JPH05157597A - Flow meter using thermal flow sensor - Google Patents

Abstract

PURPOSE:To avoid adding error of flowrate due to supply pressure variation and the like caused by detecting only positive flow and not detecting reverse flow. CONSTITUTION:Provided are an analog/digital conversion circuit 6A to add a certain pulse number Po to the pulse number proportional to the flowrate detected with a thermal flow sensor 4 and output the output pulse Ps shifted to zero as a signal B, and a Po generation circuit 17 to generate a certain pulse number Po. Also provided are a large and small judgment circuit 18 to judge the large and small relation between the pulse number Ps of the signal B and the signal Po from the Po generation circuit 17, an arithmetic circuit 19 to calculate l Ps-Po l by subtracting small one from the large one of Ps and Po according to the output from the large and small judgment circuit 18, and a microcomputer 8A to sum the flowrate by adding and subtracting the output of the calculation circuit 19 according to the output of the large and small judgment circuit 18.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flow meter using a thermal type flow sensor.

[0002]

2. Description of the Related Art As a flow meter of this type, Japanese Patent Laid-Open No. 1-30
A gas meter described in Japanese Patent No. 8921 is known.

As shown in FIG. 5, this gas meter includes a fluidic oscillator element 1 and the fluidic oscillator element 1.
A sensor 2 for detecting the fluid vibration of the and converting it into an electric signal;
A thermal flow sensor 4 that detects the flow velocity of the nozzle portion 3 of the fluidic oscillation element and converts it into an electrical signal, the fluid vibration detection sensor 2, and the flow velocity detection thermal flow sensor 4.
It has an electronic circuit 5 for calculating the integrated flow rate by calculating the signal and the display 6 for displaying the integrated flow rate obtained by the electronic circuit 5.

Then, it is determined whether the frequency of the electric signal of the fluid vibration detecting sensor 2 is above or below a certain value, and when the frequency is below a certain value, intermittent drive power is supplied to the thermal flow sensor 4 for detecting the flow velocity. This is a so-called two-stage metering type gas meter that obtains the flow rate by the signal of the fluidic oscillation element 1 at a large flow rate above a certain value and by the signal of the thermal type flow sensor 4 at a small flow rate below a certain value.

The use of the two-stage metering method as described above means that the fluid vibration of the fluidic oscillation element does not oscillate at a small flow rate below a certain level, or the oscillation becomes unstable, which makes it difficult to measure the flow rate. In order to compensate, the fact that the flow velocity of the nozzle portion 3 of the fluidic oscillation element 1 is high is utilized, and a thermal flow sensor 4 for detecting the flow velocity is arranged in this nozzle portion 3 to measure the flow amount in a small flow rate region. Yes (Actual Kaihei 1-
58118).

As the fluid vibration detection sensor 2, a well-known polymer piezoelectric film sensor is used, and a flow velocity detection thermal type flow sensor 4 is used.
As such, a thermal flow sensor as described in JP-A-59-182315 is used.

The fluid vibration detecting sensor 2 produces an electric signal having a frequency corresponding to the fluid vibration, and the thermal flow sensor 4 produces an analog electric signal corresponding to the flow velocity of the nozzle portion 3.

The thermal type flow sensor 4 has a fluid temperature detecting portion arranged on both sides of the heat generating portion on the surface of the silicon chip on which the flow hits. The electric resistance of the fluid temperature detecting portion on both sides of the heat generating portion depends on the flow rate. Since it changes, the change is detected as a voltage signal, amplified, A / D converted, and the flow rate is obtained by the microcomputer.

The thermal type flow sensor 4 is arranged at one end of the short side of a nozzle having a rectangular flow path section cut at a right angle to the flow. The electronic circuit 5 has the configuration shown in FIG.

Reference numeral 6 denotes an analog / digital conversion circuit, which converts an analog electric signal in the small flow rate region detected by the thermal flow sensor 4 into an electric pulse signal having a frequency proportional to the flow rate. Reference numeral 7 is a counter for temporarily stocking high-speed electric pulses (signal B) output from the analog / digital circuit 6 to the microcomputer 8, 9 is a power source, and 10 is a piezoelectric film circuit section 11 and a thermal flow sensor. It is a voltage control circuit that controls the drive voltage supplied to the circuit unit 12.

