JP3169116B2 - Gas flow meter and composite gas flow meter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas flow meter for use with fuel gas such as LP gas and natural gas.

[0002]

2. Description of the Related Art Fluidic type flow meters have been widely used because they can be miniaturized and have excellent durability because of no moving parts. In this method, when gas passes through a fluidic oscillator, measurement is performed using the frequency of a pressure pulse generated by a fluid vibration phenomenon. As a method of obtaining the gas flow rate from the frequency of the pressure pulse, there is a technique known in JP-A-1-308921, JP-A-3-44512, or JP-A-3-95420.

Here, in the fluid gas flow meter, it is assumed that the flow rate and the frequency of the pressure pulse are in a proportional relationship. However, the flow rate is not proportional to the actual one and is corrected by a large number of correction coefficients, or It was necessary to devise a technique such as switching the calibration curve to be used according to the change. In obtaining the flow rate from the frequency of the pulse also in the above-described prior art,
A table having a large number of constants is prepared, or a complicated operation is performed. Therefore, the means required for these operations consumes large power, and thus such prior art is
For example, it cannot be applied to an application that requires long-term measurement with a built-in battery such as a fuel gas meter. In addition, the complicated arithmetic means as described above is generally difficult to customize and is expensive, which has been a factor of increasing the cost of the flowmeter.

[0004] A fluidic oscillator whose shape has been improved by the present applicant has been disclosed in Japanese Utility Model Laid-Open Publication No. 4-10.
Although disclosed in Japanese Patent No. 9327 and the like, there has been a demand for a fluidic type gas flow meter which uses such an excellent oscillator, exhibits sufficient performance, has low power consumption, and can be easily customized. Also in the improved fluidic oscillator described above, although the correspondence between the flow rate and the oscillation frequency has been improved, there is still a problem in machining accuracy, so the relationship between the flow rate and the oscillation frequency is completely reduced. I could not say that they were in a proportional relationship. Therefore, in the production of these fluidic oscillators, the yield is low, which has been a problem.

On the other hand, it is said that the fluidic flow meter is difficult to apply when the flow rate change is large such that the difference between the minimum flow rate and the maximum flow rate is about 1000 times. Here, it has been known from Japanese Patent Application Laid-Open No. 1-308921 to form a composite gas flow meter by combining a fluidic flow meter and a thermal flow meter to improve this drawback. In the case of a low flow rate, the flow rate is measured using a thermal flow meter section, and when the flow rate is high, the flow rate is measured using a fluidic type flow meter section. When the flow rate is high, heating of the heater of the thermal flow meter that is not involved in the measurement is stopped, and when the flow rate is low, the heater is heated and measured intermittently to suppress power consumption. However, this composite gas flow meter measures intermittently, especially at low flow rates, and the measured values are not reliable and pose a problem. Thus, there has been a demand for a composite gas flow meter with high accuracy and low power consumption.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems, that is, to provide a gas flow meter which consumes very little power and can be easily customized.

[0007]

The gas flow meter of the present invention comprises:
As shown in the basic configuration diagram of FIG. 1, a gas flow meter using a fluidic oscillator E, wherein the fluidic oscillator E has a flow rate Q of a gas to be measured per fixed time t,
In relation to the number of fluid oscillation pulses f generated in the oscillator per t, the relationship substantially satisfies the following equation: Q = af (a: proportional constant). Timer signal means 1 for outputting a timer signal every t, frequency counting means 2a for starting counting the number of pulses of the sensor in response to a timer signal input, and outputting a frequency-divided signal every constant number k, and the sensor in response to a timer signal input. The second counting means 2 which starts counting the number of pulses and outputs the remainder m of the counted number of pulses f by k when the next timer signal is input.
b and a are added each time a frequency-divided signal is input by the above-described frequency division count, and when the timer signal is input, the integrated value is multiplied by k by performing an arithmetic shift using the integrated value as a k-ary number and multiplied by k. And a calculating means 3 for calculating the flow rate Q by adding a number obtained by multiplying m output from to a by a.

