Humidity meter

Abstract

This invention discloses a hygrometer, comprising a humidity sensor, a capacitance detection module, a backflushing module, and a main controller. The humidity sensor is used to detect the humidity of the environment to be tested. The capacitance detection module is electrically connected to the humidity sensor and is used to measure the capacitance value of the humidity sensor. The backflushing module is used to deliver cleaning gas to the humidity sensor to clean it. The main controller is electrically connected to the capacitance detection module and the backflushing module, and is used to adjust the capacitance bias of the capacitance detection module based on the capacitance detection results and to perform automatic zero calibration to optimize humidity measurement. This invention improves the accuracy of measured humidity data.

Description

Technical Field

[0001] This invention relates to the field of flue gas humidity measurement technology, and particularly to a humidity meter. Background Technology

[0002] The resistance-capacitance method is a widely used technique in various humidity measurement devices. It measures relative humidity by utilizing the change in capacitance of a material. This method is based on the principle that the capacitance of humidity-sensitive materials (usually polymers or ceramics) changes under different humidity conditions. When the ambient humidity increases, the humidity-sensitive material absorbs moisture, causing a change in its dielectric constant, which in turn causes a change in the material's capacitance. By measuring this change in capacitance, the relative humidity of the environment can be accurately calculated. This method is widely used in industries, environmental monitoring, and household appliances due to its relative simplicity and cost-effectiveness.

[0003] In practical applications, especially in flue gas humidity measurement, several practical problems exist. Since the actual temperature of the flue often exceeds the temperature resistance limit of the sensor circuit board (PCB), the sensor is typically placed in the center of the flue, while the detection circuit is placed outside. This configuration requires connecting cables of appropriate length to connect the sensor and the detection circuit, depending on the site conditions. Changes in cable length can alter the overall capacitance of the circuit, thus affecting measurement accuracy. How to effectively avoid the influence of the connecting cables on the measurement results is a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0004] The main objective of this invention is to provide a hygrometer that addresses the technical problem of inaccurate measurement results in existing hygrometers when measuring ambient humidity.

[0005] To achieve the above objectives, the present invention proposes a humidity meter comprising a humidity sensor, a capacitance detection module, a backflushing module, and a main controller. The humidity sensor is used to detect the humidity of the environment to be tested. The capacitance detection module is electrically connected to the humidity sensor and is used to measure the capacitance value of the humidity sensor. The backflushing module is used to deliver clean gas to the humidity sensor to clean it. The main controller is electrically connected to the capacitance detection module and the backflushing module, and is used to adjust the capacitance bias of the capacitance detection module based on the capacitance detection results and to perform automatic zero calibration to optimize humidity measurement.

[0006] Optionally, the capacitance detection module is model AD7745.

[0007] Optionally, the capacitance detection module has a CIN(+) interface, an EXCA interface, an EXCB interface, a first RDY interface, a first SCL interface, and a first SDA interface;

[0008] The main controller has a second RDY interface, a second SCL interface, and a second SDA interface;

[0009] The CIN(+) interface is electrically connected to the output terminal of the humidity sensor, and the input terminal of the humidity sensor is electrically connected to the EXCA interface and the EXCB interface respectively.

[0010] The first RDY interface is electrically connected to the second RDY interface;

[0011] The first SCL interface is electrically connected to the second SCL interface through a first electrical connection line, and the first electrical connection line is connected to the positive terminal of the power supply through a first resistor;

[0012] The first SDA interface is electrically connected to the second SDA interface through the second electrical connection line, and the second electrical connection line is connected to the positive terminal of the power supply through the second resistor;

[0013] The VDD interface of the capacitance detection module and the VDD interface of the main controller are electrically connected to the positive terminal of the power supply, and the GND interface of the capacitance detection module and the GND interface of the main controller are grounded.

[0014] Optionally, the hygrometer further includes an operational amplifier, the output of which is electrically connected to the input of the humidity sensor, and the non-square input of which is electrically connected to the EXCA interface and the EXCB interface, respectively. The operational amplifier is used to adjust the signal between the humidity sensor and the capacitance detection module.

[0015] Optionally, the operational amplifier is model AD8615.