Reference numeral 13 is an analog amplifier for amplifying the electric signal of the sensor 2, 14 is a waveform shaping circuit for shaping the output signal of the analog amplifier 13 into a rectangular wave, and 15 is a waveform shaping circuit 14.
Is a signal determination circuit that receives the output (signal A) of (1) as an input and transmits the signal A to the microcomputer 8 as the signal J of the same frequency when the frequency is a certain value or more.

A clock control circuit 16 receives a command from the microcomputer 8 and sends a 32 KHz clock signal H to the analog / digital conversion circuit 6 for analog / digital conversion.

When the signal frequency of the fluid vibration detecting sensor 2, that is, the frequency of the signal A is equal to or higher than a certain value, the signal J is calculated by the microcomputer 8 and becomes a flow rate integrated value.
Further, in the minute flow rate region where the frequency of the signal A is a fixed value or less, the signal B based on the thermal type flow sensor 4 is calculated by the microcomputer 8, and the total flow rate integrated value of the signal J and the signal B is calculated to obtain the display 6 Displayed in.

In a small flow rate region where the frequency of the electric signal of the fluid vibration detecting sensor 2 is a fixed value or less, the flow sensor circuit section 1
The power is intermittently supplied to the unit 2 at intervals (cycles) T _{0 of} several seconds for a short time of 40 mS, and the thermal flow sensor 4 detects the flow rate (flow velocity).

The analog voltage signal of the thermal type flow sensor 4 is converted by the analog / digital conversion circuit 6 into a flow rate signal B having a pulse number proportional to the flow rate in synchronization with the clock signal H of 32 KHz.

This signal B is output at every interval (cycle) T ₀ , and the number of pulses at each time is 0 pulse at a flow rate of 0 [l / h] and 300 pulses at a flow rate of 50 [l / h], which is proportional to the flow rate. The characteristics of the analog / digital conversion circuit 6 are determined so that the number of pulses is the same. This characteristic is shown by the straight line B in FIG.

The microcomputer 8 calculates a signal B based on the thermal flow sensor 4 in the small flow rate range, and a signal A in which the piezoelectric film sensor 2 detects the fluid vibration frequency of the fluidic oscillation element 1 in the flow rate range above a certain value. , The total flow integrated value is obtained.

An actual gas meter is disclosed in JP-A 1-3
As disclosed in Japanese Patent No. 08921, it is well known as a gas meter with a safety function that determines an abnormal flow rate and closes a built-in shutoff valve.

Further, such a gas meter with a safety function has a sensitivity capable of surely measuring a flow rate even at a minute flow rate of about 3 [l / h] for determining a flow rate leak in a gas pipe.

[0020]

In the gas meter installed in the gas pipe, even when the gas appliance downstream of the meter is closed and no gas is used, a small amount of gas flows due to pressure fluctuations in the supply system. Thermal flow sensor 4 for gas flow
Is detected, and the microcomputer 8 integrates them to calculate an integrated flow rate.

As described above, the output pulse P of the analog-digital conversion circuit 6 when the thermal type flow sensor 4 detects the flow rate due to the pressure fluctuation of the supply system in the state where the cock of the gas appliance downstream of the meter is closed. _{When S} was observed for 24 hours a day, it was distributed in the range of 0 to 300 pulses as shown in FIG. 7.

Then, the output pulse (signal B) is multiplied by the pulse constant k by the microcomputer 8 to calculate an integrated value L = Σk. As shown by the curve B in FIG. 4, P _S monotonically increased with time, and it was observed that P _S sometimes increased by about 3 [l] in 1 hour and continued for 3 hours.

In the gas meter with safety function, it is judged whether or not there is a flow rate leak, and the integrated flow rate is 3 [l / h] in 1 hour.
Since the basic unit is whether or not to exceed,
In the above-mentioned conventional technique, there is a problem that a flow rate leak is erroneously determined even though it is not a flow rate leak.

The thermal type flow sensor 4 detects the gas of a high flow velocity narrowed by the nozzle portion 3 with high sensitivity, and the characteristics of the analog / digital W conversion circuit 6 are as shown by the straight line B in FIG. Since only the flow in the forward direction was converted into the number of pulses, the backflow could not be detected, and the result was that the microcomputer 8 could not integrate the backflow.

Therefore, an object of the present invention is to provide a flow meter capable of solving such a problem.

