A power adjustment circuit, an adjustment method, and a constant-power thermal mass flowmeter

Abstract

The present invention provides a power regulation circuit and regulation method, and a constant-power thermal mass flowmeter. The circuit first detects the voltage across a temperature sensor and the voltage across a linear element, then calculates the actual power of the temperature sensor based on the voltage across the temperature sensor and the voltage across the linear element. An intermediate voltage is then determined based on the voltage across the temperature sensor and the voltage across the linear element, and the intermediate voltage is compared with an externally input threshold voltage to determine the current flow state of the intermediate medium and the current power state of the driving power. A driving power is then selected based on the current flow state of the intermediate medium and the current power state of the driving power, and power regulation is performed based on the driving power and the actual power of the temperature sensor, outputting a constant power to the temperature sensor. The present invention can perform power regulation to maintain a constant power level for the temperature sensor and maintain the original reliability of the temperature sensor even at high temperatures.

Description

Technical Field

[0001] The present invention relates to the field of metering and measurement technology, and in particular to a power regulation circuit and a power regulation method for a constant power thermal mass flowmeter, and a constant power thermal mass flowmeter including the power regulation circuit. Background Art

[0002] Constant-power thermal mass flowmeters are gaining increasing attention and application in the field of metering and measurement due to their advantages, such as low pressure drop, wide measurement range, and direct mass flow measurement. However, in current constant-power thermal mass flowmeters, the power of the internal temperature sensor remains essentially fixed. Without the flow of an intermediate medium (such as gas), this heat cannot be removed, causing the temperature of the temperature sensor probe to rise to hundreds of degrees Celsius due to the unremoved heat. When exposed to temperatures exceeding hundreds of degrees Celsius, the reliability and service life of the temperature sensor are significantly reduced, thus affecting subsequent metering and measurement results. Summary of the Invention

[0003] In view of the above-mentioned shortcomings of the prior art, the purpose of the present invention is to provide a power regulation circuit for a constant power thermal mass flowmeter, which is used to solve the problem that the temperature sensor is too high when detecting the intermediate medium due to the lack of intermediate medium flow.

[0004] To achieve the above and other related objectives, the present invention provides a power regulation circuit for a constant power thermal mass flowmeter, comprising:

[0005] Temperature sensor, used to detect the temperature of the intermediate medium flow;

[0006] A linear element connected in series with the temperature sensor;

[0007] A voltage detection module, used to detect the voltage across the temperature sensor and the voltage across the linear element;

[0008] a multiplier connected to the voltage detection module, and configured to determine the actual power of the temperature sensor according to the voltage across the temperature sensor and the voltage across the linear element;

[0009] a divider connected to the voltage detection module, and configured to determine an intermediate voltage according to the voltage across the temperature sensor and the voltage across the linear element;

[0010] a flow state determination module, connected to the multiplier and the divider, for comparing the intermediate voltage with an externally input threshold voltage to determine the flow state of the intermediate medium and the power state of the driving power at the current moment;

[0011] The power regulation module is connected to the multiplier and the flow state determination module, and is used to perform power regulation according to the flow state of the intermediate medium and the power state of the driving power at the current moment, so as to provide constant power to the temperature sensor.

[0012] Optionally, the power regulation module includes: a power switching module and an operational amplifier;

[0013] The power switching module is connected to the flow state determination module and is used to select the driving power according to the flow state of the intermediate medium at the current moment and the power state of the driving power at the current moment;

[0014] The operational amplifier is connected to the multiplier and the power switching module, and is used to perform power regulation according to the driving power and the actual power of the temperature sensor, and output constant power to the temperature sensor.

[0015] Optionally, the voltage detection module includes:

[0016] a first differential amplifier, connected in parallel with the temperature sensor, and configured to detect a voltage across the temperature sensor;

[0017] a second differential amplifier connected in parallel with the linear element and configured to detect a voltage across the linear element;

[0018] Optionally, the voltage detection module further includes a gain amplifier, which is connected to the second differential amplifier and the divider respectively, and is used to amplify the voltage across the linear element and transmit the amplified voltage to the divider.

[0019] Optionally, the resistance of the linear element is 10 ohms, and the gain of the gain amplifier is 10.

[0020] Optionally, the temperature sensor is an electroheating element, and the temperature and resistance of the electroheating element vary with the flow state of the intermediate medium.

[0021] Optionally, the electroheating element is a platinum resistor.