In the present invention, the fluidic oscillator E
Is the flow rate Q of the gas to be measured per fixed time t,
Substantially satisfying the relationship of the equation Q = af (a: proportional constant) in relation to the number of fluid vibration pulses f generated in the oscillator means the following.

In the case of a flow meter using a fluidic oscillator, the relationship between the flow rate Q and the pulse number f in a certain time is
Actually, it is known that Equation 2 Q = af + b (a and b are constants specific to the element) (Equation 2).

Generally, tolerances are recognized for flow meters used in applications such as fuel gas. The tolerance is
When the maximum measured flow rate of the flow meter is Q _max , when the flow rate is 1/20 or more and less than 1/10 of Q _max : 3% of the actual flow rate, and the flow rate is 1/10 or more and less than 4/5 of Q _max when 1.5% of the actual flow rate, when the flow rate is less than 4/5 or more Q _max of Q _max: 3%, the actual flow rate. Therefore, based on these relationships, the following tolerance is satisfied if | b | ≦ 0.3672 a (Equation 3) is satisfied in the constants a and b specific to the element in Equation 2.

That is, in the present invention, when the relationship of the above equation 3 is satisfied, it can be said that the relationship is substantially Q = af (a: proportional constant). Here, it is sufficient to satisfy Expression 3, and it is not necessary to completely satisfy Expression 1. Therefore, the production of such a fluidic oscillator is facilitated in terms of processing accuracy, and the product yield in production is improved. In addition, the cost can be kept low. Here, a fluidic oscillator that satisfies such a specific relationship is disclosed in Japanese Utility Model Application Laid-Open No. HEI 4-104 filed by the present applicant.
No. 109327, and the like.

On the other hand, the composite gas flow meter according to the present invention has two flow sensors for high flow rate measurement and low flow rate measurement as shown in the basic configuration diagram of FIG. A composite gas flow meter for switching a flow sensor for measuring a flow rate according to a flow rate Q of a measurement target gas, wherein a flow sensor for measuring a high flow rate is a fluidic oscillator E1, and the fluidic oscillator E1 is used for a predetermined time t. The relationship between the flow rate Q of the gas to be measured and the number of fluid vibration pulses f generated in the oscillator per t substantially satisfies the relationship of Q = af (a: proportional constant) in Expression 1; and the low flow measuring flow rate sensor is an orifice differential pressure gauge E2, the output of the orifice differential pressure gauge number of pulses f ₂ per predetermined time t so as to satisfy the formula Q = af ₂ ...... (equation 4) conversion Signal conversion means 4; switching means 5 for selecting and outputting one of the output pulses of these two flow sensors; timer signal means 1 for outputting a timer signal at regular time intervals t; Frequency dividing means 2a which starts counting the number of pulses to be output and outputs a frequency dividing signal at every constant number k, and starts counting the number of pulses supplied from the switching means in response to a timer signal input. A second counting means 2b for outputting the remainder m of the counted pulse number f by k, and a for each input of the frequency-divided signal by the frequency-dividing count, and when the timer signal is input, the integrated value is calculated as a k-ary number. An operation of calculating the flow rate Q by adding a number obtained by multiplying a by a multiplied by k outputted from the second counting means to this value and multiplying the value by k by carrying out by shifting. Calculation means 3 as a configuration.

The relationship between the output V and the flow rate Q of the orifice differential pressure gauge for low flow rate measurement is expressed by equation (5).

(Equation 1)

Here, the signal converting means for converting the above equation 5 into the number of pulses f ₂ per a fixed time t so as to satisfy Q = af ₂ in the equation 4 may be, for example, a method in which the output of the flow sensor for low flow rate measurement is a voltage. When the signal is output, it can be configured by combining a general-purpose analog subtraction circuit, square root circuit, amplification circuit, and voltage-frequency conversion circuit (hereinafter referred to as “V / F conversion circuit”).

