WO2012163285A1

WO2012163285A1 - Gas meter

Info

Publication number: WO2012163285A1
Application number: PCT/CN2012/076352
Authority: WO
Inventors: 黄忠; 董胜龙
Original assignee: 新奥科技发展有限公司
Priority date: 2011-05-31
Filing date: 2012-05-31
Publication date: 2012-12-06
Also published as: CN102809400A

Abstract

Disclosed is a gas meter. The gas meter comprises: a gas flow rate sensor unit, an analog-digital conversion unit and a master control unit; the gas flow rate sensor unit being used to convert the gas flow rate into a flow rate signal using a silicon microphone; the analog-digital conversion unit being connected to the gas flow rate sensor unit and being used to collect the flow rate signal resulting from conversion by the gas flow rate sensor unit, and converting the flow rate signal from analog to digital; the master control unit connected to the analog-digital conversion unit being used to restore the gas flow rate according to the flow rate signal converted from analog to digital by the analog-digital conversion unit, and acquire an accumulated gas flow quantity according to the restored gas flow rate and the time interval for collecting the gas flow rate signals. The gas meter of the present invention uses a silicon microphone sensor unit and, given that silicon microphones are extremely sensitive to external pressures changes and stable, using a silicon microphone as a sensor unit significantly improves the precision of the gas meter.

Description

Gas meter

The present invention relates to the field of Micro-Electro & Mechanical System (MEMS), and more particularly to a gas meter. Background technique

In the field of domestic gas meters, the existing gas meters are mechanical gas meters and electronic gas meters. The mechanical gas meter is represented by a mechanical membrane gas meter; the electronic gas meter is represented by an ultrasonic gas meter.

For mechanical membrane gas meters, when the flowing gas passes through the gas meter, it is blocked by the friction of the pipeline, and the internal gas will generate a pressure difference at the inlet/outlet of the gas meter. The pressure difference pushes the diaphragm of the membrane gas meter to move in the metering chamber, and drives the gas distribution mechanism to coordinate the gas distribution, so that the movement of the diaphragm can be continuously reciprocated, and the membrane gas meter passes the internal mechanical structure to straighten the line. The reciprocating motion is converted into a circular motion, and then the mechanical roller counter is rotated by the circular motion; each time the diaphragm reciprocates, a certain amount of gas is discharged, and finally the roller is rotated through a technical unit to realize the roller rotation measurement display effect. Due to the principle of mechanical transmission, the measurement accuracy of mechanical membrane gas meters depends on the fine adjustment of parts manufacturing and assembly, the measurement accuracy is not high, and the dispersion is large; the mechanical parts wear over time, resulting in the measurement accuracy decreasing with time, the longer the time The more obvious the error. In addition, since the volume of the gas changes with temperature, the measurement error caused by the temperature is large.

For ultrasonic gas meters, the time difference method is often used for measurement. Figure 1 is a schematic diagram of the prior art ultrasonic gas meter flow measurement principle. As shown in Fig. 1, in the ultrasonic gas meter flow measurement, a pair of ultrasonic transducers are used to alternately transmit (or simultaneously) ultrasonic waves, and indirectly measure the flow velocity of the fluid by observing the difference in the forward and reverse flow propagation time of the ultrasonic waves in the medium. The flow rate is then calculated by the flow rate. The ultrasonic gas meter has strict requirements on the straight pipe section (top 20D, rear 5D), otherwise the dispersion is large and the measurement accuracy is poor. Uncertainty in actual installation can cause large errors in flow measurement. In addition, measuring pipe fouling can seriously affect measurement accuracy. Moreover, ultrasonic gas meters are expensive to use and have a short life, and the accuracy is generally only maintained for one year.

As described above, in the prior art, whether it is a mechanical membrane type gas meter or an ultrasonic gas meter, there are many defects such as poor precision, high cost, and large volume. Summary of the invention

(1) Technical problems to be solved

In view of the above problems, the present invention provides a gas meter to improve measurement accuracy, reduce cost, and reduce volume.

