JP3517070B2 - Flow meter utilizing differential pressure - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a differential pressure flow meter which measures the flow rate of a fluid by utilizing the differential pressure between two pressures related to the flow rate of the fluid.

[0002]

2. Description of the Related Art As one of methods for measuring the flow rate of a fluid, there is a method of utilizing a differential pressure between two pressures related to the flow rate of the fluid. The differential pressure utilizing flow meter utilizing this differential pressure includes, for example, the Pitot tube type differential pressure utilizing flow meter shown in FIG. 3 and the orifice type differential pressure utilizing flow meter shown in FIG.

As shown in FIG. 3, the Pitot tube type differential pressure utilizing flow meter utilizes the differential pressure between the dynamic pressure and the static pressure of the fluid in the fluid channel 1 which changes according to the flow rate of the fluid. It measures the flow rate of the fluid. This Pitot tube type differential pressure utilizing flow meter is provided with, for example, two pressure chambers 10A and 10B partitioned by a polymer piezoelectric film 11, and introduces the dynamic pressure of the fluid into one pressure chamber 10A and keeps the fluid static. Pressure to the other pressure chamber 10B
It is supposed to be introduced in. That is, in this Pitot tube differential pressure flow meter, the differential pressure between the dynamic pressure and the static pressure of the fluid is detected by utilizing the piezoelectricity of the polymer piezoelectric film 11, and the flow rate of the fluid is measured thereby.

As shown in FIG. 4, the orifice type differential pressure flowmeter has a shielding plate 2 having an orifice 2a formed in a fluid flow path 1, and the difference in flow velocity before and after the orifice 2a is fluid. The flow rate of the fluid is measured by utilizing the fact that it changes according to the flow rate of. This orifice type differential pressure flow meter is similar to the Pitot tube differential pressure flow meter.
For example, two pressure chambers 10A and 10B partitioned by the polymer piezoelectric film 11 are provided, and pressures corresponding to the flow velocity before and after the orifice 2a are introduced into the two pressure chambers 10A and 10B, respectively. That is, in this orifice type differential pressure utilizing flow meter, the piezoelectricity of the polymer piezoelectric film is used to detect the difference between two pressures according to the flow velocity before and after the orifice 2a, and thereby the flow rate of the fluid is measured.

Further, in the Pitot tube type differential pressure flowmeter, as shown in FIG. 5, a part of the fluid flow path 1 is narrowed to increase the flow velocity, and a pressure corresponding to the flow velocity is applied to the fluid dynamic pressure. In some cases, the pressure is introduced into one of the pressure chambers 10A and at the same time, the pressure corresponding to the flow velocity in another portion having a wide flow path is introduced into the other pressure chamber 10B as the static pressure of the fluid.

Of these differential pressure flowmeters, the orifice type differential pressure flowmeter shown in FIG. 4 and the Pitot tube differential pressure flowmeter shown in FIG. 5 are both suitable for measuring minute flow rates. , Used for measuring minute flow rates.

[0007]

However, in these differential pressure flowmeters, the flow rate of the fluid is measured by detecting the differential pressure between the two pressures using the polymer piezoelectric film 11 or the like. However, the polymeric piezoelectric film 11 is deformed due to temperature changes and changes over time, resulting in an error in the detection of the differential pressure.
There was a case where an error occurred in the flow rate. In particular, in the case of a minute flow rate, the differential pressure becomes small, so the influence of such a detection error is large, and there is a problem that the measurement accuracy of the flow rate is significantly reduced. Therefore, for example, even if these differential pressure utilizing flowmeters are used for a gas meter, various safety functions may not work when a gas leak occurs because a gas leak with a minute flow rate cannot be detected accurately,
It could not be used as it was for a gas meter.

The present invention has been made in view of the above problems, and an object thereof is to provide a differential pressure utilizing flow meter capable of accurately measuring even a minute flow rate.