[0016] The humidity meter of the present invention has the following advantages:

[0017] First, in different detection environments, the wire length between the humidity sensor and the detection circuit often varies. Sometimes, the combined capacitance of the humidity sensor and the connecting wire exceeds the normal detection range of the capacitance detection module. In this case, the main controller can adjust the capacitance bias of the capacitance detection module. For example, when the measurement finds that the capacitance of the humidity sensor and the connecting wire exceeds the maximum detection range of the detection module, the main controller can effectively adjust the total capacitance value of the system to the effective detection range of the capacitance detection module through capacitance bias. Such adjustment not only ensures the effectiveness of the measurement but also enhances the system's adaptability to environmental changes.

[0018] Next, since humidity sensors are prone to accumulating dust and other contaminants in harsh environments, these impurities, if not removed, will affect the sensor's performance and measurement accuracy. Clean gas is then introduced into the humidity sensor through the backflushing module to remove these accumulated contaminants, ensuring that the sensor remains in optimal working condition and thus maintaining the accuracy of the measurement data.

[0019] Finally, the main controller also integrates automatic zero-calibration compensation technology. After adjusting the capacitor bias and cleaning the sensor, the main controller performs zero-calibration compensation to accurately measure the capacitance value of the humidity sensor under preset detection conditions. If the measurement result deviates from the preset standard result, the system will continue to fine-tune until the detection result meets the preset standard. This automatic adjustment and calibration process greatly improves the measurement accuracy and ease of operation of the system. Attached Figure Description

[0020] 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.

[0021] Figure 1 This is a schematic diagram of the structure of an embodiment of the humidity meter of the present invention;

[0022] Figure 2 This is a partial circuit diagram of a humidity meter.

[0023] Explanation of icon numbers:

[0024] 1. Humidity sensor; 2. Capacitive sensing module; 3. Backflushing module; 4. Main controller; 5. Operational amplifier.

[0025] 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

[0026] 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.

[0027] 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.

[0028] Furthermore, the use of terms such as "first" and "second" in this invention is 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 term "and / or" throughout the text includes three solutions; taking A and / or B as an example, it includes technical solution A, technical solution B, and a technical solution that simultaneously satisfies A and B. Furthermore, the technical solutions of various embodiments can be combined with each other, provided that they are feasible for those skilled in the art. When 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.

[0029] This invention proposes a humidity meter.

[0030] In embodiments of the present invention, such as Figure 1 and Figure 2 As shown, the hygrometer includes a humidity sensor 1, a capacitance detection module 2, a backflushing module 3, and a main controller 4. The humidity sensor 1 is used to detect the humidity of the environment to be tested. The capacitance detection module 2 is electrically connected to the humidity sensor 1 and is used to measure the capacitance value of the humidity sensor 1. The backflushing module 3 is used to deliver clean gas to the humidity sensor 1 to clean it. The main controller 4 is electrically connected to the capacitance detection module 2 and the backflushing module 3. The main controller 4 is used to adjust the capacitance bias of the capacitance detection module 2 based on the capacitance detection results and to perform automatic zero calibration to optimize humidity measurement.

[0031] In specific implementation, the humidity sensor 1 can be an IST AG MK33-W capacitive relative humidity sensor 1 or a Honeywell HIH-4000 series humidity sensor 1. The capacitive detection module 2 can be an AD7745 capacitor-to-digital converter or a Texas Instruments FDC1004. The backflushing module 3 can include an electric fan or an air pump assembly. The electric fan can blow air to the sensor to remove accumulated dust or moisture, while the air pump assembly releases compressed air through a control valve for powerful cleaning. It is worth noting that an air supply pipe can be adaptively set between the electric fan and the humidity sensor 1, or between the valve of the air pump assembly and the humidity sensor 1. The specific shape of the pipe is adaptively adjusted according to the type of sensor, and this application does not impose specific limitations on it.

[0032] The main controller 4 can use a microcontroller based on the ARM Cortex-M series or an Atmel AVR series microcontroller.

[0033] The main controller 4 achieves automatic zero calibration through internal software algorithms. Automatic zero calibration is a calibration process designed to ensure that the hygrometer correctly displays zero or a reference value under conditions of no humidity change. The process involved in automatic zero calibration includes:

[0034] Initial testing: The system first performs a baseline test, measuring the output in a theoretically “dry” or moisture-free environment, which is typically done at system startup or within a set calibration cycle.

[0035] Data logging: The main controller 4 records the results of this baseline measurement and uses it as a reference point or zero point.

[0036] Of course, the aforementioned reference point or zero point can also be provided by the manufacturer of humidity sensor 1.

[0037] Continuous monitoring: During normal operation, the system periodically or continuously monitors the current measurement value and compares it with the stored zero-point value.