[0022] Optionally, the divider includes an AD734 chip, and the power switching module includes a MUX508 chip.

[0023] The present invention also provides a constant power thermal mass flowmeter, comprising any power regulating circuit as described above.

[0024] The present invention also provides a power regulation method for a constant power thermal mass flowmeter, wherein the constant power thermal mass flowmeter includes a temperature sensor and a linear element, and the temperature sensor and the linear element are connected in series; the regulation method comprises the following steps:

[0025] detecting a voltage across the temperature sensor and a voltage across the linear element;

[0026] Calculating the actual power of the temperature sensor based on the voltage across the temperature sensor and the voltage across the linear element;

[0027] Determining an intermediate voltage based on the voltage across the temperature sensor and the voltage across the linear element;

[0028] Comparing the intermediate voltage with an externally input threshold voltage to determine a flow state of the intermediate medium and a power state of the driving power at a current moment;

[0029] Selecting the driving power according to the flow state of the intermediate medium at the current moment and the power state of the driving power at the current moment;

[0030] Power is adjusted based on the driving power and the actual power of the temperature sensor, and constant power is output to the temperature sensor.

[0031] As described above, the present invention provides a power regulation circuit and regulation method, as well as a constant power thermal mass flowmeter. The present invention has the following beneficial effects:

[0032] The present invention first detects the voltage across a temperature sensor and the voltage across a linear element, then calculates the actual power of the temperature sensor based on the voltage across the temperature sensor and the voltage across the linear element; then determines an intermediate voltage based on the voltage across the temperature sensor and the voltage across the linear element, and compares the intermediate voltage with an externally input threshold voltage to determine the flow state of the intermediate medium and the power state of the driving power at the current moment; then selects a driving power based on the flow state of the intermediate medium and the power state of the driving power at the current moment, and performs power adjustment based on the driving power and the actual power of the temperature sensor to output a constant power to the temperature sensor. The present invention can select a driving power based on the actual power state of the temperature sensor when there is no flow of the intermediate medium (e.g., gas), and then perform power adjustment to reduce the actual power of the temperature sensor to maintain a constant power, thereby allowing the temperature sensor to maintain its original reliability even at high temperatures. When there is flow of the intermediate medium, the actual power of the temperature sensor is increased through power adjustment to ensure that the temperature sensor always maintains its reliability. In addition, when there is flow, the temperature of the temperature measuring sensor in the present invention will only rise slightly, which will not damage the temperature measuring sensor and thus will not affect the service life of the temperature measuring sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 A schematic diagram of a power regulation circuit for a constant power thermal mass flowmeter provided in one embodiment;

[0034] Figure 2 A schematic diagram of a power regulation circuit for a constant power thermal mass flowmeter provided in another embodiment;

[0035] Figure 3 A circuit connection diagram of a divider provided in one embodiment;

[0036] Figure 4a and Figure 4b A schematic diagram of circuit connections of a flow state determination module provided in one embodiment;

[0037] Figure 5 A schematic diagram of circuit connections of a power switching module provided in one embodiment;

[0038] Figure 6 A schematic flow chart of a power regulation method for a constant power thermal mass flowmeter provided in one embodiment. DETAILED DESCRIPTION

[0039] The following describes the embodiments of the present invention through specific examples. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments. The details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the following embodiments and features in the embodiments can be combined with each other unless they conflict.

[0040] It should be noted that the illustrations provided in this embodiment are only used to schematically illustrate the basic concept of the present invention. Therefore, the illustrations only show components related to the present invention and are not drawn according to the number, shape and size of components in actual implementation. In actual implementation, the type, quantity and proportion of each component can be changed at will, and the component layout type may also be more complicated.

[0041] See also Figure 1 As shown, by setting a fixed voltage in the power setting module, when the op amp is stable, the multiplier output voltage is equal to the power setting module voltage. If there is no intermediate medium (such as gas) flow in the temperature sensor at this time, the heat in the temperature sensor cannot be taken away, causing the probe temperature of the temperature sensor to be heated to hundreds of degrees Celsius by the heat that is not taken away, thereby affecting the reliability and service life of the temperature sensor. Therefore, it is necessary to change this constant power thermal mass flowmeter so that the temperature sensor can work at a constant power and ensure the reliability and service life of the temperature sensor. Figure 1 In the figure, PT100 is a temperature sensor; R1 is a linear element (i.e., a current-sense resistor) with a resistance of 10Ω; I is the current flowing through the two ends of the temperature sensor. The current I is output by the current output module. The output of the operational amplifier can be used to adjust the output current I of the current drive module. When the operational amplifier is stable, the output voltage of the multiplier is equal to the voltage of the power setting module. Figure 1 ,have:

[0042] The output voltage of differential amplifier 1 is: V O1 =I*PT100.