[0009]

A differential pressure utilizing flowmeter according to claim 1 of the present invention is a first pressure for introducing a first pressure relating to a flow rate of a fluid in a fluid channel into a first pressure chamber. The introduction pipe and the second pressure related to the flow rate of the fluid in the fluid passage are set to the second pressure.
Second pressure introducing pipe for introducing into the first pressure chamber, the first pressure chamber and the second pressure chamber, and the first pressure chamber and the second pressure chamber.
Differential pressure detection chamber that detects the differential pressure between the pressure chamber and the pressure chamber, flow rate calculation means that calculates the flow rate of the fluid based on the differential pressure detected by this differential pressure detection chamber, and minute flow rate where the flow rate of the fluid is less than the reference value. Difference between the minute flow rate determining means for determining whether or not it is and the minute flow rate determining means determines the minute flow rate.
The pressure in the first pressure chamber and the second pressure detected by the pressure detection chamber
Uses a first differential pressure and a second differential pressure in which the pressures of the force chambers are opposite to each other.
In addition, there is provided a zero point adjusting means using a back pressure for adjusting the zero point of the differential pressure detected by the differential pressure detecting chamber.

In this differential pressure utilizing flow meter, the first pressure relating to the flow rate of the fluid is introduced into the first pressure chamber through the first pressure introducing pipe, and the second pressure relating to the flow rate of the fluid is introduced to the second pressure. It is introduced into the second pressure chamber by a pipe. Thus, the differential pressure between the first pressure and the second pressure is detected by the differential pressure detection chamber, and the flow rate calculation means determines the flow rate of the fluid based on this differential pressure. When the minute flow rate determination means determines that the flow rate of the fluid is a minute flow rate, the pressure in the first pressure chamber is reduced.
Force and the pressure of the second pressure chamber are opposite to each other
The zero point of the differential pressure detected by the differential pressure detection chamber is adjusted by the reverse pressure utilizing zero point adjusting means using the differential pressure of. Therefore, it is possible to adjust the shift of the zero point due to the temperature change or the change over time.

[0011]

[0012]

According to a second aspect of the present invention, in the differential pressure utilizing flowmeter according to the first aspect , the reverse pressure utilizing zero point adjusting means introduces the second pressure into the first pressure chamber. A pressure introducing pipe, a fourth pressure introducing pipe for introducing the first pressure into the second pressure chamber, and either one of the first pressure introducing pipe and the third pressure introducing pipe is selectively cut off, and First to open the other
And the first switching valve, and the first switching valve opens the first pressure introducing pipe and opens the third switching valve.
When shutting off the pressure introducing pipe, the second pressure introducing pipe is opened to shut off the fourth pressure introducing pipe, and the first switching valve shuts off the first pressure introducing pipe and opens the third pressure introducing pipe. When opening, the second switching valve that shuts off the second pressure introducing pipe and opens the fourth pressure introducing pipe, and the first switching valve and the second switching valve are switched to detect the differential pressure detection chamber. It is provided with a comparison calculation means for performing a comparison calculation on the basis of the first differential pressure and the second differential pressure and adjusting the zero point of the differential pressure detected by the differential pressure detection chamber.

In this differential pressure utilizing flow meter, the first pressure is introduced into the first pressure chamber through the first pressure introducing pipe, and the second pressure is introduced through the third pressure introducing pipe. Also, the second pressure is introduced into the second pressure chamber by the second pressure introducing pipe, and the first pressure is introduced by the fourth pressure introducing pipe. At this time, when the first switching valve opens the first pressure introducing pipe, the second switching valve opens the second pressure introducing pipe, and the first switching valve opens the third pressure introducing pipe. Sometimes the second switching valve causes the fourth
Open the pressure introducing pipe. This makes it possible to detect a first differential pressure and a second differential pressure in which the pressure in the first pressure chamber and the pressure in the second pressure chamber are opposite to each other, and the differential pressure is calculated by the comparison calculation means based on this. Performs zero adjustment of the differential pressure detected by the detection chamber.

A differential pressure utilizing flowmeter according to a third aspect of the present invention is the flowmeter according to the first or second aspect , wherein the minute flow rate determining means interrupts the fluid flow path, and Is also provided for the downstream fluid flow path, and the flow rate of the fluid is below a reference value by detecting the rate of pressure decrease in the fluid flow path when the fluid flow path is blocked by the blocking means. And a pressure detecting means for determining whether or not the flow rate is minute.