[0038] Deviation correction: If a deviation is found between the current measurement value and the zero point value, the system corrects the deviation by adjusting internal settings or parameters to ensure that the displayed value reflects the true ambient humidity.

[0039] Environmental factor compensation: During the zero calibration process, the system can also take into account the impact of environmental factors such as temperature and make corresponding compensations.

[0040] The automatic zeroing function is implemented by a dedicated software algorithm running in the main controller 4. This algorithm includes a deviation detection algorithm (used to detect the deviation between the current measurement value and the preset zero point), an adjustment algorithm (used to calculate the amount of adjustment that needs to be made and apply these adjustments to calibrate the equipment), and a compensation algorithm (used to calculate the necessary compensation based on temperature or other environmental factors and adjust the measurement results in real time).

[0041] It is easy to understand that the wire length between the humidity sensor 1 and the detection circuit often varies in different detection environments. Sometimes, the capacitance of the humidity sensor 1 and the connecting wire may exceed the normal detection range of the capacitance detection module 2. In this case, the main controller 4 can adjust the capacitance bias of the capacitance detection module 2. For example, when the measurement finds that the capacitance of the humidity sensor 1 and the connecting wire exceeds the maximum detection range of the detection module, the main controller 4 can effectively adjust the total capacitance value of the system to the effective detection range of the capacitance detection module 2 through capacitance bias. Such adjustment not only ensures the effectiveness of the measurement, but also enhances the system's adaptability to environmental changes.

[0042] Next, since the humidity sensor 1 is prone to accumulating dust and other contaminants in harsh environments, these impurities will affect the performance of the sensor and the accuracy of the measurement if they are not removed. Clean gas is sent to the humidity sensor 1 through the backflushing module 3 to remove these accumulated contaminants, ensuring that the sensor maintains its optimal working condition and thus maintaining the accuracy of the measurement data.

[0043] Finally, the main controller 4 also integrates automatic zero-calibration compensation technology. After adjusting the capacitor bias and cleaning the sensor, the main controller 4 performs zero-calibration compensation to accurately measure the capacitance value of the humidity sensor 1 under preset detection conditions. If the measurement result deviates from the preset standard result, the system will continue to fine-tune until the detection result meets the preset standard. This automatic adjustment and calibration process greatly improves the measurement accuracy and ease of operation of the system.

[0044] Optionally, the capacitance detection module 2 is model AD7745. The high resolution of the AD7745 ensures that even very small capacitance changes can be accurately detected and converted, thereby improving the response speed and accuracy of the entire humidity measurement system. Furthermore, the low noise characteristics of the AD7745 guarantee the reliability of the measurement results, reducing errors and biases, and making humidity measurements more accurate.

[0045] Specific circuit connections are as follows Figure 2 As shown, the capacitance detection module 2 has a CIN(+) interface, an EXCA interface, an EXCB interface, a first RDY interface, a first SCL interface, and a first SDA interface;

[0046] The main controller 4 has a second RDY interface, a second SCL interface, and a second SDA interface;

[0047] The CIN(+) interface is electrically connected to the output terminal of humidity sensor 1, and the input terminal of humidity sensor 1 is electrically connected to the EXCA interface and the EXCB interface respectively.

[0048] The first RDY interface is electrically connected to the second RDY interface;

[0049] The first SCL interface is electrically connected to the second SCL interface through the first electrical connection line, and the first electrical connection line is connected to the positive terminal of the power supply through the first resistor.

[0050] The first SDA interface is electrically connected to the second SDA interface through the second electrical connection line, and the second electrical connection line is connected to the positive terminal of the power supply through the second resistor.

[0051] The VDD interface of the capacitance detection module 2 and the VDD interface of the main controller are electrically connected to the positive terminal of the power supply, and the GND interface of the capacitance detection module 2 and the GND interface of the main controller are grounded.

[0052] Specifically, the direct connection of the CIN(+) interface ensures that the capacitance signal received from humidity sensor 1 can be accurately measured by the AD7745, while the configuration of the EXCA and EXCB interfaces further enhances the stability and reliability of the measurement signal. Furthermore, through precise data communication interface settings (RDY, SCL, SDA), the system can achieve efficient data synchronization and processing, reducing latency and error rates during data transmission, and improving measurement response speed and overall system performance.

[0053] The hygrometer also includes an operational amplifier 5. The output of the operational amplifier 5 is electrically connected to the input of the humidity sensor 1. The non-square input of the operational amplifier 5 is electrically connected to the EXCA interface and the EXCB interface, respectively. The operational amplifier 5 is used to adjust the signal between the humidity sensor 1 and the capacitance detection module 2.