[0015]

According to the gas flow meter of the present invention, a fluidic oscillator having a flow rate and a frequency of an output pulse substantially proportional to each other is used, so that the output pulse can be easily processed. Further, it is sufficient to use only one constant a for the calculation, and it is not necessary to provide a large number of constants according to the flow rate. In addition, since a table in which these constants are described becomes unnecessary, customization of means for calculating both quantities from the frequency of the output pulse becomes easy, and the manufacturing cost is reduced.

A timer signal means for outputting a timer signal at regular time intervals t; a frequency dividing count means for starting counting of the number of pulses of the sensor in response to the timer signal input and outputting a frequency dividing signal at regular time intervals k; A second counting means for starting counting of the number of pulses of the sensor in response to a signal input and outputting a remainder m of the counted number of pulses f by the k in response to a next timer signal input, so that the calculation of the flow rate in the calculating means can be reduced to one. Sometimes, it is not necessary to perform all of the operations, and the operation means has a high performance and is not inevitable. Therefore, it is possible to select an operation means with low power consumption.

On the other hand, in the arithmetic means, a is added each time a frequency-divided signal is input by the frequency division count, and when the timer signal is input, the integrated value is multiplied by k by performing a carry by arithmetic shift using the integrated value as a k-ary number. By selecting a value for calculating the flow rate Q by adding a number multiplied by a to the value of m output from the second counting means to the value, multiplication of a large digit becomes unnecessary, so that the power consumption is low and the power consumption is low. It is possible to cope with low cost operation means.

The composite gas flow meter according to the present invention has all the advantages of the gas flow meter according to the present invention,
Uses an orifice-type pressure sensor as a flow sensor for low flow measurement, consumes less power than conventional compound flowmeters, and therefore can always measure flow even when the flow rate is in the low flow rate range Therefore, an accurate integrated flow rate value can be obtained. Further, the output of the flow sensor for low flow rate measurement is also converted into the number of pulses per fixed time, and the constant a is the same as that at the time of high flow rate measurement.
Even if the flow sensor involved in the measurement is switched, an operation such as a new reading of a constant from the constant table is not required, and therefore, there is no need for a calculation means capable of performing a high-speed calculation.

[0019]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 3 shows an embodiment of the composite gas flow meter according to the present invention. In the figure, the symbol Inlet is the inlet of the gas to be measured, and the outlet is the outlet of the gas. Fluidic oscillator E1 which is a flow sensor for measuring high flow rate in the gas flow path
A sensor E1d that detects a pulse due to airflow and outputs the pulse as an electric pulse is installed in the inside, and a sensor E2d that outputs a pressure difference as a voltage is attached to the orifice differential pressure gauge E2, which is a flow sensor for low flow rate measurement. ing. In addition, pressure regulators R1, R2, and R3 are arranged in the gas flow path and adjusted in advance in order to adjust the flow rate flowing through these sensors so that accurate and highly reliable flow rate measurement can be performed in a low flow rate range. ing.

The above-mentioned fluidic oscillator is constructed as follows.
According to the technique described in Japanese Patent No. 109327, the relationship between the flow rate Q of the gas to be measured per a certain time t and the number of fluid oscillation pulses f generated in the oscillator per the t is substantially equal to
It satisfies the relationship of equation Q = af (a: proportionality constant). That is, Q = af + b (where a and b are constants specific to the element) (Equation 2) where, when t is 1 second, the flow rate between a and b in Equation 3 is obtained at a flow rate of 0.8 to 17 l / min. The one that satisfies the relationship.