In this differential pressure utilizing flow meter, the fluid flow passage is shut off by the shut-off means, and the rate of decrease of the pressure in the fluid flow passage is detected by the pressure detection means to determine whether the flow rate is a minute flow rate or less than the reference value. To judge. Therefore, the zero point adjustment of the differential pressure detected by the differential pressure detection chamber can be performed while the fluid flow path is blocked by the blocking means, and the zero point can be accurately adjusted without being affected by the flow rate change. Further, since the flow rate is monitored by the pressure detecting means while the fluid flow path is blocked by the blocking means, the fluid flow path can be immediately opened when there is a large change in the flow rate. It is possible to adjust the zero point by blocking the fluid flow path without significantly affecting the flow.

A differential pressure utilizing flowmeter according to a fourth aspect of the present invention is the flowmeter according to any one of the first to third aspects, further when the flow rate calculated by the flow rate calculating means is smaller than a reference value. A control means for controlling the minute flow rate determination means to determine whether or not the flow rate is a minute flow rate equal to or less than a reference value is provided.

In this differential pressure utilizing flow meter, when the flow rate calculated by the flow rate calculating means by controlling the minute flow rate determining means by the control means is smaller than the reference value, whether or not the flow rate is a minute flow rate or less than the reference value. Make a decision.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows the structure of a differential pressure flow meter according to an embodiment of the present invention. This differential pressure flow meter
For example, it is used as a gas meter and is provided for the gas pipe (that is, the fluid flow path) 1.

This differential pressure utilizing flow meter has a dynamic pressure (that is, a first pressure relating to the flow rate of gas in the gas pipe 1) and a static pressure (that is, in the gas pipe 1) according to the flow rate of gas in the gas pipe 1. A differential pressure detection chamber 10 for detecting a differential pressure with respect to a gas flow rate (second pressure) is provided. This differential pressure detection chamber 10 has a first
Has a pressure chamber 10A as a pressure chamber and a pressure chamber 10B as a second pressure chamber.
A polymeric piezoelectric film 11 partitions the space between A and 10B.

One end of a pressure introducing pipe 20 as a first pressure introducing pipe is connected to the pressure chamber 10A. The other end of the pressure introducing pipe 20 is inserted into the gas pipe 1 and is open so as to face the gas flow direction. That is, the dynamic pressure of the gas in the gas pipe 1 is introduced into the pressure chamber 10A. Further, one end of a pressure introducing pipe 30 as a second pressure introducing pipe is connected to the pressure chamber 10B.
The other end of the pressure introducing pipe 30 is inserted into the gas pipe 1,
It is open vertically to the gas flow. That is, the static pressure of the gas in the gas pipe 1 is introduced into the pressure chamber 10B.

The polymer piezoelectric film 11 is made of a polymer piezoelectric material which has appropriate elasticity and is electrically charged by deformation, and is stretched between the two pressure chambers 10A and 10B. That is, this polymer piezoelectric film 11
Is deformed according to the differential pressure between the two pressure chambers 10A and 10B (that is, the differential pressure between the dynamic pressure and the static pressure of the gas), and outputs an electric signal according to the differential pressure. Although not shown in FIG. 1, electrodes 12, 1 made of a metal (for example, aluminum (Al)) are formed on both surfaces of the polymer piezoelectric film 11.
3 are provided (see FIG. 2). These electrodes 12,
Reference numeral 13 denotes a flow rate calculation unit 6 which will be described later by a lead wire not shown
0 (see FIG. 2).

The flowmeter using differential pressure according to the present embodiment also has a zero point adjusting section as a reverse pressure utilizing zero point adjusting means (that is, zero point adjusting means) for adjusting the zero point of the differential pressure detected by the differential pressure detecting chamber 10. 40 is provided. This zero adjustment unit 40
Is a pressure introducing pipe 41 as a third pressure introducing pipe for introducing a static pressure of gas into the pressure chamber 10A, and the pressure chamber 1
It has a pressure introduction pipe 42 as a fourth pressure introduction pipe for introducing a dynamic pressure of gas to 0B.

One end of the pressure introducing pipe 41 has a pressure introducing pipe 30.
And the other end is connected to the pressure introducing pipe 20 via a switching valve 43 serving as a first switching valve. The switching valve 43 includes the pressure introducing pipe 20 and the pressure introducing pipe 4.
One of the two is selectively opened and the other is blocked. Further, one end of the pressure introducing pipe 42 is connected to the pressure introducing pipe 20, and the other end thereof is connected to the pressure introducing pipe 30 via a switching valve 44 as a second switching valve. The switching valve 44 selectively opens one of the pressure introducing pipe 30 and the pressure introducing pipe 42 and shuts off the other.