(ii) Technical solutions

According to an aspect of the invention, a gas meter is provided. The gas meter comprises: a gas flow rate sensing unit, an analog to digital conversion unit and a main control unit; wherein: a gas flow rate sensing unit for converting a gas flow rate into a flow rate signal using a silicon microphone; an analog to digital conversion unit, and a gas flow rate transmission The sensing unit is connected to collect a flow rate signal converted by the gas flow rate sensing unit, and perform analog-to-digital conversion on the flow rate signal; the main control unit is connected to the analog-to-digital conversion unit, and is configured to be converted according to the analog-to-digital conversion unit. The flow rate signal restores the gas flow rate, and obtains the accumulated gas flow rate according to the collected gas flow rate and the flow rate signal collection interval time.

(3) Beneficial effects

The gas meter of the invention has the following beneficial effects:

(1) In the gas meter of the present invention, the silicon microphone is very sensitive and stable to changes in external pressure, so the use of the silicon microphone as the sensing unit of the present invention will greatly improve the accuracy of the gas meter;

(2) In the gas meter of the present invention, the silicon microphone manufactured by the MEMS process is very mature, and a silicon microphone having a very small volume and a very low cost can be prepared, so that the gas meter of the present invention has a simple structure and a low cost;

(3) In the gas meter of the present invention, the gas density is compensated by temperature and static pressure, thereby achieving accurate calibration of the gas flow rate, and further improving the accuracy of the gas meter. DRAWINGS

1 is a schematic diagram of a prior art ultrasonic gas meter flow measurement principle;

2 is a schematic structural view of a gas meter according to an embodiment of the present invention;

3 is a schematic cross-sectional view showing a silicon microphone in a gas meter according to an embodiment of the present invention;

4 is an enlarged view of a silicon crystal diaphragm in the silicon microphone shown in FIG. 3;

5 is a circuit diagram of a semiconductor silicon microphone in a gas meter according to an embodiment of the present invention;

6 is a schematic diagram of a silicon microphone gas flow rate sensing unit using a DC coupling method in a gas meter according to an embodiment of the present invention; 7 is a schematic structural view of a gas meter including a temperature-static pressure supplement mechanism according to an embodiment of the present invention; and FIG. 8a is a sensor rod for installing a flow rate sensing unit, a temperature sensing unit, and a static pressure sensing unit in the gas meter of the embodiment of the present invention; back image;

Figure 8b is a cross-sectional view of the sensor rod shown in Figure 8a;

Figure 8c is a side view of the sensor rod shown in Figure 8a;

Figure 9 is a flow chart showing the operation of the gas meter in accordance with an embodiment of the present invention. detailed description

The present invention will be described in detail below with reference to the accompanying drawings and drawings.

In an exemplary embodiment of the invention, a gas meter is provided. Fig. 2 is a schematic structural view of a gas meter according to an embodiment of the present invention. The gas meter of the embodiment includes: a gas flow rate sensing unit, an analog to digital converter (ADC) and a main control unit (MCU), wherein: a gas flow rate sensing unit is used for The silicon microphone converts the gas flow rate into a flow rate signal; the analog to digital conversion unit is connected to the gas flow rate sensing unit for collecting the flow rate signal of the gas flow rate sensing unit, and performing analog to digital conversion on the flow rate signal; the main control unit, The method is connected to the analog-to-digital conversion unit, and is configured to restore the gas flow rate according to the flow rate signal after the analog-to-digital conversion by the analog-to-digital conversion unit, and obtain the accumulated gas flow rate according to the collected gas flow rate and the flow rate signal collection interval time.

In this embodiment, the gas flow rate sensing unit comprises: a capacitive silicon microphone and a voltage dividing circuit subunit. The capacitive silicon microphone is connected to the voltage dividing circuit sub-unit and the analog-to-digital conversion unit respectively, and is used for converting the gas flow rate into a corresponding impedance signal by using a silicon crystal diaphragm. The voltage dividing circuit sub-unit is connected to the capacitive silicon microphone for converting the impedance signal into a flow rate signal in the form of voltage by means of voltage division. Preferably, the silicon crystal diaphragm is a silicon-free floating crystal (free-floatmg) diaphragm. Of course, it should be clear to those skilled in the art that in addition to the capacitive silicon microphone, the gas flow rate sensing unit can also adopt other forms of silicon microphone, and the silicon crystal diaphragm is not limited to the silicon floating diaphragm.