[0043] The output voltage of differential amplifier 2 is: V O2 =I*R1.

[0044] The output voltage of the multiplier is: V O3 =I*I*PT100*R1.

[0045] The actual power of the temperature sensor is: P = I*I*PT100.

[0046] Because the resistance of linear component R1 is 10Ω, the output voltage of the multiplier can be expressed as: This voltage can be used to represent the actual power across the temperature sensor. For example, if the output voltage of the multiplier is 10V, the actual power across the temperature sensor is 1W. The voltage across the temperature sensor PT100 can be represented by the output voltage of differential amplifier 1, and the voltage across the linear component or current-sense resistor can be represented by the output voltage of differential amplifier 2.

[0047] According to the above records, if Figures 2 to 5 As shown, the present invention provides an exemplary embodiment, which provides a power regulation circuit for a constant power thermal mass flowmeter, including:

[0048] Temperature sensor, used to detect the temperature of the intermediate medium flow;

[0049] A linear element connected in series with the temperature sensor;

[0050] A voltage detection module, used to detect the voltage across the temperature sensor and the voltage across the linear element;

[0051] a multiplier connected to the voltage detection module, and configured to determine the actual power of the temperature sensor according to the voltage across the temperature sensor and the voltage across the linear element;

[0052] a divider connected to the voltage detection module, and configured to determine an intermediate voltage according to the voltage across the temperature sensor and the voltage across the linear element;

[0053] a flow state determination module, connected to the multiplier and the divider, for comparing the intermediate voltage with an externally input threshold voltage to determine the flow state of the intermediate medium and the power state of the driving power at the current moment;

[0054] a power switching module, connected to the flow state determination module, for selecting the driving power according to the flow state of the intermediate medium and the power state of the driving power at the current moment;

[0055] An operational amplifier is connected to the multiplier and the power switching module, and is used to perform power regulation according to the driving power and the actual power of the temperature sensor, and output constant power to the temperature sensor.

[0056] Among them, the power switching module and the operational amplifier can constitute a power regulation module, and the power regulation module can be connected to the multiplier and the flow state determination module, and is used to perform power regulation according to the flow state of the intermediate medium at the current moment and the power state of the driving power at the current moment, and provide constant power to the temperature sensor.

[0057] According to the above description, the voltage detection module in this embodiment includes: a first differential amplifier and a second differential amplifier; wherein the first differential amplifier is connected in parallel with the temperature sensor to detect the voltage across the temperature sensor; the second differential amplifier is connected in parallel with the linear element to detect the voltage across the linear element. As an example, Figure 2 As shown, in this embodiment, differential amplifier 1 can be used as the first differential amplifier, and differential amplifier 2 can be used as the second differential amplifier. That is, in this embodiment, the output voltage of differential amplifier 1 is used to represent the voltage across the temperature sensor, and the output voltage of differential amplifier 2 is used to represent the voltage across the linear element. The temperature sensor in this embodiment is an electrothermal element, and the temperature and resistance of the electrothermal element vary with the flow state of the intermediate medium. Specifically, the temperature sensor can be a platinum resistor, such as PT100. At the same time, the linear element in this embodiment can be a resistor, such as a current sensing resistor R1, that is, the resistance of the linear element in this embodiment is 10Ω.

[0058] According to the above description, the voltage detection module in this embodiment also includes a gain amplifier, which is connected to the second differential amplifier and the divider respectively, and is used to amplify the voltage across the linear element and transmit the amplified voltage to the divider. As an example, the gain of the gain amplifier in this embodiment is 10. It can be seen that this embodiment is different from Figure 1 In comparison, this embodiment adds a divider, a flow state determination module and a power automatic switching module, and then uses the divider, the flow state determination module and the power automatic switching module to form a gain automatic switching circuit.