The two switching valves 43 and 44 operate in conjunction with each other to operate in a flow rate measurement mode (A side indicated by a solid line in FIG. 1) and a zero adjustment mode (B side indicated by a broken line in FIG. 1). It is controlled to switch. That is, in the flow rate measurement mode (A side), the switching valve 43 opens the pressure introducing pipe 20 and shuts off the pressure introducing pipe 42 to introduce the dynamic pressure of gas into the pressure chamber 10A, and the switching valve 44 causes the pressure introducing pipe to move. It is controlled so that 30 is opened and the pressure introduction pipe 42 is cut off to introduce the static pressure of gas into the pressure chamber 10B to detect the first differential pressure. Further, in the zero adjustment mode (B side), the switching valve 43 is operated by the pressure introducing pipe 20.
And the pressure introducing pipe 41 is opened to introduce the static pressure of the gas into the pressure chamber 10A, and the switching valve 44 causes the pressure introducing pipe 3 to move.
It is controlled so that 0 is shut off and the pressure introducing pipe 42 is opened to introduce the dynamic pressure of gas into the pressure chamber 10B to detect the second differential pressure.

Although not shown in FIG. 1, the zero-point adjusting section 40 performs a comparison calculation based on the two differential pressures detected by the polymer piezoelectric film 11 to detect the differential pressure detected by the differential pressure detecting chamber 10. A comparison calculation circuit 45 for adjusting the zero point is also provided (see FIG. 2). The comparison calculation circuit 45 is configured to obtain the average value of the detection signal value of the first differential pressure and the detection signal value of the second differential pressure output from the signal detection circuit 62 of the flow rate calculation unit 60 described later. ing.

The differential pressure utilizing flow meter according to the present embodiment further comprises a minute flow rate judging section 50 for judging whether or not the gas flow rate is a minute flow rate below a predetermined reference value. The minute flow rate determination unit 50 includes a shutoff valve 51 that shuts off the gas pipe 1.
And a pressure sensor 52 as pressure detecting means for detecting whether or not the flow rate of the gas is below a predetermined reference value by detecting the rate of decrease of the pressure in the gas pipe 1. The shutoff valve 51 is arranged upstream of the pressure introducing pipes 20 and 30, and the pressure sensor 52 is arranged downstream of the pressure introducing pipes 20 and 30. Further, the pressure sensor 52 determines that the gas flow rate is larger than the predetermined reference value and is not the minute flow rate when the detected pressure decrease rate is larger than the predetermined reference value, and outputs a signal. There is.

Although not shown in FIG. 1, the flowmeter utilizing the differential pressure according to the present embodiment additionally determines the flow rate of the gas in the gas pipe 1 based on the differential pressure detected by the differential pressure detection chamber 10. It is provided with a flow rate calculation unit 60 for obtaining, and a control unit 70 for controlling the operations of the switching valves 43, 44 and the shutoff valve 51.

FIG. 2 is a circuit diagram of the flow rate calculating section 60 and the control section 70 in the differential pressure utilizing flow meter shown in FIG.

The flow rate calculation unit 60 includes an amplifier circuit 61 for amplifying an electric signal output from the polymer piezoelectric film 11 of the differential pressure detection chamber 10, and a signal for detecting the amplified signal output from the amplifier circuit 61. A detection circuit 62 and an arithmetic circuit 63 for obtaining the flow rate of the gas in the gas pipe 1 based on the detection signal output from the signal detection circuit 62 are provided.

The first input end and the second input end of the amplifier circuit 61 are the electrodes 1 arranged on both surfaces of the polymer piezoelectric film 11.
2 and 13, respectively, and the output end is connected to the input end of the signal detection circuit 62. Signal detection circuit 62
The first output terminal of is connected to the input terminal of the arithmetic circuit,
The second output end is connected to the input end of the comparison operation circuit 45 of the zero adjustment unit 40.