The principle of the gas flow rate sensing using the silicon microphone of the present invention will be described in detail below. According to the gas flow rate-wind pressure relationship derived from the Bernoulli equation, the dynamic pressure generated by the gas flow rate is:

w _p =0.5 · r ₀ · V ² ( 1) Where w _p is the wind pressure [kN/m ² ], r. For the gas density [kg/m ³ ], v is the gas flow rate [m/s]. It can be known from the formula (1) that the gas density is r. When known, the wind pressure w _p is only related to the gas flow rate V.

3 is a cross-sectional view showing a silicon microphone in a gas meter according to an embodiment of the present invention. Figure 4 is an enlarged view of the silicon crystal diaphragm in the silicon microphone shown in Figure 3. As shown in Fig. 3 and Fig. 4, when the silicon crystal diaphragm is subjected to pressure, deformation occurs, and the degree of deformation is monotonous with the magnitude of the pressure received. In combination with the silicon microphone of the present invention, the deformation of the silicon crystal diaphragm is related to the wind pressure tolerated, that is, it is related to the gas flow rate, and is monotonous.

Fig. 5 is a circuit diagram of a semiconductor silicon microphone in a gas meter according to an embodiment of the present invention. Referring to FIG. 3, FIG. 4 and FIG. 5, when the silicon crystal diaphragm is deformed, the voltage across the silicon crystal film changes, and the voltage change and the deformation are monotonous. The change in voltage causes a change in the conduction level of the MOSFET (FET in the figure), that is, the change in the impedance R _d J , and the voltage change and the impedance change are monotonous, thereby realizing the conversion of the physical quantity (gas flow rate) to the electric quantity (impedance). The present invention is based on the above principle for performing gas flow metering.

In the currently used silicon microphones, sound waves can also cause changes in air pressure. Among them, sound waves are an alternating wave, that is, the microphone needs to perceive this kind of alternating current change. Finally, the direct current component in the signal generated by the microphone is meaningless (or even harmful) to the restored sound wave, so the microphone is used for sound collection. AC coupling.

When a silicon microphone is used for sound collection, an AC coupling method is used, but this method cannot achieve a one-to-one correspondence between voltage and flow rate. According to the above-mentioned Bernoulli equation, the gas flow-wind pressure relationship does not distinguish between DC and AC due to the pressure change caused by the gas flow. In a preferred embodiment of the invention, the silicon microphone converts the gas flow rate to a corresponding impedance signal by means of DC coupling. 6 is a schematic diagram of a silicon microphone gas flow rate sensing unit using a DC coupling method in a gas meter according to an embodiment of the present invention. As shown in Figure 6, the gas flow rate sensor portion of the silicon microphone is used to convert the flow rate to the impedance, and then a voltage divider circuit converts the impedance change into a voltage change. Wherein, the drain of the silicon microphone is grounded, and the two sources are respectively connected to the voltage dividing circuit subunit and the analog to digital conversion unit.

As shown above, since the silicon microphone is very sensitive and stable to changes in external pressure, the use of a silicon microphone as the sensing unit will greatly improve the accuracy of the gas meter. Silicon microphones consume substantially no energy, so the gas meter of the present invention has lower power consumption than existing gas meters. In addition, The manufacturing process of the silicon microphone has been quite mature, its volume can be made small, and its cost is low. Therefore, the gas meter of the present invention has the advantages of small volume and low cost which the existing gas meter does not have.

In order to improve the accuracy of the signal, as shown in FIG. 5, the gas meter of the embodiment further includes: a high frequency filtering unit located at the front end of the analog to digital conversion unit for filtering the high frequency interference portion of the detection signal of the gas flow rate sensing sensor . Since the gas flow rate changes slowly, the filter circuit does not cause damage to the useful signal. As an indispensable part of the gas meter of the present embodiment, the analog-to-digital conversion unit is used for sampling, and digitalization of the analog voltage signal is performed, so that the main control unit at the back end can perform nonlinear compensation and flow calculation.