[0026]

[Means for Solving the Problems] To achieve the above object
In addition, the flowmeter using the thermal flow sensor of the present invention is
A thermal flow sensor for detection, and an array of the thermal flow sensor.
A signal with the number of pulses that periodically changes the analog output signal according to the flow rate.
An analog / digital conversion circuit for converting to B and a signal B
A microcomputer that integrates the
In the flowmeter with the thermal flow sensor (4)
Constant number of pulses P to the number of pulses proportional to the flow rate_OTo
Output pulse P added and zero-shifted_SIs output as signal B
An analog / digital conversion circuit (6A)
Constant number of pulses P_OTo generate P _OGenerator circuit (17)
And the pulse number P of the signal B_SAnd P_OGenerator circuit (17)
Signal P_OSize determination circuit (18) for determining the magnitude relationship of
And P according to the output of the magnitude judgment circuit (18)._SAnd P_O
Whichever is larger, the smaller one is subtracted | P _S
-P_OAn arithmetic circuit (19) for computing |, and the arithmetic circuit
According to the output of the magnitude judgment circuit (18), the output of (19)
A microcomputer (8
And A).

[0027]

The pulse number P _S of the output signal B of the analog / digital circuit (6A) is P _S > when the gas flow is a positive flow.
In the case of P _O and backflow, the relation of P _S <P _O is established.

Therefore, the output of the magnitude judgment circuit (18) differs depending on whether the gas flow is a normal flow or a reverse flow. In accordance with the output of the magnitude judgment circuit (18), the arithmetic circuit (19) outputs P _S
-P _O or P _O -P _S is calculated and | P _S -P _O | is output.

This output of the arithmetic circuit (19) | P _S -P _O
| Is input to the microcomputer (8A), and is added or subtracted depending on whether the output of the magnitude judgment circuit (18) is a forward flow or a reverse flow to calculate a flow rate integrated value.

[0030]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The embodiment of FIG. 1 is modified and improved only in part as compared with the block diagram of the prior art of FIG. 6, so the modified part will be mainly described below.

6A is an analog-digital conversion circuit,
An output pulse P _S in which an analog voltage signal proportional to the flow rate detected by the thermal flow sensor 4 is zero-shifted by adding a constant pulse P _O to the number of pulses proportional to this analog voltage.
And outputs as a signal B at every 6 second interval (period) T _O.

The relationship between the flow rate and the output pulse P _S is a straight line obtained by zero-shifting P _O, that is, 300 pulses, as shown in FIG. It should be noted that the value of the constant pulse P _O is set to a value larger than the maximum value pulse when the gas flows backward.

Reference numeral 7 is a counter, which is the number of pulses P of the signal B._STo
Count, interval T_OStock each time temporarily. 17 is
The constant pulse number P_OTo generate P_OGenerating circuit, 18
Is the output pulse P _SAnd the number of pulses P_OThe size relationship of
The output is P in the size judgment circuit_S> P_OH, P_S
<P_OThen L, P_S= P_OWhen is set to L or H
is there. Therefore, when this output is H, the gas flow is normal.
Then, when it is L, it means a backflow.

An arithmetic circuit 19 subtracts P _S -P _O or P _O -P _S depending on whether the output of the magnitude judgment circuit 18 is H or L. Therefore, the output is | P _S −P _O |.

8A is a microcomputer, an arithmetic circuit
19 output | P_S-P_OInput |, and the magnitude judgment circuit 18
Output P of the arithmetic circuit 19 depending on whether the output of H is L or L._S−
P _OIn the small flow rate range below a certain flow rate by adding or subtracting |
Z to calculate the integrated flow rate. At this time, the output of the arithmetic circuit 19
Power | P_S-P_OAdd / subtract the value of | multiplied by the pulse constant k
As a result, Σk · (P_S-P_O) Is calculated
, Both the forward flow and the reverse flow are integrated to obtain the correct integrated flow rate.
Will ask.

A gas meter constructed by the block diagram of FIG. 1 is installed in a gas pipe, and a gas appliance downstream of the gas meter is closed, that is, in a state where no gas is used.
The value obtained by subtracting a constant pulse P _O (in this case, P _O = 300) from the output pulse P _S output every 6 seconds for 4 hours fluctuated as shown in FIG.

This fluctuation is due to the forward and reverse flow of gas due to the pressure fluctuation and the temperature fluctuation of the supply system. When P _S -P _O is positive, the flow is positive, and when P _S -P _O is negative, the flow is reverse. Means FIG. 4 shows the integrated value L = Σk · (P _S −P _O ) [liter] obtained by closing the cock of the gas appliance downstream of the meter in this way for 24 hours a day by integrating the forward and reverse flows of FIG. 3 with the microcomputer 8A. Is shown in curve a.

