CN106840287B - Flow sensor, flowmeter and flow detection method - Google Patents

Abstract

The invention discloses a flow sensor, a flow meter and a flow detection method. The flow sensor includes: a heating element and one or more detection units; wherein, the detection unit includes: an upstream detection resistor, a downstream detection resistor, and an upstream detection resistor in series A first constant current source connected, and a second constant current source connected in series with the downstream detection resistor; the upstream detection resistor and the downstream detection resistor are respectively arranged on the upstream and downstream sides of the flow path of the measured medium, and the heating element is arranged upstream between the sense resistor and the downstream sense resistor. The constant current source is used to provide a constant current for the detection resistor, which can avoid the influence of the temperature of the measured medium on the flow detection result, and ensure the accuracy of the flow measurement.

Description

Flow sensor, flow meter and flow detection method

technical field

The invention relates to the technical field of sensors, and in particular, to a flow sensor, a flow meter and a flow detection method for detecting the flow of a measured medium.

Background technique

In the flow measurement process, the commonly used flow detection method is generally based on the temperature difference detection method. The working principle of the temperature difference detection method is to set a heating element in the middle of the flow sensor, and control the heating element through the temperature control circuit to keep the temperature difference with the measured medium constant. A pair of symmetrical sense resistors are also provided upstream and downstream of the heating element. When the measured medium (such as gas) passes over the heating element in a laminar flow state, the temperature of the upstream detection resistor will decrease and the temperature of the downstream detection resistor will increase due to the influence of the flow direction of the measured medium. high, that is, the temperature field will migrate, resulting in a temperature difference ΔT between the two sense resistors. Corresponding to the measured medium of different types and different flow rates, the temperature difference ΔT formed between the detection resistors is different. Using the characteristics of different resistance values corresponding to the detection resistors at different temperatures, the difference change of the resistance values of the two detection resistors can be used to reflect the temperature difference ΔT between the detection resistors, and the difference change of the resistance values of the two detection resistors It can be output in the form of differential voltage, so that the temperature difference generated by the two detection resistors caused by the flow of the measured medium can be converted into a differential voltage output. This differential voltage has a one-to-one correspondence with the flow of the measured medium, such as As shown in Figure 1, the corresponding mass flow rate of the measured medium can be obtained from this differential voltage.

In practical applications, as shown in FIG. 2 , the above-mentioned differential voltage ΔU of the sensor is usually measured by a Wheatstone bridge circuit to represent the temperature difference ΔT between the two detection resistors R1 and R2 . However, a problem with using the Wheatstone bridge is that, in addition to the change in the resistance values of the two detection resistors R1 and R2 caused by the flow direction of the measured medium, the temperature of the measured medium itself will change. The difference will also cause the resistance value of the two sense resistors R1 and R2 to change. Since the fixed voltage U0 in the Wheatstone bridge does not change, the change in the resistance values of the two detection resistors R1 and R2 will cause the current flowing through the detection resistors R1 and R2 to change, which in turn will cause the differential voltage ΔU to change, that is, when When the temperature of the measured medium is different, the output differential voltage ΔU also includes the change caused by the temperature of the measured medium, so the differential voltage ΔU cannot truly represent the flow rate of the measured medium.

Generally, the method of temperature compensation coefficient can be used to eliminate the influence of the temperature of the measured medium on the flow detection, but the method of temperature compensation coefficient is more complicated and cannot meet the requirements of measurement accuracy in the flow measurement process.

Aiming at the problem in the related art that the temperature of the measured medium affects the flow detection result and thus the measurement accuracy, no effective solution has yet been proposed.

SUMMARY OF THE INVENTION

Aiming at the problem in the related art that the temperature of the measured medium affects the flow detection result and thus the measurement accuracy, the present invention proposes a flow sensor, a flow meter and a flow detection method for detecting the flow of the measured medium, which can avoid the influence of the temperature of the measured medium. The problem of flow detection results, so as to ensure the accuracy of flow measurement.

The technical scheme of the present invention is realized as follows:

According to one aspect of the present invention, a flow sensor is provided, comprising: a heating element and one or more detection units; wherein, the detection unit includes: an upstream detection resistor, a downstream detection resistor, a first constant voltage connected in series with the upstream detection resistor flow source, and a second constant current source connected in series with the downstream detection resistor; the upstream detection resistor and the downstream detection resistor are respectively arranged on the upstream side and the downstream side of the flow path of the measured medium, and the heating element is arranged on the upstream detection resistor and the downstream detection resistor between the resistors.