[0059] The specific operating method of the automatic gain switching circuit is as follows: First, the output voltage of differential amplifier 2 is amplified by 10 times by the gain amplifier. The amplified voltage is then input into the divider. The divider calculates an intermediate voltage based on the amplified voltage and the output voltage of differential amplifier 1, namely, the divider output voltage. The relationship between the divider output voltage and the resistance value of the temperature sensor is determined based on the divider output voltage. The divider output voltage is then compared with an externally input threshold voltage to determine whether the current resistance value of the temperature sensor is greater than 100Ω, thereby determining the current flow state of the intermediate medium. In other words, this embodiment can determine the current flow state of the intermediate medium based on the resistance value of the temperature sensor PT100. Simultaneously, this embodiment compares the divider output voltage with the externally input threshold voltage to determine the current power state of the driving power. Finally, the power switching module selects the driving power based on the current flow state of the intermediate medium and the current power state of the driving power.

[0060] Specifically, according to Figure 3 It can be seen that the divider is mainly composed of AD734 chips. According to the above records, the intermediate voltage or the output voltage of the divider in this embodiment is: Since R1 is 10Ω, the intermediate voltage or divider output voltage is PT100 / 10. Therefore, the intermediate voltage or divider output voltage can be represented by the resistance value of the temperature sensor PT100 at this time. That is, the relationship between the divider output voltage and the temperature sensor resistance is:

[0061] In this embodiment, the external input threshold voltage includes VREF1, VREF2 and VREF3. Among them, VREF1 and VREF2 are resistance detection threshold voltages, and the voltage value of VREF1 is greater than the voltage value of VREF2. The threshold voltages VREF1 and VREF2 are used to determine the flow state of the intermediate medium in the temperature sensor; VREF3 is the power switching circuit detection threshold voltage, which is used to detect the power state of the driving power at this time. Figure 4a and Figure 4b As can be seen, this embodiment can output an IN0 state after comparing the threshold voltage VREF1 with the output voltage of the divider, an IN1 state after comparing the threshold voltage VREF2 with the output voltage of the divider, and an IN2 state after comparing the threshold voltage VREF3 with the power state voltage W_POWER of the power switching module. The IN0 state in this embodiment indicates the state of the low flow rate probe being monitored. That is, when the output voltage of the divider is greater than the threshold voltage VREF1, IN0 outputs 1; otherwise, IN0 outputs 0. The IN1 state indicates the state of the high flow rate probe being monitored. That is, when the output voltage of the divider is greater than the threshold voltage VREF2, IN1 outputs 1; otherwise, IN1 outputs 0. The IN2 state indicates the current power state of the driving power. That is, when the high-power heating voltage of the power switching module is greater than the threshold voltage VREF3, IN2 outputs 1; otherwise, when the low-power heating voltage of the power switching module is less than the threshold voltage VREF3, IN2 outputs 0.

[0062] According to the above records, the power switching module in this embodiment is mainly composed of the MUX508 chip. Figure 5As shown, MUX508 is a single-channel analog multiplexer, pin 8 is the common terminal D, W_H is the high power voltage when there is flow, and W_L is the low power voltage when there is zero flow. The power switching module jointly determines the driving power to be selected through the outputs of IN0, IN1, and IN2, and then transmits the selected driving power to the power amplifier. The operational amplifier performs power regulation according to the driving power and the actual power of the temperature sensor, and outputs constant power to the temperature sensor. Specifically, the control logic truth table of the power switching module is shown in Table 1 below. In this embodiment, when the power regulation circuit operates normally and stably, the driving power and the actual power of the temperature sensor are equal. Only when the device is out of adjustment, there will be a difference of milliwatts between the driving power and the actual power of the temperature sensor, but this embodiment ignores this difference. At the same time, when switching between high and low power, because this embodiment uses an analog circuit, this embodiment can achieve instantaneous switching within milliseconds.

[0063] Table 1 Control logic truth table of power switching module

[0064] state IN2 IN1 IN0 Power state of drive power 0 0 0 0 High power 1 0 0 1 High power 2 0 1 0 Low power 3 0 1 1 Low power 4 1 0 0 High power 5 1 0 1 High power 6 1 1 0 High power 7 1 1 1 Low power

[0065] According to Table 1, in state 0, IN2 is 0, indicating low power heating; IN1 is 0, indicating that the resistance value is lower than the threshold voltage VREF2; IN0 indicates that the resistance value is lower than the threshold voltage VREF1. This indicates that the flow rate is high and the probe resistance is low. At this time, high power should be used to quickly heat the probe. (000)

[0066] State 1: At this point, the corresponding logic value is 001. That is, IN2 is 0, indicating low-power heating; IN1 is 0, indicating a low temperature sensor resistance; and IN0 indicates a high temperature sensor resistance. At this point, IN1 and IN0 conflict because VREF1 > VREF2. This logic is not acceptable. High-power drive power is used to heat the temperature sensor probe, increasing its resistance and avoiding this logic error.