In the present invention, as is clear from the curve a, the integrated value L is almost zero in 24 hours, and only the forward current is added (integrated) as in the prior art shown by the curve b to integrate the integrated value. Is never monotonically increasing.

In the block diagram of FIG. 1, the detailed configuration of the electronic circuit is partly different from that of the prior art block diagram of FIG. 6, so the electronic circuit is indicated by reference numeral 5A. Similarly, the thermal type flow sensor circuit portion is indicated by reference numeral 12A.

[0040]

Since the flow meter using the thermal type flow sensor of the present invention is configured as described above, a constant pulse number P _O can be obtained even when the output pulse of the analog-digital conversion circuit is 0. By doing so, the integrated value L of the forward / reverse flow can be obtained by the magnitude determination circuit (18) provided in the rear part of the counter (7), the arithmetic circuit (19) and the microcomputer (8A).
= Σk · (P _S −P _O ) can be calculated, and the problem of erroneously recognizing a flow of about 3 [l / h] for confirming the flow rate leakage of the conventional technique can be solved.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention.

FIG. 2 is a diagram showing a relationship between a flow rate and an output pulse of an analog / digital conversion circuit.

FIG. 3 is a diagram showing a relationship between time and P _S -P _O.

FIG. 4 is a diagram showing a relationship between time and integrated value.

FIG. 5 is a schematic diagram of a two-stage metering type flow meter.

FIG. 6 is a block diagram of a conventional technique.

FIG. 7 is a diagram showing a relationship between time and an output pulse of an analog-digital conversion circuit in a conventional technique.

[Explanation of symbols]

1 Fluidic oscillator 3 Nozzle part 4 Thermal flow sensor 6A Analog-digital conversion circuit 7 Counter 8A Microcomputer 17 _Po generation circuit 18 Large / small judgment circuit 19 Arithmetic circuit

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Katsuhito Sakai 3-2-7-123 Takasago, Katsushika-ku, Tokyo (72) Inventor Shigenori Okamura 4-1-2 1-2 Hiranocho, Chuo-ku, Osaka Osaka Gas Co., Ltd. In-house (72) Inventor Kaoru Kawamoto 4-1-2, Hirano-cho, Chuo-ku, Osaka City Osaka Gas Co., Ltd. (72) Inventor Yukio Kimura 507-2 Shinpakucho, Tokai-shi, Aichi Toho Gas Co., Ltd. In-house (72) Inventor Masahito Naganuma 1-270, Sennen 1-chome, Atsuta-ku, Nagoya, Aichi Prefecture

Claims (4)

[Claims] 1. A thermal type flow sensor for detecting a flow velocity, an analog / digital conversion circuit for periodically converting an analog output signal of the thermal type flow sensor into a signal B having a pulse number corresponding to a flow rate, and the signal B. In a flowmeter having a microcomputer for integrating and calculating an integrated flow rate, an output pulse P zero-shifted by adding a constant pulse number P _O to the pulse number proportional to the flow rate detected by the thermal flow sensor (4)
An analog-digital conversion circuit (6A) that outputs _S as a signal B, and P _O that generates the constant number of pulses P _O
Generating circuit (17) and the number of pulses P _S and P _{O of the} signal B
The magnitude judgment circuit (18) for judging the magnitude relation of the signal P _O of the generation circuit (17) and the larger or smaller one of P _S and P _O depending on the output of the magnitude judgment circuit (18). Arithmetic circuit (19) that subtracts and calculates | P _S −P _O |
And the output of the arithmetic circuit (19) is compared with the magnitude judgment circuit (18).
A flow meter using a thermal type flow sensor, comprising: a microcomputer (8A) that adds and subtracts in accordance with the output of the above to integrate the flow rate. 2. The flowmeter according to claim 1, wherein the thermal type flow sensor (4) is arranged in the nozzle portion (3) of the fluidic oscillator (1). 3. The flow meter according to claim 1, wherein the thermal type flow sensor (4) is arranged in the nozzle portion (3) of the fluidic oscillation element (1) of the gas meter. 4. An analog-digital conversion circuit (6A)
The flowmeter according to any one of claims 1 to 3, further comprising a counter (7) for counting and temporarily stocking the number of output pulses P _s of the above.