Here, the output of the sensor E1d of the above-described fluidic oscillator E1 is connected to an input port 3Ia of an MPU 3mp to be described later. On the other hand, the output of the sensor E2d of the orifice differential pressure gauge E2, which is a flow rate sensor for low flow rate measurement, passes through a conversion circuit A comprising a subtraction circuit A1, a square root circuit A2, an amplification circuit A3, and a V / F conversion circuit A4.
After being converted into a frequency corresponding to the above, the signal is input from the input port 3Ia to the inside of the MPU 3mp. Incidentally, the conversion circuit A be previously adjusted, the output of the low flow rate measurement area sensor 2d of the orifice differential pressure gauge E2 have the formula Q = af ₂ (a: proportional constant, f _2: Electric per fixed time t pulse number, Q: is converted into an electrical pulse number f ₂ per predetermined time t satisfying the flow rate) per fixed time t.

The MPU 3mp has a central processing unit (hereinafter referred to as "CPU") 3cp,
ROM 3ro (see FIG. 4 (a)) for storing the PU3cp program, the sensor constant a, the interval time t of the timer signal, or the threshold value q1 between the high flow rate measurement area and the low flow rate measurement area, etc. Time data (hereinafter referred to as a "timer") T of the elapsed time and a frequency division counter C1
, A second counter C2, a k-ary counter C3, a RAM 3ra (see FIG. 4B) for storing various data such as a measurement sensor setting variable u and an integrated flow rate Bt.

The MPU 3mp has an input port 3ia for receiving a signal output from the fluidic oscillator E1, an input port 3ib for a signal output from the orifice differential pressure gauge E2, and a display device LCD. Has an output port 3oa for outputting the measurement result (integrated flow rate Bt).

In the composite gas flow meter of this embodiment, I
A vortex corresponding to the gas flow rate Q from nlet to Outlet is generated in the fluidic oscillator E1, and a pressure difference corresponding to the gas flow rate is generated in the orifice differential pressure gauge E2. When the power is turned on to the gas flow meter, an electric pulse corresponding to the vortex in the fluidic oscillator E1 is generated by the sensor E1d, and the MPU 3mp is input from the input port 3ia.
Is input to

On the other hand, the differential pressure generated by the orifice differential pressure gauge E2 is output as an electric signal (voltage) by the sensor E2d, and is converted by the conversion circuit A into a pulse signal having a frequency corresponding to the flow rate Q. It is input to MPU3mp. This MPU3mp is RAM3
After the data in rm is initialized, the timer T starts, and among the signals input to these MPUs,
The signal from the orifice differential pressure gauge E2 input from the input port 3ib is counted.

The counting is continued until the time t is reached by the frequency dividing counter C1 and the second counter C2. During this time, every time the value of the frequency division counter C1 becomes a multiple of k (k = 10 in this embodiment), the k-ary counter C3 stores the sensor constant a
Is added. When the time t (1 second in this embodiment) is reached, the k-ary counter C3 is set to k by arithmetic shift.
Then, the remainder m of the number of pulses k at time t output from the second counter C2 is a sensor constant a
Is added to this, and the gas flow rate Q at time t
Is calculated, and Q is added to the integrated flow rate Bq.

The frequency dividing counter C1, the second counter C2 and the k-ary counter C3 are reset to 0, and a new count becomes possible. Here, the integrated flow rate Bq is output to the display device LCD via the output port O3 and displayed.

It should be noted that the value of the flow rate Q calculated as described above is a threshold value q1 which is a threshold value between the high flow rate measurement area and the low flow rate measurement area.
In the following case, the above operation is repeated for the signal from the orifice differential pressure gauge E2 input from the input port 3ib after the timer t is reset to 0, and the value of the flow rate Q becomes q
When it is 1 or more, the subsequent counting is repeated after the timer t is reset to 0 for the signal from the fluidic oscillator E1 input from the input port 3ia. If the value of the flow rate Q decreases again after the input sensor is switched, the signal from the input port 3ib is selected again.