[0067] State 2: At this point, the corresponding logic value is 010. That is, IN2 is 0, indicating low-power heating. IN1 is 1, indicating that the temperature sensor's resistance is higher than the threshold voltage VREF2. IN0 is 0, indicating that the temperature sensor's resistance is lower than the threshold voltage VREF1. This state indicates that the flow rate of the intermediate medium is low, and the temperature sensor's resistance has increased slightly. Therefore, maintain IN2 unchanged and use low-power heating.

[0068] State 3: At this point, the corresponding logic value is 011. That is, IN2 is 0, indicating low-power heating; IN1 is 1, indicating that the temperature sensor resistance is higher than the threshold voltage VREF1; and IN0 is 1, indicating that the temperature sensor resistance is high. This state indicates that the flow rate of the intermediate medium is low, the temperature sensor probe is overheated, and the temperature sensor resistance is high, so low-power heating is used.

[0069] State 4: At this point, the corresponding logic value is 100, meaning IN2 is 1, indicating high-power heating. IN1 is 0, indicating the temperature sensor's resistance is lower than the threshold voltage VREF2. IN0 is 0, indicating the temperature sensor's resistance is lower than the threshold voltage VREF1. This indicates that the intermediate medium is flowing at a high velocity, the temperature sensor's resistance is low, and IN2 continues to maintain high-power heating.

[0070] State 5: At this point, the corresponding logic value is 101. That is, IN2 is 1, indicating high-power heating; IN1 is 0, indicating that the temperature sensor's resistance is lower than the threshold voltage VREF2; and IN0 is 1, indicating that the temperature sensor's resistance is higher than the threshold voltage VREF1. At this point, IN1 and IN0 conflict because VREF1 > VREF2. This logic is not acceptable. High-power heating of the temperature sensor's probe increases the temperature sensor's resistance, thus preventing this logic error.

[0071] State 6: At this point, the corresponding logic value is 110. That is, IN2 is 1, indicating high-power heating. IN1 is 1, indicating that the temperature sensor resistance is higher than the threshold voltage VREF2. IN0 is 0, indicating that the temperature sensor resistance is lower than the threshold voltage VREF1. This indicates that in high-power heating mode, the flow rate of the intermediate medium is not very high. The voltage corresponding to the temperature sensor resistance is greater than VREF2 but less than VREF1, and high-power heating is maintained.

[0072] State 7: At this point, the corresponding logic value is 111. That is, IN2 is 1, indicating high-power heating; IN1 is 1, indicating that the temperature sensor resistance is higher than the threshold voltage VREF2; and IN0 is 1, indicating that the temperature sensor resistance is higher than the threshold voltage VREF1. This indicates that in high-power heating mode, the flow rate of the intermediate medium has decreased to a very low level, causing the temperature sensor probe to overheat. To protect the probe, low-power heating mode is used.

[0073] Therefore, it can be seen from the control logic truth table of the power switching module that this embodiment sets the truth table according to the change of the intermediate medium flow rate in actual use, and ultimately realizes automatic gain switching of the constant power thermal mass flowmeter by changing the power output.

[0074] In summary, the present invention provides a power regulation circuit for a constant-power thermal mass flowmeter. The circuit first detects the voltage across a temperature sensor and the voltage across a linear element, then calculates the actual power of the temperature sensor based on the voltage across the temperature sensor and the voltage across the linear element. An intermediate voltage is then determined based on the voltage across the temperature sensor and the voltage across the linear element, and the intermediate voltage is compared with an externally input threshold voltage to determine the current flow state of the intermediate medium and the current power state of the driving power. A driving power is then selected based on the current flow state of the intermediate medium and the current power state of the driving power, and power regulation is performed based on the driving power and the actual power of the temperature sensor, outputting a constant power to the temperature sensor. The present invention can select a driving power based on the actual power state of the temperature sensor when there is no flow of the intermediate medium (e.g., gas), and then perform power regulation to reduce the actual power of the temperature sensor, maintaining the temperature sensor at a constant power, thereby allowing the temperature sensor to maintain its original reliability even at high temperatures. When there is flow of the intermediate medium, the actual power of the temperature sensor is increased through power regulation to ensure that the temperature sensor always maintains its reliability. In addition, when there is flow, the temperature of the temperature measuring sensor in the present invention will only rise slightly, which will not damage the temperature measuring sensor and thus will not affect the service life of the temperature measuring sensor.