According to an embodiment of the present invention, the detection unit further includes: a differential voltage output port for outputting a differential voltage; wherein the first output node of the differential voltage output port is connected to the first end of the upstream detection resistor Ru, and the differential voltage output port The second output node of Rd is connected to the first terminal of the downstream detection resistor Rd, and the second terminal of the upstream detection resistor Ru and the second terminal of the downstream detection resistor Rd are connected to the ground terminal.

According to an embodiment of the present invention, the detection unit further includes: a pull-up resistor, the pull-up resistor is a low temperature drift resistor, and both the upstream detection resistor and the downstream detection resistor are connected to the ground terminal through the pull-up resistor.

According to an embodiment of the present invention, the current values of the first constant current output by the first constant current source and the second constant current output by the second constant current source are equal.

According to one embodiment of the present invention, the flow sensor is a MEMS sensor.

According to an embodiment of the present invention, the current values of the first constant current output by the first constant current source and the second constant current output by the second constant current source are both within 100 μA-300 μA.

According to an embodiment of the present invention, the resistance value of the pull-up resistor is within 500Ω-2000Ω.

According to another aspect of the present invention, a flow meter is provided, comprising: the above-mentioned flow sensor; and a processing module connected to the flow sensor for obtaining the flow rate of the measured medium according to the differential voltage.

According to another aspect of the present invention, a flow detection method is provided, comprising: providing a constant current for an upstream detection resistor and a downstream detection resistor; using the constant current to generate a differential voltage related to the flow rate of the medium to be measured; media flow.

According to an embodiment of the present invention, obtaining the measured medium flow rate according to the differential voltage includes: obtaining a correspondence between the differential voltage and the measured medium flow rate; and obtaining the measured medium flow rate according to the corresponding relationship and the differential voltage.

According to an embodiment of the present invention, obtaining the corresponding relationship between the differential voltage and the flow rate of the measured medium includes: obtaining a plurality of calibrated differential voltages corresponding to the flow rate of the measured medium; obtaining the corresponding relationship according to the flow rate of the measured medium and the calibrated differential voltage , where the corresponding relationship is linear.

By setting a constant current source to provide a constant current for the detection resistor, the invention can avoid the influence of the temperature of the measured medium on the flow detection result and ensure the accuracy of the flow measurement.

Description of drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the accompanying drawings required in the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some of the present invention. In the embodiments, for those of ordinary skill in the art, other drawings can also be obtained according to these drawings without any creative effort.

1 is a schematic diagram of the correspondence between the differential voltage between the detection resistors and the mass flow rate of the measured medium in the prior art;

2 is a schematic diagram of the prior art using a Wheatstone bridge circuit to measure differential voltage;

3 is a schematic diagram of a flow sensor according to an embodiment of the present invention;

4 is a schematic circuit diagram of a detection unit of a flow sensor according to an embodiment of the present invention;

5 is a schematic circuit diagram of a detection unit of a flow sensor according to another embodiment of the present invention;

FIG. 6 is a flowchart of a flow detection method according to an embodiment of the present invention.

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art fall within the protection scope of the present invention.

According to an embodiment of the present invention, a flow sensor is provided.

3, 4 and 5, the flow sensor according to the embodiment of the present invention includes: a heating element Rh and one or more detection units 100; wherein, the detection unit 100 includes: an upstream detection resistor Ru, a downstream detection resistor Rd, the first constant current source Is1 connected in series to the upstream detection resistor Ru, and the second constant current source Is2 connected in series to the downstream detection resistor Rd; the upstream detection resistor Ru and the downstream detection resistor Rd are respectively set in the circulation of the measured medium On the upstream and downstream sides of the path, heating elements are provided between the upstream detection resistor Ru and the downstream detection resistor Rd.

The first constant current source Is1 and the second constant current source Is2 are used to provide a constant current for the upstream detection resistor Ru and the downstream detection resistor Rd respectively, so as to obtain the difference between the upstream detection resistor Ru and the downstream detection resistor Rd generated by the constant current and the measured value. Differential voltage related to medium flow. Constant current source refers to a circuit that can provide constant current. The characteristic of constant current source is that it does not change due to changes in ambient temperature, and can ensure the stability of the output current. Therefore, the above-mentioned differential voltage does not include the change caused by the temperature of the measured medium, that is, the temperature of the measured medium can not affect the flow detection result, and the accuracy of the flow measurement is ensured.