FIG. 5 is a time chart showing the operation states of the pulse from the sensor, the timer signal means, the frequency dividing counter, the second counter and the CPU. In the present invention, the calculation of the flow rate by the timer signal by the timer signal means,
Further, the calculation of the integrated flow rate does not need to be performed at one time, and when the pulse from the sensor becomes a multiple of a fixed number k as shown in FIG. Since it is performed, it can be seen that the operations are dispersed. As described above, since it is not necessary to perform all the operations at one time, it is possible to sufficiently cope with the use of a relatively low-speed and low-power-consumption type operation means.

Next, the operation of the MPU 5mp in this embodiment will be described with reference to the flowcharts of FIGS.
In FIG. 6, the MPU 3mp starts operating when the power is turned on by turning on a switch (not shown). First, step S1
, The RAM 3ra and the like are initialized. Step S2
In step S3, the measurement sensor setting variable u is set to 0.
Starts the timer T.

In step S4, the value of the timer T is set to a predetermined time t.
It is checked whether the predetermined time t has been reached. If the predetermined time t has been reached, the process proceeds to step S20 from (α) shown in FIG. 7, and if not, the process proceeds to step S5. Step S5
, The measurement sensor setting variable u is checked, and
In step S6b, the orifice differential pressure gauge E
Check whether the signal from 2 is input from input port 3ib. On the other hand, if the variable u is other than 0, it is checked in step S6a whether a signal from the fluidic oscillator E1 is being input from the input port 3ia.

If the signals from these sensors are input in steps S6a and S6b, step S6
Go to step 7, if no signal is input, go to step S
Return to 4. If a signal has been input, step S7
In step S8, the frequency dividing counter C1 and the second
1 is added to the counter C2.

In step S9, the value of the frequency division counter C1 is k
If (K = 10 in this embodiment) has not been reached, the process returns to step S4, and if equal, a is added to the k-ary counter C3, and then the value of the frequency dividing counter C1 is reset to 0, and then step S4 Return to

On the other hand, the case of branching to (α) in step S4 will be described with reference to FIG. Step S20
, The value in the k-ary counter C3 is increased by k by an arithmetic shift and multiplied by k.
Step S in which the remainder of k of the value of 2 (the remainder when divided by k) m is multiplied by a and added to this to calculate the flow rate Q
21, in steps S22 and S23, the frequency dividing counter C1, the counter C2, and the k-ary counter C3
Is reset to 0, and in step S24, the integrated flow rate B
The value q is calculated, output from the output port 3ic in step S25, and displayed on the display device LCD.

In step S26, the gas flow rate Q at the predetermined time k calculated as described above is compared with a threshold value q1, and if it is larger than this value, the variable u for setting the measurement sensor is set to 1 in step S27a. Is measured by a fluidic oscillator E1, which is a high flow rate measurement sensor. If the value is smaller than this value, the measurement sensor setting variable u is set to 0 in step S27b, and the subsequent measurement is performed with the low flow rate measurement sensor. Orifice differential pressure gauge E2. After the timer T is reset in step S28, the process returns to step S3 from (β) in FIG. 6, and the measurement is continued.

As is clear from the description given with reference to the flowchart, the MPU 3mp executes the flowchart to select and output one of the output pulses of these two flow rate sensors. Timer signal means 1 for outputting a timer signal to the input means, counting of the number of pulses supplied from the switching means in response to the timer signal input, frequency division counting means 2a for outputting a frequency division signal every constant number k, and timer signal input Starts counting the number of pulses supplied from the switching means, and outputs the remainder m of the counted number of pulses f by the k at the time of the next timer signal input; A is added each time a frequency-divided signal is input, and when a timer signal is input, the accumulated value is converted to a k-ary number to carry the arithmetic shift. It multiplied k I serve as operation means 3 for calculating the flow rate Q by adding the number obtained by multiplication of a to m output from the second counting means to this value.

In the above description, the composite gas flowmeter according to the present invention has been described. However, if the switching means and the low flow rate measuring flow sensor E2 are omitted from the composite gas flowmeter, the present invention is applicable. Since the gas flow meter is used, the description of the embodiment will be omitted.

