this embodiment, the low-voltage drive circuit provides voltage to the second power supply V2 of the working power supply circuit. When the low-voltage drive circuit does not output drive voltage, the second power supply V2 is not powered on, and the working branch cannot work. When the thermistor detected by the preheating judgment circuit 40 has not reached the preset temperature, the low-voltage drive circuit provides voltage to the second voltage source, and the heating power supply circuit works. When the thermistor reaches the preset temperature, the power supply to the working power supply branch 10 is stopped, and the working power supply branch 10 does not work.

[0073] Reference Figures 1 to 5 The present invention proposes a sensor for measuring the moisture content of air, wherein the sensor for measuring the moisture content of air includes the low-power thermistor measurement circuit described above.

[0074] The detailed structure of the low-power thermistor measurement circuit can be referred to the above embodiments, and will not be repeated here. It is understood that since the above-mentioned low-power thermistor measurement circuit is used in the sensor for measuring air moisture content of the present invention, the embodiments of the sensor for measuring air moisture content of the present invention include all the technical solutions of all the embodiments of the above-mentioned low-power thermistor measurement circuit, and the technical effects achieved are exactly the same, and will not be repeated here.

[0075] In one embodiment of the present invention, the sensor for measuring air moisture content further includes:

[0076] A barometric pressure sensor is used to detect the air pressure in the current environment.

[0077] Temperature sensors are used to detect the temperature in the current environment;

[0078] The processor is connected to the output terminals of the barometric pressure sensor, the temperature sensor, and the thermistor measurement circuit. The processor is used to calculate the absolute humidity of the current environment based on the output voltage of the thermistor measurement circuit. The processor is also used to calculate the relative humidity of the current environment based on the barometric pressure detected by the barometric pressure sensor, the temperature detected by the temperature sensor, and the absolute humidity of the current environment.

[0079] In this embodiment, a standard absolute humidity tester and a constant temperature and humidity chamber can be used to test the sensor, adjust different absolute humidity levels, record the sensor output voltage, measure the relationship between the sensor output voltage and absolute humidity, and obtain the relationship between absolute humidity and air absolute water content AH (g / m3) based on the sensor output voltage.

[0080] A barometric pressure sensor can measure barometric pressure B (Pa), and a temperature sensor can measure air temperature t (°C).

[0081] Moist air has the following parameters: T - Kelvin temperature (K), Pq - partial pressure of water vapor (Pa), Pqb - partial pressure of saturated water vapor (Pa), d - moisture content (g / kg), ρ - density of moist air (kg / m3), and RH - relative humidity;

[0082] The parameters of moist air have the following relationship: T = 273.15 + t;

[0083] Saturated water vapor partial pressure: ln(P) qb )=C8 / T+C9+C10 T+C 11 T 2 +C 12 T 3 +C 13 ln(T), where C8~C13 are constant coefficients in the above formula;

[0084] Water vapor partial pressure: P q =P qb *RH;

[0085] Air humidity: d = 622P q / (BP q );

[0086] Moist air density: ρ = 0.003484B / T - 0.00134P q / T;

[0087] Absolute moisture content: AH = 1000ρd / (d+1000);

[0088] Even in high humidity or supersaturated environments, as long as the measuring module measures the absolute water content AH (g / m3), air pressure B (Pa), and air temperature t (°C), the current relative humidity can be calculated using the above-mentioned formulas.

