JP3039114B2 - Flowmeter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to, for example, city gas and LP.
The present invention relates to a flow meter for measuring a flow rate of a fluid such as G gas, and particularly to a control device having a highly accurate calculation function.

[0002]

2. Description of the Related Art Heretofore, there has been proposed a flow meter of this type using a fluidic oscillation element having no characteristic change due to temperature as a sensor for detecting a flow rate. But,
In this case, the flow rate range that can be measured is about 50 times, and there is a big problem in applying it to a situation where measurement of a flow rate area of 1000 times is required like a city gas meter.

Therefore, as shown in Japanese Patent Application Laid-Open No. 3-308921, a flow sensor for detecting a flow velocity is provided on a fluidic oscillation element, and in a small flow rate range, the output from the flow sensor is measured. In a medium to large flow rate range, a method of measuring the oscillation frequency of a fluid oscillation element has been proposed.

That is, in the flow meter of FIG. 3, 1 is a flow meter main body, 2 is a gas pipe, and 3 is a fluidic oscillation element, which generates fluid oscillation by utilizing kinetic energy of the fluid. A piezoelectric sensor 4 detects the frequency of fluid oscillation. Reference numeral 5 denotes a flow sensor that detects a fluid flow rate at a nozzle portion (not shown) of the fluid oscillation element and generates an analog signal proportional to the flow rate. Reference numeral 6 denotes a shutoff valve that supplies gas when an abnormal use state is detected. Cut off. 7 is a control device. When the frequency detected by the piezoelectric sensor 4 is equal to or higher than a certain value, the controller 7 calculates the flow rate from the frequency. When the frequency is equal to or lower than the certain value, the controller 7 measures the flow rate by obtaining the flow rate from the output of the flow sensor 5. In a normal use state, the shut-off valve 6 is driven.

[0005] As shown in FIG. 4, the flow sensor 5 has a temperature sensor 5a,
The heater 5b and the temperature sensor 5c are arranged in this order, and the heater 5b is heated by energization. When there is no fluid flow, the temperature distribution is symmetrical with respect to both the upstream and downstream directions of the flow path centering on the heater 5b, but when a flow occurs, the temperature sensor 5c on the downstream side of the upstream temperature sensor 5a Has a higher temperature, and the temperature difference at this time causes a difference in electric resistance between the temperature sensors 5a and 5c.
At this time, the difference between the generated electric resistances is output as an analog signal corresponding to the flow velocity.

[0006]

In the above-mentioned conventional configuration,
Although the relationship between the output of the flow sensor and the flow rate is not disclosed in detail, generally even when the flow rate is zero, the output is as if a minute flow rate was generated due to the influence of the temperature drift of the sensor. This caused a measurement error.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has as its object to provide a flow meter capable of performing accurate flow measurement.

[0008]

In order to achieve the above object, the present invention provides a flow rate detecting means for detecting a flow rate of a fluid and outputting a flow rate signal; a change amount detecting means for detecting a change amount of the flow rate signal; A control rule storing means for storing, as a control rule, a relationship between the flow rate signal and the output of the change amount detecting means and the correction amount of the flow rate signal; and a control rule storing means for storing the control rule storing means based on the flow rate signal and the output of the change amount detecting means. Inference means for performing an inference process with reference to a control rule to obtain a correction amount of the flow velocity signal; correction value setting means for setting a correction value of the flow velocity signal in accordance with the flow velocity signal and an output of the inference means; And a flow rate calculating means for obtaining a flow rate from the output of the correction value setting means and the function stored in the flow rate function storing means.

[0009]