Specifically, as shown in FIG. 3 , when the measured medium in the pipeline 200 flows in the direction indicated by the arrow in the figure, the measured medium takes away the heat generated by the heating element Rh when it flows through the heating element Rh and transfers it to the heating element Rh. The downstream detection resistor Rd can therefore cause the resistance value of the upstream detection resistor Ru of the heating element Rh to decrease, and the resistance value of the downstream detection resistor Rd to increase. The first constant current I _u and the second constant current I _d applied by the source Is2 to the upstream detection resistor Ru and the downstream detection resistor Rd respectively remain unchanged, then the corresponding voltage values u _u and ud _d are obtained according to Ohm’s law, and then we can obtain The differential voltage Δu between the upstream sense resistor Ru and the downstream sense resistor Rd.

According to an embodiment of the present invention, referring to FIG. 4 and FIG. 5 at the same time, the detection unit 100 further includes a differential voltage output port for outputting a differential voltage; wherein, the first output node of the differential voltage output port is connected to the upstream detection resistor Ru The first terminal, the second output node of the differential voltage output port is connected to the first terminal of the downstream detection resistor Rd, and the second terminal of the upstream detection resistor Ru and the second terminal of the downstream detection resistor Rd are connected to the ground terminal.

According to an embodiment of the present invention, the current values of the first constant current I _u output by the first constant current source Is1 and the second constant current I _d output by the second constant current source Is2 are equal.

According to an embodiment of the present invention, the current values of the first constant current I _u output by the first constant current source Is1 and the second constant current I _d output by the second constant current source Is2 are both within 100 μA-300 μA.

Preferably, the current values of the first constant current I _u and the second constant current I _d are both 200 μA.

The first constant current source Is1 and the second constant current source Is2 with high precision and low temperature drift respectively provide constant current to the upstream detection resistor Ru and the downstream detection resistor Rd, in order to avoid the upstream detection resistor Ru and the downstream detection resistor caused by excessive current The resistor Rd generates heat by itself, and thus cannot truly reflect the temperature transmitted by the flowing measured medium. Therefore, it is necessary to apply a current with a small current value to both the upstream detection resistor Ru and the downstream detection resistor Rd. The applied current varies depending on the upstream sense resistor Ru and the downstream sense resistor Rd. Specifically, when the resistance values of the upstream detection resistor Ru and the downstream detection resistor Rd are relatively large, a current with a relatively small current value can be applied; and when the resistance values of the upstream detection resistor Ru and the downstream detection resistor Rd are relatively small, a current with a relatively small current value can be applied A current with a relatively large current value. Otherwise, if the current is too large, the upstream detection resistor Ru and the downstream detection resistor Rd may heat themselves; if the current is too small, the differential voltage Δu output by the detection unit 100 may be too small, affecting the measurement accuracy. Therefore, the first constant current I _u and the second constant current I _d whose current values are both within 100 μA to 300 μA can be applied to the upstream detection resistor Ru and the downstream detection resistor Rd. Preferably, the current values of the first constant current I _u and the second constant current I _d are both 200 μA.

According to an embodiment of the present invention, the flow sensor is a MEMS (Microelectro Mechanical Systems, Micro Electro Mechanical Systems) sensor.

According to an embodiment of the present invention, it further includes: an analog-to-digital conversion module, connected to one or more detection units 100, for converting the differential voltage from an analog quantity to a digital quantity. Optionally, the analog-to-digital conversion module is a 24-bit AD sampling module. The analog-to-digital conversion is performed by a high-precision 24-bit AD sampling module, and the corresponding relationship between the output differential voltage Δu and the flow rate of the measured medium can be obtained.

According to an embodiment of the present invention, as shown in FIG. 5 , the detection unit 100 further includes: a pull-up resistor Rs, the pull-up resistor Rs is a low temperature drift resistor, and the upstream detection resistor Ru and the downstream detection resistor Rd are both pulled-up Resistor Rs is connected to ground. Low temperature drift resistance refers to the resistance whose resistance value changes little with temperature. The main purpose of the pull-up resistor Rs is to raise the output differential voltage Δu in order to meet the minimum sampling input voltage requirements of some 24-bit AD sampling modules. If the AD sampling module used does not require the minimum sampling input voltage, it is not necessary to set the pull-up resistor Rs.