The controller 70 is connected to the comparison operation circuit 45, the operation circuit 63, the drive devices 46 and 47 for driving the switching valves 43 and 44, the drive device 53 for driving the shutoff valve 51, and the pressure sensor 52, respectively. There is. The control unit 70 drives the drive device 53 to operate the shutoff valve 51 to shut off the gas pipe 1 when the flow rate obtained by the arithmetic circuit 63 is smaller than a predetermined reference value, and at the same time, the signal from the pressure sensor 52 is output. Switching valve 4 when not input
3, 44, the comparison calculation circuit 45 and the calculation circuit 63 are controlled to adjust the zero point of the differential pressure. This zero point adjustment control detects the first differential pressure in the flow rate measurement mode (A side), and sets the switching valves 43 and 44 by the drive devices 46 and 47 to the zero point adjustment mode (B side), respectively. Is detected, the average value of the detection signal value of the first differential pressure and the detection signal value of the second differential pressure is calculated by the comparison calculation circuit 45, and the average value is set as the zero point value of the differential pressure 0. An instruction is given to the arithmetic circuit 63.

When a signal is input from the pressure sensor 52, the control unit 70 does not adjust the zero point or interrupts it midway, operates the shutoff valve 51 to open the gas pipe 1, and When the switching valves 43 and 44 are in the zero adjustment mode (B side), the flow rate measurement mode (A
Side). That is, when the pressure sensor 52 determines that the flow rate of the gas is a minute flow rate equal to or less than a predetermined reference value and the state continues,
It is designed to adjust the zero point.

The differential pressure utilizing flow meter according to this embodiment having such a configuration operates as follows and measures the flow rate of the gas in the gas pipe 1.

In this differential pressure flow meter, the switching valve 4
The flow rate is measured in a state in which the flow rate measuring modes 3 and 44 are on the A side. That is, the dynamic pressure of the gas in the gas pipe 1 is introduced into the pressure chamber 10A of the differential pressure detection chamber 10, and the static pressure is introduced into the pressure chamber 10B. The polymer piezoelectric film 11 is deformed according to the differential pressure between the dynamic pressure and the static pressure,
An electric signal corresponding to the differential pressure is output. Flow rate calculation unit 60
Then, the amplification circuit 61 amplifies the electric signal output from the polymer piezoelectric film 11, the signal detection circuit 62 detects the amplified signal, and the calculation circuit 63 calculates the flow rate based on the detection signal.

Here, when the flow rate obtained by the arithmetic circuit 63 is larger than the predetermined reference value, the measurement of the flow rate is continued in this state.

When the flow rate calculated by the arithmetic circuit 63 is less than the predetermined reference value, the controller 70 drives the drive device 53 to operate the shutoff valve 51 to shut off the gas pipe 1. After that, the pressure sensor 52 detects the rate of decrease of the pressure in the gas pipe 1. The pressure sensor 52 determines that the flow rate of the gas is a minute flow rate smaller than the predetermined reference value when the pressure decrease rate is smaller than the predetermined reference value, and when the pressure decrease rate is larger than the predetermined reference value. A signal is output to the control unit 70 only when it is determined that the flow rate is not the minute flow rate and when it is determined that the flow rate is not the minute flow rate.

When no signal is input from the pressure sensor 52, the control unit 70 controls the switching valves 43 and 44, the comparison operation circuit 45 and the operation circuit 63 to adjust the zero point. That is, after detecting the first differential pressure in the flow rate measurement mode (A side), the drive devices 44 and 45 set the switching valves 43 and 44 to the zero adjustment mode (B side), respectively.
The second differential pressure in which the pressures of the two pressure chambers 10A and 10B are opposite to the first differential pressure is detected.

The polymer piezoelectric film 11 outputs electric signals corresponding to the first pressure difference and the second pressure difference. This electric signal is amplified by the amplifier circuit 61 and output as a detection signal by the signal detection circuit 62. Comparison arithmetic circuit 4
Reference numeral 5 obtains the average value of the detection signal value of the first differential pressure and the detection signal value of the second differential pressure detected by the signal detection circuit 62.

At this time, when the polymeric piezoelectric film 11 has no strain, 0 is an average value, and when the polymeric piezoelectric film 11 is strained, a value corresponding to the strain is an average value. The control unit 70 gives an instruction to the arithmetic circuit 63 so that the average value thereof becomes a zero point value at which the differential pressure is zero. As a result, the zero point adjustment is performed, and when measuring the flow rate, the flow rate is calculated with reference to this zero point value. After that, the control unit 70
Causes the drive device 53 to operate the shut-off valve 51 to open the gas pipe 1, and the drive devices 46 and 47 to switch the switching valves 43 and 44 to the flow rate measurement mode (A side).