[0089] The above description is only a preferred embodiment of the present invention and does not limit the patent scope of the present invention. All equivalent structural transformations made under the concept of the present invention using the contents of the present invention specification and drawings, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A low-power thermistor measurement circuit, used in a sensor for measuring air moisture content, characterized in that, The low-power thermistor measurement circuit includes: Thermistor; A heating power supply branch and a working power supply branch, wherein the heating power supply branch is used to provide heating power and the working power supply branch is used to provide power supply. A dual-control switch, wherein the first end of the dual-control switch is connected to the thermistor, and the second end of the dual-control switch is used to connect to the heating power supply branch or the working power supply branch according to an external control signal; A preheating judgment circuit is provided, wherein the current detection terminal of the preheating judgment circuit is connected to the thermistor, and the control terminal of the preheating judgment circuit is connected to the controlled terminal of the dual-control switch. The preheating judgment circuit is used to detect the temperature of the thermistor, and control the second terminal of the dual-control switch to be connected to the heating power supply branch or the working power supply branch according to the detected temperature, so that the heating power supply branch is connected to the thermistor, or the working power supply branch is connected to the thermistor. The preheating judgment circuit is specifically used to control the second terminal of the double-control switch to connect to the heating power supply branch when the detected current flowing through the thermistor is less than the preset current, and to control the second terminal of the double-control switch to connect to the working power supply branch when the detected current flowing through the thermistor is greater than or equal to the preset current. The heating power supply branch includes a first voltage source and a first resistor, the first voltage source being connected to a first end of the first resistor; the working power supply branch includes a second voltage source and a second resistor, the second voltage source being connected to a first end of the second resistor. The preheating judgment circuit is specifically used to control the second terminal of the dual-control switch to connect to the second terminal of the first resistor when the detected current flowing through the thermistor is less than the preset current, and to control the second terminal of the dual-control switch to connect to the second terminal of the second resistor when the detected current flowing through the thermistor is greater than or equal to the preset current. The low-power thermistor measurement circuit also includes a high-voltage drive circuit. The enable terminal of the high-voltage drive circuit is connected to the control terminal of the preheating judgment circuit, and the output terminal of the high-voltage drive circuit is connected to the first voltage source. The preheating judgment circuit is also used to control the high-voltage drive circuit to provide voltage to the heating power supply branch when the detected temperature of the thermistor is lower than the preset temperature. The low-power thermistor measurement circuit also includes a low-voltage drive circuit. The enable terminal of the low-voltage drive circuit is connected to the control terminal of the preheating judgment circuit, and the output terminal of the low-voltage drive circuit is connected to the second voltage source. The preheating judgment circuit is also used to control the low-voltage drive circuit to provide voltage to the working power supply branch when the detected temperature of the thermistor is greater than or equal to a preset temperature.

2. The low-power thermistor measurement circuit as described in claim 1, characterized in that, The thermistor is two in number, referred to as the first thermistor and the second thermistor respectively. The first thermistor and the second thermistor are connected in series between the first terminal of the dual-control switch and the ground electrode. The first output terminal of the thermistor measurement circuit is the common terminal of the first thermistor and the second thermistor.

3. The low-power thermistor measurement circuit as described in claim 2, characterized in that, The first thermistor is sealed in an absolutely dry gas, while the second thermistor is not sealed.

4. The low-power thermistor measurement circuit as described in claim 1, characterized in that, The low-power thermistor measurement circuit further includes a third resistor and a fourth resistor, which are connected in series between the first terminal of the dual-control switch and the ground electrode. The second output terminal of the thermistor measurement circuit is the common terminal of the third resistor and the fourth resistor.

5. A sensor for measuring the moisture content of air, characterized in that, The sensor for measuring air moisture content includes a low-power thermistor measurement circuit as described in any one of claims 1 to 4.

6. The sensor for measuring air moisture content as described in claim 5, characterized in that, The sensor for measuring air moisture content also includes: A barometric pressure sensor is used to detect the air pressure in the current environment. Temperature sensors are used to detect the temperature in the current environment; The processor is connected to the output terminals of the barometric pressure sensor, the temperature sensor, and the thermistor measurement circuit. The processor is used to calculate the absolute humidity of the current environment based on the output voltage of the thermistor measurement circuit. The processor is also used to calculate the relative humidity of the current environment based on the barometric pressure detected by the barometric pressure sensor, the temperature detected by the temperature sensor, and the absolute humidity of the current environment.

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