According to an embodiment of the present invention, the resistance value of the pull-up resistor Rs is within 500Ω-2000Ω.

Preferably, the resistance value of the pull-up resistor Rs is 1000Ω. Specifically, the resistance value of the pull-up resistor Rs can be set according to the requirement that the differential voltage Δu needs to be too high. For example, when the pull-up resistor Rs is 1000Ω and the current values of the first constant current I _u and the second constant current I _d are both 200 μA, the ground voltage of the differential voltage Δu can be raised by about 400 mV.

According to an embodiment of the present invention, a flow meter is also provided, including: the above-mentioned flow sensor and a processing module; the processing module is connected to the flow sensor and can be used to obtain the flow rate of the measured medium according to the differential voltage. Through the processing module, the flowmeter can directly output the flow rate of the measured medium.

Optionally, the processing module may include an acquiring module for acquiring the corresponding relationship between the differential voltage and the measured medium flow; and a generating and outputting module for obtaining and outputting the measured medium flow according to the corresponding relationship and the differential voltage.

Further, the above acquisition module may include: a first sub-module for acquiring a plurality of calibration differential voltages corresponding to a plurality of determined measured medium flow rates; and a second sub-module for calibrating differential voltages according to the measured medium flow rates and The corresponding relationship is obtained, where the corresponding relationship is a linear relationship.

As shown in FIG. 6 , according to an embodiment of the present invention, a traffic detection method is provided, including the following steps:

Step S110, providing a constant current for the upstream detection resistor and the downstream detection resistor;

Step S120, using a constant current to generate a differential voltage related to the flow rate of the measured medium;

In step S130, the measured medium flow rate is obtained according to the differential voltage.

In step S110, a constant current may be provided for the upstream detection resistor and the downstream detection resistor through the first constant current source and the second constant current source respectively; in step S120, the upstream detection resistor and the downstream detection resistor use this constant current to generate and measure The differential voltage related to the medium flow, so the differential voltage does not include the change caused by the temperature of the measured medium, that is, the temperature of the measured medium can not affect the flow detection result, and the accuracy of the flow measurement is guaranteed.

According to an embodiment of the present invention, step S130 may include the following steps:

Step S131, obtaining the corresponding relationship between the differential voltage and the flow rate of the measured medium;

In step S132, the measured medium flow rate is obtained according to the corresponding relationship and the differential voltage.

Further, step S131 may include the following steps:

Obtain multiple calibration differential voltages corresponding to multiple determined measured medium flow rates;

The corresponding relationship is obtained according to the flow rate of the measured medium and the calibration differential voltage, and the corresponding relationship is a linear relationship.

Step S130 will be specifically described below. The calibration can be completed through the relationship of Δu corresponding to q _m under different gas mass flow rates. It can be found that using a constant current source, the differential voltage signal Δu has a linear relationship with the measured medium flow q _m .

According to Ohm's law, the expression of differential voltage Δu can be deduced as:

Δu=u _d −u _u =(I _d R _d −I _u R _u )

Preferably, set I _u =I _d =I, and differential resistance ΔR=R _d -R _u , then there are:

Δu=u _d −u _u =I(R _d −I _u )=IΔR,

So there are:

ΔR=Δu/I

Further, the relationship between the resistance value R _u of the upstream detection resistor and the temperature T _u of the upstream detection resistor, and the relationship between the resistance value R _d of the downstream detection resistor and the temperature T _d of the downstream detection resistor can be expressed as:

R _u =R _u0 (1+a _u T _u ); R _d =R _d0 (1+a _d T _d )

Among them, R _u0 and R _d0 are the resistance values of the upstream sensing resistor and the downstream sensing resistor at zero degrees Celsius, respectively, and a _u and a _d are the temperature coefficients of the upstream sensing resistor and the downstream sensing resistor, respectively; so the above expression can be deduced as :

Δu=I(R _d0 +R _d0 a _d T _d −R _u0 −R _u0 a _u T _u )

And because R _u =R _d =R ₀ , a _d =a _u =a, so:

R _u =R _u0 (1+aT _u ), R _d =R _d0 (1+aT _d );

The temperature difference between the upstream detection resistor and the downstream detection resistor of the heating element is T _d −T _u =ΔT, then:

Δu=IR ₀ a(T _d −T _u )=IR ₀ aΔT; (1)

Among them, I, R ₀ , and a are all fixed constants, and k=IR ₀ a can be set, then ΔT=Δu/IR ₀ a is substituted into the relational formula (1), and the mass flow rate q _m can be obtained as:

It can be seen that through theoretical derivation, it is proved that the differential voltage Δu obtained by the method of the constant current source circuit is only related to the mass flow qm of the measured medium, and has nothing to do with the temperature change of the measured medium.