When the zero point adjustment is completed in this way, the dynamic pressure in the gas pipe 1 is again introduced into the pressure chamber 10A of the differential pressure detection chamber 10, and the static pressure is introduced into the pressure chamber 10B. The flow rate calculation unit 60 calculates the minute flow rate based on the zero point value designated by the zero point adjustment. As a result, even if the polymeric piezoelectric film 11 is deformed due to a change in temperature and a change over time and the zero point of the differential pressure detected by the differential pressure detection chamber 10 is displaced, the minute flow rate can be accurately measured.

On the other hand, when the shutoff valve 51 shuts off the gas pipe 1 and then a signal is input from the pressure sensor 52, the control unit 70 drives the drive device 53 to operate the shutoff valve 51 to open the gas pipe 1. Open. Further, even when a signal is input from the pressure sensor 52 during the zero point adjustment, the control unit 70 interrupts the zero point adjustment at that time, operates the shutoff valve 51, and opens the gas pipe 1. , Switching valve 4
When 3 and 44 are in the zero adjustment mode (B side), the flow rate measurement mode (A side) is switched to. This allows
Again, the dynamic pressure in the gas pipe 1 is introduced into the pressure chamber 10A of the differential pressure detection chamber 10, and the static pressure is introduced into the pressure chamber 10B.
The flow rate is calculated.

These steps are repeated each time the flow rate obtained by the arithmetic circuit 63 becomes equal to or less than a predetermined reference value. As a result, the arithmetic circuit 63 always calculates the flow rate with the new zero point value as a reference, and the shift of the zero point of the differential pressure due to the temperature change or the change over time during the measurement of the flow rate is sequentially adjusted.

As described above, according to the differential pressure utilizing flow meter according to the present embodiment, when the minute flow rate judging section 50 judges that the gas flow rate is a minute flow rate, the zero point adjusting section 40 adjusts the zero point. Therefore, it is possible to adjust the zero point of the differential pressure which has been deviated due to the temperature change and the temporal change. Therefore, it is possible to accurately measure even a minute flow rate. Therefore, the reliability is improved, and it becomes possible to use the differential pressure flow meter as a gas meter. That is,
Since the differential pressure flow meter consumes less power than a hot-wire flow meter or the like, the power consumption of the gas meter can be reduced and the size can be reduced. Further, since the flowmeter utilizing differential pressure has a simple structure, the structure of the gas meter can be simplified.

Further, according to this differential pressure utilizing flow meter, the average value of the detection signal value of the first differential pressure and the detection signal value of the second differential pressure output by the signal detection circuit 62 is 0. Since the zero point value of the differential pressure is adjusted as the zero point value of, the accuracy of the zero point adjustment can be increased as compared with the case where the zero point adjustment is performed based on only one differential pressure.

In addition, according to this differential pressure utilizing flow meter, since the gas pipe 1 is shut off by the shutoff valve 51 to adjust the zero point, even if the flow rate changes while the zero point is adjusted. Zero adjustment can be performed without being affected by it. That is, it is possible to accurately detect two differential pressures in which the pressures of the two pressure chambers 10A and 10B are opposite to each other, and it is possible to accurately perform zero point adjustment.

Furthermore, according to this differential pressure utilizing flow meter,
Since the pressure sensor 52 detects the decrease rate of the pressure in the gas pipe 1 while the gas pipe 1 is shut off and monitors the change in the flow rate, the flow rate is large while the gas pipe 1 is shut off. When there is a change, the gas pipe 1 can be opened immediately. That is, the zero adjustment can be performed by blocking the gas pipe 1 without significantly affecting the gas flow.

Although the present invention has been described above with reference to the embodiments, the present invention is not limited to the above-mentioned embodiments and can be variously modified. For example, in the above embodiment, the dynamic pressure of the gas is introduced into the pressure chamber 10A so that the pressure chamber 10A
Although the Pitot tube type in which the static pressure of gas is introduced into B has been described, the present invention can be widely applied to those in which the differential pressure between two pressures related to the flow rate is detected by the differential pressure detection chamber. For example, the orifice type (see FIG. 4) described in the related art can also be applied.