As shown in FIG. 5, the gas meter of this embodiment further includes: a memory unit connected to the main control unit for storing gas flow information. The main control unit includes an update subunit connected to the memory unit for updating gas flow information recorded in the memory unit when the accumulated gas flow reaches a preset flow value. In this embodiment, the memory unit uses a conventional solid state memory for recording and storing the accumulated gas consumption information of the gas meter user, which is convenient for the gas operator to perform billing and various management. The master unit is actually a microcontroller that can perform computational functions. In the main control unit, the method of reducing the gas flow rate according to the flow rate signal may be in the form of a look-up table. The method of obtaining the gas flow rate according to the gas flow rate and the acquisition time interval may be integrated, and is of course not limited to these two methods.

In order to measure the gas flow rate more accurately, the present invention also specifically sets a mechanism for compensating the gas flow rate according to temperature and static pressure. FIG. 7 is a schematic structural view of a gas meter including a temperature-static pressure supplement mechanism according to an embodiment of the present invention. As shown in FIG. 7, in a preferred embodiment of the present invention, the gas meter may further include: a temperature sensing unit for converting a temperature of the gas environment into a temperature signal; and/or a static pressure transmission The sensing unit is configured to convert the static pressure of the gas environment into a static pressure signal; the analog to digital conversion unit is connected to the temperature sensing unit and/or the static pressure sensing unit for collecting temperature sensing The unit converts the temperature signal and/or the static pressure signal converted by the static pressure sensing unit, and performs analog-to-digital conversion on the temperature signal and/or the static pressure signal; the main control unit is configured to perform analog-to-digital conversion according to the analog-to-digital conversion unit The temperature signal and/or static pressure obtain temperature information and/or static pressure information of the gas environment, and calibrate the gas flow rate according to the temperature information and/or the static pressure information. Preferably, the temperature sensing unit is a thermistor, and of course other types of temperature sensing circuits can be used instead; static pressure The sensing unit is a MEMS pressure sensor, and of course, it can also be replaced by a discrete device. In this embodiment, the main control unit has a non-volatile memory, and a pressure/temperature-density comparison table is stored therein (see Table 1). The gas density is calculated in real time according to equation (1) through the pressure and temperature sensors in the cavity and the pressure/temperature-density table.

Table 1 Static pressure / temperature - density comparison table

It should be noted that two parameters - static pressure and temperature - are used in this embodiment to correspond to the gas density. In fact, it is also possible to fix one of the parameters and another parameter to calibrate the gas density, as well as the coarseness correction of the gas flow rate. In addition, the method of calibrating the gas density by static pressure and temperature is not limited to the look-up table method, and the formula method may be used, that is, the formula using the static pressure and the temperature as the independent variables and the gas density as the dependent variable is used. The measured static pressure information and temperature information obtain an accurate gas density, thereby obtaining an accurate gas flow rate.

In order to realize that the analog-to-digital conversion unit separately collects the signals of the flow rate sensing unit, the temperature sensing unit and the static pressure sensing unit, as shown in FIG. 7, in this embodiment, the acquisition period, frequency or electrical signal of the analog-to-digital conversion unit is required. The amplitude value is limited. The simplest method is to use the time-segment switch, that is, the gas meter further includes an analog switch; the analog switch is located at the front end of the analog-to-digital conversion unit, and is used for selective opening/closing according to a preset time period. The number conversion unit is connected to the gas flow rate sensing unit, the temperature sensing unit, and the static pressure sensing unit according to the preset time period, and samples the flow rate signal, the temperature signal or the static pressure signal.