Further, the test verification of the G4 type MEMS household watch also confirms the correctness of the present invention. As shown in Table 1, it is the test data of the G4 type MEMS household meter using the Wheatstone bridge circuit in the prior art, and Table 2 is the test data of the G4 type MEMS household meter using the flow sensor of the present invention.

As can be seen from the data in Table 1 and Table 2, when the ambient temperature is 20 ° C, the errors of the detection results obtained by using the prior art and the flow sensor of the present invention are all smaller, but when the ambient temperature is lower (for example, 0 °C) or higher (for example, 40 °C), the error of the detection result obtained by using the flow sensor of the present invention is significantly lower than the error of the detection result obtained by using the prior art. To further illustrate, the present invention can avoid the influence of the temperature of the measured medium on the flow detection result in the prior art, and improve the measurement accuracy.

Table 1

Table 2

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the scope of the present invention. within the scope of protection.

Claims (10)

1. A flow sensor, comprising: a heating element and one or more detection units;

wherein the detection unit includes: an upstream detection resistor, a downstream detection resistor, a first constant current source connected in series with the upstream detection resistor, and a second constant current source connected in series with the downstream detection resistor;

the upstream detection resistor and the downstream detection resistor are respectively arranged on the upstream side and the downstream side of a circulation path of a detected medium, and the heating element is arranged between the upstream detection resistor and the downstream detection resistor;

the detection unit further comprises a differential voltage output port, and the differential voltage output port is used for outputting the differential voltage;

the first output node of the differential voltage output port is connected to the first end of the upstream detection resistor Ru, the second output node of the differential voltage output port is connected to the first end of the downstream detection resistor Rd, and the second end of the upstream detection resistor Ru and the second end of the downstream detection resistor Rd are connected to the ground terminal.

2. The flow sensor according to claim 1, wherein the detection unit further comprises:

the pull-up resistor is a low-temperature drift resistor, and the upstream detection resistor and the downstream detection resistor are both connected to the ground terminal through the pull-up resistor.

3. The flow sensor of claim 1,

the first constant current outputted by the first constant current source and the second constant current outputted by the second constant current source have the same current value.

4. The flow sensor of claim 1, wherein the flow sensor is a MEMS sensor.

5. The flow sensor of claim 1,

the current values of the first constant current output by the first constant current source and the second constant current output by the second constant current source are both within 100-300 muA.

6. The flow sensor of claim 2,

the pull-up resistor has a resistance value within 500-2000 omega.

7. A flow meter, comprising:

a flow sensor according to any one of the preceding claims 1 to 6; and

and the processing module is connected with the flow sensor and used for obtaining the flow of the measured medium according to the differential voltage.

8. A method for detecting traffic, comprising:

disposing a heating element between the upstream sensing resistor and the downstream sensing resistor;

providing constant currents for an upstream detection resistor and a downstream detection resistor, wherein a first constant current provided for the upstream detection resistor is equal to a second constant current provided for the downstream detection resistor in current value;

generating a differential voltage related to the flow of the measured medium by using the constant current;

and obtaining the flow of the measured medium according to the differential voltage.

9. The flow rate detection method according to claim 8, wherein obtaining the measured medium flow rate from the differential voltage comprises:

acquiring the corresponding relation between the differential voltage and the flow of the measured medium;

and obtaining the flow of the measured medium according to the corresponding relation and the differential voltage.

10. The flow rate detection method according to claim 9, wherein obtaining the correspondence between the differential voltage and the flow rate of the medium to be detected comprises:

obtaining a plurality of corresponding calibrated differential voltages under the flow of a plurality of determined media to be measured;

and obtaining the corresponding relation according to the measured medium flow and the calibrated differential voltage, wherein the corresponding relation is a linear relation.

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