According to the present invention, the inference means determines the correction amount of the flow velocity signal based on the flow velocity signal output from the flow velocity detection means and the change amount thereof according to the control rule defined in the control rule storage means. The correction value setting means sets a correction value of the flow velocity signal based on the flow velocity signal and the correction amount obtained by the inference means. Further, the flow rate calculating means obtains the flow rate from the correction value of the flow velocity signal according to a function defined in the flow rate function storing means. That is, a rule is set in the control rule storage means so as to correct the fluctuation of the zero point due to the temperature drift, and the flow rate calculation is performed after correcting the flow velocity signal according to this rule, so that the flow rate is accurately obtained. be able to.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is a block diagram of a flow meter according to the present invention. In the figure, reference numeral 8 denotes a flow rate detecting means, which is a flow sensor 5 for generating a voltage proportional to the flow rate, and an A / A for generating a pulse number P proportional to the output of the flow sensor 5 at regular intervals.
It is composed of a D conversion unit 8a. 9 is a variation detecting means for calculating a change amount ΔP per unit time of the output flow rate signal of the flow rate detecting unit 8, a flow rate storage unit 9a for storing the previous velocity signal P _o, the flow rate storage unit from a flow rate signal P by subtracting the output P _o of 9a is composed of a change amount calculating means 9b for outputting. Reference numeral 10 denotes a control rule storage unit that stores the flow velocity signal P and the relationship between the change amount ΔP and the correction amount U of P as a control rule. Here, as an example of the stored control rule, the control rule is stored in the form of if-then, such as "If P is large and ΔP is positive and large, make U small." . Here, a part corresponding to “if〜” is defined as a condition part, and a part corresponding to “then〜” is defined as an output part. The control rule storage means 10 includes a condition part storage means 10a for storing a condition part of the control rule, and an output part storage means 10b for storing an output part of the control rule. In the rules stored in the condition part storage means 10a and the output part storage means 10b, the variables "positive and large" and "small" are defined in FIG.
4 is defined as a membership function shown in FIG.
In the condition part of the control rule, fifteen conditions are set according to the magnitude combination of the flow velocity signal P and the change amount ΔP, and the output part sets outputs for the fifteen conditions. Here, some examples of the control rules will be described.

Example 1 "If P is large and ΔP is positive and large, let U be small." Example 2 "If P is large and ΔP is small, let U be large." Means that when the change in the flow velocity signal P is large, the correction amount U is reduced because the possibility of the occurrence of the fluid flow is large, and the meaning shown in Example 2 is that the flow velocity signal P is large and However, when the change amount is small, the correction amount U is increased because the possibility of the influence of the temperature drift is large. The same applies to 1
The five control rules are shown in (Table 1).

[0012]

[Table 1]

Numeral 11 denotes inference means for inferring the correction amount U of the flow velocity signal P based on the flow velocity signals P and the change amount ΔP of P in accordance with the rule defined in the control rule storage means 10. The inference means 11 receives the flow velocity signal P and the change amount ΔP, and calculates a fitness calculation means 11a for determining the fitness of the control rule to the condition part.
Weighting means 11b for performing a weighting operation on the output part of the control rule based on the determined degree of conformity and the output of the output part storage means 10b; And a center-of-gravity calculating means 11c for obtaining the quantity U. Numeral 12 is a correction value setting means, based on the flow velocity signal P and its correction amount U, the correction value P '= P
Find and output -U. Reference numeral 13 denotes a flow rate function storage unit, which stores the relationship between the flow velocity signal P and the flow rate Q as a function.
Numeral 14 denotes a flow rate calculating means for obtaining an instantaneous flow rate from the correction value P 'of the flow velocity signal and a function defined in the flow rate function storing means 13. Numeral 15 integrates the flow rate obtained by the flow rate integrating means to obtain an integrated value. 16 is a display means for displaying the integrated value.

Next, the operation of the above configuration will be described. The flow sensor 5 is provided in a fluid flow path, and generates an analog voltage proportional to the flow velocity. The A / D converter 11 generates the number of pulses proportional to the output voltage of the flow sensor 5 within a unit time (t), and detects the flow rate from the number P of pulses. The output P at this time is output to the change amount detecting means 9.
The flow velocity signal P before the unit time t seconds is stored in the flow velocity storage means 9a.
_o is stored. In the change amount calculation unit 9b, PP- _Po
Comprising operation is performed, the value ΔP = P-P _o at this time is output as a variation. At the same time, the current output value P is stored in the flow velocity storage means 9a.

Subsequently, the flow velocity signal P and the variation detecting means 9
From the output ΔP of the correction value P ′ by the correction value setting means 12.
Will be described. Flow rate signal p _l, the amount of change in that time and was Delta] p _l. The suitability calculating means 11a calculates the suitability for the condition based on the condition defined in the condition storage means 10a. The conditions defined in the condition part storage means 10a are defined in the form of "A and B", for example, "P is large and ΔP is large". In this case, asking condition A, adaptability omega _A against B, omega _B respectively, omega _A, the smaller value of omega _B, and adaptability omega _AB for the condition "A and B".