In this embodiment, in order to achieve an accurate measurement effect, the positions of the gas flow rate sensing unit, the temperature sensing unit, and the static pressure sensing unit need to be set. In the actual scene, the gas meter airflow chamber includes a gas rectifying passage and a sensor rod. The sensor rod is installed in the gas rectifying passage, the lower part of the rod is located in the middle of the rectifying passage, and the air guiding hole on the back side of the rod is located in the rectifying passage the top of. The principle of position setting of the temperature sensing unit and the static pressure sensing unit is that the gas flow rate sensing unit is disposed in the windward direction of the sensor rod; the temperature sensing unit and the static pressure sensing unit are disposed in the cavity of the sensor rod, The cavity communicates with the gas environment through a venting opening on the back side of the sensor rod.

Fig. 8a is a rear elevational view showing the sensor rod of the flow rate sensing unit, the temperature sensing unit, and the static pressure sensing unit in the gas meter of the embodiment of the present invention. Figure 8b is a cross-sectional view of the sensor rod of Figure 8a. Figure 8c is a side view of the sensor rod of Figure 8a; as shown in Figures 8a, 8b, 8c, there is an air vent (e) in the ventilating surface in the middle of the sensor rod; the air vent has a cavity inside the sensor rod The upper portion of the cavity is sealed with a sealing material. A portion of the PCB (d) is located in the cavity, and a MEMS static pressure sensor (b), a temperature sensor (c), and a front end circuit that works well with various sensors are mounted in the middle of the PCB in the cavity. The lower part of the PCB outside the cavity extends into the lower part of the sensor rod, on which is mounted a MEMS silicon microphone flow rate sensor that is directed toward the direction of gas flow. The upper part of the sensor rod is provided with five metal contacts (0, which are electrically connected through the lead wire passing through the above sealing material and the PCB board, and the five contacts correspond to the voltage output of the MEMS silicon microphone flow rate sensor, the static pressure sensor and the temperature sensor, respectively. Signal and power and ground signals Each sensor output signal is transmitted from the above five metal contacts to an external analog-to-digital conversion unit and main control unit for signal acquisition, analog-to-digital conversion and calculation processing. On the ventilating surface of the sensor rod, when the gas flows, due to the blocking action of the sensor rod, the air flow velocity near the air guiding hole and inside the cavity is approximately zero, so the static pressure inside and outside the cavity is the same and the temperature is uniform.

As described above, in the gas meter of the present embodiment, the gas density is compensated by the temperature and the static pressure, thereby achieving accurate calibration of the gas flow rate, and further improving the accuracy of the gas meter.

In addition, in order to increase the strength of the signal, as shown in FIG. 7, a programmable gain amplifier is provided between the analog switch and the analog-to-digital conversion unit for selectively gain-amplifying the sensor detection signal, thereby facilitating the back-end device pair signal. Processing.

Figure 9 is a flow chart showing the operation of a gas meter according to an embodiment of the present invention. As shown in FIG. 9, in the actual use process, the domestic gas meter first starts the gas flow rate sensor, and after it is stabilized, the analog-to-digital conversion unit (ADC) sampling circuit performs sampling and analog-to-digital conversion on the high-frequency filtered flow rate signal. The analog-to-digital converted sample values are sent to the main control unit (MCU) for nonlinear compensation and flow rate calculation, and the cumulative flow is calculated. At the same time, the gas flow rate is corrected by the temperature and static pressure compensation mechanism. Normally, the gas consumption information in the solid state memory is updated when the accumulated flow rate is over a set unit amount. This cycle works to achieve the measurement of gas.

Compared with the conventional gas meter, the gas meter of the invention adopts a sensing unit of a silicon microphone. Since the silicon microphone is very sensitive and stable to changes in external pressure, the use of a silicon microphone as a sensing unit will greatly improve the accuracy of the gas meter. . In addition, the gas meter of the present invention increases the compensation mechanism of temperature and static pressure, and further improves the accuracy of the gas meter. The specific embodiments of the present invention have been described in detail with reference to the preferred embodiments of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and scope of the present invention are intended to be included within the scope of the present invention.