[0038]

As described above, according to the present invention, by combining a specific fluidic oscillator and a specific pulse counting means, the load on the arithmetic means is reduced, and simple arithmetic means is sufficient. It is now possible to respond. As a result, low power consumption can be achieved,
In addition, customization and cost reduction have become very easy because a complicated constant table which has been required conventionally is not required. Also, since the flow rate calculation is always performed at a low flow rate, the measurement accuracy is good.

[Brief description of the drawings]

FIG. 1 is a block diagram showing basic constituent blocks of a gas flow meter of the present invention.

FIG. 2 is a block diagram showing basic constituent blocks of the composite gas flow meter of the present invention.

FIG. 3 is a view showing one embodiment of the composite gas flow meter of the present invention.

FIG. 4 shows R in one embodiment of the composite gas flow meter of the present invention.
FIG. 2 is a diagram illustrating a configuration of an OM and a RAM. (A) is a diagram showing a configuration of a ROM. FIG. 3B is a diagram illustrating a configuration of a RAM.

FIG. 5 is a time chart showing a pulse from a sensor, a timer signal unit, a frequency dividing counter, a second counter, and a calculation state of a CPU.

FIG. 6 is a flowchart showing a procedure of work performed by the MPU of FIG. 3;

FIG. 7 is a flowchart showing a procedure of work performed by the MPU of FIG. 3;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Timer signal means 2a Frequency division counting means 2b Second counting means 3 Arithmetic means 4 Signal conversion means 5 Switching means E Fluidic oscillator E1 High flow rate measurement flow sensor E2 Low flow rate measurement flow sensor

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G01F 1/20 G01F 1/00 G01F 1/42 G01F 7/00

Claims (2)

(57) [Claims] 1. A gas flow meter using a fluidic oscillator, wherein the fluidic oscillator measures a flow rate Q of a gas to be measured per a fixed time t and a number f of fluid vibration pulses generated in the oscillator per t. The relationship substantially satisfies the relationship of Q = af (a: proportionality constant), and a timer signal means for outputting a timer signal at regular time intervals t. Frequency-counting means for starting counting and outputting a frequency-divided signal at every constant number k; counting the number of pulses of the sensor by inputting a timer signal; a second counting means for outputting a remainder m by k, and a is added each time a frequency-divided signal is input by the frequency-dividing count. The integrated value by performing a carry by arithmetic shifts as k Decimal multiplies k, second to this value
Calculating means for calculating a flow rate Q by adding a number multiplied by a to m output from the counting means. 2. A composite gas flow meter having two flow sensors for high flow rate measurement and low flow rate measurement, and switching a flow rate sensor for measuring a flow rate according to a flow rate Q of a gas to be measured per fixed time t. The flow sensor for high flow rate measurement is a fluidic oscillator, and the fluidic oscillator has a relationship between the flow rate Q of the gas to be measured per a fixed time t and the number of fluid vibration pulses f generated in the oscillator per t. And the flow rate sensor for low flow rate measurement is an orifice differential pressure gauge, and the output of the orifice differential pressure gauge is expressed by the following equation: Q = af signal converting means for converting ₂ into pulses f ₂ per predetermined time t so as to satisfy these two switching means for one selects and outputs the output pulse of the flow sensor, constant at timer signal means for outputting a timer signal every t; frequency counting means for starting to count the number of pulses supplied from the switching means in response to the timer signal input and outputting a frequency-divided signal every constant number k; Starts counting the number of pulses supplied from the switching means, and upon the next timer signal input,
A second counting means for outputting a remainder m of the counted pulse number f by the k; and a is added each time a frequency-divided signal is input by the frequency-dividing count. When a timer signal is input, the integrated value is expressed as a k-ary number. Carry by arithmetic shift and multiply by k.
And a calculating means for calculating a flow rate Q by adding a number multiplied by a to m output from the counting means.