[0075] The present invention further provides a constant-power thermal mass flowmeter, comprising a power regulation circuit as described in any of the above embodiments. The technical functions, effects, and regulation methods of the constant-power thermal mass flowmeter in this embodiment are described in the above embodiments and will not be further elaborated in this embodiment.

[0076] like Figure 6 As shown, the present invention also provides a power regulation method for a constant power thermal mass flowmeter, which mainly performs power regulation based on the power regulation circuit in some of the above exemplary embodiments. The constant power thermal mass flowmeter includes a temperature sensor and a linear element, and the temperature sensor and the linear element are connected in series. This regulation method includes the following steps:

[0077] S100, detecting the voltage across the temperature sensor and the voltage across the linear element;

[0078] S200, calculating the actual power of the temperature sensor based on the voltage across the temperature sensor and the voltage across the linear element;

[0079] S300, determining an intermediate voltage according to the voltage across the temperature sensor and the voltage across the linear element;

[0080] S400, comparing the intermediate voltage with an externally input threshold voltage to determine a current flow state of the intermediate medium and a current power state of the driving power;

[0081] S500, selecting a driving power according to a current flow state of the intermediate medium and a current power state of the driving power;

[0082] S600 , performing power adjustment based on the driving power and the actual power of the temperature sensor, and outputting constant power to the temperature sensor.

[0083] The technical functions and effects of this method are described in the above embodiments, and this embodiment will not be described in detail. In summary, the present invention provides a power regulation method for a constant power thermal mass flowmeter, which first detects the voltage across the temperature sensor and the voltage across the linear element, and then calculates the actual power of the temperature sensor based on the voltage across the temperature sensor and the voltage across the linear element; then determines an intermediate voltage based on the voltage across the temperature sensor and the voltage across the linear element, and compares the intermediate voltage with an externally input threshold voltage to determine the flow state of the intermediate medium at the current moment and the power state of the driving power at the current moment; then selects the driving power based on the flow state of the intermediate medium at the current moment and the power state of the driving power at the current moment, and performs power regulation based on the driving power and the actual power of the temperature sensor to output a constant power to the temperature sensor. The present invention can select the driving power based on the actual power state of the temperature sensor when there is no flow of the intermediate medium (such as gas), and then perform power regulation to reduce the actual power of the temperature sensor so that the temperature sensor is at a constant power, thereby allowing the temperature sensor to maintain its original reliability even at high temperatures. When the intermediate medium flows, the actual power of the temperature sensor is increased through power regulation, ensuring that the temperature sensor maintains its reliability. Furthermore, the temperature of the temperature sensor in the present invention only rises slightly when there is flow, which does not damage the temperature sensor and thus does not affect its service life. Therefore, the present invention effectively overcomes the shortcomings of the existing technology and has high industrial application value.

[0084] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the present invention. Anyone skilled in the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by one of ordinary skill in the art without departing from the spirit and technical principles disclosed herein are intended to be covered by the claims of the present invention.

[0085] It should be understood that although the terms "first," "second," and "third" may be used to describe preset ranges in embodiments of the present invention, these preset ranges should not be limited to these terms. These terms are merely used to distinguish one preset range from another. For example, without departing from the scope of embodiments of the present invention, the first preset range may also be referred to as the second preset range, and similarly, the second preset range may also be referred to as the first preset range.