Claims

1. A gas meter, comprising:

a gas flow rate sensing unit for converting a gas flow rate into a flow rate signal using a silicon microphone;

An analog-to-digital conversion unit is connected to the gas flow rate sensing unit for collecting a flow rate signal converted by the gas flow rate sensing unit, and performing analog-to-digital conversion on the flow rate signal; a main control unit, and the modulus The conversion unit is connected to reduce the gas flow rate according to the flow rate signal after the analog-to-digital conversion of the analog-to-digital conversion unit, and obtain the accumulated gas flow rate according to the collected gas flow rate and the flow rate signal collection interval time.

2. The gas meter according to claim 1, wherein

The gas meter further includes: a temperature sensing unit configured to convert a temperature of the gas environment into a temperature signal; and/or a static pressure sensing unit configured to convert a static pressure of the gas environment into a static pressure signal ;

The analog-to-digital conversion unit is connected to the temperature sensing unit and/or the static pressure sensing unit, and is configured to collect a temperature signal converted by the temperature sensing unit and/or a static pressure converted by the static pressure sensing unit. Signaling, and performing analog-to-digital conversion on the temperature signal and/or the static pressure signal;

The main control unit is configured to obtain temperature information and/or static pressure information of the gas environment according to the analog-to-digital conversion temperature signal and/or static pressure signal of the analog-to-digital conversion unit, and according to the temperature information And/or static pressure information calibrates the gas flow rate.

The gas meter according to claim 2, wherein the gas meter comprises: a temperature sensing unit and/or a static pressure sensing unit; and the main control unit comprises:

a storage subunit, a static pressure/temperature-density comparison table for storing gas; a calibration subunit connected to the analog to digital conversion unit and the storage subunit for static pressure/temperature in the gas The gas density corresponding to the temperature information and/or static pressure information is searched in the density comparison table, and the gas flow rate is calibrated using the gas density.

4. The gas meter of claim 2, further comprising:

An analog switch, located at a front end of the analog-to-digital conversion unit, for selectively opening/closing according to a preset time period, wherein the analog-to-digital conversion unit separately and the gas flow rate according to a preset time period The sensing unit is connected to the temperature sensing unit and/or the static pressure sensing unit to sample the flow rate signal, the temperature signal or the static pressure signal.

5. The gas meter of claim 4, further comprising:

a high frequency filtering unit, and a rear end of the analog switch, for filtering high frequency noise in the flow rate signal, the temperature signal or the static pressure signal;

A programmable gain amplifier is coupled between the high frequency filtering unit and the analog to digital conversion unit for selectively gain amplifying the flow rate signal, the temperature signal or the static pressure signal.

The gas meter according to claim 2, wherein the gas flow rate sensing unit is disposed in a windward direction of the sensor rod;

The temperature sensing unit and/or the static pressure sensing unit are disposed in a cavity of the sensor rod, and the cavity communicates with the gas environment through a vent hole of the back surface of the sensor rod.

The gas meter according to claim 2, wherein the temperature sensing unit is a thermistor; and the static pressure sensing unit is a MEMS pressure sensor.

8. The gas meter according to claim 1, wherein the gas flow rate sensing unit comprises a capacitive silicon microphone and a voltage dividing circuit subunit;

The capacitive silicon microphone is connected to the analog-to-digital conversion unit for converting the gas flow rate into a corresponding impedance signal by a DC coupling method using a silicon crystal diaphragm; the voltage dividing circuit subunit, and the capacitive type The silicon microphone is connected to convert the impedance signal into a flow rate signal in the form of voltage by means of voltage division.

The gas meter according to claim 8, wherein the silicon crystal diaphragm is a silicon crystal floating diaphragm; the voltage dividing circuit subunit is a voltage dividing resistor;

The drain of the silicon floating diaphragm is grounded, the first source is connected to the working power source through a voltage dividing resistor, and the second source is connected to the analog to digital conversion unit by DC coupling.

The gas meter according to any one of claims 1 to 9, further comprising: a memory unit connected to the main control unit for storing gas flow information;

The main control unit includes an update subunit connected to the memory unit, and is configured to update the gas flow information recorded in the memory unit when the accumulated gas flow reaches a preset flow value.