In this case, an orifice is formed in the fluid passage. The first pressure introducing pipe is connected to the fluid flow passage located on one side of the orifice, and introduces a pressure corresponding to the flow velocity of the fluid on one side of the orifice into the first pressure chamber. The second pressure introducing pipe is connected to the fluid flow path located on the opposite side of the orifice, and introduces a pressure corresponding to the flow velocity of the fluid on the opposite side of the orifice into the second pressure chamber (see FIG. 4).

Further, in the above-mentioned embodiment, the pressure difference between the two pressures related to the flow rate is detected by the polymer piezoelectric film 11 stretched in the pressure difference detection chamber 10, but other than the polymer piezoelectric film 11 is detected. You may make it detect by a thing.

Further, in the above embodiment, the pressure sensor 52 detects the rate of decrease of the pressure in the gas pipe 1 shut off by the shutoff valve 51 to monitor the change in the flow rate. As long as it can detect the change in the flow rate, it can be used instead of the pressure sensor 52.

In addition, in the above embodiment, the gas pipe 1 is shut off by the shutoff valve 51 and the pressure sensor 52 is used.
Although the rate of decrease of the pressure in the gas pipe 1 is detected by the above to determine whether or not the flow rate is minute, it is also possible to directly measure the flow rate of the fluid without using the shutoff valve 51.

Furthermore, in the above embodiment, the zero adjustment unit 40 calculates the average value of the detection signal value of the first differential pressure and the detection signal value of the second differential pressure output from the signal detection circuit 62. Although the zero point is adjusted by obtaining it, the zero point is adjusted by obtaining the average value of the flow rate of the first differential pressure and the flow rate of the second differential pressure obtained by the arithmetic circuit 63. Good.

In addition, in the above embodiment,
The zero point adjusting unit 40 adjusts the zero point of the differential pressure detected by the differential pressure detecting chamber 10 using two differential pressures in which the pressures of the two pressure chambers 10A and 10B are opposite to each other. It also includes a means for adjusting the zero point by the zero point adjusting means.

[0056]

As described above, according to the differential pressure utilizing flowmeter according to the first aspect of the present invention, the differential pressure is detected when the minute flow rate determining means determines that the gas flow rate is the minute flow rate.
Between the pressure in the first pressure chamber and the pressure in the second pressure chamber detected by the chamber
Reverse by using a first differential pressure and a second differential pressure whose pressures are opposite to each other
Since the zero point of the differential pressure detected by the differential pressure detecting chamber is adjusted by the pressure utilizing zero point adjusting means, it is possible to adjust the zero point of the differential pressure which has been deviated due to the temperature change and the change over time, so that one difference When adjusting the zero point based only on pressure
Compared with this, the zero point can be adjusted more accurately. Therefore,
It is possible to accurately measure even a minute flow rate. Therefore, the reliability is improved, the differential pressure flow meter can be used as a gas meter, and the advantage of the differential pressure flow meter is that it has a small power consumption, a small size, and a simple structure. Play.

[0057]

Further, according to the differential pressure utilizing flowmeter according to claim 3 of the present invention, in the one according to claim 1 or 2 , since the shutoff means is provided, the fluid flow path is shut off. The zero point can be adjusted, and even if the flow rate changes during the zero point adjustment, the zero point adjustment can be performed accurately without being affected by the change.

In addition, according to the differential pressure utilizing flowmeter of claim 3 of the present invention, in the flowmeter according to claim 1 or 2 , the flow rate of the fluid by the pressure detecting means is a minute flow rate not more than the reference value. Since it is determined whether or not there is a large change in the flow rate while the fluid flow path is blocked, the fluid flow path can be opened immediately, which greatly affects the fluid flow. The effect that the zero point adjustment can be performed without interrupting the fluid flow path is achieved.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an overall configuration of a differential pressure utilizing flow meter according to an embodiment of the present invention.

FIG. 2 is a circuit configuration diagram relating to a flow rate calculating unit and a control unit in the differential pressure utilizing flow meter shown in FIG.

FIG. 3 is a sectional view showing a conventional differential pressure flow meter.

FIG. 4 is a cross-sectional view showing a conventional differential pressure utilizing flowmeter.

FIG. 5 is a cross-sectional view showing a conventional differential pressure flow meter.