[0054] In practice, the operational amplifier 5 can be of the model AD8615, OPA211, or LT6015, etc.

[0055] By precisely adjusting the sensor signal, operational amplifier 5 ensures that the signal in the circuit has appropriate voltage level and impedance characteristics, thereby reducing signal loss and distortion, and improving data accuracy and system response speed. Furthermore, the connection to the AD7745's EXCA and EXCB interfaces allows operational amplifier 5 to finely control the excitation signal, which is especially important when dealing with complex or weak signals. In this way, the hygrometer can provide more stable and reliable measurement results under various environmental conditions, particularly suitable for industrial and laboratory environments where signal quality directly affects the accuracy and reliability of the final measurement.

[0056] Based on the above, taking the MK33-W humidity sensor as an example, its capacitance is 300pF±40pF at 30%RH and +23°C. When backflushing to clean the humidity-sensitive capacitive sensor, the system adjusts the common-mode capacitance bias based on the difference between the currently measured capacitance value and the standard capacitance value corresponding to 30% relative humidity. If the measured capacitance value is higher or lower than the standard capacitance value at 30% relative humidity, the system will increase or decrease the capacitance bias accordingly to ensure that the detection result remains near the standard capacitance value at 30% relative humidity.

[0057] When the common-mode capacitor bias changes, the detected capacitance will also change accordingly. The slope of the change is: register resolution × full-scale capacitor bias × range extension factor = 1 / 127 × 21 × 21 = 3.47.

[0058] For the MK33-W humidity-sensitive capacitor, the actual capacitance used in humidity calculation is:

[0059] pF - (Common-mode capacitor bias - 86) * 3.47.

[0060] This calculation method effectively offsets capacitance deviations caused by different connection wire lengths, ensuring the accuracy of humidity calculation.

[0061] In practical applications, the range extension factor of the product will change significantly within the operating temperature range of -40°C to 180°C, which may cause deviations in the detected capacitance. By calibrating the environmental conditions of the backflushing gas during the zero calibration process, these temperature-induced deviations can be effectively offset. At the same time, by using the capacitance at the zero calibration point as a benchmark, the capacitance changes caused by humidity changes will affect the calculation of humidity data, thereby ensuring the accuracy of humidity measurement.

[0062] The above description is merely a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformations made using the contents of the present invention's specification and drawings under the inventive concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A humidity meter, characterized in that, include: A humidity sensor (1) is used to detect the humidity of the environment to be detected; A capacitance detection module (2) is electrically connected to the humidity sensor (1). The capacitance detection module (2) is used to measure the capacitance value of the humidity sensor (1). The model of the capacitance detection module (2) is AD7745. Backflush module (3) is used to deliver clean gas to the humidity sensor (1) to clean the humidity sensor (1); The main controller (4) is electrically connected to the capacitance detection module (2) and the backflush module (3). The main controller (4) is used to adjust the capacitance bias of the capacitance detection module (2) based on the capacitance detection result and to perform automatic zero calibration to optimize humidity measurement. The capacitance detection module (2) has a CIN(+) interface, an EXCA interface, an EXCB interface, a first RDY interface, a first SCL interface, and a first SDA interface; The main controller (4) has a second RDY interface, a second SCL interface, and a second SDA interface; The CIN(+) interface is electrically connected to the output terminal of the humidity sensor (1), and the input terminal of the humidity sensor (1) is electrically connected to the EXCA interface and the EXCB interface respectively; The first RDY interface is electrically connected to the second RDY interface; The first SCL interface is electrically connected to the second SCL interface through a first electrical connection line, and the first electrical connection line is connected to the positive terminal of the power supply through a first resistor; The first SDA interface is electrically connected to the second SDA interface through the second electrical connection line, and the second electrical connection line is connected to the positive terminal of the power supply through the second resistor; The VDD interface of the capacitance detection module (2) and the VDD interface of the main controller are electrically connected to the positive terminal of the power supply, respectively, and the GND interface of the capacitance detection module (2) and the GND interface of the main controller are grounded. The hygrometer also includes an operational amplifier (5), the output of which is electrically connected to the input of the humidity sensor (1), and the non-square input of which is electrically connected to the EXCA interface and the EXCB interface respectively. The operational amplifier (5) is used to adjust the signal between the humidity sensor (1) and the capacitance detection module (2). The operational amplifier (5) is model AD8615.

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