Claims

1. A power regulation circuit for a constant power thermal mass flowmeter, characterized in that: Includes: Temperature sensor, used to detect the temperature of the intermediate medium flow; A linear element connected in series with the temperature sensor; A voltage detection module, used to detect the voltage across the temperature sensor and the voltage across the linear element; a multiplier connected to the voltage detection module, and configured to determine the actual power of the temperature sensor according to the voltage across the temperature sensor and the voltage across the linear element; a divider connected to the voltage detection module, and configured to determine an intermediate voltage according to the voltage across the temperature sensor and the voltage across the linear element; a flow state determination module, connected to the multiplier and the divider, for comparing the intermediate voltage with an externally input threshold voltage to determine the flow state of the intermediate medium and the power state of the driving power at the current moment; A power regulation module comprising: a power switching module and an operational amplifier; wherein the power switching module is connected to the flow state determination module and is configured to select a driving power based on the current flow state of the intermediate medium and the current power state of the driving power; the operational amplifier is connected to the multiplier and the power switching module and is configured to perform power regulation based on the driving power and the actual power of the temperature sensor, outputting a constant power to the temperature sensor; The external input threshold voltage includes VREF1, VREF2 and VREF3; VREF1 and VREF2 are resistance detection threshold voltages, and the voltage value of VREF1 is greater than the voltage value of VREF2. The threshold voltages VREF1 and VREF2 are used to determine the flow state of the intermediate medium in the temperature sensor; VREF3 is the power switching circuit detection threshold voltage, which is used to detect the power state of the driving power at this time; the flow state determination module includes: comparing the threshold voltage VREF1 with the output voltage of the divider, outputting the IN0 state, comparing the threshold voltage VREF2 with the output voltage of the divider, outputting the IN1 state, and comparing the threshold voltage VREF3 with the power switching module The power state voltage W_POWER is compared and the IN2 state is output; among them, the IN0 state represents the state of monitoring the low flow rate probe. When the output voltage of the divider is greater than the threshold voltage VREF1, IN0 outputs 1, otherwise IN0 outputs 0; the IN1 state represents the state of monitoring the high flow rate probe. When the output voltage of the divider is greater than the threshold voltage VREF2, IN1 outputs 1, otherwise IN1 outputs 0; the IN2 state represents the power state of the driving power at the current moment. When the high power heating voltage of the power switching module is greater than the threshold voltage VREF3, IN2 outputs 1, otherwise, when the low power heating voltage of the power switching module is less than the threshold voltage VREF3, IN2 outputs 0; The power switching module determines the driving power to be selected through the outputs of IN0, IN1 and IN2, and then transmits the selected driving power to the operational amplifier.

2. The power regulating circuit for a constant power thermal mass flowmeter according to claim 1, characterized in that: The voltage detection module includes: a first differential amplifier, connected in parallel with the temperature sensor, and configured to detect a voltage across the temperature sensor; The second differential amplifier is connected in parallel with the linear element and is used to detect the voltage across the linear element.

3. The power regulating circuit for a constant power thermal mass flowmeter according to claim 2, characterized in that: The voltage detection module further includes a gain amplifier, which is connected to the second differential amplifier and the divider respectively, and is used to amplify the voltage across the linear element and transmit the amplified voltage to the divider.

4. The power regulating circuit for a constant power thermal mass flowmeter according to claim 3, characterized in that: The resistance of the linear element is 10 ohms, and the gain of the gain amplifier is 10.

5. The power regulating circuit for a constant power thermal mass flowmeter according to claim 1, characterized in that: The temperature sensor is an electroheating element, and the temperature and resistance of the electroheating element change with the flow state of the intermediate medium.

6. The power regulating circuit for a constant power thermal mass flowmeter according to claim 5, characterized in that: The electroheating element is a platinum resistor.

7. The power regulating circuit for a constant power thermal mass flowmeter according to claim 1, characterized in that: The divider includes an AD734 chip, and the power switching module includes a MUX508 chip.

8. A constant power thermal mass flowmeter, characterized in that: The invention comprises a power regulating circuit as claimed in any one of claims 1 to 7.

9. A power regulation method for a constant power thermal mass flowmeter according to claim 8, wherein the constant power thermal mass flowmeter comprises a temperature sensor and a linear element, and the temperature sensor and the linear element are connected in series; characterized in that: The adjustment method comprises the following steps: detecting a voltage across the temperature sensor and a voltage across the linear element; Calculating the actual power of the temperature sensor based on the voltage across the temperature sensor and the voltage across the linear element; Determining an intermediate voltage based on the voltage across the temperature sensor and the voltage across the linear element; Comparing the intermediate voltage with an externally input threshold voltage to determine the flow state of the intermediate medium and the power state of the driving power at the current moment; Selecting the driving power according to the flow state of the intermediate medium at the current moment and the power state of the driving power at the current moment; Power is adjusted based on the driving power and the actual power of the temperature sensor, and constant power is output to the temperature sensor.

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