[Explanation of symbols]

1 gas pipe (fluid flow path) 2a Orifice 10 Differential pressure detection chamber 10A pressure chamber (first pressure chamber) 10B Pressure chamber (second pressure chamber) 20 Pressure introducing pipe (first pressure introducing pipe) 30 Pressure introducing pipe (second pressure introducing pipe) 40 Zero adjustment unit 41 Pressure introducing pipe (third pressure introducing pipe) 42 Pressure introducing pipe (4th pressure introducing pipe) 43 Switching valve (first switching valve) 44 Switching valve (second switching valve) 45 Comparison operation circuit 50 Micro flow rate determination unit 51 Shut-off valve (shut-off means) 52 Pressure sensor (pressure detection means) 60 Flow rate calculator 70 Control unit

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) G01F 1/00-9/02

Claims (6)

(57) [Claims] 1. A first pressure introducing pipe for introducing a first pressure related to a flow rate of a fluid in a fluid flow path into a first pressure chamber, and a second pressure related to a second pressure related to a flow rate of a fluid in a fluid flow path. A second pressure introducing pipe for introducing into the second pressure chamber, a first pressure chamber and a second pressure chamber, and a differential pressure detecting a differential pressure between the first pressure chamber and the second pressure chamber. A pressure detection chamber, a flow rate calculation means for calculating the flow rate of the fluid based on the differential pressure detected by the differential pressure detection chamber, and a minute flow rate determination for determining whether the flow rate of the fluid is a minute flow rate or less than a reference value. Means and the pressure in the first pressure chamber detected by the differential pressure detection chamber when the minute flow rate determination means determines that the flow rate is minute.
Force and the pressure of the second pressure chamber are opposite to each other
And a differential pressure utilizing zero point adjusting means for adjusting a zero point of the differential pressure detected by the differential pressure detecting chamber by using the differential pressure of the differential pressure. 2. The back pressure utilizing zero point adjusting means comprises a third pressure introducing pipe for introducing a second pressure into the first pressure chamber, and a fourth pressure introducing pipe for introducing a first pressure into the second pressure chamber. Pressure introducing pipe, a first switching valve that selectively blocks one of the first pressure introducing pipe and the third pressure introducing pipe, and opens the other, and the first switching valve. They are interlocked, and when the first switching valve opens the first pressure introducing pipe and shuts off the third pressure introducing pipe, the second pressure introducing pipe is opened and the fourth pressure introducing pipe is opened. And the first switching valve shuts off the first pressure introducing pipe and opens the third pressure introducing pipe, the second pressure introducing pipe is shut off and the fourth pressure introducing pipe is opened. Switching the second switching valve, the first switching valve, and the second switching valve A comparison calculation means for performing a comparison calculation based on the first differential pressure and the second differential pressure detected by the differential pressure detection chamber and performing zero adjustment of the differential pressure detected by the differential pressure detection chamber. The flowmeter using differential pressure according to claim 1 . 3. The minute flow rate determining means is provided for a shutoff means for shutting off the fluid flow passage and a fluid flow passage on the downstream side of the shutoff means, and the cutoff means shuts off the fluid flow passage. A pressure detecting means for determining whether or not the flow rate of the fluid is a minute flow rate equal to or less than a reference value by detecting a rate of decrease in pressure in the fluid flow path in the cutoff state. The flowmeter utilizing differential pressure according to 1 or 2 . 4. When the flow rate calculated by the flow rate calculating means is smaller than a reference value, the minute flow rate determining means is controlled to determine whether the flow rate is a minute flow rate or less than the reference value. The flowmeter utilizing differential pressure according to any one of claims 1 to 3 , further comprising a control means for controlling the flowmeter. 5. The first pressure introducing pipe applies a dynamic pressure of a fluid to the first pressure introducing pipe.
Is introduced into the pressure chamber of the second pressure introduction pipe differential pressure based flow according to any one of claims 1 to 4, characterized in that introducing the static pressure of the fluid in the second pressure chamber Total. 6. An orifice is formed in the fluid flow path, and the first pressure introducing pipe introduces a pressure corresponding to the flow velocity of the fluid on one side of the orifice into the first pressure chamber, and The differential pressure utilizing flowmeter according to any one of claims 1 to 4 , wherein the second pressure introducing pipe introduces a pressure corresponding to the flow velocity of the fluid on the opposite side of the orifice into the second pressure chamber. .