Based on this concept, P = p _l , ΔP = Δp
_Find the degree of conformity to each condition at _l . First, the value of each membership function at the time of P = p ₁ is obtained from FIG.
P at that time is small, in the P is, each of the goodness-of-fit P is for large, 0, 0, and ω _a. Similarly, FIG.
at the time of the p _l, Δp is large in the negative, in ΔP is negative, ΔP is small,
The degree of conformity to ΔP is positive and medium and ΔP is positive and large is 0, 0, 0, ω _b , and ω _o , respectively. As a result, for example, the degree of conformity to the condition “P is large and ΔP is large” is ω _a >
because it is ω _c, a ω _o. Similarly, the degree of conformity to the 15 conditions defined in the condition part storage means 10a is shown in Table 2
Shown in

[0017]

[Table 2]

Next, the weighting calculation means 11b performs weighting calculation by multiplying the output part of the control rule determined in the output part storage means 10b by the fitness calculated by the fitness calculation means 11a. Table 3 shows the results of the weighting calculation when P = p ₁ and ΔP = Δp ₁ .

[0019]

[Table 3]

Next, the center-of-gravity calculating means 11c synthesizes the function of the output part of the control rule subjected to the weighted calculation and obtains the center of gravity. The synthesized function is indicated by the hatched portion in FIG. The center of gravity of the synthesized function is defined as a point where the area of the hatched portion is halved. When the center of gravity in FIG.
It becomes ₁ . This value is a correction amount for P = p _l and ΔP = Δp _l .

The correction value setting means 12 obtains an output correction value P 'by subtracting the correction amount U from the flow velocity signal P. In the example shown in this case 5, the P '= p _l -u _l.

The relationship between the flow rate Q and the flow rate signal P is stored in the flow rate function storage means 13 in the form of a function Q = F (P). In the flow rate calculating means 14, the instantaneous flow rate is obtained by substituting the correction value P 'of the flow velocity signal into the function Q = F (P) determined in the flow rate function storing means 13.

[0023] Subsequently, the flow rate signal P calculates the correction amount U when p _n variation ΔP of Delta] p _n. Where p
_It is assumed that _n is a value sufficiently larger than _ps shown in FIG. In this case, 15
Are all 0. In this case, the output U of the center-of-gravity calculating means 10c outputs the value obtained last time as it is. That is, the value of p _s is
If it is set near the maximum value considered as the influence of the temperature drift, if there is an output far exceeding this value, it is determined that the output is due to the flow of the fluid, and the correction amount U is held.

According to this embodiment, when the output of the flow velocity detecting means is due to the influence of the temperature drift, the flow rate is obtained after correcting the amount, so that the flow rate can be accurately obtained. it can.

[0025]

As described above, the flow meter according to the present invention has the following features.
Since the flow velocity is corrected according to a control rule that cancels the fluctuation of the zero point, and the flow rate calculation is performed based on the corrected value, the flow rate can be accurately obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram of a flow meter according to an embodiment of the present invention.

FIG. 2 is a diagram showing a membership function relating to a flow velocity signal used in a control rule storage means of the flow meter.

FIG. 3 is a diagram showing a membership function relating to a change amount of a flow velocity signal used in a control rule storage means of the flow meter.

FIG. 4 is a diagram showing a membership function relating to a correction amount of a flow velocity signal used in a control rule storage unit of the flow meter.

FIG. 5 is a view showing a calculation result of a center-of-gravity calculating means of the flow meter.

FIG. 6 is a block diagram of a conventional flow meter.

[Explanation of symbols]

 8 Flow velocity detecting means 9 Change amount detecting means 10 Control rule storing means 11 Inference means 12 Correction value setting means 13 Flow function storing means 14 Flow calculating means

Claims (1)

(57) [Claims] 1. A flow rate detecting means for detecting a flow rate of a fluid and outputting a flow rate signal, a change amount detecting means for detecting a change amount of the flow rate signal, a flow rate signal, an output of the change amount detecting means and a flow rate signal. A control rule storing means for storing a relationship with the correction amount as a control rule; and a flow rate signal correction by performing inference processing with reference to the control rule of the control rule storing means based on the flow rate signal and the output of the change amount detecting means. Inference means for determining the amount, a flow rate signal and a correction value setting means for setting a correction value of the flow rate signal in accordance with the output of the inference means, a flow rate function storage means for storing a function indicating the relationship between the flow rate signal and the flow rate,
A flow meter comprising flow rate calculating means for obtaining a flow rate from an output of the correction value setting means and a function stored in the flow rate function storing means.